Citation
The role of the cocoons of orb-weaving spiders

Material Information

Title:
The role of the cocoons of orb-weaving spiders
Creator:
Hieber, Craig S., 1951-
Publication Date:
Language:
English
Physical Description:
xii, 155 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Cocoons ( jstor )
Egg masses ( jstor )
Eggs ( jstor )
Larvae ( jstor )
Parasite hosts ( jstor )
Parasites ( jstor )
Predators ( jstor )
Silk ( jstor )
Spiders ( jstor )
Suspension systems ( jstor )
Cocoons ( lcsh )
Dissertations, Academic -- Zoology -- UF
Spiders ( lcsh )
Zoology thesis Ph. D
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1984.
Bibliography:
Includes bibliographical references (leaves 146-154).
Additional Physical Form:
Also available online.
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Craig S. Hieber.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Resource Identifier:
030585908 ( ALEPH )
11940457 ( OCLC )

Downloads

This item has the following downloads:


Full Text













THE ROLE OF THE COCOONS OF ORB-WEAVING SPIDERS








By



CRAIG S. HIEBER













A DISSERTATION SUBMITTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY




UNIVERSITY OF FLORIDA 1984















ACKNOWLEDGEMENTS


It is a pleasure to acknowledge the many friends and colleagues who aided me in this work. My major professor, John F. Anderson, has been a source of stimulation and encouragment. His comments on Mr work were always critical but fair, and he always emphasized the importance of doing good, solid research. Most importantly, he encouraged me to be as independent as possible while doing my research. To John I extend my sincerest thanks. The other members of my dissertation committee, Lincoln P. Brower, Jonathon Reiskind, and Reese I. Sailer, and the additional colleague, David H. Evans, who sat at my defense, all provided ready assistance during the research phase and many helpful editorial suggestions, from which I benefitted. I also recognize the advice or equipment provided by Drs. L. Berner, P. Feinsinger, M.H. Greenstone, F.J. Maturo, and B.K. McNab.

I was also fortunate to have the cooperation of a number of

people in positively identifying my egg predators. Thanks for this service go to H. Townes (ichneumonids), American Entomological Institute; Dr. M.E. Schauff (eulophids), Systematic Entomology Lab, USDA; and Dr. L. Stange (mantispids), Division of Plant Industries, FDACS. Further thanks go to Mr. and Mrs. H.M. Chitty, who generously allowed me access to the Stardust Ranch for many of my experiments. I also acknowledge the Department of Zoology, Sigma




i











Xi, The Research Society, and the Florida Entomological Society for their generous financial support during ay graduate program.

Numerous other post doctoral associates and graduate students in the Zoology Department have listened to qy ideas and provided helpful suggestions. Among these I would especially like to thank J.B. Anderson, W.W. Henneman, J.R. Lucas, S.B. and B.J. Malcolm, P.G. May, M.S. Obin, K. Prestwich, N.E. Stamp, and N.T. Wheelwright. I also extend qy thanks to A.D. Austin and K.E. Redborg for providing me with relevant manuscripts concerning my research.

I would like to separately thank qy office mate and friend James A. Cohen (UVPD) for the countless stimulating discussions concerning my work and biology in general, the lovebug collaboration, and, in particular, for his influence on ayr writing. Jim, the "big chair" will always be open!

1 would also like to separately thank Sherry M. Hieber for

putting up with the late nights, the wild talk, and the oftentimes crazed behavior of this researcher. I could not have done this without her support and love.

Finally, I would like to thank Wy parents, Bernie and Doris

Hieber, who have always told me I could be anything I wanted to be.














TABLE OF CONTENTS


ACKNOWLEDGEMENTS ................................................. ii

LIST OF TABLES ............................................... ... vi

LIST OF FIGURES .................................................. ix

ABSTRACT ......................................................... xi

CHAPTER I INTRODUCTION ............................ .......... 1

CHAPTER II THE EXPERIMENTAL ANIMALS, THEIR
COCOONS, AND THEIR HABITATS .......... o ............ *5

Mecynogea lemniscata ............. ............. 5
Argiope aurantia ......... o ....................... 8

CHAPTER III THE ''INSULATION'' LAYER IN THE
COCOONS OF ARGIOPE AURANTIA ....................... 12

Introduction.... ........................ *.... 12
Materials and Methods ........................... 13
Results ......................................... 15
Discussion ...................................... 20

CHAPTER IV THE ROLE OF SPIDER EGGS AND
COCOONS IN RESISTING WATER LOSS .. ...... ..... 25

Introduction ........................ .......... 25
Materials and Methods ............................ 26
Results ....................................... .29
Discussion ....................................... 36

CHAPTER V THE ROLE OF THE COCOON IN
LIMITING EXCESS WATER AND
FUNGAL ATTACK ................... o ................. 42

Introduction ............ o .......... o ............. 42
Materials and Methods ............................ 43
Results .......................................... 47
Discussion ....................................... 54








iv










CHAPTER VI THE ROLE OF THE COCOON IN
LIMITING EGG AND SPIDERLING
PREDATORS .......................................... 62

Introduction ..................................... 62
Materials and Methods ............................ 64
Results .......................................... 71
Discussion .............................. ........ 89

CHAPTER VII COCOON SPACING AND THE TIMING OF
PRODUCTION AS METHODS TO AVOID
EGG AND SPIDERLING PREDATORS ............ ......... 100

Introduction .................................... 100
Materials and Methods ...................... *..*.102
Results .......................... # .............. 104
Discussion ...................................... 115

CHAPTER VIII GENERAL DISCUSSION AND
CONCLUSIONS ....................................... 125

General Discussion ............ ........ o ... o....125
Conclusions ..... o .................. ........... 143

LITERATURE CITED ....................... o ........................ 146

BIOGRAPHICAL SKETCH ...... o ......... o .............






























v















LIST OF TABLES


Table 4-1. The distributions of sphere sizes found on the chorionic surfaces of Mecynogea lemniscata and Argiope aurantia eggs ................................................... 31

Table 4-2. Mean percentages of eggs successfully hatched at the four experimental humidities for intact Mecynogea lemniscata and Argiope aurantia egg masses with and without cocoons, and for reduced A. aurantia egg masses without cocoons ......................................................... 32

Table 4-3. Mean percentages for molting success and spiderling survival at the four experimental humidities for Mecynogea lemniscata egg and spiderling masses with and without cocoons ...... ........................... .. .... 34

Table 4-4. Mean percentages for hatching and molting success and spiderling survival in the field for the spiders Mecynogea lemniscata and Argiope aurantia ................................. 35

Table 4-5. Mean percentages for molting success and spiderling survival at the four experimental humidities for Argiope aurantia egg and spiderling masses with and without cocoons ...................... 37

Table 5-1. The effect of modification of the cocoon suspension system and cover on the incidence of fungal attack on the eggs of Mecynogea lemniscata ......................... .52

Table 5-2. The effect of modification of the cocoon suspension system and cover on the incidence of fungal attack on the spiderlings of Mecyncgea lemniscata ............................. 53

Table 5-3. The effect of modification of the cocoon suspension system and cover on the incidence of fungal attack on the eggs of Argiope aurantia .................................... 55





vi









Table 5-4. The effect of modification of the cocoon suspension system and cover on the incidence of fungal attack on the spiderlings of Argiope aurantia ................................ 56

Table 6-1. Numbers of Mecynogea lemniscata cocoons attacked by various predators for the years 1981 to 1983.......................................... 72

Table 6-2. The effect of modification of the cocoon suspension system and cover on the incidence of predator attack on the eggs of Mecynogea lemniscata ....................................... 74

Table 6-3. The effect of modification of the cocoon suspension system and cover on the incidence of predator attack on the spiderlings of Mecynogea lemniscata ............................. 76

Table 6-4. Numbers of Argiope aurantia cocoons suspended in the vegetation which were successfully attacked by various predators for the years 1981 to 1983 ...................... #............... ..... 77

Table 6-5. The mean percentage of eggs which survive in Argiope aurantia cocoons attacked solely by various predators .................................... 81

Table 6-6. Means for the variables cocoon diameter, cocoon length, egg mass diameter, egg mass length, distance to the egg mass, and ovipositor length ........................................... 84

Table 6-7. The mean numbers of suspension line deltas and oviposition holes in the upper, middle, and lower thirds of the covers of Argiope aurantia cocoons .............................. 85

Table 6-8. The effect of modification of the cocoon suspension system and cover on the incidence of predator attack on the eggs of Argiope aurantia ............................................. 87

Table 6-9. The effect of modification of the cocoon suspension system and cover on the incidence of predator attack on the spiderlings of Argiope aurantia ................................. 88








vii









Table 7-1. Densities of Mecynogea lemniscata cocoons, and the percentages of cocoons attacked for the years 1981 to 1983 ............................ 105

Table 7-2. Mean numbers of Mecynogea lemniscata cocoons per string, and the mean number of eggs in each cocoon in the string for the years 1981 to 1983 ............................................. 109

Table 7-3. A comparison of the contents of attacked Mecynogea lemniscata cocoons .......................... 110

Table 7-4. The number and distribution in space and time of all Mecynogea lemniscata web-sites with cocoons, and of sites with cocoons in the proper stage for attack in the experimental plot for 1983 ....................... 112

Table 8-1. The mean sphere density and median clutch size for individual spiders from different families ... .......................................... 131






































viii















LIST OF FIGURES


Figure 2-1. A string of Mecynogea lemniscata cocoons.................................... o o ........6

Figure 2-2. The cocoon of Argiope aurantia ....................... 9

Figure 3-1. Cooling rates in still air in the laboratory for whole and modified Argiope aurantia cocoons. ............. ............... o........... 16

Figure 3-2. Cooling rates outdoors for whole and modified Argiope aurantia cocoons in an artificial closed habitat over a 50 min period during an approximate 2.50 C change in ambient temperature....................... ..... ..... 18

Figure 3-3. Heating rates in still air outdoors for whole and modified Argiope aurantia cocoons under radiant loads of 2 and 10 min duration .................. 19

Figure 3-4. The relationship of internal cocoon temperature to habitat position for two Argiope aurantia cocoons. ............................ 21

Figure 4-1. The layer of spherical mucoid granules on the chorionic surface of a Mecynogea lemniscata egg and an Argiope aurantia egg .............................................. 30

Figure 5-1. The rate of water loading in the laboratory for the covers of Mecynogea lemniscata cocoons submerged in distilled water .................................................... ....... 50

Figure 6-1. A schematic view of an Argiope aurantia cocoon showing the four measurements taken to determine the position of the egg mass in relation to the cocoon cover ................................. 66

Figure 6-2. The relationship between the diameter of Argiope aurantia cocoons and the number of spiderlings (eggs) therein ........................................................ 68





ix










Figure 6-3. The covers of the cocoons of Mecynogea lemniscata and Argiope aurantia comparing the differences in the tightness of the weaving ........................................ 92

Figure 6-4. The ovipositor of the ichneumonid Tromatobia ovivora rufopectus showing recessed pits along its length and concentrated at the tip ....................................... 95

Figure 7-1. The relationship between proportional survival and cocoon density for Mecynogea lemniscata cocoons in four different sites ........................................... 107

Figure 7-2. The relationship between proportional survival and cocoon density for Mecynogea lemniscata cocoons within one site ................................................ 108

Figure 7-3. The number of Meycynogea lemiscata cocoons in a three-cocoon string available to a Tetrastichus wasp or her emerging progeny assuming an 11-day period for attack, or a more conservative 5-day period ............................ 119

Figure 7-4. The spatial distribution of all the Mecynogea lemniscata web-sites in the experimental plot for 1983 ................................. 121

Figure 8-1. The relationship between mean sphere density and clutch size for individual spiders from different families ....................................................... 133






















x














Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment
of the Requirements for the Degree of Doctor of Philosophy


THE ROLE OF THE COCOONS OF ORB-WEAVING SPIDERS


By


Craig S. Hieber


December, 1984


Chairman: John F. Anderson
Major Department: Zoology


The cocoons of spiders are believed to function in protecting the enclosed eggs and spiderlings from a number of biotic and abiotic factors. It has also been suggested that the wide diversity in cocoon architecture is the result of a "coevolutionary arms-race" between spiders and predators of their offspring. However, few studies have provided evidence to support these claims. This study provides evidence for some of these suggested functions by comparing the abilities of the cocoons of Mecnogea lemniscata and Argiope aurantia to control or limit temperature extremes, dessication, and attack by fungi and predators.

Results indicate that the cocoon of M. lemniscata limits

dessication and fungal attack on the spiderling stage. In contrast, the cocoon of A. aurantia does not. Both cocoons probably play a




xi










limited role in controlling temperature extremes from short-term radiant loads.

The cocoons of both species play a significant role in

protecting the eggs and spiderlings from generalist and specialist predators. The association between the various layers making up these cocoons, and the specific methods used to gain entrance by their predators strongly supports the notion of a co-evolved system. However, the multiple functions of many cocoon components suggest the architectural details have probably resulted from diffuse evolutionary pressure from a number of simultaneously operating factors, instead of as counter-adaptations to specific predators.

In general, these results support many of the previous

suggestions concerning cocoon function. Although specific functions are related to specific components within the cocoon, there can be great interspecific variation with relation to cocoon size and the relative sizes or thicknesses of the component parts of the cocoon. In addition, factors such as the size of the egg mass, the ultrastructure of the eggs, the habitat used for oviposition, the position of the cocoon within the habitat, and the reproductive behavior of the spider may also influence the ability of any part of the cocoon, or the whole structure, to limit the effects of any or all of the suggested factors affecting egg and spiderling survival.













Xii















CHAPTER !
INTRODUCTION


All spiders place their eggs in some form of silken cocoon (Turnbull 1973). For some, the cocoon is a relatively simple structure consisting of a few threads (e.g., the Pholcidae) and is used to move the egg mass about the web. In others, the cocoon provides a more complete container for carrying the eggs while hunting (e.g., the Lycosidae) or an additional level of protection for spiders which actively guard their eggs (e.g., the Oxyopidae). For many web-building spiders (e.g., the Araneidae), the cocoon is an elaborate structure composed of a variety of layers and is suspended in the habitat by different devices (McCook 1890, Scheffer 1905, Kaston 1948, Turnbull 1973). In many araneids where active care is non-existent, the cocoon represents the sum total of maternal care given to the eggs and spiderlings by the female.

Many web-building spiders deposit large clutches of eggs

(Kaston 1948, Foelix 1982). Within the cocoon, the eggs undergo embryonic development, hatch to the deutova stage, and molt to the spiderling stage. The spiderlings can spend as long as 6 to 10 months in the cocoon overwintering until emergence in the spring (Anderson 1978). This long time interval, the large clutch sizes, and the absence of active maternal care have led to many suggestions concerning the function of cocoons. These include providing physical support for the egg mass (Christenson and Wenzl 1980),


-I







2


protecting the enclosed eggs and spiderlings from thermal extremes (McCook 1890, Kaston 1948, Turnbull 1973, Gertsch 1979), dessication (Foelix 1982), fungal attack (Christenson and Wenzl 1980), drowning (Reichert 1981), UV light (Yoshikura 1969), and predator and parasite attack (Moore 1977, Austin and Anderson 1978, Robinson 1980, Austin, In press). Few studies, however, have examined the cocoons' effectiveness in controlling these factors.

I present here the results of several studies bearing on the functional roles that the cocoons of Mecynogea lemniscata (Walckenaer) and Argiope aurantia Lucas (Araneidae) play in protecting eggs and spiderlings from a number of biotic and abiotic factors. I also present results on the significance of cocoon timing and spacing, and how they interact with cocoon architecture to reduce predation. Both of these spiders use cocoons with dense covers (as opposed to the flocculent silk cocoon used by other araneids). However, they inhabit different environments, construct cocoons of different size and complexity, produce differing numbers of clutches, reproduce at different times of the year, and are attacked by different parasites. These differences are discussed in detail in Chapter II.

In Chapter III, I examine the role that cocoons, and in

particular the flocculent silk layer within many cocoons, play in controlling temperature extremes. Many authors have suggested that the flocculent silk layer acts as insulation (McCook 1890, Kaston 1948, Turnbull 1973, Gertsch 1979). Published reports on this function have been contradictory. Schaefer (1976) reported that







3


the cocoons of Floronia bucculenta (Clerck) (Linyphiidae) protect the eggs from daily changes in ambient temperature. In contrast, Austin and Anderson (1978) concluded that the flocculent silk cocoon of Nephila edulis (Koch) (Araneidae) does not do so.

Chapter IV presents a comparative analysis of the capabilities of the cocoons of A. aurantia and M. lemniscata to control water loss. Although this is commonly assumed to be one of their major functions (e.g. Bristowe 1941, Foelix 1962), the data supporting this view are contradictory. Schaefer (1976) showed that the cocoon of F. bucculenta effectively controlled water loss from diapausing eggs. However, Austin and Anderson (1978) demonstrated that the flocculent silk cocoon of N. edulis had no effect on egg hatching success. Casual observations by McEwon (1963) suggest that the cocoon of an Australian Nephila species limits spiderling desiccation.

Closely related to the problem of desiccation is the problem of excess water which, if allowed to enter the cocoon, could dissolve materials from the surface of the eggs and increase their susceptibility to disease (Austin and Anderson 1978). Water entering the cocoon could also carry pathogens (Christenson and Wenz! 1980) or could drown the eggs or developing spiderlings. Although Reichert (1981) strongly suggests that the cocoons of Agelenopsis aperta (Gertsch) (Agelenidae) protect eggs from flooding, only Schaefer (1976) and Austin (1984) have demonstrated such a role for a cocoon or brood nest, respectively. In Chapter V, I compare the abilities of the cocoons of M. lemniscata and







14


A. aurantia to control the entrance of excess water and to limit fungal attack.

In Chapter VI, I examine the architecture of the cocoons of M. lemniscata and A. aurantia and its relation to the control of predator and parasite attack. Although considered one of the primary roles of cocoons (Austin and Anderson 1978, Robinson 1980, Austin, In press), this function has not been examined for any spider.

Many parasites locate their hosts in a stepwise manner using a variety of chemical and physical cues (Salt 1935, Vinson 1975, 1976). A number of biotic and abiotic factors have been suggested as disrupting these cues, thereby affecting the success of the parasites (Hassell 1971, Hassell and May 1973, Vinson 1976, Morrison and Strong 1980, Stiling and Strong 1982). However, host behaviors such as the phenology of emergence and their effects on the temporal and spatial distribution of the host have not often been considered as factors affecting parasite success. In Chapter VII, I examine the seasonal timing of reproduction, the length of the reproductive season, the timing of cocoon production, and the resulting spatial and temporal distribution of cocoons as methods used in conjunction with cocoons to interrupt the foraging behavior of egg predators.

Chapter VII sum nrizes my major results and discusses their

relevance to the architecture of cocoons and to the diversity of reproductive tactics displayed by orb-weaving spiders.















CHAPTER II
THE EXPERIMENTAL ANIMALS, THEIR COCOONS, AND THEIR HABITATS


Mecynogea lemniscata (Walkenaer), the Basilica Spider


In northern Florida (at my study sites), M. lemniscata emerges in late March. Males mature in May and are found on the webs of females from early June to early July. The females mature in late May. Oviposition starts in mid-June and extends to mid-August with a peak in mid-July. Females disappear from their webs by late August.

The eggs of M. lemniscata take 16 days to eclose to the

deutoval stage at 25 C and 70% RH. The deutoval stage lasts 4 days until the molt to the first instar spiderling stage (Hieber 1984). The spiderlings remain in the cocoon through the late summer, fall, and winter, and emerge in mid- to late March the following year after spending approximately 290 days in the cocoon (Anderson 1978).

The webs of M. lemniscata are placed in the shrub layer of deciduous forests, approximately 1-2 m above the ground. The cocoons are deposited at the web site, suspended above the domed orb-web from a single support line (Fig. 2-1a). The cocoons are produced sequentially, and the strings may contain 1-10 cocoons (X =

3.1 cocoons, SD = 1.6, n = 38). The individual cocoons are small (3-4 mm dia.) (Fig. 2-1b), and contain 8-30 eggs (R = 13.5 eggs, SD = 6.3, n = 35) (Hieber 1984). The cocoon covering is olive-green in


5





















































4 mm





Fig. 2-1. A string of Mecynogea lemniscata cocoons suspended in the vegetation (A), showing the relative size of the cocoons (B), and with the external layer of silk peeled away to show the individual cocoons underneath (C). The external layer of siLk is composed of old orb-webs applied to the cocoon string by the female spider. This layer also contains detritus and prey remains.







7


color, extremely hard, and tightly woven. internally, there is a thin flocculent silk layer between the loose, non-agglutinated mass of eggs and the cocoon cover. The eggs are not enclosed in a membranous silk bag. The cocoons in a string are periodically covered with the damaged orb-web when it is replaced by the spider, giving the cocoon string an additional layer of loose dirty grey silk, detritus, and prey remains (Fig. 2-1c).

The eggs in M. lemniscata cocoons are attacked by two principal predators, the neuropteran Mantispa viridis Walker (Mantispidae) and the hymenopteran Tetrastichus sp. (Eulophidae) [near T. banksii Howard; see Hieber (1984)A. T"1ne eggs and spiderlings may also occasionally be attacked by ants, particularly if the support line breaks and the cocoons contact nearby vegetation or fall to the ground.

Mecynogea lemniscata is found in the shrub layer of southern deciduous forests (Levi 1980). In Florida, this spider prefers mesic hammocks, but can occasionally be found in more open habitats such as upland woods. In its preferred habitat, the humidity remains relatively constant (75-85% RH) during June and July (the egg laying and molting period) due to the overhead vegetation. From August on, the habitat dries and the RH may fall to 50% between rains. During the fall and winter, RH may fall as low as 30-40%. The temperature in this habitat is somewhat buffered due to the overhead vegetation which blocks the sun and it remains relatively constant (25-290 C) during the summer. From fall on, the temperature in the habitat follows the ambient temperature closely.







8


Argiope aurantia Lucas,
the Black and Yellow Garden Spider


In northern Florida (at my study sites), male A. aurantia mature in July and are seen on the webs of females from approximately mid-July to mid-August (see Levi 1968). Females mature in late July to August (see Levi 1968). Oviposition starts in early August and continues to October, with the greatest number of clutches laid in mid-August to mid-September. Females disappear from most study sites by late October.

Development to the deutoval stage (eclosion) takes

approximately 20-25 days in the laboratory at 250 C and 70-100% RH (see also Anderson 1978, Riddle and Markezich 1981). The deutoval stage lasts approximately 6 days before the molt to the pigmented first instar spiderlings. These spiderlings remain in the cocoon until late April or early May of the following year when they emerge.

Argiope aurantia builds its webs primarily in old field

vegetation, or in the vegetation at field edges. Its cocoons are large brown spheres, 1-2 cm in diameter. Females deposit their cocoons singly, away from the web site, suspended in the vegetation

0.5 to 4.0 m above the ground by a cloud of fine support lines originating from "minute conical or pyramidal deltas" on the cocoon surface (McCook 1890; pg. 75) (Fig. 2-2a). The cocoons are multi-layered (Fig. 2-2b). The outer covering is usually composed of a thin, stiff, parchmentlike material with a glazing applied to it (almost like fiberglass), although it may occasionally be made of













A. B.




1A
scd
SC






i cm










Fig. 2-2. The cocoon of Argiope aurantia suspended in the vegetation (A), and in cut away view (B) showing the position of the egg mass (em), silk cap (sc), silken cone and cord (scd), and flocculent silk layer (fsl) within the cocoon cover (cv).






10


a soft, thick, feltlike material. The agglutinated egg mass of 800-2000 eggs (R = 978.7 eggs, SD = 419.2, n = 40) is suspended within the cocoon from a thick silk cup, which in turn is attached to a cone and cord of strong silk which fills the stalk of the cocoon. The egg mass is covered by a fine membranous layer of silk, and is separated from the cover by a thick flocculent silk layer (see McCook 1890, pp. 79-80 for a complete description of the internal structure of the cocoon).

The eggs and spiderlings in A. aurantia cocoons are attacked by a number of general and specialized predators including the hymenopterans Tromatobia ovivora rufopectus (Cresson) (Ichneumonidae) (Cresson 1870, Keobele 1887, McCook 1890, Howard 1892, Champlain 1922, Enders 1974, Tolbert 1976), Pimpla aquilonia aquilonia (Cresson) (Ichneumonidae) (Davidson 1896), Chrysocharis banksii and Chrysocharis pikei (Entodontimidae) (McCook 1890), and Pediobius wilderi (Howard) (Entodontimidae) (McCook 1890) [this is probably a hyperparasite attacking T. ovivora rufopectus]; the dipterans Pseudogaurax signata (Loew) (Chloropidae) (Coquillet 1898), Pseudogaurax anchora (Loew) (Kaston and Jenks 1937, Eason et al. 1967), and Megaselia sp. (Phoridae) (Kaston and Jenks 1937); the neuropteran Mantispa viridis Walker (Mantispidae) (Enders 1974, Tolbert 1976); the coleopteran Chauliognathus sp. (Cantharidae) (Enders 1974); salticid spiders (Salticidae) (Enders 1974); and birds (Enders 1974, Tolbert 1976).

Argiope aurantia prefers vegetation along water courses in

Florida (Levi 1968), and is common in roadside hedgerows bordering







11


drainage ditches. In these ha-,bitats, the relative humidity is usually quite high (70-90% RH) in late August-September (the egg-laying and molting period), although exposure to high levels of insolation may cause periodic fluctuations of the RH over a wide range. By late fall, the RH may drop to 30-40%. The temperatures may be buffered somewhat by the vegetation in the summer, but are usually relatively close to ambient, although they may be quite high (35-400 C) in southern exposures. From fall on, the temperatures in the habitat follow ambient air temperature closely.














CHAPTER III
THE "INSULATION" LAYER IN THE COCOONS OF ARGIOPE AURANTIA


Introduction


All spiders place their eggs in some form of silken cocoon

(Turnbull 1973). These structures must provide protection for the eggs, create a proper microclimate for embryonic development, hatching, and subsequent molting, and provide a safe retreat for the spiderlings to overwinter until emergence in the spring. Because of the lengthy development and overwintering period of some spiders (Anderson 1978), many cocoons are exposed to severe temperature extremes. Fluctuations in cocoon temperature have been shown to have a direct effect on the development and survival of spider eggs (Norgaard 1956, Schaefer 1976) and spiderlings (Norgaard 1956). Several authors have observed spider behaviors which presumably modify the thermal environment of the cocoon. These include burying the cocoon (Levi and Levi 1969), shuttling the cocoon between different microclimates (Norgaard 1951, Humphreys 1974), and placing it in protected microclimates. Others have suggested that a layer of silk within some cocoons functions as insulation, modifying the thermal environment experienced by the eggs or spiderlings (McCook 1890, Kaston 1948, Turnbull 1973, Gertsch 1979). Schaefer (1976) reported that the cocoons of Floronia bucculenta (Clerck) (Linyphiidae) are capable of protecting the eggs from daily


12







13


fluctuations in ambient temperature. However, Austin and Anderson (1978) found no significant differences in the hatching success of spider egg masses, with or without cocoons, exposed to a range of constant temperatures. They concluded that the flocculent silk cocoons of Nephila edulis (Koch) (Araneidae) did not function to protect the eggs from temperature extremes.

The cocoon of Argiope aurantia Lucas (Araneidae) is a

multilayered structure, with a flocculent layer of silk located between the eggs or spiderlings and the cocoon cover (see Fig. 2-2b). In late August-September, the cocoons are usually placed in the upper strata of the vegetation where they may be exposed to direct sunlight, wind, and the night sky, all of which may alter the internal temperature of the cocoon throughout the development and overwintering period. Here, I examine the the role of the cocoon, and in particular the effectiveness of the flocculent silk layer within A. aurantia cocoons, in buffering temperature extremes. I also examine the role that cocoon positioning in the habitat plays as an adjunct method of temperature regulation.


Materials and Methods


I used three types of cocoons: whole, nonparasitized cocoons containing spiderlings, and two types of modified cocoons, "insulated" and "non-insulated". The latter two types were created by halving whole cocoons 'longitudinally with a razor blade and removing either the eggs alone, or the eggs and the flocculent silk layer. The halves of these modified cocoons were rejoined with







14


clear nail polish. These whole and modified cocoons were mounted on thermal probes (YSI #513, time constant of 0.02 s), with the tip of the probe in the approximate position of the egg or spiderling mass.

Cocoons were allowed to equilibrate to room temperature (T a 260 C) in a large cardboard enclosure, and then placed in a styrofoam cooler packed with salted ice. The internal temperature of the cocoon in the cooler was recorded every 30 s until it reached the ambient temperature of the cooler (T a = 8-9 0 C). The cooling trials were performed in a dark room to avoid radiant loading from the overhead lights, and with the air conditioning off to minimize the effects of convective cooling from air movement. The walls of the cardboard enclosure and the cooler were monitored with banjo probes (YSI #427, time constant of 1.10 s) taped to the inner surfaces. The temperatures of these surfaces matched the ambient air temperatures within each container. Only data from trials where the ambient temperature in the cooler varied by no more than

0-50C were used for the calculation of the cooling curves.

In the field, the changes in internal temperatures of whole and modified cocoons (using YSI #513 probes) in an artificial closed habitat (1 x I x 1 m cardboard enclosure) were recorded at one min intervals for 50 min over an approximate 2.5 0 C drop in ambient air temperature. On a different day, changes in internal temperatures (YSI #513) of whole and modified cocoons exposed to 10 min radiation loads, and to 2 min loads followed by 8 min of cooling were also recorded. This experiment was conducted between 1100 and 1300 h when the sun was at its zenith. During this time, ambient







15


temperature was relatively constant (12.9-13.60 C), and there was no wind. All the cocoons used in this experiment were approximately the same size, color, and mass. On a third day, the hourly changes in ambient air temperature (YSI #405 probe, time constant of 0.60 s) and in the internal (YSI #513) and surface temperatures (Ysi #427) of two cocoons in two different habitats (closed canopy under trees, open canopy in an old field) were recorded for 24 h. Simultaneous measurements of the sky and vegetation temperatures or enclosure wall temperatures were made with a Stoll-Hardy HL4 radiometer during all of the field experiments to measure the radiant heat load in the respective test habitats.


Results


There were no significant differences between the slopes of the cooling curves for the modified cocoons (Fig. 3-1). Both types of modified cocoons showed cooling rates of approximately 11 0 C/ min. In contrast, the whole cocoons cooled significantly more slowly than the modified cocoons (F = 356-71, p < 0.001); the presence of spiderlings (total cocoon weights 0.63 to 0.93 g; spiderling weights

0.56 to 0.83 g) decreasing the cooling rate to approximately 2.0 0 C/ min (Fig. 3-1).

Outdoors, in the artificial closed habitat, there were no

significant differences between the rates of cooling for the whole cocoon (total weight 0.809 g; spiderling weight 0.682 g), and the modified cocoons with and without the flocculent silk layer.















3.0






00
2.5- 1





C 0



0
1.0 0
00



0.5


0-0

0 I 2 3 4 5
TIME (min)



Fig. 3-1. Cooling rates in still air in the laboratory for whole and modified Argiope aurantia cocoons. The whole cocoons (squares) contained spiderlings and the flocculent silk layer; the modified cocoons contained only the flocculent silk layer (open circles), or were empty (closed circles). Th cooling curve for the whole cocoons is Y = -0.208X + 2.73 (r = 0.95, n = 6); for te modified cocoons with the flocculent layer Y = -0.824X + 2. 5 (r = 0.96, n = 10); for the empty cocoons Y = -0.810X + 2.66 (r = 0.90, n = 8). During cooling T a= 8-9 C. The data points represent the range for each set of experimental trials.







17


The internal temperatures of all three cocoons closely followed the change in ambient temperature (Fig. 3-2).

Among the cocoons exposed to radiation loads for 10 min, there was no significant difference between the rates of heating for the modified cocoon with the flocculent silk layer and the cocoon without it (Fig. 3-3). Both cocoons heated rapidly to an equilibrium temperature of 22.5 0 C in approximately 5 min. The rate of heating for the whole cocoons (total weights 0.9735 g and 0.9025 g; spiderling weights 0.7500 g and 0.7400 g, respectively) was significantly different from that for the modified cocoons (F 26.11, p < 0.0001; calculated for the first 4 min). These cocoons heated to approximately 19.0 0 C in 5 min; an internal temperature some 3.5 0 C cooler. Beyond this point, they heated at a slower rate. An extension of this second, flatter heating curve suggests that the whole cocoons would not reach the equilibrium temperature of the modified cocoons until another 15 min had elapsed.

The whole and modified cocoons exposed to the 2 min loads

heated at the same rates as their counterparts in the 10 min group (Fig. 3-3). The rates for the two groups of cocoons were significantly different from one another as well (F = 7.490, p

0.034; calculated on the first 2 min). When the radiation load was removed, the modified cocoons rapidly cooled to ambient air temperature. The whole cocoons also cooled upon removal of the load, but at a much slower rate (Fig. 3-3).

The absolute internal temperature achieved by whole cocoons in the field depended on their location in the habitat. While the






18



3.2


o 2.8


2.4

,0co cc


1.6 oc
2-0 man"



2 1.2
o O0
0.8





0.4
C 0 0
0.0 .o
0 10 20 30 40 50

TIME (min)


Fig. 3-2. Cooling rates outdoors for whole and modified Argiope aurantia cocoons in an artificial closed habitat (1 x 1 x 1 m cardboard enclosure) over a 50 min period during an approximate
2.50 C change in ambient temperature. The whole cocoon (squares) contained spiderlings and the flocculent silk layer; the modified cocoons contained only the flocculent layer (open circles), or were empty (closed circles). The cooling curve for the whole cocoon is Y = o.067X 1.57 (r = 0.99, n = 1); for t e modified cocoon with the flocculent layer Y = 0.066X 21.61 (r = 0.99, n = 1); for the empty cocoon Y = 0.065X 1.50 (r = 0.98, n = 1). The curve for2 the change in ambient temperature (stars) is Y = 0.060X 1.90 (r = 0.99). The temperatures of the top and sides of the enclosure during this period were 40 C and 50 C, respectively.






19


24.01

*o 0
0
0 @ 0 0
22.0 0 o




20.0.0

0
WU

10.0 -U


18.0 7




16.0




14.0

13.1*

0 1 2 3 4 5 6 7 8 9 10

TIME (min)




Fig. 3-3. Heating rates in still air outdoors for whole and modified Argiope aurantia cocoons exposed to radiant loads of 2 and 10 min duration. The whole cocoons (open squares, 2 min; closed squares, 10 min) contained spiderlings and the flocculent silk layer; the modified cocoons contained only the flocculent layer (stars, 2 min; open circles, 10 min), or were empty (closed circles, 10 min).2 The heating curve for the whole cocoons is Y = 0.50X + 13.44 (r = 0.98, n = 2); for the modified cocoons with the flocculent layer Y = 1.01X + 14.29 (r = 0.93, n = 1); for the empty cocoons Y = 0.96X + 14.47 (r2 = 0.94, n = 1). The ambient air temperature during the experiment ranged from 12.90 C to 13.70 C. The vegetation and sky temperatures during the experiment were +15 C and -20 C, respectively.







20


cocoon (total weight 0.820 g; spiderling weight 0.724 g) in the sheltered site (under overhanging vegetation) attained highs and lows close to the ambient air temperature, the internal temperature of the cocoon (total weight 0.991 g; spiderling weight 0.842 g) in the exposed site (open field) fluctuated widely, attaining much higher and lower values (Fig. 3-4). The surface temperatures of the cocoons equaled the ambient temperature in the shade (T surf = T a ) and were greater than both ambient and the internal temperature of the cocoons in the sun (T < T > M
a surf c


Discussion


Under laboratory conditions, the internal temperatures of whole and modified A. aurantia cocoons exposed to sudden drops in ambient temperature (from 260 C to 8-90 C) do not change instantaneously (see Fig. 3-1), indicating that some part of the cocoon acts as insulation. However, under these conditions the cooling rates for cocoons with and without the flocculent silk layer are identical, suggesting that it is the cover of the cocoon, and not the flocculent layer, that creates the dead air space that acts as insulation (Kaufman et al. 1982). This explains why Austin and Anderson (1978) found that the coverless, flocculent cocoons of N. edulis offered no protection to their egg masses; these cocoons have little or no dead air space. The whole cocoons also cooled four times more slowly than the modified cocoons (see Fig. 3-1). Presumably, this additional thermal inertia is due to the mass of the spiderlings, which are approximately 70% water (Anderson 1978).







21

[=Direct Sunlight MShade or Darkness Habitat/ OPen
Closed .




4 o Open Habitat
14 / *Closed Habitat
14 -,
121







6
LU
CL 4


2




-2 1

-4 I





1200 1800 2400 0600 1200

TIME OF DAY (h

Fig. 3-4. The relationship of internal cocoon temperature to habitat position for two Argiope aurantia cocoons. The solid lines
( -) are ambient temperatures, and the dashed lines ( --- ) are internal cocoon temperatures. Over 24 h, the cocoon in the open habitat (old field) was exposed to extended periods of direct sunlight, and faced greater reflected radiation from the vegetation (320 C to -150 C), and colder skyj temperatures (20 C to -39 C) than the cocoon in the closed habitat (old field edge under trees) faced from the vegetation (25 0 C to -10O0 C), or from the sky (250 C to -17 0 C).







22


The cocoon, in combination with the egg or spiderling mass,

acts as a buffer against rapid temperature changes (Fig. 3-1). Such rapid changes could result from exposure to the night sky immediately after sundown, particularly in the winter (see Fig. 3-4). However, most A. aurantia cocoons are placed within the vegetation. In these protected locations, radiant heat loss to the cold night sky is reduced by the warmer overhead vegetation. Under these conditions, cooling is slower and follows the change in ambient air temperature (see Fig. 3-2). Cold hardiness (Schaefer 1977, Riddle 1981) resulting from physiological solutions such as freezing point depression (Kirchner and Kestler 1969) probably protects the eggs or spiderlings from extremely cold temperatures.

Cocoons in open habitats but under a layer of vegetation, or in closed habitats such as woods may still be exposed to periodic "1sunflecks" as the sun moves across the sky. These short lived, but potentially intense, radiant loads could present a serious thermal challenge to the cocoon. The field experiments indicate that the cocoon and the mass of the eggs or spiderlings provide a significant buffer against short-term loads (see Fig. 3-3), extending the heating time to equilibrium by approximately 15 min. However, the level of protection provided by a cocoon is directly related to the ambient air temperature, the duration of the load, and the elapsed time between consecutive loads. The radiant loading experiments were conducted in the winter, when the ambient air temperature was relatively low (12-l40 C). Even with constant exposure to insolation, low ambient temperatures such as these would result in a







23


low equilibrium temperature (Heath 1964) that is probably below the danger level for the spiderlings in the cocoon. However, during the early part of the reproductive season, when the ambient temperature is relatively high, radiant loads may represent a more serious problem. Under these conditions, a load of long duration could raise the equilibrium temperature of the cocoon past the safe limit for the eggs or spiderlings. Loads of short duration also pose a problem if they occur in rapid enough succession. Under these conditions, the internal temperature of the cocoon would "step" up with each successive load due to the slow rate of heat loss from the egg or spiderling mass (see Fig. 3-3), finally rising above the lethal limit.

Other behaviors may play a role in insuring that the cocoon is not exposed to lethal thermal loads. Argiope aurantia prefers to oviposit beneath a layer of vegetation or among the leaves of broad-leafed plants. Such sites would limit the number and length of insolation bouts the cocoon encounters, particularly during the late summer when oviposition occurs. The comparison of internal temperatures from cocoons in open and closed habitats supports maternal positioning of the cocoon as an important control measure (see Fig. 3-4). Positioning the cocoon in a closed site rather than in an open site resulted in a 10 0 C difference between the highest internal temperature achieved (because of radiation loading), and a 40 C difference in the lowest temperature achieved (because of exposure to cold night sky temperatures). Although spiderlings can t Tolerate high temperatures (Tolbert 19719), proper site choice could







24


mean a few degrees difference in internal cocoon temperature. This difference may be important when the ambient temperature approaches the upper critical temperature of the eggs or spiderlings.

The limited ability of the relatively large A. aurantia cocoons to resist temperature fluctuations suggests that cocoons with smaller masses of eggs or spiderlings will have more difficulty in controlling temperature extremes. The non-functional role of the flocculent silk layer as insulation further suggests that cocoons may function to regulate other factors in the environment. Due to the small size of the eggs and spiderlings, and their consequent high surface area to volume ratio, it seems likely that cocoons may play a role in limiting water loss. This role is explored in Chapter IV.














CHAPTER IV
THE ROLE OF SPIDER EGGS AND COCOONS IN RESISTING WATER LOSS


Introduction


All spiders enclose their eggs in some form of silken cocoon

(Turnbull 1973). Within these structures the eggs undergo embryonic development, hatch to the deutova stage, and molt to the spiderling stage. The spiderlings then spend from 6 to 10 months in the cocoons until emergence in the spring. Dessication may be a problem for these developmental stages. Many insects use cocoon-like structures to limit dessication (Chapman 1967, Chauvin et al. 1979), and this is commonly assumed to be the function of cocoons as well (Bristowe 1941, pg. 421; Foelix 1982, pg. 200). Few data exist, however, to support this view. Schaefer (1976) showed that the parchmentlike cocoon of Floronia bucculenta (Clerck) (Linyphiidae) increased the survival time of post-diapause eggs exposed to a RH of 32% (at 50 C) from 37 to 68 days. Austin (1984) has demonstrated that the silk nests containing eggs of Clubiona robusta L. Koch (Clubionidae) increases humidity levels. The casual observations of McEwon (1963) also suggest that the flocculent cocoon of an Australian Nephila sp. (Araneidae) provides desiccation protection for the spiderlings. Austin and Anderson (1978), however, have showed that the flocculent silk cocoon of the congener N. edulis



25







26


(Koch) has no effect on the hatching success of spider egg masses at different controlled humidities.

Some spider eggs are dessication-resistant as well (Schaefer 1976). This resistance may result from a layer of spherical granules on the chorion surface (Austin and Anderson 1978, Grim and Slobodchikoff 1978, 1982, Humphreys 1983). Overwintering spiderlings within the cocoon can also attenuate water loss by reducing their rates of metabolism (Schaefer 1976, Anderson 1978), or by metabolizing lipids. Presumably, the cuticle of spiderlings also impedes water loss (Lees 1947, Davies and Edney 1952).

I investigate here the role of the cocoon in controlling water loss from the egg and spiderling masses of Mecynogea lemniscata (Walckenaer) and Argiope aurantia Lucas (Araneidae) during egg development, deutoval molting, and spiderling overwintering. I also examine the effect of clutch size, and egg morphology (Austin and Anderson 1978, Grim and Slobodchikoff 1978, 1982) on water loss.


Materials and Methods


The Cocoons and Their Habitats


The cocoons of M. lemniscata and A. aurantia differ in size, density of the cover, and internal construction. The preferred habitats of the two spiders also differ, the habitat of M. lemniscata being more consistently humid than that of A. aurantia (see Chapter II).







27


Experimental Material


The cocoons and egg masses of A. aurantia were obtained from spiders collected in the field and maintained at 24-250C and 60-70% RH in 500 ml jars in the laboratory. The M. lemniscata cocoons and egg masses were obtained by daily censusing 100-150 marked web-sites. The cocoons used in the experiments on spiderling survival were collected in the field in late August (for M. lemniscata), and during September-October (for A. aurantia). Only undamaged, nonparasitized cocoons were utilized. The experimental spiderling masses were obtained by removing the cocoon cover and as much of the internal flocculent layer of silk as possible.


Egg Surface Morphology


The surfaces of M. lemniscata and A. aurantia eggs were

photographed with a Hitachi S-415A SEM. They were prepared by attaching them to SEM stubs with double-sided tape, and coating with 75 A of gold. The densities of the spherical granules (spheres) on egg surfaces were measured by placing a grid system (4 x 4 lines) over the electronmicrographs of five eggs of each species and counting all spheres within 2 randomly chosen grid-squares. Since the spheres on both species' eggs are distributed essentially as monolayers (Humphreys 1983), densities were expressed as the mean
2
number of spheres/ 100 11m Sphere diameters were determined directly by measuring all the spheres within the 10 grid-squares.







28


Effect on Dessication


The effects of the sphere layer, clutch size, and the cocoon on hatching success, molting success, and spiderling survival were determined by rearing intact egg and spiderling masses without cocoons (and appropriate controls) at 25-260 C in one liter jars controlled at four different RH levels (0%, 33%, 66%, and 100%). The controlled humidities were achieved by using dry anhydrous KOH pellets (0% RH), and saturated salt solutions of 300+ g CaC12/ 100ml H 20 (33% RH), 100 g NaNO2/ 100 ml H20 (66% RH), and 15 g K2 s4/ 100 ml H20 (100% RH) (Winston and Bates 1960, Peterson 1964). The pellets and solutions controlling the humidities were changed every two weeks. Since the egg masses of A. aurantia contain more eggs than those of M. lemniscata (approximately 970 to 20, respectively), artificially reduced egg masses of 15-25 A. aurantia eggs were also reared under these conditions to control for the possible effects of egg mass size on hatching success.

The effect of the cocoon was also tested under field conditions by placing intact egg and spiderling masses (and appropriate controls) in individual screen-covered vials within styrofoam-cup housings. These housings protected the replicates from precipitation, predators, and parasites, and were hung in the shade in locations where females had previously constructed cocoons.

Hatching and molting success was calculated after 30 days. Hatching success was the percentage of total eggs in which the chorion ruptured and a deutova successfully emerged. Molting







29


success was the number of these deutova which successfully molted to the first instar spiderling stage. Spiderling survival was determined using separate masses, and was calculated after the experiments had run for 90 days.


Results


The Sphere Layers


The spheres associated with the eggs of M. lemniscata and

A. aurantia are shown in Fig. 4-1. For both, the sphere diameter ranged from 0.40 to 7.20 pm. The mean diameter in M. lemniscata eggs was not significantly different from that of A. aurantia eggs (Table 4-1). However, the mean sphere density (spheres/ 100 PM2 ) of M. lemniscata eggs was significantly greater (t = 2.11, df = 20, p < 0.05) than that of A. aurantia eggs. The Effect of Clutch Size and the Sphere Layer


No significant differences in hatching success at 100% RH were found between intact and reduced A. aurantia egg masses without cocoons at each humidity (Table 4-2). Reduction of the egg mass, however, did have a significant effect at 66%, 33%, and 0% RH, indicating that the size of the egg mass of this spider is important to dessication control. There were no significant differences at oo%, 66%, and 33% RH when the hatching success of intact M. lemniscata and A. aurantia egg masses without cocoons was






30



A.




















B.





















Fig. 4-1. The layer of spherical mucoid granules on the chorionic surface of a Mecynogea lemniscata egg (A), and an Argiope aurantia egg (B). The scale line in each case equals 15 um. Both eggs were plated with 75 A of gold and observed using secondary electrons.







31


Table 4-1. The distributions of sphere sizes found on the chorionic surfaces of Mecynogea lemniscata and Argiope aurantia eggs. The mean sphere sizes and mean sphere densities ( 1 SD; n in parentheses) are given below the frequency column for each species.




Frequency


Sphere Size
Diam. (jm) M. lemniscata A. aurantia


0.40 0.79 9 2
0.80 1.19 57 17
1.20 1.59 104 117
1.60 1.99 47 26
2.00 2.39 12 2
2.40 2.79 3 0
2.80 3.19 1 0
3.20 3.59 2 0
3.60 3.99 0 0
4.00 4.39 2 0
4.40 4.79 0 1
4.80 5.19 1 2
5.20 5.59 1 0
5.60 5.99 1 0
6.oo00 6.39 1 0
6.40 6.79 0 0
6.80 7.19 1 1


Mean Sphere X = 1.56 0.79 X = 1.52 0.70
Size (242) (168)


Mean Sphere X = 21.60 5.46 R = 17.00 4.22
Density (10) (10)






32


Table 4-2. Mean percentages of eggs successfully hatched ( 1 SD; n in parentheses) at the four experimental humidities for intact Mecynogea lemniscata and Argiope aurantia egg masses with and without cocoons, and for reduced A. aurantia egg masses without cocoons. Pair-wise comparisons between treatments are by Mann-Whitney U Tests; pair-wise comparisons between humidities within treatments are by nonparametric multiple comparison tests (Zar 1984).



% Hatching Success


M. lemniscata A. aurantia


Relative No Cocoon/ No Cocoon/ No Cocoon/
Humidity Cocoon Intact Reduced Intact Cocoon

94.9 98.3 96.2 99.7
100% 13.5% 3.1% 4.0% 0.5% 100%
(10) (8) (5) (8) (8)


95.4 97.4 49.2 94.3 90.0
66% 14.6% 4.6% 36.8% ** 11.3% 24.8%
(1O) (10) (8) (8) (7)



96.9 88.7 28.7 87.9 96.6
33% 7.9% 15.5% 32.3% ** 7.0% ** 5.8%
(10) (10) (10) (9) (7)



3.4 3.6 6.7 70.4 88.2
0% 7.3% 8.3% 5.7% 22.8% 17.5%
(10) (10) (O) (8) (8)


KruskallWallis H 29.43 25.80 17.70 21.70 8.29
"p" < 0.001 < 0.001 < 0.001 < 0.001 < 0.05


p < 0.05; ** p < 0.01; *** p < 0.001)







33


compared at each humidity. There was a significant difference at 0% RH, underscoring t.he advantage of a large egg mass.

A different pattern of hatching success was revealed when

intact M. lemniscata egg masses without cocoons were compared to reduced A. aurantia egg masses without cocoons at each humidity (Table 4-2). The significant advantage previously demonstrated by the whole A. aurantia egg masses at 0% RH disappeared, and hatching success dropped significantly below that of M. lemniscata at 66% and 33% RH, presumably because of differences in the densities of the the sphere layers covering the eggs of each species. There were no significant differences at 100% RH, where dessication is obviously not a problem.


The Effects of the Cocoons


Cocoon removal had no effect on the hatching success of

M. lemniscata at any experimental humidity (Table 4-2). Below 33% RH, there were significant decreases in hatching success for egg masses with and without cocoons. Molting success showed no significant reduction with cocoon removal at any experimental humidity (Table 4-3). Since few eggs hatched at 0% RH, however, the percentage of total eggs which ultimately molted was small. The cocoon did have a significant effect on spiderling survival. At all the experimental humidities survival was greater with a cocoon (Table 4-3). The field results support these findings (Table 4-4); only spiderling survival was significantly affected by removal of the cocoon.







34

Table 4-3. Mean percentages for molting success and spiderling survival ( 1 SD; n in parentheses) at the four experimental humidities for Mecynogea lemniscata egg and spiderling masses with and without cocoons. Pair-wise comparisons between treatments are by Mann-Whitney U Tests; pair-wise comparisons between humidities within treatments are by multiple range tests (Zar 1984).




% Molting % Spiderling
Success Survival

Relative
Humidity Cocoon No Cocoon Cocoon No Cocoon


99.1 80.0
100% 100% 2.5% 100% *** 25.1%
(8) (8) (13) (6)



81.9 56.2
66% 100% 100% 29.8% ** 28.8%
(10) (10) (13) (14)



47.4 1.0
33% 100% 100% 38.1% 2.7%
(10) (10) (11) (14)



6.8
0% 100% 100% 13.7% ** 0%
(10) (10) (14) (14)

KruskallWallis H 0.00 0.00 35.44 38.22

p 1.00 1.00 < 0.001 < 0.001


p < 0.05; ** p < 0.01; *** p < 0.001)






35

Table 4-4. Mean pecentages ( i1 SD; n in parentheses) for hatching and molting success and spiderling survival in the field for the spiders Mecynogea lemniscata (ML) and Argiope aurantia (AA). Conditions in the field (60-80% RH and 24-32uC) approximated the laboratory conditions at 66% RH. The data are presented as percentages, but were arc-sine transformed for the statistical analyses (Sokal and Rohlf 1969).



% Hatching % Molting % Spiderling
Success Success Survival


Spider Cocoon No Cocoon Cocoon No Cocoon Cocoon No Cocoon


99.6 99.3 98.2 50.7
ML 1.9% 2.7% 100% 100% 12.7% 27.0%
(19) (17) (19) (17) (21) (10)
[-- *** ICocoon No Cocoon Cocoon No Cocoon Cocoon No Cocoon


99.8 99.8 93.3 91.8
AA 0.7% 0.4% 100% 100% 0.9% 2.9%
(10) (10) (10) (10) (10) (10)


*** F-test: F = 15.12, df = 29, p = 0.005.







36


The results for A. aurantia differed from those for

M. leinniscata. In the laboratory, cocoon removal had no significant effect on watching success at 100%, 66%0, or 0%Y RH, although it did significantly affect success at 33% RH (Table 4-2). Cocoon removal had no significant effect on molting success at any experimental humidity. However, at 33% and 0% RH the variances in the non-cocoon cells were mu~ch larger, suggesting that an effect may have been

difficult to detect. Molting success fell off significantly below 66% RH with and without a cocoon (Table 4-5). The absence of a cocoon also made no difference in spiderling survival at either 100% RH or 66% RH (Table 4-5). However, below 100% RH spiderling survival significantly declined with and without cocoons, and below 66% RH all the spiderlings died after 90 days regardless of the treatment. The results from the field experiments support the laboratory results at 100% and 66% RH (Table 4-4). Under field conditions, cocoon removal had no significant effect on egg hatching success, molting success, or spiderling survival.


Discussion


The results indicate that the enclosed cocoons of M. lemniscata and A. aurantia do not affect water Loss from the egg stage. These findings are paradoxical, since they support the findings of Austin and Anderson (1978) for a flocculent cocoon, but do not agree with Schaefer's (1976) findings for a covered cocoon. This paradox may be explained by the amount of time the eggs of these spiders spend in the cocoon. The developmental times of M. lemniscata






37


Table 4-5. Mean percentages for Molting Success and Spiderling Survival ( 1 SD; n in parentheses) at the four experimental humidities for Argiope aurantia egg and spiderling masses with and without cocoons. Pair-wise comparisons between treatments are by Mann-Whitney U tests; pair-wise comparisons between humidities within treatments are by nonparametric multiple comparson tests (Zar 1984).



% Molting % Spiderling
Success Survival

Relative
Humidity Cocoon No Cocoon Cocoon No Cocoon


98.8 93.7
100% 100% 100% 1.5% 8.2%
(8) (8) (7) (5)



99.1 61.5 63.5
66% 100% 2.0% 27.5% 19.6%
(7) (8) (6) (8)


96.0 76.2
33% 4.2% 34.8$ 0% 0%
(7) (9) (8) (8)

84.4 56.1
0% 19.0% 48.o% 0% 0%
(8) (8) (9) (9)

KruskallWallis H 22.40 11.09 27.18 27.99
itp"i < 0.001 < 0.01 < 0.001 < 0.001


p < 0.05; ** p < 0.01; *** p < 0.001)







38


and A. aurantia are relatively short (15-20 days and 20-30 days, respectively), and even at low humidities this may not be long enough to demonstrate the water retaining qualities of the cocoon. In contrast, the eggs of F. bucculenta remain within the cocoon in winter diapause for approximately 180 days. Since the eggs are not particularly drought resistant (Schaefer 1976), they probably lose

water during this time. The significant effect of the cocoon on egg survival, that Schaefer demonstrated, can probably be attributed to his use of post-diapause eggs, from which enough water had already been lost to make the effect of cocoon removal apparent.

The significant difference in hatching success between intact

and reduced A. aurantia egg masses without cocoons demonstrates that clutch size can affect hatching success as well. Spider egg masses are usually agglutinated, and as the mass gets larger, its surface area to volume ratio declines as a greater number of eggs are positioned completely within the mass. Presumably, this difference also accounts for the difference in hatching success between intact M. lemniscata and A. aurantia egg masses without cocoons at 05% El (see Table 4-2).

The ability of intact M. lemniscata egg masses without cocoons to maintain hatching success rates equal to those of the much larger A. aurantia egg masses at humidities above 0% RH indicates that some factor other than clutch size is also operating to control water loss (see Table 4-2). A number of authors have suggested that a layer of spherical mucoid granules (Austin and Anderson 1978) on the chorions of spider eggs funct ions to control water loss by reducing







39


the free surface area through which water can pass (Austin and Anderson 1978, Grim and Slobodchikoff 1978, 1982, Humphreys 1983). The eggs of M. lemniscata have a significantly denser coating of these spheres than do the eggs of A. aurantia (see Table 4-1). Although a direct comparison of the eggs of each of these species with and without spheres is difficult (due to problems in stripping the sphere layer from the eggs and still maintaining viability), the comparison of intact M. lemniscata egg masses with reduced A. aurantia egg masses strongly suggests that the sphere layer does reduce water loss (Table 4-2). However, the drop in hatching success at 0% RH indicates that this barrier has limits in its ability to control water loss at very low humidities.

Molting is a dangerous period of time for deutova with their high surface area to volume ratio (Horner and Starks 1972). At molting, with the breaking and subsequent shedding of the egg chorion, dessication protection shifts back to the level of the cocoon. In spite of this, removal of the cocoons of M. lemniscata and A. aurantia demonstrate no effect on molting success (see Tables 4-3 and 4-5). However, the variances among the no-cocoon treatments of A. aurantia at 33% and 0% RH are high, which may make detection of the cocoon's effect on molting success difficult. Presumably, the main factor affecting molting success for these spiders is the ambient RH at the oviposition site, although the greater molting success of M. lemniscata at low humidities suggests that there may be morphological or physiological differences in the abilities of the deutova of these species to reduce water loss.







4o


The cocoon of A. aurantia also appears to have little effect on spiderling survival. The lack of a cocoon effect on hatching and molting success, and the significant drops in molting success and spiderling survival below 66% RH suggest that other considerations are more important to reducing desiccation. Field observations of damaged A. aurantia cocoons suggest that the large clutch size of this species may protect the eggs from dessication [which may also explain McEwon's (1963) observation for the Nephila sp.1. However, the RH within the habitat or microhabitat used for oviposition is probably most critical for A. aurantia. Indeed, Levi (1968) notes that of the Argiope species in Florida, A. aurantia prefers moist habitats such as pond edges and stream borders, and is one of the first Argiope species to disappear during drought years.

Removal of the cocoon does have a significant effect on the

spiderling survival of M. lemniscata at all experimental humidities (see Table 4-1), and in the field under ambient conditions (see Table 4-3). This spider is the first of the orb-weavers to become active in the spring, emerging in late March. Growth is rapid. Reproduction begins by late June and the adults die by early to mid-August. This early emergence and rapid disappearance is apparently a means of taking advantage of the abundant prey in the habitat, while avoiding competition with other orb-weavers whose populations increase rapidly by August (Anderson 1978). The spiderlings then spend approximately 290 days in the cocoon until they emerge the following March; 2 to 3 months longer than most other orb-weavers (Anderson 1978). The cocoon is apparently part of







41


a suite of adaptations for controlling water loss [including depressed metabolic rates (Schaefer 1976, Anderson 1978), and lipid-rich eggs (Anderson 1978)], and fits into the foraging/ reproductive strategy of this spider by providing a desiccation-resistant refuge in which the spiderlings spend these additional months overwintering.

A number of the egg and spiderling replicates of M. lemniscata and A. aurantia held at 100% RH in the laboratory were attacked and destroyed by fungus. Although these replicates were removed prior to data analysis, in some cases there was still a significant reduction in survival without cocoons at 100% RH (see Table 4-3 for M. lemniscata spiderlings), a humidity where survival should be unaffected by desiccation. This suggests that the covers of cocoons may be related to resisting fungal attack (Christenson and Wenzl 1980), possibly by limiting the amount of water which can enter the cocoon. Chapter V addresses this possibility, and considers the cocoon as a barrier to fungal attack.















CHAPTER V
THE ROLE OF THE COCOON IN LIMITING EXCESS WATER AND FUNGAL ATTACK


Introduction


Although desiccation is a problem for developing spider eggs and overwintering spiders, too much water may also cause adverse effects. Water, entering the cocoon, could dissolve materials from the egg surface and lower the resistance of the eggs to disease (Austin and Anderson 1978). It could also drown the contents of the cocoon (Schaefer 1976, Reichert 1981). Water may also introduce fungal spores that are pathogenic to the eggs or spiderlings. Christenson and Wenzl (1980) suggested that the cocoon of Nephila clavipes (Linneaus) (Araneidae) protects against fungal attack by reducing the chance of spores gaining access to the egg mass. A role in protecting the eggs and spiderlings from fungi seems reasonable, since both spiders (Bijl and Paul 1922, Nellist 1965) and their eggs (Seligy 1971, Christenson and Wenzl 1980) are attacked by fungus.

Both Mecynogea lemniscata and Argiope aurantia utilize a covered cocoon (see Figs. 2-1 and 2-2), in contrast to the flocculent silk type used by many other orb-weavers (McCook 1890, Scheffer 1905, Kaston 1948). Both spiders also utilize habitats where high humidity during the egg laying period may promote fungal attack (see Chapter II). In this chapter, I examine the roles of


42







43


the suspension systems, the internal flocculent layers, and the coverings of the cocoons of these spiders in protecting the eggs and spiderlings from excess water, drowning, and fungal attack.


Materials and Methods


Laboratory Experiments


The abilities of the cocoon suspension system, the cocoon

cover, and the internal flocculent silk layer to limit the access of water to, or into the cocoon were examined in the laboratory using M. lemniscata or A. aurantia cocoons as appropriate. The temperature and humidity in the laboratory during all the experiments were 25 0 C and 50-60% RH, respectively.

To examine the function of cocoon suspension systems in

shedding water, M. lemniscata cocoon strings were hung between two vertical supports by their silk suspension lines (see Fig. 2-1). The angle of inclination of the suspension lines was set at 10, 20, 30, and 45 0 from the horizontal. At each of these angles, water was applied to the suspension lines with a dropper, and its course down the lines noted.

The ability of cocoons to shed water was examined by applying

1.00 ml of water with a syringe directly to hanging strings of M. lemniscata cocoons. The runoff was collected, and the amount retained by the cocoon string calculated. Both naked strings, and those covered with a layer of silk and detritus (see Fig. 2-1c) were tested in this manner. The abilities of both M. lemni4scata and







44


A. aurantia cocoons to shed water were also examined in the field during periods of rain.

To determine whether water actually penetrates the cocoon

cover, 10 samples of 2-3 dry M. lemniscata cocoons were submerged in distilled water for time periods of 7, 15, 30, 6o, 120, 24o, and 48o min. Upon removal from the water, they were blotted on Whatman #1 filter-paper discs for 1 min to remove surface water, and weighed on a Mettler AK 160 balance to the nearest 0.0001 gm. The 10 samples were air dried for 24 hrs between each submersion. After the last submersion bout (480 min), the 22 cocoons comprising the 10 samples were opened and examined under a microscope for the presence of water.

The volume of water absorbed by each cocoon sample was

calculated from the increased weight of the sample (1 gm water = 1 ml = 1 cc). This was normalized to ml/ cm 2 by dividing the volume of water by the combined surface area of the cocoons in each sample. A mean value was then calculated from the 10 values for each submersion time.

'"he role of the flocculent silk layer in resisting water was also tested. Here, flocculent silk from A. aurantia. cocoons was used. Uncompressed pieces of this layer were placed on glass slides and drops of distilled water were applied to the silk. The pieces were observed for approximately 10 min, and any wetting of the silk through wicking was noted.







45


Field Experiments


The function of the cocoon suspension system and the cocoon cover in limiting fungal attack and drowning were investigated by modifying these components in the field, and assessing their effect on egg hatching success and spiderling survival. The cocoons used in these studies were either reared in the laboratory, or collected in the field from marked web-sites. Only nonparasitized cocoons were used.

The cocoons were assigned to the four experimental groups

listed below. The experiments using cocoons with eggs were run for 30 days; those using cocoons with spiderlings for 90 days. The cocoons not associated with apparatus were marked by plastic

flagging attached to the vegetation.

Vegetation contact. The effect of cocoon suspension systems in preventing fungal attack was examined by placing M. lemniscata cocoons in contact with the vegetation. This simulated partial collapse of the suspension system, and placed limitations on the cocoons drying normally. Placement was accomplished by cutting the cocoon free, and tying it in place to the vegetation with its support line. Access to the cocoons by terrestrial predators was controlled by applying tack-trap to the branches below the cocoons, and pruning the branches above the cocoon so they did not contact the surrounding vegetation. Argiope aurantia cocoons were not subjected to this treatment.








46


Ground placement. This manipulation also tested the function of the suspension system, but placed the cocoons in a wetter microhabitat where drying was more difficult and the chance of fungal attack or drowning was greater. Both M. lemniscata and A. aurantia cocoons were placed on the ground in enclosures. For A. aurantia cocoons, these were constructed of hardware cloth (1/411 mesh), and were 10 x 10 x 10 cm. in size. The enclosure for M. lemniscata cocoons was similar in design, but was constructed of aluminum window screen, and was 5 x 5 x 5 cm in size. These enclosures allowed exposure of the cocoon to the elements, protected

them from large predators (although ants could still get in), and prevented them from washing away during heavy rain storms. They were placed below positions where cocoons had previously been collected.

Cover removal. To determine the roles that the covers of

M. lemniscata and A. aurantia cocoons play in controlling fungal attack, approximately 20-30% of their covers were removed. During the cover modification, care was taken not to disturb the flocculent silk layer (see Fig. 2-2b), or damage the eggs or spiderlings. The cocoons of M. lemniscata were modified in place in their respective strings. They were treated normally by the female spiders, which remained at the web-site after the modification. The laboratory produced cocoons of A. aurantia were modified, and attached by alligator clips to the arms of a support system. The support was placed in the vegetation in areas where cocoons where already







47


hanging. Tack-trap was applied to the support arms to limit the access of terrestrial predators (primarily ants).

Cover removal control. This group functioned as a control for possible contaminating effects of the alligator clips. The clips were attached to the necks of cocoons hanging normally in the habitat, and the cocoons were observed for any detrimental effects.

Control. A number of cocoons were subjected to no structural intervention, and functioned as a control for the handling effects in the vegetation placement, ground placement, and cover removal experiments.


Results


Laboratory Experiments


The suspension lines of M. lemniscata cocoons are relatively

poor conductors of water. At all the inclinations tested, dry lines were not easily wetted, and consequently tended to shed water. Suspension lines could be wetted by rubbing them between wet fingers, but even here water moved with difficulty. At the lower angles of inclination (10 and 200), 'water applied to the wetted line formed drops or beads and hung in place. At the higher inclinations (30 and 450), water moved down the line toward the cocoons. However, the suspension lines of M. lemniscata cocoons are made of multiple strands of silk and contain "knots" and incorporated debris. When water moving down the line got to these points it built to a drop and fell from the line.







48


The cocoons of M. lemniscata also shed water well. Depending on whether the cocoon string is naked, or covered with a layer of old web and detritus (see Fig. 2-1), approximately 0.85 to 0.95 ml of the 1.00 ml of water applied to the cocoon string with a syringe was shed immediately. Most of the remaining water forms a droplet at the end of the last cocoon in the string, or remains in the silk over-layer where it disappears by evaporation. Observations of M. lemniscata and A. aurantia cocoons under rainy conditions in the field yielded results similar to those observed in the laboratory. The suspension lines of both species had beads of water hanging on them and appeared not to conduct water toward the cocoons. Both cocoons also shed drops of water from the bottom of the cocoon or end of the cocoon string.

The ability of cocoons with covers to rapidly shed water

appears to be related to the slow rate at which their covers absorb water (Fig. 5-1). Over a 2-hr period, the covers of averaged sized
2 .
M. lemniscata cocoons (0.5 cm, In total surface area), absorb only 0.0014 ml of water. Even after 8 hrs of immersion, the amount of water absorbed has increased to only 0.0020 ml.

The thickness of the covers of M. lemniscata cocoons vary between 0.3 and 0.8 mm. The cover is not solid, rather it is a matrix of fibers with included air spaces, similar to fiberglass insulation. Assuming that approximately 50% of the cover is airspace that can be replaced with water, the cover should be able to hold between 0.0015 and 0.0039 m! of water. The 0.0020 ml of water absorbed by the cocoon after 8 hrs of immersion is consistent















4-)












H
cn


0)



4-)




04-' c






~0J







0 4-) C) 4-) P4




P.4
CU) 4J 4 W

3



0)

.p-q
4-)4-' C 4'd ) 4-' ac0) to W 0) Cd






50









0 co














0







0 cm


0 to

0 0
ui to N

(0001%) aoo;jnS uooooo 2 wo /Japm jw







51


with these calculations, and suggests that it is the cover alone which absorbs water before the excess is shed by the cocoon. Examination of the cocoons under the microscope supports this. None of the 22 cocoons had water inside them after 4 hrs of submersion.

The flocculent layer of A. aurantia cocoons was completely

non-wettable. Water applied to the silk simply formed beads and sat upon the silk until it disappeared by evaporation.


Field Experiments


The incidence of fungal attack on M. lemniscata cocoons containing eggs in the control group was 7.3% (Table 5-1). Chi-square tests between this group, and the Vegetation Contact, Ground Placement, and Cover Removal groups revealed no significant differences in the number of cocoons in the egg stage attacked by fungus. This suggests that neither the cocoon cover, nor the cocoon suspension system function to protect the eggs from fungal attack. There was, however, a significant increase in egg mortality among

2
those cocoons placed on the ground (X = 12-39, df = 1, P < 0.005). The eggs in these cocoons were all killed, presumably by drowning. They were not covered with fungus.

The natural incidence of fungal attack on M..lemniscata cocoons in the spiderling stage was 1.0% (Table 5-2). Contact with the vegetation did not significantly increase the number of cocoons attacked by fungus in this stage. However, there were significant. increases in the number of cocoons attacked by fungus among those

2
placed on the ground (X = 9.93, df = 1, P < 0.005). Cocoons with







52


Table 5-1. The effect of modification of the cocoon suspension system and cover on the incidence of fungal attack on the eggs of Mecynogea leinniscata. Cocoons in the "Other" category contained eggs which were not attacked by fungi, but did not hatch due to inviability or drowning. In many cases the eggs rotted. All cocoons were collected after 30 days.




Experimental Sample Successful Fungal % Cocoons
Modification Size Hatching Attack Attacked Other


Control 171 153 12 7.3% 6

Vegetative
Contact 21 18 3 1)4.3% 0

Ground
Placement 19 12 2 14.3% 5

Cover
Removal 13 12 1 7.7% 0







53


Table 5-2. The effect of modification of the cocoon suspension system and cover on the incidence of fungal attack on the spiderlings of Mecynogea lemniscata. Cocoons in the "Other" category contained spiderlings which were not attacked by fungi, but did not survive due to drowning. All cocoons were collected after 90 days, except for those placed on the ground. They were collected after 45 and 90 days.




Experimental Sample Successful Fungal % cocoons Modification Size Survival Attack Attacked Other


Control 239 236 3 1.7% 0

Vegetation
Contact 65 63 2 3.2% 0

Ground
Placement (45) 22 17 3 17.6% 2


(90) 12 a 11 1 11.0% 0

Cover
Removal 37 32 5 15.6% 0


a A number of cocoons were attacked by ants in this group and
could not be used for the analysis. This explains the low percentage of fungal attack after the longer 90-day period.







54


modified covers also had significantly higher rates of fungal attack (X2 = 13.03, df = 1, p < 0.005). In addition, spiderling mortality due to other causes, probably submersion and subsequent drowning,
2
was significantly higher on the ground (X = 13.34, df = 1, p <

0.005).

The incidence of fungal attack on the cocoons of A. aurantia was very low in both the egg stage (4.9%; Table 5-3), and the spiderling stage (0%; Table 5-4). Chi-square tests between the Control group, and the Ground Placement and Cover Removal groups revealed no significant differences in the number of cocoons attacked by fungus in either the egg stage or the spiderling stage. The two Control groups were not significantly different from each other.


Discussion


The suspension systems of both M. lemniscata and A. aurantia cocoons are difficult to wet, and conduct water poorly.

Consequently, they act to discourage water from moving down the lines to the cocoons. The covers of both cocoons shed water effectively, and apparently absorb only a small amount. Presumably, the flocculent silk layers of both cocoons are also difficult to wet, and function further to limit the water from entering the cocoon. All of these structures ultimately function to keep the cocoon dry by channeling water away from it. However, the connection between this function, and the prevention of fungal attack is not clear. Modification of the cocoon cover and partial







55


Table 5-3. The effect of modification of the cocoon suspension system and cover on the incidence of fungal attack on the eggs of Argiope aurantia. Cocoon modification had no effect on egg inviability or drowning. All cocoons were collected after 30 days.



Experimental Sample Successful Fungal % Cocoons Modification Size Hatch Attack Attacked


Control 41l 39 2 4.9%

Ground
Placement 12 10 2 20.0%

Cover
Removal 13 11 2 15.4%







56


Table 5-4. The effect of modification of the cocoon suspension system and cover on the incidence of fungal attack on the spiderlings of Argiope aurantia. No spiderlings were killed by drowning in these experiments. All cocoons were collected after 90 days.



Experimental Sample Successful Fungal % Cocoons Modification Size Survival Attack Attacked


Control 4o 4o 0

Ground
Placement 22 22 a Q

C over
Removal 20 20 0


a Of the 22 cocoons, 2 had small patches of fungus on the
shell, but the contents were unaffected.







57


collapse of the suspension system of M. lemniscata cocoons is unrelated to the incidence of fungal attack in the egg stage (see Table 5-1). Even total failure of the suspension system did not result in increased fungal attack, although cocoons placed on the ground did suffer higher egg mortality due to drowning.

The integrity of the suspension system and cocoon cover was

important to M. lemniscata cocoons that contained spiderlings (see Table 5-2). In this stage, total collapse of the suspension system resulted in increased mortality due to drowning. The incidence of fungal attack also increased with modification of the cocoon cover. However, it is unclear whether the spiderlings were attacked by fungus because of damage to the cover, or died for some other reason and were subsequently attacked. Modifying the cocoon cover does increase dessication problems for M. lemniscata spiderlings (see Chapter IV), and this may have been the real cause of the increased spiderling death. However, I have also had fungus attack spiderlings in the laboratory under conditions of high relative humidity (66-100% RH) where dessication should not be a problem.

Christenson and Wenzl (1980) found that 17.5% of the cocoons of N. clavipes were attacked in the egg stage by fungus. They cited the loss of protection from the rain (removal of a leaf canopy above the cocoon), and falling to the ground (support line failure) as reasons why the flocculent silk cocoons of this spider failed. Overall, the lack of any effect on the incidence of fungal attack through manipulation of the covers and suspension systems of M. lemniscata and A. aurantia cocoons is surprising, particularly







58


since these components presumably perform the same functions as the leaf layer and support system of N. clavipes cocoons. These results may be partially explained by differences in the cocoons of the three species. The cocoons of M. leinniscata and A. aurantia have dense covers, and layers of flocculent silk between the cover and the egg mass. While the covers of both these cocoons are wettable, the flocculent silk layer is not. The cocoon of N. clavipes is composed primarily of a basket-like mesh, with little or no flocculent layer between the eggs and the mesh. The eggs in M. lemniscata, and A. aurantia cocoons with damaged covers are still protected from water (and fungal spores?) by their flocculent silk layer (which was not damaged in this study). The mesh cocoons of N. clavipes, which are also wettable, have no flocculent layer to turn water away from the egg mass once their protective leaf canopy is gone. Other explanations for this difference, such as a layer of spherical granules on the surface of the eggs of these two species which repel water (Austin and Anderson 1978, Grim and Slobodchikoff 1978, 1982, Humphreys 1983), or relatively short developmental periods are not adequate, since all three spiders share these traits.

The differences in the incidence of drowning between

M. lemniscata and A. aurantia cocoons in the egg and spiderling

stages (see Tables 5-2 and 5-4) are probably related to differences in the size of these cocoons, and the thicknesses of their flocculent silk layers. The cocoons of M. lemn-iscata are small, and are worked down into the soil by rain action when placed on the







59


ground. In this location, the cocoons are in constant contact with soil moisture. Argiope aurantia cocoons are relatively large (see Figs. 2-1 and 2-2), and remain on the surface if they fall to the ground. In this position, the area of the cocoon contacting the soil is minimized, which probably allows the cocoon to dry out between exposure to rain or submersion.

The spiderlings in M. lemniscata cocoons are also packed

together tightly, with no room to move about within the cocoon. In addition, the flocculent silk layer in these cocoons is relatively thin. Fungal infection, once established, can spread more easily to all the spiderlings within the cocoon. The thicker flocculent silk layer in the cocoons of A. aurantia provides protection from water entering the cocoon, even when the cover is damaged. The large size of these cocoons also allows the spiderlings to move about in the cocoon, which may further reduce the probability of infection moving through the mass. Indeed, in cocoons damaged naturally or modified by me, the spiderlings are almost always appressed against the cocoon cover opposite the site of the damage.

The differences between the overall levels of fungal attack on the cocoons of these two spiders are also interesting. The cocoons of M. lemniscata are covered by layers of discarded orb-web that contains detritus composed primarily of prey remains. These remains may provide a high quality medium for fungal spores to germinate on, and from them, extend their hyphae into the cocoons. On occasion, I have observed M. lemniscata cocoons completely enswathed by a fuzzy layer of grey or white fungus. I have also had M. lemniscata







6o


cocoons that were stripped of their outer layer of silk (see Fig. 2-1c) attacked by fungi in the laboratory. In contrast, A. aurantia cocoons, which have a naked cover with an almost lacquered surface finish, are never covered by fungus. In fact, it

is rare to find small patches of fungus on the covers of these cocoons at all, even after they have been lying on the ground for 90 days (see Table 5-4).

Spiders produce a variety of silks and associated materials in a number of different glands located in their abdomens (Witt et al. 1968, Mullen 1969, Foelix 1982). One of these, the aggregate gland, produces the glue-like material found on the catching spiral

of orb-webs. Schildknecht et al. (1972) have demonstrated that this glue-like material contains nitrates (KNO 3), phosphates (KH 2PO 4), and pyrrolidines (C 4H2 NO 2). They suggest that one of the functions of these compounds is to protect the web from bacterial and fungal attack. If spiders are protecting their webs from such attack, it seems reasonable that they would protect their cocoons, which represent a much greater expenditure of energy and time, as well. Given that these compounds can be manufactured in the silk glands associated -with web building, it seems likely that the tubiliform and aciniform glands associated with cocoon production may also able to manufacture similar compounds, so they can be applied to the covers of cocoons.

The preceeding Chapters III, IV, and V have both considered and demonstrated the role of the cocoon, or its various parts, in limiting the effects of temperature extremes, dessication, and










fungal attack on the egg and spiderling stages of M. lemniscata and A. aurantia. However, many predator groups have specialized on the eggs of spiders, and it is probable that cocoons also function to control their attacks. This possibility is considered in Chapter VI.















CHAPTER VI
THE ROLE OF THE COCOON IN LIMITING EGG AND SPIDERLING PREDATORS


Introduction


A major portion of modern ecology is concerned with the relationship between heterotrophic organisms and their food supplies. Such interactions (e.g., predator vs. prey, host vs. parasite) occur both in ecological time, and in evolutionary time (Brower and Brower 1972, Dawkins and Krebs 1979). As such, natural selection may be presumed to act within interacting populations to optimize both the ability to acquire resources (Schoener 1971, Pyke et al. 1977), and the ability to avoid becoming the acquired resources of similarly-selected organisms of higher trophic levels. Within this context, the strategy of any host organism should be to protect itself, or its offspring, from the effects of predator or parasite attack through processes or

behaviors which limit the types and numbers of attackers that are capable of using it. Ideally, the strategy should result in the total exclusion of all the attackers. In reality, their effect is only partially reduced due to the reciprocal nature of the interaction over evolutionary time.

Spiders deposit their eggs in one or more discreet clutches. These clutches can be extremely large (up to 2000 eggs; Kaston 1948). The individual eggs within the clutch are also


62







63


quite large when compared to eggs of other groups such as insects. The eggs are lipid rich and represent a considerable amount of energy (Anderson 1978). In addition, during the reproductive season, clutches may occur in large numbers in the habitat and may be relatively conspicuous. They therefore represent a potential and highly desirable resource for many predators and parasites. Indeed, insects from a number of groups have specialized on spider eggs (Auten 1925, Eason et al. 1967, Evans 1969, Askew 1971, Austin, In press).

All spiders deposit their eggs in some form of silken cocoon

(Turnbull 1973). For many spiders this structure represents the sum total of maternal care bestowed on the eggs by the female spider. The large and diverse number of predators attacking cocoons, and the wide range in complexity of cocoon architecture (McCook 1890, Kaston 1948) have led to speculation that the primary function of the cocoon is to protect the eggs and spiderlings from attack (Austin and Anderson 1978, Robinson 1980). Austin (In press) recently reviewed the literature on cocoon attack by egg predators, and proposed that the wide diversity of cocoon types arose because spiders have attempted to reduce the total number of predators that can use their cocoons by forcing them to "specialize" on a particular cocoon type. The predators have responded in evolutionary time, and the relationships between cocoons and their attackers that we observe today can be attributed to a 11coevolutionary arms-race" (Dawkins and Krebs 1979). While some observations have been reported on parasite difficulty in entering







64


cocoons (Kaston and Jenks 1937), there is still no evidence that cocoons, or the various layers comprising them, function to turn away or reduce the success of specific parasites or predators.

In this chapter, I investigate the roles that the suspension systems, outer covers, and internal flocculent silk layers of the cocoons of Mecynogea lemniscata Walckenaer and Argiope aurantia Lucas (Araneidae) play in controlling the access of predators to the eggs and spiderlings within. If the suggestions of various researchers, and in particular Austin (In press), are correct, these cocoons should demonstrate defenses which reflect the manner in which their predators attempt to introduce themselves or their

offspring into the cocoon.


Materials and Methods


Population Data


The numbers and kinds of parasites and predators attacking the cocoons of M. leinniscata and A. aurantia were determined by collecting cocoons in the field and returning them to the laboratory where they were opened and scored for parasites. Scoring was relatively easy since each parasite leaves distinctive evidence in

the cocoon such as the type of hole in the cover, or remains such as pupal cases, shed exuviae, or eggs. The M. lexnniscata cocoons were collected in late August in 1981 to 1983 after the eggs in the last cocoons laid had hatched. A single sample of A. aurantia cocoons was collected in late October in 1981. In 1982 and 1983, a







65


different 31 in of a 400 m stretch of roadside hedgerow was sampled every two weeks. For each sample, all of the cocoons in the 31 mn section were collected. In 1982, the cocoons were collected from August through November; in 1983, from August through October.

In addition to these data, specific information was also

collected regarding attacks on A. aurantia cocoons by ichneumonid wasps and chloropid flies. For the ichneumonid attacks, these data included two indices relating the distance of the egg mass to the cocoon cover along the X and Y axis. These indices were calculated by first measuring the following four variables: egg mass length, egg mass width, cocoon length, and cocoon width (Fig. 6-1). These values were then used in the following formulas:


Distance to the egg (Cocoon Width Egg Mass Width)
mass from the cocoon cover = ,and
(x-axis) 2



Distance to the egg (Cocoon Length Egg Mass Length)
mass from the cocoon cover =
(y-axis) 2


These two measures were compared to the average ovipositor length of the ichneumonid to predict where the wasp might prefer to attack the cocoon. The predicted preference was checked by examining the shells of attacked cocoons collected in the field for the distribution of ovipositor drill holes. Data on the number of cocoons that the wasp attacked without ovipositing, and the distribution of support line "deltas" (the structure on the cocoon surface the support lines emanate from; McCook 1890) were also






66





















J1
eml c










emw


CW








Fig. 6-i. A schematic view of an Argiope aurantia cocoon illustrating the four measurements; cocoon length (cl), cocoon width
(cw), egg mass length (eml), and egg mass width (emw) taken to determine the position of the egg mass in relation to the cocoon cover.








67


collected. For the chioropid fly attacks, the number of cocoons successfully attacked (producing pupae), the number of cocoons successfully attacked in conjunction with another predator, and the number of cocoons unsuccessfully attacked (eggs laid on the cocoon surface but no pupae produced) were recorded.

The relationship between the size of an A. aurantia cocoon and the number of eggs it contained was established by measuring a number of cocoon dimensions and counting the spiderlings in 40 cocoons. Figure 6-2 shows that there is a strong relationship (r 2 = 0.90) between the diameter of the cocoon and spiderling number. This relationship was used to estimate the original number of eggs in attacked cocoons. The percentage of eggs surviving the attack, a measure of the damage caused by a given predator, was then calculated by the following:


Percentage of Eggs No. of Survivors
Surviving -X 100.
Parasite Attack Estimated No. of Eggs


The relationship of cocoon size to egg number was not calculated for M. lemniscata because all of the eggs in a cocoon are utilized when attacked by its egg predators.


Field Experiments


The roles of suspension systems and cocoon covers in

controlling egg predator attacks were investigated by modifying these components in the field and assessing the effects of their change on egg hatching success and spiderling survival. The cocoons






68







2000 *




1500 *


W0

100 0 00
" 000 0@ @0
2 *
z *



500 ** **




0
0 I i I I I
1.3 1.5 1.7 1.9 2.1 2.3 2.5
Cocoon Diameter (cm)






Fig. 6-2. The relationship (Y = 1522.2X 1886.9; n = 40) between the diameter of Argiope aurantia cocoons and the number of spiderlings (eggs) therein. The coefficient of determination (r2) for the relationship is 0.90.







69


used for these modifications were either produced in the laboratory, or collected in the field. They were assigned to the experimental groups listed below. The cocoons in all the experimental groups were marked either by flagged stakes placed beneath them, or by flagging in the vegetation.

Vegetation contact. The function of cocoon support lines as a deterrent to arboreal predators was examined by repositioning cocoons so that they contacted the vegetation. This was done only for M. lemniscata cocoons and was accomplished by tying cocoon strings to branches with their suspension lines. This mimicked the position of cocoons whose suspension systems had collapsed normally.

Ground placement. The role of the suspension system in keeping cocoons off of the ground and away from terrestrial predators was investigated by placing the cocoons of both species on the ground in open-topped wire corrals. These corrals allowed cocoons to be attacked but prevented them from being washed away in the rain. The corral used for A..aurantia cocoons was constructed of hardware cloth (1/4" mesh) and was 12.5 cm. in diameter and 5 cm in height. The corral for M. lemniscata cocoons was constructed of aluminum window screen and was 5 cm in diameter and 5 cm in height. The corrals were located below sites where cocoons had been collected previously.

Cover removal. The function of the cocoon cover in limiting predator attack was examined by removing approximately 25% of the cccocn cover with a razor blade. Individual cocoons of M. lemniscata were modified in the cocoon string and the string was







70


left suspended in place at the web site. Female spiders treated these modified cocoons normally. The laboratory reared cocoons of A. aurantia were modified and attached to the arms of a support system using alligator clips. The support systems were placed in the vegetation where normally oviposited cocoons were hanging. They held the cocoons approximately 1 m off of the ground (the average cocoon height as determined by collecting).

Cover removal control. This group was to control for the

possible contaminating effects of the alligator clip used in the apparatus to suspend A. aurantia cocoons. Clips were attached to cocoons hanging normally in the habitat and the cocoons were observed for any effect.

Control. Control cocoons were subj ected to no structural

intervention. These cocoons controlled for handling effects in the ground placement, vegetation placement, and cover removal groups.

Bird damage. These A. aurantia cocoons were subjected to no mechanical modification. They were marked and collected after 150 days in the field to determine whether bird predation increases later in the year after the plants lose their leaves (see also Tolbert 1976). They were compared to the control group. Laboratory Experiments


The role of the flocculent silk layer in the cocoons of A. aurantia as a barrier to predator attack was tested in the laboratory by placing the eggs of Tromatobia ovivora rufopectus (Cresson) (Ichneumonidae) at two depths in the cocoon: 1) just under







71


the cover, and 2) on the host egg mass. Successful parasitism was scored as the number of ichnewnonid larvae found in the host egg mass just prior to pupation.

The wasps were maintained in the laboratory at 23-25 0 C and 50-60% RH. They were provided with white refined sugar, a mixture of honey and yeast, and water. Colony size was maintained by the addition of new wasps collected from the field. Their eggs were obtained by allowing a number of wasps to attack a cocoon produced in the laboratory. The cocoon was then opened, and the white, elongate wasp eggs were removed using a fine brush and forceps. Known numbers of these eggs were then transferred to other laboratory produced cocoons 1-3 days old, and placed in either of the two test locations.

The cocoons were obtained from spiders held in the laboratory in 50 x 50 x 10 cm cages (Witt 1971) or in 500 ml jars with screen tops. Oviposition and cocoon construction in both of these enclosures was normal.


Results


Field Experiments


The cocoons of.M. lemniscata are attacked in the egg stage by two major predators, a Tetrastichus sp. wasp (Eulophidae) and the neuropteran Mantispa, viridis Walker (Mantispidae) (Hieber 1984) (Table 6-1). Both of these predators utilize all of the eggs in a cocoon during their attacks. However, they attack the cocoons in








72


Table 6-1. Numbers of Mecynogea lemniscata cocoons attacked by the eulophid wasp Tetrastichus sp., the mantispid Mantispa viridis, and ants/ unknown predators for the years 1981 to 1983. The cocoons were collected in late August in 1981 and 1982 at the end of the reproductive season, and in July, August, and December in 1983. The percentages of attacked cocoons are in parentheses.




Sample Total No. Eulophid Ants/
ab
Year Size Attacked Wasp Mantispid Unknown


1981 290 26 21 (80.8%) 0 (0%) 5 (19.2%)

1982 252 29 17 (58.61) 5 (17.2%) 7 (24.1%)

1983

July 148 13 10 (76.9%) 2 (15.4%) 1 ( 7.7%)

Aug. 97 14 12 (85.7%) 0 (0%) 2 (14.3%)

Dec. 308 64 32 (50.0%) 12 (18.8%) 20 (31.2%)


a Cocoons contain either larvae, prepupae, and/or shed exuviae
with emergence holes.
b Cocoons contain either a larva, a pupa, or a pupal case and
emergence hole.
c Cocoons are characterized by a large chewed hole, and the
absence of the flocculent silk layer, pupal cases, pupae,
shed exuviae, or parasite.







73


different ways. Mantispa viridis deposits its eggs in the habitat, removed from the host, and the emerging triungulid larvae actively search out and burrow into previously constructed cocoons. These larvae are obligate cocoon attackers, as opposed to the mantispid larvae that ride on female spiders and attack the egg mass just prior to cocoon construction (see Redborg and McLeod, In press, for a review of Mantispid biology). The Tetrastichus wasp either deposits eggs into the cocoon, or into the upper layers of the cocoon cover where the emerging larvae burrow through the cocoon and attack the egg mass (Austin, In press). Both the wasp and the mantispid are never found together in the same cocoon. The cocoons of M. lemniscata are also occasionally attacked by ants, which also remove all of the eggs or spiderlings.

The single line suspension system of M. lemniscata cocoons

functions to prevent predation on the egg stage. Egg predation was significantly greater than control for both the cocoons placed on

2
the branches (X = 47.40, df = 1, p < 0.001) and those placed on

2
the ground (X = 23.49, df = 1, p < 0.001) (Table 6-2). In both cases, the principle predator appeared to be ants. Modification of the cocoon cover also had a significant effect on egg predation (X2 = 38.67, df = 1, p < 0.001). In this case, however, the principle predator was not ants, but the mantispid M. viridis. In no case did the wasp attack any manipulated cocoons containing eggs, suggesting that the position of the cocoon in the web or the integrity of the cocoon cover are important to the wasp.








74


Table 6-2. The effect of modification of the cocoon suspension system and cover on the incidence of predator attack on the eggs of Mecynogea lemniscata. All cocoons were collected after 30 days.




Experimental Sample Successful No. Cocoons % Cocoons
Modification Size Survival Attacked Attacked


Control 175 153 22a 12.6%

Vegetation
Contact 24 6 18b 75.0%

Ground
Placement 26 12 14b 53.8%

Cover
Removal 32 12 20c 62.5%


a Of the 22 cocoons attacked, 2 were attacked by ants/ unknown
predators, 19 by the eulophid wasp Tetrastichus sp., and
1 by the mantispid M. viridis.
b
In both cases the cocoons were attacked by ants/ unknown predators.
c All 20 cocoons were attacked solely by the mantispid M. viridis.








75


The effect of the suspension system in protecting M. lemniscata spiderlings from predators was not as pronounced (Table 6-3). There were no differences in predation between the Control group and either the cocoons placed on the ground for 45 days or the cocoons placed in contact with the vegetation. The cocoons placed on the ground for 90 days, however, were preyed upon at significantly

2
higher levels (X = 70.40, df = 1, p < 0.001). These results probably reflect the generally lower densities of ants foraging on the vegetation and ground late in the year (pers. ob.). Cover removal also had no significant effect on spiderling predation when compared to control, again because the the cocoons are inaccesible on their support line.

The eggs of A. aurantia are attacked by four primary

predators; the wasp T. ovivora rufopectus (Ichneumonidae), the neuropteran M. viridis, and the flies Pseudogaurax signata (Loew) (Chloropidae) and Megaselia sp. (Phoridae) (Table 6-4). Of these, the two most common predators are the ichneumonid and the mantispid. These are obligate egg predators and probably account for most of the initial attacks in cocoons attacked by multiple predators. The attack behavior of the mantispid has been previously discussed. The ichneumonid T. ovivora rufopectus attacks A. aurantia cocoons by inserting its long ovipositor through the cover into the flocculent layer. Its eggs are deposited on or near the host egg mass, and the emerging larvae make their way to the host eggs and burrow into the mass to feed.







76


Table 6-3. The effect of modification of the cocoon suspension system and cover on the incidence of predator attack on the spiderlings of Mecynogea lemniscata. All cocoons were collected after 90 days, except for those placed on the ground. They were collected after 45 and 90 days.




Experimental Sample Successful No. Cocoons Cocoons
Modification Size Survival Attacked Attacked


Control 259 239 20 a 7.7%

Vegetation
Contact 77 71 6a 78

Ground
Placement (45) 19 17 2 a10.5%

(90) 32 11 20 a62.5%

Cover
Removal 34 32 2 a 5.9%

aAll attacks were by ants/ unknown predators.










77






r-i 0 -14 w
:I +m) u w >
4-4 cd Cd (U -4 CD r-4 1-4
m Q) r-4 Cd +:t lc
m z co cn 4j
w +3 C7\ 0- Cd -4 -1
0 Iq 4) 00 w
W 0 C\ 4--)
d w (U U2
> r-I W
$.4 Cd Cc +)
cd 0 x C)
Cd r-i V ;-4 0
0 -r4 4-') 4 Vk tt H
9 > 0) 4J i 04 U'N VIN Cd
10 Cd 4.) r-I 04 P4
Cd 4-3 0 P.4 Cd C\j _x 0
A 0 El N 0 --1 0
U) 00 Cd a If., X4 r4
Iz .14 0 0 10 a\ w w a4
4-) r. r-i 4-1 C\j
0 Cd 0 0 Cd
odww ZOQ)
0 M: ro 0 -rq 0 -1 4-)
.rq 0- 0 r-q j
4-;l '0 'r4 0 C\J '0 0 0 Cd
Cd -H a 0 co Q) 0 0 >
4-) P4 0 C\ 4.) $4
w r-4 w 0 w tlk vk Cd
W w &l. s-. Co C\j r-4 r-I
Q) 4-) -4 EA W ou 0
0 -H r-i R S. co t i
Q) p 0 0
U (n r-I
Vk v 0) W 4-> 0
q WH cn C\j r-i (U -4 0
vk 9 P4Z 4J W 0 0 $-4
.,.q W W w w Cd 0
r-q (U (n -C rn a Q) 0
0 4 rn N r-4 IV u
0 4-) 0- 0 r. 0
rO 4-3 0 0 0 0 0 >
w 0 w > 0 0
4 u c 0 0 z P4 C\j cn 110 r_ (a Q)
"M 0 0 0 0 0 w .4
W4 0 84 0 0 0 0 \10 0 U-\ .14 co 4-)
U q-4 +3 Ul\ 4-) od
N 0 0 Q) 0 C
C4--4 -H u .1 4-) 0
M 4-) EO :9 --4 t-- VN 0 r-4
Cd 10 0 q (V N A CC ca
0 -q -H ; co (U r4 P4 W
0 0 $4 Cd ON 4 n 0 > z
0 > 0 Wco -:4 0
0 -rq I= U C\, ,
0 > 04 S= r. 4 '0 r-4 C" f+4 4-4
0 0 -P 10 0 0 0
Cd a) 0 W"o 0
cd 9" t) r Z to CQ oj 0 w Q)
-rj 4-) 0 Vk 0 -H Cd CS ocd u u 0
a P4 C C C: c z
cd 0 0 N WO 0 co (n cli 0 v Q)
4 4-) Cd T H W Cd CO Cd
+3 a) +.) > C\ 0) 3:
Cd I'd I r-q > I-n --r cli 4
0 V u ro rq 0 A P4 A H
w $_4 w w 0 .4-3 :1
P4 EH H -P 0 -4 U cu w (D ro
-rq '0 Cd 0 rZ4 X! 10 4ZI
W -f-I 4J 0 0 0 :5 :! "
$ 0 0 44 $-4
4 0 r-4 V P4 0 lz 10 Cd
m 91 a (U = w
4-4 : cs 0 -14 4-4 t4 10 10 10
0 W W 0 000 4-) 0 \,o all 0 (V
r. 0 W 4-3 C\ M U 0 cd d Go N N 0)
'0 cd r -4 $ 0 = -P 43 .,A M
0 4-;' Cd 0 -P 0 $4 Cd
(U -H v a r. 4--l 0 E-1 v (U C)
CA V >b Cd 4J bO 4J 4-DI 4.;
w 10 0 0 0 r-4
= (U Od Cd
4-) 4
r4 V t 4 ;.
A ,O P4 aj Id Cd :J
co-4 AD H 10 N P4
10 w 4.3 \,,o co ON Q u
10 4 X co r-4
10 -rq p 0) 0 Qj m
(v A C 4-:1 0 u
m 0 -4 C m w v Cd Cd Cd
U 4 W 0 0 0 t 0i cn 4-:1 +j -P
,i d 0 rn rn 0 :j r--i 'd co 03 ., 4,
rQ 4-) r-4 CO w u r-q 0 a\ C7\ \ 4
cd 41 1-. ON 0 0 0 PC f --A r-4 r-i
E-4 CS 0 4-3 Cd 0









78








P4 j
w 0 4.) w 0
Cd -1-4 '1 4-j' r. 1-4
Cd 41 4 w 0 Cd
-H 0
(U 0
4 0 PQ
Cd 1 P4
0 0 a.
r-A 0 1
I Id 4--l u 0 4-)
Cd 0- a
1: 0 0 0
Cd z 0 1 10
P4 0 P-i N r
w 0 Cd
0 4-)
4) +) 0 Z

c: 0 (U W 0- 0
4-, 0 v 0 F-4 0 0 0 0 Ul\
.0 10 0 cd 0 -H U ^ ()
+) 0 0 -q r. 0- 0
-14 0 cc -H Q w 0 a)
od >., 0 0 c z
A cd g C\j 0 (n 0
4-) cu 0 r-A
4-) -4 $ :: 0 ^ cd
.14 0 pq
cn r- pi 1 10
> (D 0 10. H 0
0 H Lr\ I
a) 0 0 P4 9 0 x 0
m -4 .14 4-4 (V = 0
cd 0 Cd 4-) c P4 PQ ::$
u 0 1-4 10 1 (U
0 rcl -rq .() a) u 'o
r-A 0 P4 4 0 0- =
Cc 0 0 1-4 4 0
P4 S 03 4J 0
0 0 t>j od ()
Pq (V 4-) :3 a) -4 4-) C- Z C 0 Q) 0
o c 4) ): o 41 --q 0 11" 0
4-) (U c 0 !>, N x A 0 4-3 r-4
4-) X: to Q S o Cd
Cd F*4 V. 0 C: ro 0 0 >11
> 0 0 0 C 10 (V = 0 0 ca
Q 0 cd u c 4.> 10
(U (U u -14 0 bo 4 1 10 q
rl w )z 4 0 10 0 r-4 r. 0 W -r-4
d 0 4J C) -4 ad cc H 1 4
44 4--) 0 -4 -P lt CA x 0
0 r- ci (n 0 .0 0 1- Cd
a) 0 14. cd 0 4-) r-i 2:
(U u ri tio P4 r-j
$4 v 0 cd r-4
a) S-4 ? 'D 4-4 ^ W
P4 rc: w 0 a) 10
4-3 +m) lt C -4 4) ca 0 4 C
r 0 (U cd
w 4-4 -4 4 4J 0 Q
4 0 -4 a) r- N -rq 0 0 0
Cd JL4 od P4 d 0 0 0 (v
a) 1-4 0 0
()j (u $. 0 'IV) 0
Cd >. a) = 0 0 cd $4 10 r--4
0 -14 C-4 -14 r-i 0 ,o a) Cc
51 s 0 W r. 4) 4-)
4) Cd 0 cd U 4 cd I
$ 4-) 0 4-) 4) 10 0 X Id
"o ro 4-) (D ej 4-1 4.) C 4
V 0 C :: 0 Cd 4.>
N 4-) 0 0 v
-,q (V co -4 r-4
C: cc N 0 0 P4
0 0 A 0 0- z z 0
4-') 4-) 0 0 0 0 z 0 0 ;
o 0 0 > o t- 0 0 0 0 0
cd u 0 0 0 0 0
$4 $4 Cd Q 0 0
Cd 4 0 0 C.)
0 .14 CN Q) ;2: 0
r-q -4 co r. CN cu
r-i 0 P4 0 Q) -4
19 14 od 0) 0 (V r-4 4 (D 4-)
u 0 -r-4 I"- P4 4 Z Cd 4) 4J 0 .1.
Cd ci 4.) 0 4-) r. x 0 4-)
4-1 4-' 4 (D 0 1 (1 Q
+-, Cd z r-I P 0 4-4
P4 Cd r-i







79


The status of P. signata is less clear. This fly deposits eggs on cocoon surfaces. The eggs hatch and the emerging larvae push their way through the cover into the cocoon (Kaston and Jenks 1937, Kessel and Kessel 1937, Hickman 1970). The literature suggests that chloropid flies are obligate spider egg parasites (see Austin, In press), a fact supported by the large number of A. aurantia cocoons attacked by this fly in 1982. However, only 17 of 42 cocoons were singly attacked by this fly (Table 6-4). The remaining cocoons were attacked along with other predators (particularly mantispids), and in many cases the fly deposited its eggs in the emergence holes of these previous attackers. In addition, Hall (1937) lists this fly as attacking the egg masses of the praying mantis. This suggests that this fly is a facultative egg predator that attacks eggs in any container, as well as utilizing dead or damaged eggs from other attacks when located. The phorid is found alone in cocoons approximately 50% of the time and it is probably an obligate egg predator, attacking cocoons in the same manner as P. signata.

The observed levels of egg predation for T. ovivora rufopectus, P. signata, and M. viridis in this study are similar to the levels of attack reported by Enders (1974) and Tolbert (1976) for A. aurantia cocoons. The A. aurantia cocoons in this study were also attacked by birds, ants, and moth larvae, although it is unclear whether these attacks occured in the egg or spiderling stage. The level of bird attack was lower (9%) than that found by Tolbert (35-50%). Argiope aurantia cocoons containing spiderlings are attacked by ants and other spiders (particularly salticids which







80


use damaged cocoons as retreats), and by small rodents if cocoons fall to the ground.

The amount of damage done to the eggs in an A. aurantia cocoon by each of the four primary predators varies greatly (Table 6-5). The ichneumonid, on average, does the greatest amount of damage, destroying approximately 90% of the host eggs. By themselves, the chloropid fly and the mantispid attack roughly the same number of cocoons. However, the average mantispid attack damages approximately 20% more eggs than the average chlorpid attack. The phorid fly destroys approximately 97% of the eggs in a cocoon. Birds also damage the contents of the cocoon heavily (74%), but the damage is usually done in the spiderling stage.

Tromatobia ovivora rufopectus was successful in attacking 34 cocoons in 1982 (see Table 6-4). However, an examination of the covers of 167 cocoons collected that year (the other 18 covers were to damaged to inspect) for ichneumonid oviposition holes indicated that 92 cocoons were actually sampled by the wasps. Thus, 58 cocoons were sampled but had no eggs deposited in them, presumably because they were in the wrong stage for attack (Vinson 1976). The other 75 cocoons were either never found by the ichneumonids, or were found and rejected based on criteria which did not require insertion of the ovipositor to determine.

The number of cocoons containing pupal cases of P. signata was also not a valid measure of the total number of cocoons attacked by this fly (see Table 6-4). Of the 69 cocoons in 1982 with attached P. signata eggs, 27 (39.1%) were apparently unsuccessful in that






81


Table 6-5. The mean percentage of eggs which survive in an Argiop aurantia cocoon attacked solely by the ichneumonid Tromatobia ovivora rufopectus, the mantispid Mantispa viridis, the chloropid fly Pseudogaurax signata, the phorid fly Megaselia sp., or birds. SD is in parentheses.




No. Cocoons Percent Eggs
Parasite Sampled Surviving


Ichneumonid 35 10.2 (13.7)

Mantispid 15 39.1 (27.6)

Chloropid Fly 15 63.7 (35.6)

Phorid Fly 4 4.7 ( 9.5)

Birds 16 26.4 (28.3)









82


emerging larvae failed to gain entrance into the cocoon (no pupal cases inside the cocoon). The remaining 42 cocoons were successfully attacked and can be divided into two groups; 17 cocoons attacked by the fly alone, and 25 cocoons attacked by the fly and one or more other predators. Of the 17 singly attacked cocoons, 13 had eggs on the surface and a fewer number of pupae inside, 2 had more pupae than eggs present, and 2 had pupae and no eggs present. Of the remaining exhibiting multiple attacks, 11 had eggs on the outside and inside of the shell and contained less (8 cocoons) or more pupae (3 cocoons) than eggs. The other 14 cocoons had pupae, but no evidence of eggs could be found because the cocoon and its contents were heavily damaged.

The large number of cocoons attacked by t. signata in

conjunction with other predators suggests that shell damage may be advantageous to this fly (see Table 6-4). Indeed, the average rate of success (number of pupae/ number of eggs X 100) for the cocoons attacked by the fly alone was 29.8% (SD = 30.2%) (based on the 13 cocoons which had visible eggs). The average rate of success for the flies which attacked cocoons with other predators was 82-7% (SD = 19-74%) (based on 11 cocoons; the 3 with more pupae than eggs were counted as 100% successful). This level of success is significantly greater (t = 10-05, df = 22, p < 0.001) than that achieved by P. signata attacking cocoons alone.

It is difficult to determine whether the success rates for

mantispids and phorid fies attacking A. aurantia cocoons are due to an inability to locate the cocoons, or to the inability of the







83


respective larvae to penetrate the cocoon cover. The large increase in successful mantispid attacks on artificially damaged M. lemniscata cocoons suggests that mantispid larvae are generally abundant and probably have no trouble locating cocoons, but have difficulty penetrating the dense cocoon cover. This suggests that the cover of A. aurantia cocoons is also responsible for the relatively low rate of successful mantispid attack. Presumably, the larvae of the phorid fly are also hindered by the cover, although this is a rare parasite and the low numbers of successful attacks mnay be a reflection of low numbers of searching parasites. It seems likely that birds, once they find a cocoon, have little trouble in exploiting it.

In A. aurantia cocoons, the egg mass is closest to the cocoon cover at its top edge, farthest from the cocoon cover at its bottom, and approximately the same distance as the average ovipositor length from the cocoon cover in the middle of the cocoon (Table 6-6). The cocoons are suspended in the vegetation by a cloud of lines emanating from suspension line "deltas" on the surface of the cocoon (see Fig. 2-2a). There are significantly more of these deltas, and thus significantly more lines, in the middle third of the cocoon surface than in either the upper (t = 4.48, df = 140, p < 0.00) or lower third (t = 156.40, df = 140, p < 0.00) (Table 6-7). The distribution of ichneumonid drill holes matches the delta distribution; there are significantly more holes in the middle third than in either the upper (t = 4.69, df = 166, p < 0.001) or lower third (t = 3.92, df = 166, p < 0.001) of the cocoon (Table 6-7).







84


Table 6-6. Mean cocoon diameter, cocoon length, egg mass diameter, egg mass length, distance to the egg mass (X-Axis), and distance to egg mass (Y-Axis) for Argiope aurantia cocoons, and mean ovipositor length for the ichneumonid Tromatobia ovivora rufopectus. The two distance variables indicate the length of an ovipositor needed to deposit eggs directly on the surface of the host egg mass. SD is in parentheses.




Sample
Variable Size Mean (mm)


Cocoon Diameter 25 19.2 (2.2)

Cocoon Length 25 24.4 (2.4)

Egg Mass Diameter 25 10.2 (1.4)

Egg Mass Length 25 11.1 (I.4)

Distance to Egg Mass
from cover: X-axis 25 4.5 (0.7)

Distance to Egg Mass
from cover: Y-axis 25 6.7 (1.2)

Ovipositor Length 57 3.9 (0.5)







85


Table 6-7. The mean number of suspension line deltas and oviposition holes of the ichneumonid Tromatobia ovivora rufpectus in the upper, middle, and lower thirds of the cover of Argiope aurantia cocoons. SD is in parentheses.




Sample Upper Middle Lower
Size Third Third Third


Suspension
Line Deltas 71 18.7 (6.2) 22.3 ( 9.2) 3.9 (3.7)

Ichneumonid
Oviposition Holes 84 2.4 (3.7) 9.5 (13.4) 3.4 (5.0)







86


The location of the egg mass within the cocoon and the distribution

of drill holes suggests that the ichneumonid prefers to attack the cocoon in this specific area.

For A. aurantia, egg predation due to the cocoon falling to the ground was not statistically different from the control in terms of the number of cocoons attacked (Table 6-8). However, the individual survival of eggs in each cocoon was reduced substantially. All of the cocoons on the ground discovered by predators suffered 100% egg mortality as compared to about 59.4% mortality for cocoons remaining in place in the vegetation. The cocoons on the ground that escaped attack were buried by falling leaves and were presumably hidden from predators. The level of predation on eggs in cocoons with modified covers was also not significantly different from the Control group. However, in all cases the cocoons were attacked by the chloropid fly P. signata, further suggesting that damaged cocoons appeal to this egg predator. The lack of mantispids in the modified cocoons is most likely related to the apparatus used to suspend the cocoons, which prevented the larvae from locating the cocoons, and not because of their inability to use them.

The effect of cover modification also had no effect on

predation in the spiderling stage when compared to the Control group (both controls were not significantly different from one another) (Table 6-9). Placement on the ground, mimicking suspension failure, resulted in significantly greater predation IX=24.37, df = 1,p on the ground (5.9%) was also much lower then for spiderlings in







87


Table 6-8. The effect of modification of the cocoon suspension system and cover on the incidence of predator attack on the eggs of Argiope aurantia. All cocoons were collected after 30 days.




Experimental Sample Successful No. Cocoons. % Attacked Modification Size Survival Attacked Attacked


Control 21 10 11a 52.4%

Ground
Placement 10 2 8b 80.0%

Cover
Removal 17 10 7c 41.2%

a Of the 11 cocoons attacked, 8 were attacked by the chloropid
fly P. signata, 8 were attacked by the mantispid M. viridis,
1 by the phorid fly Megaselia sp., 1 by the ichneumonid T. ovivora rufopectus, and 5 by birds.
b
b Rodent (mice) damage. The cocoon covers were shredded and the contents destroyed.
c
All 7 cocoons were attacked solely by the chloropid fly P. signata.







88


Table 6-9. The effect of modification of the cocoon suspension system and cover on the incidence of predator attack on the spiderlings of Argiope aurantia. All cocoons were collected after 90 days, except for those in the bird damage group. They were collected after 150 days.




Experimental Sample Successful No. Cocoons 10 Cocoons
Modification Size Survival Attacked Attacked


Control 23 20 3 a 13.0%

Cover Removalb Control 15 14 1b 6.7%

Ground
Placement 19 2 17 c 89.5%

Cover
Removal 21 20 1d 4.8%

Bird
Damage 23 15 8e 34.8%


a Bird damage. Of the 3 cocoons, 2 had part of their cover
removed, and 1 had cover damage and the contents removed. b Bird damage.

cRodent (mice) or bird damage. Characterized by the cover being shredded and the contents removed. d Bird damage. Contents removed from the cocoon. e Bird damage. Of the 8 cocoons, 2 were removed completely,

5 had 25-50% of their covers removed, and 1 had the cover
damaged and the contents removed.




Full Text
65
different 31 m of a 400 m stretch of roadside hedgerow was sampled
every two weeks. For each sample, all of the cocoons in the 31 m
section were collected. In 1982, the cocoons were collected from
August through November; in 1983, from August through October.
In addition to these data, specific information was also
collected regarding attacks on A. aurantia cocoons by ichneumonid
wasps and chloropid flies. For the ichneumonid attacks, these data
included two indices relating the distance of the egg mass to the
cocoon cover along the X and Y axis. These indices were calculated
by first measuring the following four variables: egg mass length,
egg mass width, cocoon length, and cocoon width (Fig. 6-1). These
values were then used in the following formulas:
Distance to the egg (Cocoon Width Egg Mass Width)
mass from the cocoon cover = and
(x-axis) 2
Distance to the egg (Cocoon Length Egg Mass Length)
mass from the cocoon cover =
(y-axis) 2
These two measures were compared to the average ovipositor length of
the ichneumonid to predict where the wasp might prefer to attack the
cocoon. The predicted preference was checked by examining the
shells of attacked cocoons collected in the field for the
distribution of ovipositor drill holes. Data on the number of
cocoons that the wasp attacked without ovipositing, and the
distribution of support line "deltas" (the structure on the cocoon
surface the support lines emanate from; McCook 1890) were also


80
use damaged cocoons as retreats), and by small rodents if cocoons
fall to the ground.
The amount of damage done to the eggs in an A. aurantia cocoon
by each of the four primary predators varies greatly (Table 6-5).
The ichneumonid, on average, does the greatest amount of damage,
destroying approximately 90% of the host eggs. By themselves, the
chloropid fly and the mantispid attack roughly the same number of
cocoons. However, the average mantispid attack damages
approximately 20% more eggs than the average chlorpid attack. The
phorid fly destroys approximately 97% of the eggs in a cocoon.
Birds also damage the contents of the cocoon heavily (74%), but the
damage is usually done in the spiderling stage.
Tromatobia ovivora rufopectus was successful in attacking 34
cocoons in 1982 (see Table 6-4). However, an examination of the
covers of 167 cocoons collected that year (the other 18 covers were
to damaged to inspect) for ichneumonid oviposition holes indicated
that 92 cocoons were actually sampled by the wasps. Thus, 58
cocoons were sampled but had no eggs deposited in them, presumably
because they were in the wrong stage for attack (Vinson 1976). The
other 75 cocoons were either never found by the ichneumonids, or
were found and rejected based on criteria which did not require
insertion of the ovipositor to determine.
The number of cocoons containing pupal cases of _P. signata was
also not a valid measure of the total number of cocoons attacked by
this fly (see Table 6-4). Of the 69 cocoons in 1982 with attached
P. signata eggs, 27 (39*1%) were apparently unsuccessful in that


135
For some, the impact of the rain was enough to crush the cocoons and
kill the contents. This suggests that the cover and suspension
system of many cocoons function to cushion the contents by
deflecting falling rain and absorbing its shock, or to keep the
cocoons off non-yielding surfaces where the force of the rain may be
concentrated. Such a protective role also explains the increase in
fungal attack that N. clavipes cocoons suffered when their
protective leaf canopies were removed (Christenson and Wenzl 1980).
With no canopy above the cocoon, rain would not be deflected from
the cocoon nor would its velocity be diminished. In this condition,
water would be driven deep into the cocoon carrying fungal spores
with it. In contrast, the cocoons of M. lemniscata and A. aurantia,
even with some cover damage, might still be able to deflect much of
the rain striking the cocoon or reduce its velocity.
The importance of the leaf canopy to N. clavipes illustrates
the importance in selecting specific sites for oviposition. Many
spiders locate their cocoons in crevices, under bark, or in the leaf
litter (McCook 1890, Kaston 19^8, Turnbull 1973, Gertsch 1979),
presumably to avoid abiotic problems. If such sites are limiting,
covered cocoons, by creating protective microclimates, would allow
spiders to use a wider variety of potential habitats and web-sites.
The large and diverse number of predators and parasites
attacking spider cocoons, and the wide range in complexity of cocoon
architecture have led many to speculate that the primary purpose of
cocoons is to protect the eggs and spiderlings from attack (Austin
and Anderson 1978, Christenson and Wenzl 1980, Robinson 1980). More


46
Ground placement. This manipulation also tested the function
of the suspension system, hut placed the cocoons in a wetter
microhahitat where drying was more difficult and the chance of
fungal attack or drowning was greater. Both M. lemniscata and
A. aurantia cocoons were placed on the ground in enclosures. For
A. aurantia cocoons, these were constructed of hardware cloth (1/4"
mesh), and were 10 x 10 x 10 cm in size. The enclosure for
M. lemniscata cocoons was similar in design, but was constructed of
aluminum window screen, and was 5 x 5 x 5 cm in size. These
enclosures allowed exposure of the cocoon to the elements, protected
them from large predators (although ants could still get in), and
prevented them from washing away during heavy rain storms. They
were placed below positions where cocoons had previously been
collected.
Cover removal. To determine the roles that the covers of
M. lemniscata and A. aurantia cocoons play in controlling fungal
attack, approximately 20-30% of their covers were removed. During
the cover modification, care was taken not to disturb the flocculent
silk layer (see Fig. 2-2b), or damage the eggs or spiderlings. The
cocoons of M. lemniscata were modified in place in their respective
strings. They were treated normally by the female spiders, which
remained at the web-site after the modification. The laboratory
produced cocoons of A. aurantia were modified, and attached by
alligator clips to the arms of a support system. The support was
placed in the vegetation in areas where cocoons where already


The cocoons of M. lemniscata also shed water well. Depending
on whether the cocoon string is naked, or covered with a layer of
old web and detritus (see Fig. 2-1), approximately O.85 to 0.95 ml
of the 1.00 ml of water applied to the cocoon string with a syringe
was shed immediately. Most of the remaining water forms a droplet
at the end of the last cocoon in the string, or remains in the silk
over-layer where it disappears by evaporation. Observations of
M. lemniscata and A. aurantia cocoons under rainy conditions in the
field yielded results similar to those observed in the laboratory.
The suspension lines of both species had beads of water hanging on
them and appeared not to conduct water toward the cocoons. Both
cocoons also shed drops of water from the bottom of the cocoon or
end of the cocoon string.
The ability of cocoons with covers to rapidly shed water
appears to be related to the slow rate at which their covers absorb
water (Fig. 5-1). Over a 2-hr period, the covers of averaged sized
2
M. lemniscata cocoons (0.5 cm in total surface area), absorb only
0.0014 ml of water. Even after 8 hrs of immersion, the amount of
water absorbed has increased to only 0.0020 ml.
The thickness of the covers of M. lemniscata cocoons vary
between 0.3 and 0.8 mm. The cover is not solid, rather it is a
matrix of fibers with included air spaces, similar to fiberglass
insulation. Assuming that approximately 50% of the cover is
airspace that can be replaced with water, the cover should be able
to hold between 0.0015 and 0.0039 ml of water. The 0.0020 ml of
water absorbed by the cocoon after 8 hrs of immersion is consistent


5 6
Table 5-4. The effect of modification of the cocoon suspension
system and cover on the incidence of fungal attack on the
spiderlings of Argiope aurantia. No spiderlings were killed by
drowning in these experiments. All cocoons were collected after 90
days.
Experimental
Modification
Sample
Size
Successful
Survival
Fungal
Attack
% Cocoons
Attacked
Control
40
40
0

Ground
Placement
22
22
0

Cover
Removal
20
20
0
cL
Of the 22 cocoons, 2 had small patches of fungus on the
shell, but the contents were unaffected.


81
Table 6-5. The mean percentage of eggs which survive in an Argiope
aurantia cocoon attacked solely by the ichneumonid Tromatobia
ovivora rufopectus, the mantispid Mantispa viridis, the chloropid
fly Pseudogaurax signata, the phorid fly Megaselia sp., or birds.
SD is in parentheses.
No. Cocoons
Parasite Sampled
Percent Eggs
Surviving
Ichneumonid
Mantispid
Chloropid Fly
Phorid Fly
35
10.2
(13.7)
15
39-1
(27.6)
15
63.7
(35-6)
4
4.7
( 9.5)
16
26.4
(28.3)
Birds


exposure to soil moisture. This is apparently not a problem with
large cocoons which are not moved down into the soil and therefore
dry out between rains.
The suspension systems and covers also retard water entry, but
the relation between this function and the prevention of fungal
attack is less clear. The covers of M. lemniscata and A. aurantia
cocoons do not control fungal attack in the egg stage. However, the
flocculent silk layers in both of these cocoons are difficult to
wet, and this layer was left intact during the field experiments.
This could account for the lack of any effect from cover damage.
Although the cover of M. lemniscata cocoons controlled fungal, attack
in the spiderling stage, the cover of A. aurantia cocoons did not.
The differences in the incidence of fungal attack in the spiderling
stage may also be related to the flocculent layer, to the time spent
in the cocoon, and cocoon size. It is also possible that the
observed differences in egg and spiderling survival between these
two cocoons have nothing to do with the size or presence of various
layers, but rather with the chemical composition of the structure
itself. Some spiders manufacture anti-fungal materials which are
applied to their webs (Scnildknecht et al. 1972). Such materials
may also be used to protect cocoons.
One obvious function of cocoons is to protect them from
mechanical shock or damage (Opell 1984). In many of ny fungal and
predator attack experiments, the cocoons of M. lemniscata tied to
vegetation, and those of M. lemniscata and A. aurantia placed on the
ground were dented or partially collapsed by the falling rain.


114
to loosely clumped (3 July). In mid-July (9-21 July) the
distribution returned to random as cocoon production declined. Late
in the season (27 July), as cocoon production drew to a close, the
distribution of web-sites with cocoons 1-5 days old became
relatively clumped again.
There were 11 cocoons attacked in 10 different strings by the
Tetrastichus wasp in the experimental plot in 1983. These attacks
occured between the 6th of July and the 8th of August, with the
majority (9 of 11) occuring between the 10th and 23rd of July.
Attacks can occur earlier in the year (Hieber 1984). Assuming that
overwintering wasps attack cocoons soon after emerging in mid-June,
the peak in attack represents the emergence of the second generation
of wasps (l6 day developmental period; 32 days later) from cocoons
attacked in late June-early July.
The concentration of wasp attacks coincided with the end of the
peak in cocoon production. Just prior to this period, the ratio of
web-sites with cocoons 1-5 days old to all sites with cocoons was at
its highest {66%) for the season (see Table 7-4). Over the
approximate 15 day period of heaviest wasp attack, however, this
ratio dropped to 14% as cocoon production slowed down. At the time
of the first attack, the average spider had already produced 584%
(SD = 22.5, n = 27) of its 3.1 cocoons. This resulted in the wasp
attacks being concentrated primarily on the third cocoon in a
string. This pattern is similar for 198l and I982 as well (Table
7-2).


83
respective larvae to penetrate the cocoon cover. The large increase
in successful mantispid attacks on artificially damaged
M. lemniscata cocoons suggests that mantispid larvae are generally-
abundant and probably have no trouble locating cocoons, but have
difficulty penetrating the dense cocoon cover. This suggests that
the cover of A. aurantia cocoons is also responsible for the
relatively low rate of successful mantispid attack. Presumably, the
larvae of the phorid fly are also hindered by the cover, although
this is a rare parasite and the low numbers of successful attacks
may be a reflection of low numbers of searching parasites. It seems
likely that birds, once they find a cocoon, have little trouble in
exploiting it.
In A. aurantia cocoons, the egg mass is closest to the cocoon
cover at its top edge, farthest from the cocoon cover at its bottom,
and approximately the same distance as the average ovipositor length
from the cocoon cover in the middle of the cocoon (Table 6-6). The
cocoons are suspended in the vegetation by a cloud of lines
emanating from suspension line "deltas" on the surface of the cocoon
(see Fig. 2-2a). There are significantly more of these deltas, and
thus significantly more lines, in the middle third of the cocoon
surface than in either the upper (t = 4.k8, df = lUO, p < 0.001) or
lower third (t = 156.1+0, df = 1^0, p < 0.001) (Table 6-7). The
distribution of ichneumonid drill holes matches the delta
distribution; there are significantly more holes in the middle third
than in either the upper (t = U.9, df = 166, p < 0.001) or lower
third (t = 3.92, df = l66, p < O.OOl) of the cocoon (Table 6-7).


IT
The internal temperatures of all three cocoons closely followed the
change in ambient temperature (Fig. 3-2).
Among the cocoons exposed to radiation loads for 10 min, there
was no significant difference between the rates of heating for the
modified cocoon with the flocculent silk layer and the cocoon
without it (Fig. 3-3). Both cocoons heated rapidly to an
equilibrium temperature of 22.5 C in approximately 5 min. The
rate of heating for the whole cocoons (total weights 0.9735 g and
0.9025 g; spiderling weights 0.7500 g and 0.7^00 g, respectively)
was significantly different from that for the modified cocoons (F =
26.ll, p < 0.0001; calculated for the first U min). These cocoons
heated to approximately 19.0 C in 5 min; an internal temperature
some 3.5 C cooler. Beyond this point, they heated at a slower
rate. An extension of this second, flatter heating curve suggests
that the whole cocoons would not reach the equilibrium temperature
of the modified cocoons until another 15 min had elapsed.
The whole and modified cocoons exposed to the 2 min loads
heated at the same rates as their counterparts in the 10 min group
(Fig. 3-3). The rates for the two groups of cocoons were
significantly different from one another as well (F = 7.^90, p =
0.03*+; calculated on the first 2 min). When the radiation load was
removed, the modified cocoons rapidly cooled to ambient air
temperature. The whole cocoons also cooled upon removal of the
load, but at a much slower rate (Fig. 3-3).
The absolute internal temperature achieved by whole cocoons in
the field depended on their location in the habitat. While the


57
collapse of the suspension system of M. lemniscata cocoons is
unrelated to the incidence of fungal attack in the egg stage (see
Table 5-1) Even total failure of the suspension system did not
result in increased fungal attack, although cocoons placed on the
ground did suffer higher egg mortality due to drowning.
The integrity of the suspension system and cocoon cover was
important to M. lemniscata cocoons that contained spiderlings (see
Table 5-2). In this stage, total collapse of the suspension system
resulted in increased mortality due to drowning. The incidence of
fungal attack also increased with modification of the cocoon cover.
However, it is unclear whether the spiderlings were attacked by
fungus because of damage to the cover, or died for some other reason
and were subsequently attacked. Modifying the cocoon cover does
increase dessication problems for M. lemniscata spiderlings (see
Chapter IV), and this may have been the real cause of the increased
spiderling death. However, I have also had fungus attack
spiderlings in the laboratory under conditions of high relative
humidity (66-100/ RH) where dessication should not be a problem.
Christenson and Wenzl (1980) found that 17*5% of the cocoons of
N. clavipes were attacked in the egg stage by fungus. They cited
the loss of protection from the rain (removal of a leaf canopy above
the cocoon), and falling to the ground (support line failure) as
reasons why the flocculent silk cocoons of this spider failed.
Overall, the lack of any effect on the incidence of fungal attack
through manipulation of the covers and suspension systems of
M.* lemniscata and A. aurantia cocoons is surprising, particularly


103
parasitized cocoons within a string and the total number of cocoons
in each string were also recorded.
The relationship between host density and level of parasitism
among sites of high and low host density was determined from the
four plots sampled in 1982. For each plot the proportional survival
(S/N; number of unparasitized cocoons/ total number of cocoons) was
calculated and plotted against the cocoon density (N). The
relationship between host density and level of parasitism within a
2
site was determined by dividing the UOO m volume surveyed in 1983
into fifty 8 nr sub-volumes. The proportional survival in each of
the sub-volumes with cocoons was calculated and plotted against its
cocoon density. Density dependence is indicated by a negative slope
for such plots.
Developmental rates for the host and wasp were determined by
rearing spider eggs and wasp larvae in 2 dram glass vials stoppered
with cotton and maintained at 28 C and 70-60$ RH (ambient
conditions at the study site). The age of the host at the time of
attack was determined by rearing the remaining eggs from three
cocoons in which developing wasp larvae were found.
Additional collections of cocoons were made in mid-July [during
the peak of wasp attack (Hieber I98U)1 and late December in 1983,
and in early March in I98H (just before spiderling emergence) to
establish if the parasite overwinters in the cocoon as a prepupae,
and if so, when it emerges in the spring. Cocoons from these
collections were opened in the laboratory and scored for the
presence of wasp larvae, shed exuviae and larvae, or shed exuviae


22
The cocoon, in combination with the egg or spiderling mass,
acts as a buffer against rapid temperature changes (Fig. 3-1) Such
rapid changes could result from exposure to the night sky
immediately after sundown, particularly in the winter (see
Fig. 3-4). However, most A. aurantia cocoons are placed within the
vegetation. In these protected locations, radiant heat loss to the
cold night sky is reduced by the warmer overhead vegetation. Under
these conditions, cooling is slower and follows the change in
ambient air temperature (see Fig. 3-2). Cold hardiness (Schaefer
1977, Riddle 1981) resulting from physiological solutions such as
freezing point depression (Kirchner and Kestler 1969) probably
protects the eggs or spiderlings from extremely cold temperatures.
Cocoons in open habitats but under a layer of vegetation, or in
closed habitats such as woods may still be exposed to periodic
"sunflecks" as the sun moves across the sky. These short lived, but
potentially intense, radiant loads could present a serious thermal
challenge to the cocoon. The field experiments indicate that the
cocoon and the mass of the eggs or spiderlings provide a significant
buffer against short-term loads (see Fig. 3-3), extending the
heating time to equilibrium by approximately 15 min. However, the
level of protection provided by a cocoon is directly related to the
ambient air temperature, the duration of the load, and the elapsed
time between consecutive loads. The radiant loading experiments
were conducted in the winter, when the ambient air temperature was
relatively low (12-14 C). Even with constant exposure to
insolation, low ambient temperatures such as these would result in a


10
a soft, thick, feltlike material. The agglutinated egg mass of
800-2000 eggs (X = 978.7 eggs, SD = 1+19.2, n = 1+0) is suspended
within the cocoon from a thick silk cup, which in turn is attached
to a cone and cord of strong silk which fills the stalk of the
cocoon. The egg mass is covered by a fine membranous layer of silk,
and is separated from the cover by a thick flocculent silk layer
(see McCook 1890, pp. 79-80 for a complete description of the
internal structure of the cocoon).
The eggs and spiderlings in A. aurantia cocoons are attacked by
a number of general and specialized predators including the
hymenopterans Tromatobia ovivora rufopectus (Cresson)
(ichneumonidae) (Cresson 1870, Keobele 1887, McCook 1890, Howard
1892, Champlain 1922, Enders 197, Tolbert 1976), Pimpla aquilonia
aquilonia (Cresson) (ichneumonidae) (Davidson 1896), Chrysocharis
banksii and Chrysocharis pikei (Entodontimidae) (McCook 1890), and
Pediobius wilderi (Howard) (Entodontimidae) (McCook I89O) [this is
probably a hyperparasite attacking T. ovivora rufopectus]; the
dipterans Pseudogaurax signata (Loew) (Chloropidae) (Coquillet
1898), Pseudogaurax anchora (Loew) (Kaston and Jenks 1937, Eason et
al. 1967), and Megaselia sp. (Phoridae) (Kaston and Jenks 1937);
the neuropteran Mantispa viridis Walker (Mantispidae) (Enders 1974,
Tolbert 1976); the coleopteran Chauliognathus sp. (Cantharidae)
(Enders 1974); salticid spiders (Salticidae) (Enders 1974); and
birds (Enders 1974, Tolbert 1976).
Argiope aurantia prefers vegetation along water courses in
Florida (Levi 1968), and is common in roadside hedgerows bordering


Proportional Survival (S/N)
108
1.0-
0.8-
0.6-
0.0
r 1 1 r
0 5 10 15 20 25
Cocoon Density (N)
Fig. 7-2. The relationship between proportional survival (S/N) and
cocoon density (N) for Mecynogea lemniscata cocoons within one site.
Proportional survival is not significantly correlated with cocoon
density (Y = -0.003X + 0.944; r = -0.19, df = 15, p > 0.05),
indicating no density-dependent relationship between parasite
foraging success and host density.


27
Experimental Material
The cocoons and egg masses of A. aurantia were obtained from
spiders collected in the field and maintained at 24-25C and 60-J0%
RH in 500 ml jars in the laboratory. The M. lemniscata cocoons and
egg masses were obtained by daily censusing 100-150 marked
web-sites. The cocoons used in the experiments on spiderling
survival were collected in the field in late August (for
M. lemniscata), and during September-October (for A. aurantia).
Only undamaged, nonparasitized cocoons were utilized. The
experimental spiderling masses were obtained by removing the cocoon
cover and as much of the internal flocculent layer of silk as
possible.
Egg Surface Morphology
The surfaces of M. lemniscata and A. aurantia eggs were
photographed with a Hitachi S-415A SEM. They were prepared by
attaching them to SEM stubs with double-sided tape, and coating with
o
75 A of gold. The densities of the spherical granules (spheres) on
egg surfaces were measured by placing a grid system (4x4 lines)
over the electronmicrographs of five eggs of each species and
counting all spheres within 2 randomly chosen grid-squares. Since
the spheres on both species1 eggs are distributed essentially as
monolayers (Humphreys 1983), densities were expressed as the mean
number of spheres/ 100 ym Sphere diameters were determined
directly by measuring all the spheres within the 10 grid-squares.


This dissertation was submitted to the Graduate Faculty of the
Department of Zoology in the College of Arts and Sciences and to the
Graduate School, and was accepted as partial fulfillment of the
requirements for the degree of Doctor of Philosophy.
Dean for Graduate Studies and
Research
December, 1984


9
Fig. 2-2. The cocoon of Argiope aurantia suspended in the
vegetation (a), and in cut away view (B) showing the position of the
egg mass (em), silk cap (sc), silken cone and cord (scd), and
flocculent silk layer (fsl) within the cocoon cover (cv).


126
behavioral studies (e.g., foraging behavior). In the latter, a
number of initial assumptions, often unrealistic, must be made
concerning what is being maximized and how it relates to fitness.
Many authors have suggested that cocoons, and in particular the
flocculent silk layers often found within cocoons, function as
insulation and protects the eggs and spiderlings from extremes of
temperature (McCook 1890, Kaston 19^+8, Turnbull 1973, Gertsch 1979)*
Chapter III supports this view, and indicates that the protection
provided may be directed primarily at controlling short-term
radiation loads (i.e., "sunflecks"). The limited level of
protection offered by the cocoon is due to the cocoon cover, which
creates an insulating layer of dead, and, to a greater extent, the
size of the egg or spiderling mass which provides thermal inertia.
The flocculent silk layer has no role in the insulation of the
cocoon.
The size of the cocoon and the spiderling mass must be
considered before these results are extended to all cocoons. The
cocoon and egg mass of A. aurantia are among the largest found
(Kaston 19^8, Foelix 1982). As such, the level of protection
against short-term thermal loads provided by this cocoon and its egg
or spiderling mass is probably close to some maximum value. Cocoons
without covers which cannot produce a layer of dead air (Kaufman et
al. 1982), or cocoons with smaller egg masses would show
proportionately smaller effects in attenuating thermal extremes.
The position of the cocoon in the habitat probably plays a more
effective role in controlling thermal extremes for most spiders.


CHAPTER V
THE ROLE OF THE COCOON IN LIMITING EXCESS WATER
AND FUNGAL ATTACK
Introduction
Although desiccation is a problem for developing spider eggs
and overwintering spiders, too much water may also cause adverse
effects. Water, entering the cocoon, could dissolve materials from
the egg surface and lower the resistance of the eggs to disease
(Austin and Anderson 1978). It could also drown the contents of the
cocoon (Schaefer 1976, Reichert 1981). Water may also introduce
fungal spores that are pathogenic to the eggs or spiderlings.
Christenson and Wenzl (1980) suggested that the cocoon of Nephila
clavipes (Linneaus) (Araneidae) protects against fungal attack by
reducing the chance of spores gaining access to the egg mass. A
role in protecting the eggs and spiderlings from fungi seems
reasonable, since both spiders (Bijl and Paul 1922, Nellist 1965)
and their eggs (Seligy 1971, Christenson and Wenzl 1980) are
attacked by fungus.
Both Mecynogea lemniscata and Argiope aurantia utilize a
covered cocoon (see Figs. 2-1 and 2-2), in contrast to the
flocculent silk type used by many other orb-weavers (McCook 189O,
Scheffer 1905, Kaston 19^8). Both spiders also utilize habitats
where high humidity during the egg laying period may promote fungal
attack (see Chapter II). In this chapter, I examine the roles of


Table 7-4. The number and distribution in space and time of all Mecynogea lemniscata web-sites with
cocoons, and of sites with cocoons of the proper age (1-5 days) for attack, in the experimental plot
for 1983.
Date
June July August
15
21
27
3
9
15
21
27
2
8
l4
No. web-sites
with Cocoons
2
7
21
34
34
34
35
35
35
35
35
Average No.
Cocoons/ web-site
1.0
1.1
1.3
1.6
2.4
2.9
3.0
3.2
3.2
3.2
3.2
Total No. Cocoons
for all Web-sites
2
8
28
56
80
99
106
111
112
113
ll4
No. Web-sites with
Cocoons 1-5 Days Old
2
6
i4
22
23
12
6
5
1
1
0
% Web-sites with
Cocoons 1-5 Days Old
100%
85%
67%
64 %
66%
35%
17%
l4%
3%
3%
0%
112


28
Effect on Dessication
The effects of the sphere layer, clutch size, and the cocoon on
hatching success, molting success, and spiderling survival were
determined by rearing intact egg and spiderling masses without
cocoons (and appropriate controls) at 25-26 C in one liter jars
controlled at four different RH levels (0%, 33%, 66%, and 100%).
The controlled humidities were achieved by using dry anhydrous KOH
pellets (0% RH), and saturated salt solutions of 300+ g CaCl2/
100ml HO (33% RH), 100 g NaNO^/ 100 ml H20 (66% RH), and 15 g
KgSO^/ 100 ml H20 (100% RH) (Winston and Bates 19^0, Peterson
1964). The pellets and solutions controlling the humidities were
changed every two weeks. Since the egg masses of A. aurantia
contain more eggs than those of M. lemniscata (approximately 970 to
20, respectively), artificially reduced egg masses of 15-25
A. aurantia eggs were also reared under these conditions to control
for the possible effects of egg mass size on hatching success.
The effect of the cocoon was also tested under field conditions
by placing intact egg and spiderling masses (and appropriate
controls) in individual screen-covered vials within styrofoam-cup
housings. These housings protected the replicates from
precipitation, predators, and parasites, and were hung in the shade
in locations where females had previously constructed cocoons.
Hatching and molting success was calculated after 30 days.
Hatching success was the percentage of total eggs in which the
chorion ruptured and a deutova successfully emerged. Molting


Field Experiments
The function of the cocoon suspension system and the cocoon
cover in limiting fungal attack and drowning were investigated by
modifying these components in the field, and assessing their effect
on egg hatching success and spiderling survival. The cocoons used
in these studies were either reared in the laboratory, or collected
in the field from marked web-sites. Only nonparasitized cocoons
were used.
The cocoons were assigned to the four experimental groups
listed below. The experiments using cocoons with eggs were run for
30 days; those using cocoons with spiderlings for 90 days. The
cocoons not associated with apparatus were marked by plastic
flagging attached to the vegetation.
Vegetation contact. The effect of cocoon suspension systems in
preventing fungal attack was examined by placing >1. lemniscata
cocoons in contact with the vegetation. This simulated partial
collapse of the suspension system, and placed limitations on the
cocoons drying normally. Placement was accomplished by cutting the
cocoon free, and tying it in place to the vegetation with its
support line. Access to the cocoons by terrestrial predators was
controlled by applying tack-trap to the branches below the cocoons,
and pruning the branches above the cocoon so they did not contact
the surrounding vegetation. Argiope aurantia cocoons were not
subjected to this treatment.


37
Table 4-5. Mean percentages for Molting Success and Spiderling
Survival ( 1 SD; n in parentheses) at the four experimental
humidities for Argiope aurantia egg and spiderling masses with and
without cocoons. Pair-wise comparisons between treatments are by
Mann-Whitney U tests; pair-wise comparisons between humidities
within treatments are by nonparametric multiple comparson tests (Zar
1984).
% Molting % Spiderling
Success Survival
Relative
Humidity
Cocoon
No Cocoon
Cocoon
No Cocoon
98.8
93.7
100%
100%
100%
1.5%
8.2%
(8)
(8)
(7)
(5)
**
*#
99.1
61.5 1
63.5 1
66%
100%
2.0%
27.5%
19.6 %
(7)
(8)
(6)
(8)
***
#*
***
***
96.0
76.2
33%
4.2%
34.8%
0%
0%
(7)
(9)
(8)
(8)
84.4
56.1
0%
19-0%
48.0%
0%
0%
(8)
(8)
(9)
(9)
Kruskall-
Wallis H
22.40
11.09
27.18
27.99
"p"
< 0.001
< 0.01
< 0.001
< 0.001
(* p < 0.05; ** p < 0.01; *** p < 0.001)


30
Fig. h-1. The layer of spherical mucoid granules on the chorionic
surface of a Mecynogea lemniscata egg (A), and an Argiope aurantia
egg (B). The scale line in each case equals 15 ynu Both eggs were
plated with 75 A of gold and observed using secondary electrons.


26
(Koch) has no effect on the hatching success of spider egg masses at
different controlled humidities.
Some spider eggs are dessication-resistant as well (Schaefer
1976). This resistance may result from a layer of spherical
granules on the chorion surface (Austin and Anderson 1978, Grim and
Slobodchikoff 1978, 1982, Humphreys 1983). Overwintering
spiderlings within the cocoon can also attenuate water loss by
reducing their rates of metabolism (Schaefer 1976, Anderson 1978),
or by metabolizing lipids. Presumably, the cuticle of spiderlings
also impedes water loss (Lees 19*+7, Davies and Edney 1952).
I investigate here the role of the cocoon in controlling water
loss from the egg and spiderling masses of Mecynogea lemniscata
(Walckenaer) and Argiope aurantia Lucas (Araneidae) during egg
development, deutoval molting, and spiderling overwintering. I also
examine the effect of clutch size, and egg morphology (Austin and
Anderson 1978, Grim and Slobodchikoff 1978, 1982) on water loss.
Materials and Methods
The Cocoons and Their Habitats
The cocoons of _M. lemniscata and A. aurantia differ in size,
density of the cover, and internal construction. The preferred
habitats of the two spiders also differ, the habitat of
M. lemniscata being more consistently humid than that of A. aurantia
(see Chapter II).


128
demonstrate a protective function provided by the cocoon. The
significant effect of the cocoon on the survival of M. lemniscata
spiderlings appears to be related to the exceedingly long time that
they spend in the cocoon overwintering (2-3 months longer than
orb-weavers). Overall, the results of this study and those of
Schaefer (1976) and Austin and Anderson (1978) show that covered
cocoons should be found in species that spend long periods of time
as eggs or spiderlings in the cocoon in developmental diapause or
overwintering, or where the habitat is extremly xeric for all or
part of the year.
The results also emphasize that physiological or morphological
differences in the abilities of deutova and spiderlings to limit
water loss may also be operating in conjunction with, or in place
of, the cocoon. With no cocoons present, the deutova of
M. lemniscata molted successfully at much lower humidities than
those of A. aurantia. The survival rate for M. lemniscata
spiderlings without cocoons was also higher than those of
A. aurantia at lower humidities. Both of these results suggest that
the deutova and spiderlings of M. lemniscata are better able to
handle desiccation.
Finally, the results suggest that the above mentioned
differences might be part of a behavioral solution for controlling
water loss. The limited survival of A. aurantia spiderlings with a
cocoon at low humidities points out that other considerations, such
as the RH humidity at the oviposition site, are more important for
this spider. Indeed, Levi (1968) notes that of the Argiope species


13
fluctuations in ambient temperature. However, Austin and Anderson
(1978) found no significant differences in the hatching success of
spider egg masses, with or without cocoons, exposed to a range of
constant temperatures. They concluded that the flocculent silk
cocoons of Nephila edulis (Koch) (Araeidae) did not function to
protect the eggs from temperature extremes.
The cocoon of Argiope aurantia Lucas (Araneidae) is a
multilayered structure, with a flocculent layer of silk located
between the eggs or spiderlings and the cocoon cover (see
Fig. 2-2b). In late August-September, the cocoons are usually
placed in the upper strata of the vegetation where they may be
exposed to direct sunlight, wind, and the night sky, all of which
may alter the internal temperature of the cocoon throughout the
development and overwintering period. Here, I examine the the role
of the cocoon, and in particular the effectiveness of the flocculent
silk layer within A. aurantia cocoons, in buffering temperature
extremes. I also examine the role that cocoon positioning in the
habitat plays as an adjunct method of temperature regulation.
Materials and Methods
I used three types of cocoons: whole, nonparasitized cocoons
containing spiderlings, and two types of modified cocoons,
"insulated" and "non-insulated". The latter two types were created
by halving whole cocoons longitudinally with a razor blade and
removing either the eggs alone, or the eggs and the flocculent silk
layer. The halves of these modified cocoons were rejoined with


47
hanging. Tack-trap was applied to the support arms to limit the
access of terrestrial predators (primarily ants).
Cover removal control. This group functioned as a control for
possible contaminating effects of the alligator clips. The clips
were attached to the necks of cocoons hanging normally in the
habitat, and the cocoons were observed for any detrimental effects.
Control. A number of cocoons were subjected to no structural
intervention, and functioned as a control for the handling effects
in the vegetation placement, ground placement, and cover removal
experiments.
Results
Laboratory Experiments
The suspension lines of M. lemniscata cocoons are relatively
poor conductors of water. At all the inclinations tested, dry lines
were not easily wetted, and consequently tended to shed water.
Suspension lines could be wetted by rubbing them between wet
fingers, but even here water moved with difficulty. At the lower
angles of inclination (10 and 20), water applied to the wetted
line formed drops or beads and hung in place. At the higher
inclinations (30 and 45), water moved down the line toward the
cocoons. However, the suspension lines of M. lemniscata cocoons are
made of multiple strands of silk and contain "knots" and
incorporated debris. When water moving down the line got to these
points it built to a drop and fell from the line.


ACKNOWLEDGEMENTS
It is a pleasure to acknowledge the many friends and colleagues
who aided me in this work. My major professor, John F. Anderson,
has been a source of stimulation and encouragment. His comments on
ny work were always critical but fair, and he always emphasized the
importance of doing good, solid research. Most importantly, he
encouraged me to be as independent as possible while doing ny
research. To John I extend ny sincerest thanks. The other members
of my dissertation committee, Lincoln P. Brower, Jonathon Reiskind,
and Reese I. Sailer, and the additional colleague, David H. Evans,
who sat at my defense, all provided ready assistance during the
research phase and many helpful editorial suggestions, from which I
benefitted. I also recognize the advice or equipment provided by
Drs. L. Berner, P. Feinsinger, M.H. Greenstone, F.J. Maturo, and
B.K. McNab.
I was also fortunate to have the cooperation of a number of
people in positively identifying my egg predators. Thanks for this
service go to H. Townes (ichneumonids), American Entomological
Institute; Dr. M.E. Schauff (eulophids), Systematic Entomology Lab,
USDA; and Dr. L. Stange (mantispids), Division of Plant Industries,
FDACS. Further thanks go to Mr. and Mrs. H.M. Chitty, who
generously allowed me access to the Stardust Ranch for many of ny
experiments. I also acknowledge the Department of Zoology, Sigma


150
Kessel, E.L., and B.B. Kessel. 1937 The life history of Gaurax
araneae Coq., an egg predator of the black widow spider, Lactrodectus
mactans (Fabr.). Pan-Pacific Entomol. 13: 58-60.
Kessler, A., and A. Fokkinga. 1973. Hymenopterous parasites in the egg
sacs of spiders of the genus Pardosa (Araneida, Lycosidae).
Tijdschr. Entomol. il6: 46-6l.
Kirchner, W., and P. Kestler. 1969 Untesuchungen zur Kalteresistenz
der Schilfradspinne Araneus cornutus (Araneidae). J. Insect
Physiol. 15: 41-53
Koebele, A. 1887. Some of the bred parasitic bymenoptera in the
National Collection. Insect Life 3: 46l.
Lack, D. 1954. The Natural Regulation of Animal Numbers. Oxford
University Press, New York. 343 pp.
Lack, D. 1966. Population Studies of Birds. Oxford University Press,
New York. 341 pp.
Lack, D. 1968. Ecological Adaptations for Breeding in Birds. Methuen,
London. 409 pp.
Laing, J. 1937 Host-finding by insect parasites. I. Observations on
the finding of hosts by Alysia manducator, Mormoniella vitripennis,
and Trichogramma evanescens. J. Anim. Ecol. 6: 298-317
Laing, J. 1938. Host-finding by insect parasites. II. The chance of
Trichogramma evanescens finding its hosts. J. Exp. 3iol.
15: 281-302.
Lees, A.D. 1947. Transpiration and the structure of the epicuticle in
ticks. J. Exp. Biol. 23: 379-410.
Levi, H.W. 1968. The spider genera Gea and Argiope in America
(Araneae: Araneidae). Bull. Mus. Comp. Zool7 136: 319-352.
Levi, H.W. 1980. The orb-weaver genus Mecynogea, the subfamily Metinae
and the genera Pachygnatha, Glenognatha, and Azila of the subfamily
Tetragnathinae north of Mexico (Araneae: Araneidae). Bull. Mus.
Comp. Zool. 149: 1-74.
Levi, H.W., and L.R. Levi. 1969. Sggcase construction and further
observations on the sexual behavior of the spider Sicarius
(Araneae: Sicariidae). Psyche 76: 29-40.
May, R.M. 1978. Host-parasitoid systems in patchy environments: A
phenomenological model. J. Anim. Ecol. 47: 833-844.


117
days apart in age, there are always two cocoons on the string in the
proper age for attack (Fig. 7-3a). In addition, one or two other
cocoons on the same string are available for attack when the wasp's
progeny emerge 16 days later (mating takes place on the outside of
the cocoon).
The rearing data suggests, however, that the time period for
attack is less than this 11-day period. If a more conservative
5-day period is used as the limit for successful parasite attack, a
different picture emerges (Fig. 7-3b). With cocoons produced every
six days, there is only one cocoon in the string at any given time
in the proper condition for attack. In addition, the timing of
cocoon production insures that the emerging progeny barely overlap
with one cocoon instead of two. The average string contains only
three cocoons, and if the second or third cocoon is attacked, there
are no cocoons available for emerging progeny. Thus, the
interaction between cocoon production and egg development forces the
initally attacking wasp, or its subsequent progeny, to locate other
web-sites with strings containing useable cocoons. The low number
of multiply-attacked cocoon strings (3.1^ of 286 for 1981-1983)
supports the hypothesis that timing of cocoon production is a
barrier limiting individual parasite success.
In general, web-sites, and thus host cocoons, are slightly
clumped in their distribution (Table 1-h). Spiders which utilize
sites that are spatially isolated from other web-sites or clumps of
sites may therefore have an advantage in avoiding parasites.
Although the distance between web-sites may play a role early in the


58
since these components presumably perform the same functions as the
leaf layer and support system of N_. clavipes cocoons. These results
may be partially explained by differences in the cocoons of the
three species. The cocoons of M. lemniscata and A. aurantia have
dense covers, and layers of flocculent silk between the cover and
the egg mass. While the covers of both these cocoons are wettable,
the flocculent silk layer is not. The cocoon of N. clavipes is
composed primarily of a basket-like mesh, with little or no
flocculent layer between the eggs and the mesh. The eggs in
M. lemniscata and A. aurantia cocoons with damaged covers are still
protected from water (and fungal spores?) by their flocculent silk
layer (which was not damaged in this study). The mesh cocoons of
N. clavipes, which are also wettable, have no flocculent layer to
turn water away from the egg mass once their protective leaf canopy
is gone. Other explanations for this difference, such as a layer of
spherical granules on the surface of the eggs of these two species
which repel water (Austin and Anderson 1978, Grim and Slobodchikoff
1978, 1982, Humphreys 1983), or relatively short developmental
periods are not adequate, since all three spiders share these
traits.
The differences in the incidence of drowning between
M. lemniscata and A. aurantia cocoons in the egg and spiderling
stages (see Tables 5-2 and 5-*0 are probably related to differences
in the size of these cocoons, and the thicknesses of their
flocculent silk layers. The cocoons of M. lemniscata are small, and
are worked down into the soil by rain action when placed on the


69
used for these modifications were either produced in the laboratory,
or collected in the field. They were assigned to the experimental
groups listed below. The cocoons in all the experimental groups
were marked either by flagged stakes placed beneath them, or by
flagging in the vegetation.
Vegetation contact. The function of cocoon support lines as a
deterrent to arboreal predators was examined by repositioning
cocoons so that they contacted the vegetation. This was done only
for M. lemniscata cocoons and was accomplished by tying cocoon
strings to branches with their suspension lines. This mimicked the
position of cocoons whose suspension systems had collapsed normally.
Ground placement. The role of the suspension system in keeping
cocoons off of the ground and away from terrestrial predators was
investigated by placing the cocoons of both species on the ground in
open-topped wire corrals. These corrals allowed cocoons to be
attacked but prevented them from being washed away in the rain. The
corral used for A. aurantia cocoons was constructed of hardware
cloth (1/4" mesh) and was 12.5 cm in diameter and 5 cm in height.
The corral for M. lemniscata cocoons was constructed of aluminum
window screen and was 5 cm in diameter and 5 cm in height. The
corrals were located below sites where cocoons had been collected
previously.
Cover removal. The function of the cocoon cover in limiting
predator attack was examined by removing approximately 25% of the
cocoon cover with a razor blade. Individual cocoons of
M. lemniscata were modified in the cocoon string and the string was


6k
cocoons (Kaston and Jenks 1937), there is still no evidence that
cocoons, or the various layers comprising them, function to turn
away or reduce the success of specific parasites or predators.
In this chapter, I investigate the roles that the suspension
systems, outer covers, and internal flocculent silk layers of the
cocoons of Mecynogea lemniscata Walckenaer and Argiope aurantia
Lucas (Araneidae) play in controlling the access of predators to the
eggs and spiderlings within. If the suggestions of various
researchers, and in particular Austin (in press), are correct, these
cocoons should demonstrate defenses which reflect the manner in
which their predators attempt to introduce themselves or their
offspring into the cocoon.
Materials and Methods
Population Data
The numbers and kinds of parasites and predators attacking the
cocoons of M. lemniscata and A. aurantia were determined by
collecting cocoons in the field and returning them to the laboratory
where they were opened and scored for parasites. Scoring was
relatively easy since each parasite leaves distinctive evidence in
the cocoon such as the type of hole in the cover, or remains such as
pupal cases, shed exuviae, or eggs. The M. lemniscata cocoons were
collected in late August in 1981 to 1983 after the eggs in the last
cocoons laid had hatched. A single sample of A. aurantia cocoons
was collected in late October in 1981. In 1982 and 1983
a


CHAPTER I
INTRODUCTION
All spiders place their eggs in some form of silken cocoon
(Turnbull 1973) For some, the cocoon is a relatively simple
structure consisting of a few threads (e.g., the Pholcidae) and is
used to move the egg mass about the web. In others, the cocoon
provides a more complete container for carrying the eggs while
hunting (e.g., the Lycosidae) or an additional level of protection
for spiders which actively guard their eggs (e.g., the Oxyopidae).
For many web-building spiders (e.g., the Araneidae), the cocoon is
an elaborate structure composed of a variety of layers and is
suspended in the habitat by different devices (McCook 1890, Scheffer
1905, Kaston 19^8, Turnbull 1973). In many araneids where active
care is non-existent, the cocoon represents the sum total of
maternal care given to the eggs and spiderlings by the female.
Many web-building spiders deposit large clutches of eggs
(Kaston 19^+8, Foelix 1982). Within the cocoon, the eggs undergo
embryonic development, hatch to the deutova stage, and molt to the
spiderling stage. The spiderlings can spend as long as 6 to 10
months in the cocoon overwintering until emergence in the spring
(Anderson 1978). This long time interval, the large clutch sizes,
and the absence of active maternal care have led to many suggestions
concerning the function of cocoons. These include providing
physical support for the egg mass (Christenson and Wenzl 1980),


55
Table 5-3. The effect of modification of the cocoon suspension
system and cover on the incidence of fungal attack on the eggs of
Argiope aurantia. Cocoon modification had no effect on egg
inviability or drowning. All cocoons were collected after 30 days.
Experimental
Modification
Sample
Size
Successful
Hatch
Fungal
Attack
% Cocoons
Attacked
Control
Ul
39
2
h.9%
Ground
Placement
12
10
2
20.0%
Cover
Removal
13
11
2
15. U*


39
the free surface area through which water can pass (Austin and
Anderson 1978, Grim and Slobodchikoff 1978, 1982, Humphreys 1983)
The eggs of M. lemniscata have a significantly denser coating of
these spheres than do the eggs of A. aurantia (see Table k-l).
Although a direct comparison of the eggs of each of these species
with and without spheres is difficult (due to problems in stripping
the sphere layer from the eggs and still maintaining viability), the
comparison of intact M. lemniscata egg masses with reduced
A. aurantia egg masses strongly suggests that the sphere layer does
reduce water loss (Table 4-2). However, the drop in hatching
success at 0$ RH indicates that this barrier has limits in its
ability to control water loss at very low humidities.
Molting is a dangerous period of time for deutova with their
high surface area to volume ratio (Horner and Starks 1972). At
molting, with the breaking and subsequent shedding of the egg
chorion, dessication protection shifts back to the level of the
cocoon. In spite of this, removal of the cocoons of M. lemniscata
and A. aurantia demonstrate no effect on molting success (see Tables
4-3 and 4-5). However, the variances among the no-cocoon treatments
of A. aurantia at 33$ and 0% RH are high, which may make detection
of the cocoon's effect on molting success difficult. Presumably,
the main factor affecting molting success for these spiders is the
ambient RH at the oviposition site, although the greater molting
success of M. lemniscata at low humidities suggests that there may
be morphological or physiological differences in the abilities of
the deutova of these species to reduce water loss.


a Gertsch (1979)
k Kaston (1970)
from Steatoda borealis (Kaston 19**8)
^ from Argyrodes trigona (Kaston 19**8)
e
from Theridion tepidariorum, T. differens, T. murarium, T. spirale, T. frondeum,
T. albidum, T. unimaculatum, T. punctosparsum, T. redimitum (Kaston 19**8")
f
from Araneus diadematus, A_. cornutus, A., sericatus, A. marmoreus, A. trifolium,
A. pima, A_. gemmoides TKaston 19^8)
g This study
from Agelenopsis pen [ n ] sylvanica, A_. naevia (Kaston 19^8)
^ from Lycosa carolinensis, L^. aspersa, L. rabida, L. punctulata, L^. avida,
_L. helluo, Ij. modesta, L^. gulosa, L. frondicola, Ij. avara (Kaston 19^+8)
from Pardosa distincta, P. moesta, _P. milvina, P. saxatalia, Fh floridana,
Fh rnochia, _P. lapidiana, J?. xerampelina (Kaston 19^*81
m Reiskind (1969)
0 from Philodromus praelustris, P. pernix, JP. imbecillus, Fh rufus, _P. aureolus
(Kaston 19^8)
P from Phiddlpus audax, V. purpuratus, ]?. clarus, P. princeps, IP. whitmanni,
P. insjgnarius (Kaston 19**8)
132


Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment
of the Requirements for the Degree of
Doctor of Philosophy
THE ROLE OF THE COCOONS OF ORB-WEAVING SPIDERS
By
Craig S. Hieber
December, 1984
Chairman: John F. Anderson
Maj or Department: Zoology
The cocoons of spiders are believed to function in protecting
the enclosed eggs and spiderlings from a number of biotic and
abiotic factors. It has also been suggested that the wide diversity
in cocoon architecture is the result of a "coevolutionary arms-race"
between spiders and predators of their offspring. However, few
studies have provided evidence to support these claims. This study
provides evidence for some of these suggested functions by comparing
the abilities of the cocoons of Mecynogea lemniscata and Argiope
aurantia to control or limit temperature extremes, dessication, and
attack by fungi and predators.
Results indicate that the cocoon of M. lemniscata limits
dessication and fungal attack on the spiderling stage. In contrast,
the cocoon of A. aurantia does not. Both cocoons probably play a
xi


79
The status of P. signata is less clear. This fly deposits eggs
on cocoon surfaces. The eggs hatch and the emerging larvae push
their way through the cover into the cocoon (Kaston and Jenks 1937,
Kessel and Kessel 1937, Hickman 1970). The literature suggests that
chloropid flies are obligate spider egg parasites (see Austin, In
press), a fact supported by the large number of A. aurantia cocoons
attacked by this fly in 1982. However, only 17 of 1+2 cocoons were
singly attacked by this fly (Table 6-4). The remaining cocoons were
attacked along with other predators (particularly mantispids), and
in many cases the fly deposited its eggs in the emergence holes of
these previous attackers. In addition, Hall (1937) lists this fly
as attacking the egg masses of the praying mantis. This suggests
that this fly is a facultative egg predator that attacks eggs in any
container, as well as utilizing dead or damaged eggs from other
attacks when located. The phorid is found alone in cocoons
approximately 50% of the time and it is probably an obligate egg
predator, attacking cocoons in the same manner as P. signata.
The observed levels of egg predation for T_. ovivora rufopectus,
P. signata, and M. viridis in this study are similar to the levels
of attack reported by Enders (1974) and Tolbert (1976) for
A. aurantia cocoons. The A. aurantia cocoons in this study were
also attacked by birds, ants, and moth larvae, although it is
unclear whether these attacks occured in the egg or spiderling
stage. The level of bird attack was lower (9%) than that found by
Tolbert (35-50%). Argiope aurantia cocoons containing spiderlings
are attacked by ants and other spiders (particularly salticids which


19
Fig. 3-3. Heating rates in still air outdoors for whole and
modified Argiope aurantia cocoons exposed to radiant loads of 2 and
10 min duration. The whole cocoons (open squares, 2 min; closed
squares, 10 min) contained spiderlings and the flocculent silk
layer; the modified cocoons contained only the flocculent layer
(stars, 2 min; open circles, 10 min), or were empty (closed circles,
10 min).^ The heating curve for the whole cocoons is Y = 0.50X +
13.4U (r = O.98, n = 2); for the modified cocoons with the
flocculent layer Y = 1.01X + lU.29 (r = 0.93, n = l); for the
empty cocoons Y = O.96X + 1U.U7 (r2 = 0.9^, n = l). The ambient
air temperature during the experiment ranged from 12.9 C to 13.7
C. The vegetation and sky temperatures during the experiment were
+15 C and -20 C, respectively.


101
density-dependent pattern of parasitoid attack is not observed, some
factor has usually been suggested as acting to interfere with the
parasitoids' search. Suggested factors include tidal inundation of
hosts (Stiling and Strong 1982), temperature and humidity (Vinson
1976), heavy rain fall (Stiling and Strong 1982), differential
response to hosts at different densities (Hassell and May 1973),
insufficient numerical response, dispersal and/ or reduced search
efficiency due to mutual interference (Hassell 1971, Hassell and May
1973, 197*0, or "pseudo-interference" (Free et al. 1977).
Considerations of host behaviors such as the phenology of host
emergence or the timing of host production, and their effects on the
temporal and spatial distribution of the host or its reproductive
stages have not often been considered as factors affecting
parasitoid search, although an understanding of spacing and timing
in general are important to our overall understanding of host/
parasite interactions (Murdoch and Oaten 1975, Morrison and Strong
1980). In addition, this predicted relationship has not been tested
for any spider and its parasites, although spiders and their cocoons
can be heavily attacked (see Eason et al. 1967).
Here, I test the prediction of a positive relationship between
host density and the level of parasite attack for the cocoons of the
spider Mecynogea lemniscata (Walckanear) (Araneidae) and its primary
egg predator, the wasp Tetrastichus sp. (Eulophidae) [near
T. banksii Howard; see Hieber (1984)]. I then examine the early and
narrow reproductive season of this spider, the timing of cocoon
production, the spatial distribution of the cocoons within the


51
with these calculations, and suggests that it is the cover alone
which absorbs water before the excess is shed by the cocoon.
Examination of the cocoons under the microscope supports this. None
of the 22 cocoons had water inside them after k hrs of submersion.
The flocculent layer of A. aurantia cocoons was completely
non-wettable. Water applied to the silk simply formed beads and sat
upon the silk until it disappeared by evaporation.
Field Experiments
The incidence of fungal attack on M. lemniscata cocoons
containing eggs in the control group was 7*3% (Table 5-l)*
Chi-square tests between this group, and the Vegetation Contact,
Ground Placement, and Cover Removal groups revealed no significant
differences in the number of cocoons in the egg stage attacked by
fungus. This suggests that neither the cocoon cover, nor the cocoon
suspension system function to protect the eggs from fungal attack.
There was, however, a significant increase in egg mortality among
p
those cocoons placed on the ground (X = 12.39, df = 1, p < 0.005).
The eggs in these cocoons were all killed, presumably by drowning.
They were not covered with fungus.
The natural incidence of fungal attack on M. lemniscata cocoons
in the spiderling stage was 1.0% (Table 5-2). Contact with the
vegetation did not significantly increase the number of cocoons
attacked by fungus in this stage. However, there were significant
increases in the number of cocoons attacked by fungus among those
2
placed on the ground (X =9.93, df=l, p< 0.005). Cocoons with


20
cocoon (total weight 0.820 g; spiderling weight 0.724 g) in the
sheltered site (under overhanging vegetation) attained highs and
lows close to the ambient air temperature, the internal temperature
of the cocoon (total weight 0.991 g; spiderling weight 0.842 g) in
the exposed site (open field) fluctuated widely, attaining much
higher and lower values (Fig. 3-4). The surface temperatures of the
cocoons equaled the ambient temperature in the shade (T =
T ) and were greater than both ambient and the internal temperature
of the cocoons in the sun (T < T > T ).
a surf c
Discussion
Under laboratory conditions, the internal temperatures of whole
and modified A. aurantia cocoons exposed to sudden drops in ambient
temperature (from 2 C to 8-9 C) do not change instantaneously
(see Fig. 3-1), indicating that some part of the cocoon acts as
insulation. However, under these conditions the cooling rates for
cocoons with and without the flocculent silk layer are identical,
suggesting that it is the cover of the cocoon, and not the
flocculent layer, that creates the dead air space that acts as
insulation (Kaufman et al. 1982). This explains why Austin and
Anderson (1978) found that the coverless, flocculent cocoons of
N. edulis offered no protection to their egg masses; these cocoons
have little or no dead air space. The whole cocoons also cooled
four times more slowly than the modified cocoons (see Fig. 3-1).
Presumably, this additional thermal inertia is due to the mass of
the spiderlings, which are approximately 70% water (Anderson 1978).


34
Table 4-3 Mean percentages for molting success and spiderling
survival ( 1 SD; n in parentheses) at the four experimental
humidities for Mecynogea lemniscata egg and spiderling masses with
and without cocoons. Pair-wise comparisons between treatments are
by Mann-Whitney U Tests; pair-wise comparisons between humidities
within treatments are by multiple range tests (Zar 1984).
Of
Molting
Success
% Spiderling
Survival
Relative
Humidity
Cocoon
No Cocoon
Cocoon
No Cocoon
100%
100%
(8)
99-1
2.5%
(8)
100%
(13)
80.0
*** 25.1%
(6)
**
66%
100%
do)
100%
(10)
81.9
29.8%
(13)
56.2
** 28.8%
(14)
*
#**
22%
100%
(10)
100%
(10)
47.4
38.1%
(11)
1.0
*** 2.7%
(14)
**
0%
100%
do)
100%
(10)
6.8
13.7%
(14)
** 0%
(14)
Kruskall-
Wallis H
0.00
0.00
35-44
38.22
"p"
1.00
1.00
< 0.001
< 0.001
(* p < 0.05;
** p < 1
0.01; *** p < 0.001)


CHAPTER VI THE ROLE OF THE COCOON IN
LIMITING EGG AND SPIDERLING
PREDATORS 62
Introduction 62
Materials and Methods 64
Results 71
Discussion 89
CHAPTER VII COCOON SPACING AND THE TIMING OF
PRODUCTION AS METHODS TO AVOID
EGG AND SPIDERLING PREDATORS 100
Introduction 100
Materials and Methods 102
Results 104
Discussion 113
CHAPTER VIII GENERAL DISCUSSION AND
CONCLUSIONS 125
General Discussion 123
Conclusions 143
LITERATURE CITED 146
BIOGRAPHICAL SKETCH 155
v


9b
reproductive season. Indeed, communities of cocoon parasites may be
structured by their hyperparasites response to these chemicals
(Price 1980).
Successful avoidance of the cocoon cover by initial egg
positioning during oviposition, or through the damage done by other
predators does not guarantee, per se, that the attacking larvae will
have immediate unlimited access to the host egg mass. In many
cocoons there is a thick flocculent layer of silk between the egg
mass and the cocoon cover which must be crossed. In three field
collected A. aurantia cocoons in which oviposition had recently
occured, the flocculent silk layers contained the recently hatched
eggs of a predator and 20-30 small larvae which appeared dead (no
response to gentle prodding). Presumably these larvae died because
they ran out of energy or water, but it is conceivable that this
silk layer may actually damage the soft cuticle of the larvae much
like the trichomes of some plants damage attacking lepidopteran
larvae (see Gilbert 1971).
The presence of 8-10 large larvae in the egg masses of the
above-mentioned A. aurantia cocoons points out that the flocculent
layer is not a complete barrier. However, reducing the absolute
number of larvae that can reach the egg mass may be an adequate
defense when the egg mass is large. Although the result of the
laboratory experiment was not significant, the observed trend
further supports the idea of the flocculent silk layer as a barrier
to attack


Fig. 7-3. The number of Mecynogea lemniscata cocoons in a three-cocoon string available to a
Tetrastichus wasp or her emerging progeny assuming an 11-day period for attack (a), or a more
conservative 5-day period (b). The cocoons in each string are represented by individual bars. In
both cases the cocoons are produced every 6 days. The stippled area of each bar represents the
period of time (ll or 5 days) during which attack can occur; the stippled and open areas together
represent the total l6 days the host is in the egg stage; the solid areas represent the 4 day
deutova stage after eclosin. The first cross-hatched box indicates the number of cocoons that can
be initially attacked by the wasp. The second box indicates the possible cocoons on the same string
that can be attacked by emerging progeny.


105
Table 7-1* Densities of Mecynogea leianiscata cocoons, and the
percentages of cocoons attacked by the^Tetrastichus sp. wasp for the
years 1981 to 19§3. In 1981, on 800 in volume was sampled; in
1982, four 200 m3 volumes; in 1983, one 400 mJ volume. The
experimental volume for 1983 was further divided to determine the
relationship between host density and the level of parasitism within
a site.
No.
Total
Cocoon
No.
%
Cocoon
No.
Density
Cocoons
Cocoons
Year
Strings
Cocoons
(in )
Attacked
Attacked
1981
83
290
.362
21
7.24
35
90
.450
6
6.67
1982
27
72
.360
5
6.9
27
55
.275
6
10.90
16
37
.185
1
2.70
1983
38
117
.292
11
9.40
8
22
2.750
2
9.09
6
21
2.625
2
9.52
3
10
1.250
2
20.00
3
9
1.125
1
11.11
3
9
1.125
0
0.00
2
10
1.250
1
10.00
2
6
.750
1
16.66
2
6
750
0
0.00
1983 by a
2
3
.375
1
33.33
Subvolume
1
6
.750
0
0.00
1
5
.625
1
20.00
1
5
.625
0
0.00
1
3
.375
0
0.00
1
1
.125
0
0.00
1
1
.125
0
0.00
1
1
.125
0
0.00
1
1
.125
0
0.00
a
Of the 50 subvolumes, 33 contained no cocoons at all


95
Fig. 64. The ovipositor of the ichneumonid Tromatobia ovivora
rufopectus showing recessed pres along its length and concentrated
at the tip (in the box). These pits are similar to others that have
been described as having a sensory function. The scale line equals
20 um. The ovipositor was plated with 75 A of gold and observed
with secondary electrons.


Table 8-1. The mean sphere density ( 1 SD), and median clutch size for individual spiders from
different families. The sphere density values are from Gim and Slobodchikoff (1982). The clutch
size data has
values used to
been taken from the literature. The numbers
calculate the median clutch size.
in brackets
are the
range of clutch size
Family
Genus and species
Sphere Density,-,
(spheres/ 100 ym )
Median
Clutch Size
Theraphosidae
Dugiesiella sp.
10.00
( 5.30)
812a
Theridiidae
Lactrodectus hesperus Chamberlin and Ivie
Steadota grandis complex Banks
Argyrodes baboquivari Exline and Levi
Theridion sp.
24.69
54.38
48.13
97.50
( 5.40)
(18.10)
(11.80)
(27.35)
196b
62 [37-951^
32 [15-49]
69 [ 19-442]e
Araneidae
Araneus normandii Thurell
Argiope aurantia Lucas
Mecynogea lemniscata (Walckenaer)
4.84
17.00
21.60
( 1.90)
( 4.20)
( 5.50)
700 [284-887]f
978 [350-2000]g
14 (830Is
Agelenidae
Barronopsis floridensis (Roth)
184.38
(24.20)
130h
Lycosidae
Lycosa santrita Chamberlin and Ivie
Lycosa sp.
Pardosa makenziana (Keyserling)
Pardosa yavapa Chamberlin
126.25
35.00
103.13
211.20
(30.30)
( 9.86)
(27.20)
(37.70)
207 [32-600H
207 32-600]
4l [12-106jf
4l 112-106jk
Clubionidae
Castineira luctifiera Petrunkevitch
89.38
(14.70)
l4m
Philodromidae
Philodromus sp.
78.75
(20.60)
30 [7-104]n
Salticidae
Phiddipus octopuctatus McCook
80.63
(14.60)
90 [43-166]p
131


6o
cocoons that were stripped of their outer layer of silk (see
Fig. 2-lc) attacked by fungi in the laboratory. In contrast,
A. aurantia cocoons, which have a naked cover with an almost
lacquered surface finish, are never covered by fungus. In fact, it
is rare to find small patches of fungus on the covers of these
cocoons at all, even after they have been lying on the ground for 90
days (see Table 5-^)*
Spiders produce a variety of silks and associated materials in
a number of different glands located in their abdomens (Witt et
al. 1968, Mullen 1969, Foelix 1982). One of these, the aggregate
gland, produces the glue-like material found on the catching spiral
of orb-webs. Schildknecht et al. (1972) have demonstrated that this
glue-like material contains nitrates (KNO^), phosphates (KHgPO^),
and pyrrolidines (C^^NO^). They suggest that one of the
functions of these compounds is to protect the web from bacterial
and fungal attack. If spiders are protecting their webs from such
attack, it seems reasonable that they would protect their cocoons,
which represent a much greater expenditure of energy and time, as
well. Given that these compounds can be manufactured in the silk
glands associated with web building, it seems likely that the
tubiliform and aciniform glands associated with cocoon production
may also able to manufacture similar compounds, so they can be
applied to the covers of cocoons.
The preceeding Chapters III, IV, and V have both considered and
demonstrated the role of the cocoon, or its various parts, in
limiting the effects of temperature extremes, dessication, and


4l
a suite of adaptations for controlling water loss [including
depressed metabolic rates (Schaefer 1976, Anderson 1978), and
lipid-rich eggs (Anderson 1978)], and fits into the foraging/
reproductive strategy of this spider by providing a
desiccation-resistant refuge in which the spiderlings spend these
additional months overwintering.
A number of the egg and spiderling replicates of M. lemniscata
and A. aurantia held at 100% RH in the laboratory were attacked and
destroyed by fungus. Although these replicates were removed prior
to data analysis, in some cases there was still a significant
reduction in survival without cocoons at 100% RH (see Table 4-3 for
M. lemniscata spiderlings), a humidity where survival should be
unaffected by desiccation. This suggests that the covers of cocoons
may be related to resisting fungal attack (Christenson and Wenzl
1980), possibly by limiting the amount of water which can enter the
cocoon. Chapter V addresses this possibility, and considers the
cocoon as a barrier to fungal attack


Proportional Survival (S/N)
107
0.9
0.8 -
0.0
30 50 70 90
Cocoon Density (N)
Fig. 7-1. The relationship between proportional survival (S/N) and
cocoon density (N) for Mecynogea lemniscata cocoons in four
different sites. Proportional survival is not significantly
correlated with cocoon density (Y = -0.0004X + 0.959; r = -0.32, df
= 2, p > 0.05), indicating no density-dependent relationship between
predator foraging success and host density.


3
the cocoons of Floronia bucculenta (Clerck) (Linyphiidae) protect
the eggs from daily changes in ambient temperature. In contrast,
Austin and Anderson (1978) concluded that the flocculent silk cocoon
of Nephila edulis (Koch) (Araneidae) does not do so.
Chapter IV presents a comparative analysis of the capabilities
of the cocoons of A. aurantia and M. lemniscata to control water
loss. Although this is commonly assumed to be one of their major
functions (e.g. Brispowe 19^1, Foelix 1982), the data supporting
this view are contradictory. Schaefer (1976) showed that the cocoon
of F. bucculenta effectively controlled water loss from diapausing
eggs. However, Austin and Anderson (1978) demonstrated that the
flocculent silk cocoon of N. edulis had no effect on egg hatching
success. Casual observations by McEwon (1963) suggest that the
cocoon of an Australian Nephila species limits spiderling
desiccation.
Closely related to the problem of desiccation is the problem of
excess water which, if allowed to enter the cocoon, could dissolve
materials from the surface of the eggs and increase their
susceptibility to disease (Austin and Anderson 1978). Water
entering the cocoon could also carry pathogens (Christenson and
Wenzl I960) or could drown the eggs or developing spiderlings.
Although Reichert (1981) strongly suggests that the cocoons of
Agelenopsis aperta (Gertsch) (Agelenidae) protect eggs from
flooding, only Schaefer (1976) and Austin (1984) have demonstrated
such a role for a cocoon or brood nest, respectively. In Chapter V,
I compare the abilities of the cocoons of M. lemniscata and


Attack characterized by the presence of larvae, pupal cases, and adults.
Attack characterized by a large percentage of the cocoon cover (> 10.0%) torn away, and the
partial or complete removal of the cocoon contents.
Of the 16 cocoons attacked, 11 were by the ichneumonid alone, 1 by the mantispid alone, and 1 by
the phorid fly alone. The remaining 3 cocoons were multiply attacked by the ichneumonid and
chloropid fly (2 cocoons), and the phorid and chloropid flies (l cocoon).
Of the 89 cocoons attacked, 24 were attacked by the ichneumonid (i) alone, 11 by the mantispid
(M) alone, IT by the chloropid fly (C) alone, 2 by the phorid fly alone (P), and 5 by birds (B)
alone. No cocoons were attacked by the moth (Mt) alone. The remaining 30 cocoons were attacked
by more than one predator in the following combinations: (l-M, 2 cocoons), (i-C, 4 cocoons),
(I-B, 1 cocoon), (M-C, 6 cocoons), (M-B, 1 cocoon), (C-B, 5 cocoons), (C-Mt, 2 cocoons),
(B-Mt, 1 cocoon), 1-M-C, 3 cocoons), (M-C-P, 1 cocoon), (M-C-B, 3 cocoons), and (C-P-B, 1
cocoon).
Of the 9 cocoons attacked, 2 were attacked by the ichneumonid alone, 5 by the mantispid alone,
1 by the chloropid fly alone, and 1 by birds alone.


11
drainage ditches. In these habitats, the relative humidity is
usually quite high (70-90% RH) in late August-September (the
egg-laying and molting period), although exposure to high levels of
insolation may cause periodic fluctuations of the RH over a wide
range. By late fall, the RH may drop to 30-40%. The temperatures
may be buffered somewhat by the vegetation in the summer, but are
usually relatively close to ambient, although they may be quite high
(35-40 C) in southern exposures. From fall on, the temperatures
in the habitat follow ambient air temperature closely.


expected to be found among those spiders that suspend their cocoon
because of the possibility of damage.
The results of this study point out, however, that
interpretation of cocoon function is difficult because the various
layers can perform one or more functions depending on the size of
the egg mass, the morphology of the eggs, the ability of the eggs
and spiderlings to control dessication, the habitat used for
oviposition, and the number and kinds of predators in the habitat.
The results also show that spiders use various reproductive
behaviors resulting in spatial and temporal patterns of cocoon
distribution that may aid in protecting the eggs and spiderlings by
making cocoons difficult to locate. This study further suggests
that eggs and spiderlings may be protected from pathogens by
chemicals applied to cocoon covers. Finally, this study illustrates
the need for further work in the area of cocoon architecture and
function before the role of the cocoon and its place within the
reproductive strategies of spiders can be fully understood.


138
numbers of unsuccessful fly attacks on A. aurantia cocoons, and the
apparent preference of Pseudogaurax signata for cocoons with covers
damaged by other predators provide further support for the idea of
covers as specialized layers to control certain predators.
Dense covers may also be effective against wasps with short
ovipositors. The Tetrastichus wasp probably attacks the cocoons of
M. lemniscata by ovipositing into the top layer (Austin, In press);
the first instar larvae then burrowing through the cocoon wall to
attack the eggs. Unless the eggs are initially deposited through
the extremely hard cover, the larvae probably have a hard time
penetrating the cocoon (see also Kaston and Jenks 1937) The old
web deposited on the cocoon string may act to hide the dense cocoon
cover and fool the wasps into ovipositing into what appears to be
the outer layer of the cocoon, or keep them elevated off of the true
cocoon surface so that their ovipositors cannot completely penetrate
the outer cover (Opell I98U).
Although the covers of cocoons may force some wasps to waste
time and energy drilling through the cocoon to determine host
quality or to mark previously visited cocoons (which provides cues
for hyperparasites), cocoon covers appear to be only secondarily
related to controlling wasps with long ovipositors (e.g., the
ichneumonids). However, the distance of the egg mass from the
cocoon cover and the layer of flocculent silk between the cover and
the egg mass appear to be adaptations directly related to
controlling such wasps (see also Austin, In press). The separation
makes it difficult for wasps to deposit eggs directly on the host


1+1*
A. aurantia cocoons to shed water were also examined in the field
during periods of rain.
To determine whether water actually penetrates the cocoon
cover, 10 samples of 2-3 dry M. lemniscata cocoons were submerged in
distilled water for time periods of 7, 15, 30, 60, 120, 240, and 480
min. Upon removal from the water, they were blotted on Whatman #1
filter-paper discs for 1 min to remove surface water, and weighed on
a Mettler AK l60 balance to the nearest 0.0001 gm. The 10 samples
were air dried for 2k hrs between each submersion. After the last
submersion bout (480 min), the 22 cocoons comprising the 10 samples
were opened and examined under a microscope for the presence of
water.
The volume of water absorbed by each cocoon sample was
calculated from the increased weight of the sample (l gm water = 1
2
ml = 1 cc). This was normalized to ml/ cm by dividing the volume
of water by the combined surface area of the cocoons in each sample.
A mean value was then calculated from the 10 values for each
submersion time.
The role of the flocculent silk layer in resisting water was
also tested. Here, flocculent silk from A. aurantia cocoons was
used. Uncompressed pieces of this layer were placed on glass slides
and drops of distilled water were applied to the silk. The pieces
were observed for approximately 10 min, and any wetting of the silk
through wicking was noted.


32
Table 4-2. Mean percentages of eggs successfully hatched ( 1 SD; n
in parentheses) at the four experimental humidities for intact
Mecynogea lemniscata and Argiope aurantia egg masses with and
without cocoons, and for reduced A. aurantia egg masses without
cocoons. Pair-wise comparisons between treatments are by
Mann-Whitney U Tests; pair-wise comparisons between humidities
within treatments are by nonparametric multiple comparison tests
(Zar 1984).
% Hatching Success
M. lemniscata
A.
aurantia
Relative
Humidity
Cocoon
No Cocoon/
Intact
No Cocoon/
Reduced
No Cocoon/
Intact
Cocoon
100 %
94.9
13.5%
(10)
98.3
3-1%
(8)
96.2
4.0%
(5)
99-7
0.5%
(8)
100%
(8)
**
#
66%
95.4
14.6%
(10)
97.4
4.6%
(10)
49.2
*** 36.8% **
(8)
94.3
11.3%
(8)
£
90.0
24.8%
(7)
33%
96.9
7.9%
(10)
88.7
15-5%
(10)
28.7
*** 32.3% **
(10)
87.9
7.0% **
(9)
96.6
5.8%
(7)
***
#**
0%
3.4
7.3%
(10)
3.6
8.3%
(10)
6.7
5.7% ***
(10)
70.4
22.8% *
(8)
88.2
17.5%
(8)
Kruskall-
Wallis H
29.43
25.80
17-70
21.70
8.29
"p"
< 0.001
< 0.001
< 0.001
< 0.001
< 0.05
(* P < 0.
05; ** p <
0.01; *** p
< 0.001)


generations that can occur in a given reproductive season. This
could further act to keep the overall number of parasites available
for attack low.
Escape can occur within a much shorter time scale if the
predator or parasite is limited to attacking the host within a
narrow developmental period. Both the eggs of A. aurantia and
M. lemniscata appear to present such limitations. In addition, the
timing of M. lemniscata cocoon production is such that only one
cocoon on a given string is available to an attacking wasp or her
emerging progeny. The interaction between the developmental
constraints and the timing of cocoon production for M. lemniscata
leads to two important outcomes. First, it limits the number of
cocoons at any one site which can be attacked by a wasp. This
forces the wasp to move off and look for another site. Second, it
results in a spatially variable pattern of cocoon distribution over
time. During the peak in wasp attack, this interaction results in a
random spatial distribution of useable cocoons that the wasps must
locate against a constantly increasing background of older
non-attackable cocoons.
The suspension systems and cocoons of M. lemniscata and
A. aurantia function in controlling the access to the cocoon of a
number of generalized and specialized predators (Chapter VI). These
results and the limited control that the cocoon of A. aurantia
exerts on the abiotic factors examined (Chapters III, IV, and V)
suggest that the main function of most spider cocoons and their
associated structures is to control parasite and predator attacks.


21
habitat position for two Argiope aurantia cocoons. The solid lines
( ) are ambient temperatures, and the dashed lines ( ) are
internal cocoon temperatures. Over 2k h, the cocoon in the open
habitat (old field) was exposed to extended periods of direct
sunlight, andQfaced greater reflected radiation from the vegetation
(32 C to -15 C), and colder sky temperatures (2 C to -39 C)
bhan the cocoon in the closed habitat (old field edge under trees)
faced from the vegetation (25 C to -10 C), or from the sky (25
C to -17 C).


116
generations to one or two, preventing a large build-up of predators.
The slow initial appearance of cocoons due to the asynchrony of the
hosts' reproduction further acts to keep predator numbers down by
limiting the number of cocoons initially available to the wasps
emerging from overwintering.
More importantly, the rapid rate of cocoon production (every 6
days) in relation to wasp generation time (every l6 days) allows the
spiders to produce 1-2 cocoons with high numbers of eggs prior to
the emergence of the first generation of wasps in late June-early
July. In addition, the number of eggs in the cocoons drops
significantly by the third cocoon. Thus, during the peak in attack
in mid-July, the majority of cocoons available to the wasps contain
less eggs (and less energy) than those produced earlier in the
season (see Table 7-2). Overwintering wasps result from cocoons
attacked during this peak period, and the reduction in egg number
(and energy) may act to reduce the numbers of wasps which emerge the
following year.
Many parasites are restricted in their attack to a specific
time in the hosts' developmental sequence (Vinson 1976). The eggs
of M. lemniscata take 16 days to develop to the deutoval stage. The
larvae of the wasp take 5 days to develop before pupation. If there
is no specific period of time during which attack must occur, the
wasp can initiate an attack any time during the first 11 days of
host egg appearance to have enough time for development (assuming
that the larvae cannot use deutova as food). When such a timing
scheme is plotted out for a string of three cocoons, each 6


collected. For the chloropid fly attacks, the number of cocoons
successfully attacked (producing pupae), the number of cocoons
successfully attacked in conjunction with another predator, and the
number of cocoons unsuccessfully attacked (eggs laid on the cocoon
surface but no pupae produced) were recorded.
The relationship between the size of an A. aurantia cocoon and
the number of eggs it contained was established by measuring a
number of cocoon dimensions and counting the spiderlings in UO
2
cocoons. Figure 6-2 shows that there is a strong relationship (r
= 0.90) between the diameter of the cocoon and spiderling number.
This relationship was used to estimate the original number of eggs
in attacked cocoons. The percentage of eggs surviving the attack, a
measure of the damage caused by a given predator, was then
calculated by the following:
Percentage of Eggs No. of Survivors
Surviving = X 100.
Parasite Attack Estimated No. of Eggs
The relationship of cocoon size to egg number was not calculated for
M. leraniscata because all of the eggs in a cocoon are utilized when
attacked by its egg predators.
Field Experiments
The roles of suspension systems and cocoon covers in
controlling egg predator attacks were investigated by modifying
these components in the field and assessing the effects of their
change on egg hatching success and spiderling survival. The cocoons


Table 7-2. Mean number of Mecynogea lemniscata cocoons per string, and the mean number of eggs in
each cocoon in the string for the years I98I-I983. The SD is in parentheses. The sample size (n) is
the number below each mean. The number in brackets is the number of times a cocoon in that position
in the string was attacked by the Tetrastichus sp. wasp for the sample collected that year.
Average Number of Eggs in Each Cocoon
Year
1981
1982
X No. Cocoons/
String
Cocoon
01
Cocoon
02
Cocoon
03
Cocoon
#4
Cocoon
#5
Cocoon
6
3.5 (1.3)
19.5 (6.6)
16.8 (5.5)
14.3 (6.2)
12.8 (4.1)
11.0 (3.7)
9.7 (5.5)
83
78
69
56
36
9
3
12]
[41
[6]
[31
[31
131
2.5 (1.2)
15.8 (6.1)
12.6 (4.6)
10.3 (4.3)
10.2 (4.6)
8.6 (4.4)
8.0 (0.0)
105
80
53
38
16
5
l
[41
[91
[41
[0]
[0]
HI
3.1 (1.6)
18.5 (5.6)
15.8 (5.3)
12.7 (5-9)
13.4 (5.7)
12.7 (5.4)
15.0 (0.0)
38
37
25
19
12
7
1
[0]
[2]
[41
[21
[2]
[1]
o
vo
1983


102
habitat, and the temporal appearance of the cocoons in space as host
behaviors that function to reduce egg predator success by making
hosts difficult to locate. Finally, I conclude that these behaviors
account, in part, for the low rates of parasitism and the observed
relationship between host density and the level of egg predator
attack.
Materials and Methods
This study was conducted from 1981 to 1984 in mesic,
flood-plain woods surrounding Lk. Alice on the campus of the
University of Florida, Gainesville, FL. Host density was determined
by collecting all the cocoons from areas of known volume. For 1981,
2
the sampling was done in one 800 m plot (10 x 20 x 4 m). In 1982,
2
four 200 m plots (7 x 7 x 4 m) were sampled to determine the
variation in host density within the habitat. During the sampling
of the 1982 plots, both currently produced cocoons and cocoons from
the previous year(s) were collected. In 1983, the sampling was done
2
in one 400 m plot. The sampling height of 4 m was chosen after I
observed that less than 5% of the cocoons in the population were
deposited above this height.
All the cocoon strings collected each year for the host density
determinations were brought into the laboratory and the individual
cocoons in each string were cut open and scored for parasite attack
(the presence of larvae, pupae, or shed pupal exuviae), or the
number of eggs or spiderlings they contained. The position of


B.
C.
4 mm
Fig. 2-1. A string of Mecynogea lemniscata cocoons suspended in the
vegetation (A), showing the relative size of the cocoons (B), and
with the external layer of silk peeled away to show the individual
cocoons underneath (C). The external layer of silk is composed of
old orb-webs applied to the cocoon string by the female spider.
This layer also contains detritus and prey remains.


4o
The cocoon of A. aurantia also appears to have little effect on
spiderling survival. The lack of a cocoon effect on hatching and
molting success, and the significant drops in molting success and
spiderling survival below 66% RH suggest that other considerations
are more important to reducing desiccation. Field observations of
damaged A. aurantia cocoons suggest that the large clutch size of
this species may protect the eggs from dessication [which may also
explain McEwon's (1963) observation for the Nephila sp.1. However,
the RH within the habitat or microhabitat used for oviposition is
probably most critical for A. aurantia. Indeed, Levi (1968) notes
that of the Argiope species in Florida, A. aurantia prefers moist
habitats such as pond edges and stream borders, and is one of the
first Argiope species to disappear during drought years.
Removal of the cocoon does have a significant effect on the
spiderling survival of M. lemniscata at all experimental humidities
(see Table 4-1), and in the field under ambient conditions (see
Table 4-3). This spider is the first of the orb-weavers to become
active in the spring, emerging in late March. Growth is rapid.
Reproduction begins by late June and the adults die by early to
mid-August. This early emergence and rapid disappearance is
apparently a means of taking advantage of the abundant prey in the
habitat, while avoiding competition with other orb-weavers whose
populations increase rapidly by August (Anderson 1978). The
spiderlings then spend approximately 290 days in the cocoon until
they emerge the following March; 2 to 3 months longer than most
other orb-weavers (Anderson 1978). The cocoon is apparently part of


63
quite large when compared to eggs of other groups such as insects.
The eggs are lipid rich and represent a considerable amount of
energy (Anderson 1978). In addition, during the reproductive
season, clutches may occur in large numbers in the habitat and may
be relatively conspicuous. They therefore represent a potential and
highly desirable resource for many predators and parasites. Indeed,
insects from a number of groups have specialized on spider eggs
(Auten 1925, Eason et al. 1967, Evans 1969, Askew 1971, Austin, In
press).
All spiders deposit their eggs in some form of silken cocoon
(Turnbull 1973). For many spiders this structure represents the sum
total of maternal care bestowed on the eggs by the female spider.
The large and diverse number of predators attacking cocoons, and the
wide range in complexity of cocoon architecture (McCook 1890, Kaston
19^+8) have led to speculation that the primary function of the
cocoon is to protect the eggs and spiderlings from attack (Austin
and Anderson 1978, Robinson 1980). Austin (In press) recently
reviewed the literature on cocoon attack by egg predators, and
proposed that the wide diversity of cocoon types arose because
spiders have attempted to reduce the total number of predators that
can use their cocoons by forcing them to "specialize" on a
particular cocoon type. The predators have responded in
evolutionary time, and the relationships between cocoons and their
attackers that we observe today can be attributed to a
"coevolutionary arms-race" (Dawkins and Krebs 1979). While some
observations have been reported on parasite difficulty in entering


LIST OF FIGURES
Figure 2-1. A string of Mecynogea lemniscata
cocoons 6
Figure 2-2. The cocoon of Argiope aurantia 9
Figure 3-1. Cooling rates in still air in the
laboratory for whole and modified Argiope
aurantia cocoons l6
Figure 3-2. Cooling rates outdoors for whole
and modified Argiope aurantia cocoons in
an artificial closed habitat over a 50 min
period during an approximate 2.5 0 change
in ambient temperature l8
Figure 3-3. Heating rates in still air outdoors
for whole and modified Argiope aurantia cocoons
under radiant loads of 2 and 10 min duration 19
Figure 3-4. The relationship of internal cocoon
temperature to habitat position for two
Argiope aurant ia cocoons 21
Figure 4-1. The layer of spherical mucoid
granules on the chorionic surface of a
Mecynogea lemniscata egg and an Argiope
aurantia egg 30
Figure 5-1* The rate of water loading in the
laboratory for the covers of Mecynogea
lemniscata cocoons submerged in distilled
water 50
Figure 6-1. A schematic view of an Argiope
aurantia cocoon showing the four measurements
taken to determine the position of the egg mass
in relation to the cocoon cover 66
Figure 6-2. The relationship between the
diameter of Argiope aurantia cocoons
and the number of spiderlings (eggs)
therein 68
ix


Table 6-2. The effect of modification of the cocoon suspension
system and cover on the incidence of predator attack on the eggs of
Mecynogea lemniscata. All cocoons were collected after 30 days.
Experimental
Modification
Sample
Size
Successful
Survival
No. Cocoons
Attacked
% Cocoons
Attacked
Control
175
153
22a
12.6%
Vegetation
Contact
2h
6
l8b
75.0%
Ground
Placement
26
12
iub
53.8%
Cover
Removal
32
12
20 C
62.5%
Of the 22 cocoons attacked, 2 were attacked by ants/ unknown
predators, 19 by the eulophid wasp Tetrastichus sp., and
1 by the mantispid M. viridis.
In both cases the cocoons were attacked by ants/ unknown
predators.
ATI 20 cocoons were attacked solely by the mantispid
M. viridis.


52
Table 5-1 The effect of modification of the cocoon suspension
system and cover on the incidence of fungal attack on the eggs of
Mecynogea lemniscata. Cocoons in the "Other" category contained
eggs which were not attacked by fungi, but did not hatch due to
inviability or drowning. In many cases the eggs rotted. All
cocoons were collected after 30 days.
Experimental
Modification
Sample
Size
Successful
Hatching
Fungal
Attack
% Cocoons
Attacked
Other
Control
171
153
12
7.3%
6
Vegetative
Contact
21
13
3
14.3%
0
Ground
Placement
19
12
2
14.3%
5
Cover
Removal
13
12
1
7.7%
0


7
color, extremely hard, and tightly woven. Internally, there is a
thin flocculent silk layer between the loose, non-agglutinated mass
of eggs and the cocoon cover. The eggs are not enclosed in a
membranous silk bag. The cocoons in a string are periodically
covered with the damaged orb-web when it is replaced by the spider,
giving the cocoon string an additional layer of loose dirty grey
silk, detritus, and prey remains (Fig. 2-lc).
The eggs in M. lemniscata cocoons are attacked by two principal
predators, the neuropteran Mantispa viridis Walker (Mantispidae) and
the hymenopteran Tetrastichus sp. (Eulophidae) [near T. banksii
Howard; see Hieber (1984)]. The eggs and spiderlings may also
occasionally be attacked by ants, particularly if the support line
breaks and the cocoons contact nearby vegetation or fall to the
ground.
Mecynogea lemniscata is found in the shrub layer of southern
deciduous forests (Levi 1980). In Florida, this spider prefers
mesic hammocks, but can occasionally be found in more open habitats
such as upland woods. In its preferred habitat, the humidity
remains relatively constant (7585% RH) during June and July (the
egg laying and molting period) due to the overhead vegetation. From
August on, the habitat dries and uhe RH may fall to 50$ between
rains. During the fall and winter, RH may fall as low as 30-40%.
The temperature in this habitat is somewhat buffered due to the
overhead vegetation which blocks the sun and it remains relatively
constant (25-29 C) during the summer. From fall on, the
temperature in the habitat follows the ambient temperature closely.


Chauvin, G., G. Vannier, and A. Gueguen. 1979* Larval case and water
balance in Tinea pellionella. J. Insect Phys. 25: 615-619.
Christenson, T.E., and P.A. Wenzl. 1980. Egg laying of the Golden Silk
Spider, Nephila clavipes L. (Araneae: Araneidae): Functional analysis
of the egg sac. Anim. Behav. 28: 1110-1118.
Clark, P.J., and F.C. Evans. 195^. Distance to nearest neighbor as a
measure of spatial relationships in populations. Ecology
35: L45-U53.
Clark, P.J., and F.C. Evans. 1979* Generalization of a nearest
neighbor measure of dispersion for use in K dimensions. Ecology
60: 316-317.
Coquillet, D.W. 1898. On the habits of the Oscinidae and Agronyzidae
reared at the United States Department of Agriculture. U.S.D.A. Div.
Ent. Bull. 10 (N.S.): 70-79*
Cresson, E.T. 1870. Descriptions of new species belonging to the
sub-family Pimplariae found in America north of Mexico. Trans.
Amer. Ent. Soc. 3: 1^5-148.
Davidson, A. 1896. Parasites of spider eggs. Entomol. News
7: 319-320.
Davies, M.E., and E.B. Edney. 1952. The evaporation of water from
spiders. J. Exp. Biol. 29: 571-582.
Dawkins, R., and J.R. Krebs. 1979* Arms races between and within
species. Proc. Royal Soc. Lond., B. 205: ^89-511.
DeBach, P. 19^. Environmental contamination by an insect parasite and
the effect on host selection. Ann. Entomol. Soc. Am. 37: 70-7^
Dethier, V.G. 19^7* The response of hymenopterous parasites to
chemical stimulation of the ovipositor. J. Exp. Zool. 105: 199-207.
Doutt, R.L. 1959. The biology of parasitic hymenoptera. Ann. Rev.
Entomol. U: l6l-l82.
Dowell, R.V. 1979. Effects of low host density on oviposition by
larval parasitoids of the alfalfa weevil. J. N.Y. Entomol. Soc.
87: 9-lU.
Eason R.R., W.B. Peck, and W.H. Whitcomb. 1967. Notes on spider
parasites, including a reference list. J. Kansas Entomol. Soc.
LO: L22-43U.


BIOGRAPHICAL SKETCH
Craig Stephen Hieber was born into the midst of the
urban-industrial wasteland in East Orange, New Jersey in 1951* At age
15, after constant exposure to New York city television and radio, he
moved to Chester, in northern New Jersey, where he attended West Morris
High School. After graduation from high school in 1969, he studied
mechanical engineering at the University of Virginia for 2 years. In
1975, he received a B.S. in biology from Roanoke College. He then moved
to Vermont where there were no jobs but the scenery was beautiful. From
Vermont, he moved to North Dakota where he received an M.S. in biology
in 1979 from the University of North Dakota. After three years of -20
degree winters, he moved to Florida where he expects to receive a
Ph.D. in zoology in 1984 from the University of Florida. When he is not
studying the behavioral or physiological ecology of insects and spiders,
he devotes most of his time to general tool use, the restoration of
machinery and furniture, tropical fish, and his passion, bicycles.
155


alone. All the larvae from the March collection were held in 2 dram
glass vials at 60-75/ RH and 26 C until emergence.
The rate of cocoon production, and the temporal and spatial
distribution of the hosts were determined in 1983 by mapping the
web-sites (X, Y, and Z coordinates) in the U00 m volume and
recording the daily production of cocoons. These data, along with
the parasite attack data, were used to determine the overall spacing
pattern of the hosts, the spatial distribution of the hosts through
time [in both cases using a 3-dimensional nearest neighbor
approach; Clark and Evans (195^, 1979)1, and the location and time
of individual parasite attacks.
Results
The level of cocoon parasitism in the habitat remained
relatively constant at 7-9^ for all three years (Table 7-1) This
level is relatively low compared to the 25-75 levels suffered by
other spiders (Edgar 1971, Kessler and Fokkinga 1973, Enders 197^,
Tolbert 1976, Prakash and Pandian 1978). The cocoons are not
distributed evenly in the habitat. There is variation in both their
density across the habitat and within a single plot in the habitat,
presumably because of the heterogeneous distribution of young trees
and shrubs used by this spider for web supports.
Density dependence is indicated by a negative slope in plots of
proportional survival (S/N) against density (N). In this study,
there were no density-dependent relationships between the levels of
cocoon predation and cocoon density, either among sites in the


29
success was the number of these deutova which successfully molted to
the first instar spiderling stage. Spiderling survival was
determined using separate masses, and was calculated after the
experiments had run for 90 days.
Results
The Sphere Layers
The spheres associated with the eggs of M. lemniscata and
A. aurantia are shown in Fig. 4-1. For both, the sphere diameter
ranged from 0.40 to 7*20 ym. The mean diameter in M. lemniscata
eggs was not significantly different from that of A. aurantia eggs
2
(Table 4-1). However, the mean sphere density (spheres/ 100 ym )
of M. lemniscata eggs was significantly greater (t = 2.11, df = 20,
p < 0.05) than that of A. aurantia eggs.
The Effect of Clutch Size and the Sphere Layer
No significant differences in hatching success at 100$ RH were
found between intact and reduced A. aurantia egg masses without
cocoons at each humidity (Table 4-2). Reduction of the egg mass,
however, did have a significant effect at 66$, 33$, and 0$ RH,
indicating that the size of the egg mass of this spider is important
to dessication control. There were no significant differences at
100$, 66$, and 33$ RH when the hatching success of intact
M. lemniscata and A. aurantia egg masses without cocoons was


84
Table 6-6. Mean cocoon diameter, cocoon length, egg mass diameter,
egg mass length, distance to the egg mass (X-Axis), and distance to
egg mass (Y-Axis) for Argiope aurantia cocoons, and mean ovipositor
length for the ichneumonid Tromatobia ovivora rufopectus. The two
distance variables indicate the length of an ovipositor needed to
deposit eggs directly on the surface of the host egg mass. SD is in
parentheses.
Sample
Variable
Size
Mean
i (mm)
Cocoon Diameter
25
19.2
(2.2)
Cocoon Length
25
24.4
(2.4)
Egg Mass Diameter
25
10.2
(1.4)
Egg Mass Length
25
11.1
(1.4)
Distance to Egg Mass
from cover: X-axis
25
4.5
(0.7)
Distance to Egg Mass
from cover: Y-axis
25
6.7
(1.2)
Ovipositor Length
57
3.9
(0.5)


127
Given the time that the eggs, and particularly the spiderlings,
of many species spend in the cocoon (Anderson 1978), it seems likely
that this structure functions to control water loss. This is the
most commonly held assumption about the function of cocoons (e.g.,
Foelix 1982). However, previous work relating the cocoon to
dessication control has been contradictory. Schaefer (1976)
demonstrated that the parchment-like cocoons of the linyphiid
Floronia bucculenta increased the survival time of post-diapause
eggs. However, Austin and Anderson (1978) could detect no role in
desiccation resistance for the flocculent silk cocoon of the araneid
Nephila edulis.
The results of Chapter IV demonstrate that the cocoon of
Mecynogea lemniscata has no effect on hatching or molting success
but does have a significant effect on spiderling survival. In
contrast, the cocoon of Argiope aurantia has no apparent effect on
hatching success, molting success, or spiderling survival. These
results indicate that the level of protection provided by cocoons to
eggs or spiderlings is related to the length of time these
developmental stages spend in the cocoon. The eggs Schaefer (1976)
used in his study were post-diapause eggs approximately l80 days old
(F. bucculenta overwinters in the egg stage). These eggs are
apparently not very resistant to desiccation, and the cocoon may
provide the protection necessary for the eggs to make it through
this long period. In comparison, the eggs of Nephila clavipes
(Christenson and Wenzl 1980), M. lemniscata, and A. aurantia all
hatch in approximately 16 to 30 days. This may be too short to


9k
their ovipositors into the cocoon to check on host condition. The
large number of cocoons which T_. ovivora rufopectus sampled without
ovipositing suggests that this wasp cannot determine host quality
without inserting its ovipositor into the cocoon (Dethier 19^7).
Indeed, this wasp has indentations along the tip of its ovipositor
similar to sensory pits described by other workers (Fulton 1933,
Salt 1937, Varley 1941, Fisher 1971) (Fig. 6-4).
In addition, many parasites use chemicals to mark previously
searched hosts so further time and energy are not wasted returning
to and exploring a nonproductive host (Salt 1937, Price 1970a,
Vinson 1972). These chemicals have a number of effects, including
the attraction of hyperparasites (DeBach 1944, Price 1970b, Vinson
1975, 1976). I have observed small circles of the hyperparasites of
T. ovivora rufopectus stroking the surface of A. aurantia cocoons
with their antennae and chewing into the cocoon. I have also found
the chewed entrance holes of the hyperparasites and female
byperparasites in approximately 29% of the cocoons that were
sampled, but not oviposited into, by this ichneumonid. These
observations strongly suggest that this hyperparasite is responding
to a marking chemical deposited by T. ovivora rufopectus during
oviposition. Attraction to such a chemical may partially explain
the relatively high rate of hyperparisitism (59-82%) on this wasp.
Increasing the general level of hyperparasites in the habitat by
forcing the parasites to mark cocoons would be particularly
beneficial if the spider host deposits more than one cocoon in a


2
protecting the enclosed eggs and spiderlings from thermal extremes
(McCook 1890, Kaston 1948, Turnbull 1973, Gertsch 1979), dessication
(Foelix 1962), fungal attack (Christenson and Wenzl 1980), drowning
(Reichert 1981), UV light (Yoshikura 1969), and predator and
parasite attack (Moore 1977, Austin and Anderson 1978, Robinson
1980, Austin, In press). Few studies, however, have examined the
cocoons' effectiveness in controlling these factors.
I present here the results of several studies bearing on the
functional roles that the cocoons of Mecynogea lemniscata
(Walckenaer) and Argiope aurantia Lucas (Araneidae) play in
protecting eggs and spiderlings from a number of biotic and abiotic
factors. I also present results on the significance of cocoon
timing and spacing, and how they interact with cocoon architecture
to reduce predation. Both of these spiders use cocoons with dense
covers (as opposed to the flocculent silk cocoon used by other
araneids). However, they inhabit different environments, construct
cocoons of different size and complexity, produce differing numbers
of clutches, reproduce at different times of the year, and are
attacked by different parasites. These differences are discussed in
detail in Chapter II.
In Chapter III, I examine the role that cocoons, and in
particular the flocculent silk layer within many cocoons, play in
controlling temperature extremes. Many authors have suggested that
the flocculent silk layer acts as insulation (McCook 1890, Kaston
1948, Turnbull 1973, Gertsch 1979) Published reports on this
function have been contradictory. Schaefer (1976) reported that


36
The results for A. aurantia differed from those for
M. lemniscata. In the laboratory, cocoon removal had no significant
effect on hatching success at 100%, 66%, or 0% RH, although it did
significantly affect success at 33% RH (Table 4-2). Cocoon removal
had no significant effect on molting success at any experimental
humidity. However, at 33% and 0% RH the variances in the non-cocoon
cells were much larger, suggesting that an effect may have been
difficult to detect. Molting success fell off significantly below
66% RH with and without a cocoon (Table 4-5). The absence of a
cocoon also made no difference in spiderling survival at either 100%
RH or 66% RH (Table 4-5). However, below 100% RH spiderling
survival significantly declined with and without cocoons, and below
66% RH all the spiderlings died after 90 days regardless of the
treatment. The results from the field experiments support the
laboratory results at 100% and 66% RH (Table 4-4). Under field
conditions, cocoon removal had no significant effect on egg hatching
success, molting success, or spiderling survival.
Discussion
The results indicate that the enclosed cocoons of M. lemniscata
and A. aurantia do not affect water loss from the egg stage. These
findings are paradoxical, since they support the findings of Austin
and Anderson (1978) for a flocculent cocoon, but do not agree with
Schaefer's (1976) findings for a covered cocoon. This paradox may
be explained by the amount of time the eggs of these spiders spend
in the cocoon. The developmental times of M. lemniscata


CHAPTER VIII
GENERAL DISCUSSION AND CONCLUSIONS
General Discussion
Spider cocoons range in complexity from a few threads
surrounding the egg mass (e.g., the Pholcidae) to large complex
structures composed of many layers (e.g., the Araneidae) (McCook
1890, Scheffer 1905, Kaston 19^8, Turnbull 1973). Cocoons are
believed to protect the eggs or spiderlings by reducing the
detrimental effects of a number of biotic and abiotic factors
(Turnbull 1973, Foelix 1982, Austin, In press). However, with few
exceptions, none of the roles attributed to cocoons have been
tested.
I examined the effects of cocoon architecture on two abiotic
factors, temperature extremes (Chapter III) and dessication (Chapter
IV), and on the biotic problems of fungal attack (Chapter V) and
predator attack (Chapter VI). Chapter VII is closely linked with
Chapter VI and examines the temporal and spatial strategies that
spiders have evolved to reduce the initial probability of a predator
locating a cocoon. The primary technique I used was to modify the
cocoons and relate these modifications to changes in egg hatching
success and spiderling survival. The direct connection between the
function of the cocoon or component parts and measures of fitness
avoids many of the problems found in other ecological or
125


110
Table 7-3. A comparison of the contents of attacked Mecynogea
lemniscata cocoons. Cocoons were collected in the experimental plot
in August 1983, and from random locations earlier in July (during
the peak in wasp attack), in December, and in March 1984 (two weeks
before M. lemniscata emerged from overwintering). The presence of
prepupae or exuviae in a cocoon were used as indicators of wasp
attack.
Date
No.
Cocoon
Strings
Total
No.
Cocoons
No.
Cocoons
Attacked
No. Cocoons
with
Prepupae
No. Cocoons
with only
Exuviae
July
37
125
10 (8.0%)
8 (80.0%)a
2 (20.0%)
August
38
117
11 (9.4%)
5 (45.5%)b
6 (54.4%)
December
92
357
32 (9.0%)
13 (40.6%)c
19 (59.4%)
March
59
254
21 (8.3%)
13 (6l.9%)d
8 (38.1%)
All 8 cocoons contained only prepupae.
All 5 cocoons contained only prepupae.
Of the 13 cocoons containing prepupae, 6 (18.8%) contained
only prepupae, and 7 (21.8%) contained prepupae and shed
exuviae.
Of the 13 cocoons containing prepupae, 8 (38.0%) contained
only prepupae, and 5 (23.8%) contained prepupae and shed
exuviae.


92
Figure 6-3. The covers of the cocoons of
Mecynogea lemniscata and Argiope aurantia
comparing the differences in the
tightness of the weaving
Figure 6-b. The ovipositor of the ichneumonid
Tromatobia ovivora rufopectus showing
recessed pits along its length and
concentrated at the tip 95
Figure 7-1. The relationship between
proportional survival and cocoon density
for Mecynogea lemniscata cocoons in
four different sites 107
Figure 7-2. The relationship between
proportional survival and cocoon density
for Mecynogea lemniscata cocoons
within one site 108
Figure 7-3. The number of Meycynogea lemiscata
cocoons in a three-cocoon string available
to a Tetrastichus wasp or her emerging
progeny assuming an 11-day period for attack,
or a more conservative 5-day period 119
Figure 7-^. The spatial distribution of all
the Mecynogea lemniscata web-sites in
the experimental plot for 1983 121
Figure 8-1. The relationship between mean
sphere density and clutch size for
individual spiders from different
families
133


xml version 1.0 encoding UTF-8
REPORT xmlns http:www.fcla.edudlsmddaitss xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.fcla.edudlsmddaitssdaitssReport.xsd
INGEST IEID EGWWMQJCY_DSR23W INGEST_TIME 2014-10-14T00:30:32Z PACKAGE AA00025841_00001
AGREEMENT_INFO ACCOUNT UF PROJECT UFDC
FILES


98
holes in the top of the cocoon suggests that these structures are
hard to drill through (see Table 6-7). In the bottom third of the
cocoon, the egg mass is, on average, further from the cover than the
ovipositor can reach. An attack here would result in eggs being
deposited in the flocculent silk layer where the hatching larvae
have a high probability of becoming entrapped. The number of drill
holes is low in this end of the cocoon as well. The middle of the
cocoon represents the best fit between ovipositor length and
distance to the egg mass without interference from a mechanical
barrier, and the number of drill holes is greatest in the the middle
of the cocoon's surface (see Table 6-7). However, the distribution
of drill holes is identical to the distribution of support line
deltas. This suggests that the "suspension" lines are located to
interfere with the wasp during oviposition, either by making it
difficult to get to the cocoon surface in this area, or by making it
difficult to insert the ovipositor maximally, thereby causing eggs
to be deposited in the flocculent layer.
Given the relative size and strength of foraging passerine
birds, it seems unlikely that the cocoon of A. aurantia provides
much resistance to attack. However, many birds dislike coming in
contact with spider webs and the suspension system, and consequently
A. aurantia cocoons, might be avoided for this reason. Hiding the
cocoon might be a more appropriate measure against visually hunting
predators such as birds. However, there was no significant
difference between those cocoons attacked by birds and those not
attacked with regard to how well they were concealed by dead leaves


Days
119


75
The effect of the suspension system in protecting M. lemniscata
spiderlings from predators was not as pronounced (Table 6-3). There
were no differences in predation between the Control group and
either the cocoons placed on the ground for 45 days or the cocoons
placed in contact with the vegetation. The cocoons placed on the
ground for 90 days, however, were preyed upon at significantly
p
higher levels (X =70.40, df = 1, p < 0.001). These results
probably reflect the generally lower densities of ants foraging on
the vegetation and ground late in the year (pers. ob.). Cover
removal also had no significant effect on spiderling predation when
compared to control, again because the the cocoons are inaccesible
on their support line.
The eggs of A. aurantia are attacked by four primary
predators; the wasp T. ovivora rufopectus (ichneumonidae), the
neuropteran M. viridis, and the flies Pseudogaurax signata (Loew)
(Chloropidae) and Megaselia sp. (Phoridae) (Table 6-4). Of these,
the two most common predators are the ichneumonid and the mantispid.
These are obligate egg predators and probably account for most of
the initial attacks in cocoons attacked by multiple predators. The
attack behavior of the mantispid has been previously discussed. The
ichneumonid T. ovivora rufopectus attacks A. aurantia cocoons by-
inserting its long ovipositor through the cover into the flocculent
layer. Its eggs are deposited on or near the host egg mass, and the
emerging larvae make their way to the host eggs and burrow into the
mass to feed.


THE ROLE OF THE COCOONS OF ORB-WEAVING SPIDERS
By
CRAIG S. HIEBER
A DISSERTATION SUBMITTED TO THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1984


I certify that I have read this study and that in my opinion it conforms
to acceptable standards of scholarly presentation and is fully adequate,
in scope and quality, as a dissertation for the degree of Doctor of
Philosophy.
Jofi F. Anderson, Chairman
Associate Professor of Zoology
I certify that I have read this study and that in my opinion it conforms
to acceptable standards of scholarly presentation and is fully adequate,
in scope and quality, as a dissertation for the degree of Doctor of
Philosophy.
Distinguished Professor of Zoology
I certify that I have read this study and that in my opinion it conforms
to acceptable standards of scholarly presentation and is fully adequate,
in scope and quality, as a dissertation for the degree of Doctor of
Philosophy.
¡^,^4J
-tfnathon Reiskind
Associate Professor of Zoology
I certify that I have read this study and that in ny opinion it conforms
to acceptable standards of scholarly presentation and is fully adequate,
in scope and quality, as a dissertation for the degree of Doctor of
Philosophy.
Reese I. Sailer
Graduate Research Professor of
Entomology and Nematology


53
Table 5-2. The effect of modification of the cocoon suspension
system and cover on the incidence of fungal attack on the
spiderlings of Mecynogea lemniscata. Cocoons in the "Other"
category contained spiderlings which were not attacked by fungi, but
did not survive due to drowning. All cocoons were collected after
90 days, except for those placed on the ground. They were collected
after 45 and 90 days.
Experimental
Modification
Sample
Size
Successful
Survival
Fungal
Attack
% Cocoons
Attacked
Other
Control
239
236
3
1.7%
0
Vegetation
Contact
65
63
2
3.2%
0
Ground
Placement (45)
22
17
3
n.6%
2
(90)
12a
11
1
11.0%
0
Cover
Removal
37
32
5
15.6%
0
A number of cocoons were attacked by ants in this group and
could not be used for the analysis. This explains the low
percentage of fungal attack after the longer 90-day period.


76
Table 6-3. The effect of modification of the cocoon suspension
system and cover on the incidence of predator attack on the
spiderlings of Mecynogea lemniscata. All cocoons were collected
after 90 days, except for those placed on the ground. They were
collected after 1+5 and 90 days.
Experimental
Modification
Sample
Size
Successful
Survival
No. Cocoons
Attacked
Cocoons
Attacked
Control
259
239
20a
7.7%
Vegetation
Contact
77
71
6*
7.8%
Ground
Placement
(1+5)
19
17
2a
10.5$
(90)
32
11
20a
62.5 %
Cover
Removal
31+
32
2a
5.9%
a
All attacks were by ants/ unknown predators.


35
Table 4-4. Mean pecentages ( 1 SD; n in parentheses) for hatching
and molting success and spiderling survival in the field for the
spiders Mecynogea lemniscata (ML) and Argiope aurantia (AA).
Conditions in the field (60-80% RH and 24-32C) approximated the
laboratory conditions at 66% RH. The data are presented as
percentages, but were arc-sine transformed for the statistical
analyses (Sokal and Rohlf 1969).
Spider
% Hatching
Success
% Molting
Success
% Spiderling
Survival
Cocoon
No Cocoon
Cocoon
No Cocoon
Cocoon
No Cocoon
99-6
99.3
98.2
50.T
ML
1-9%
2.1%
100%
100%
12.1%
2T.o%
(19)
(IT)
(19)
(IT)
(21)
(10)
1 *#* 1
Cocoon
No Cocoon
Cocoon
No Cocoon
Cocoon
No Cocoon
99.8
99-8
93.3
91.8
AA
0.1%
0.4%
100%
100%
0.9%
2.9%
(10)
(10)
(10)
(10)
do)
(10)
*** F-test: F = 15.12, df = 29, p = 0.005.


7130 60 120 240 480
2
ml Water/cm Cocoon Surface (xIOOO)
_ ro oj k cti
o b b b b
\
\
\
i
o
0 9


CHAPTER IV
THE ROLE OF SPIDER EGGS AND COCOONS IN RESISTING WATER LOSS
Introduction
All spiders enclose their eggs in some form of silken cocoon
(Turnbull 1973)- Within these structures the eggs undergo embryonic
development, hatch to the deutova stage, and molt to the spiderling
stage. The spiderlings then spend from 6 to 10 months in the
cocoons until emergence in the spring. Dessication may be a problem
for these developmental stages. Many insects use cocoon-like
structures to limit dessication (Chapman 1967, Chauvin et al. 1979),
and this is commonly assumed to be the function of cocoons as well
(Bristowe 1941, pg. 421; Foelix 1982, pg. 200). Few data exist,
however, to support this view. Schaefer (1976) showed that the
parchmentlike cocoon of Floronia bucculenta (Clerck) (Linyphiidae)
increased the survival time of post-diapause eggs exposed to a RH of
32/i (at 5 C) from 37 to 68 days. Austin (1984) has demonstrated
that the silk nests containing eggs of Clubiona robusta L. Koch
(Clubionidae) increases humidity levels. The casual observations of
McEwon (1963) also suggest that the flocculent cocoon of an
Australian Nephila sp. (Araneidae) provides desiccation protection
for the spiderlings. Austin and Anderson (1978), however, have
showed that the flocculent silk cocoon of the congener N. edulis
25


66
Fig. 6-1. A schematic view of an Argiope aurantia cocoon
illustrating the four measurements; cocoon length (cl), cocoon width
(cw), egg mass length (eml), and egg mass width (emw) taken to
determine the position of the egg mass in relation to the cocoon
cover.


129
in Florida, A. aurantia prefers moister habitats and is one of the
first Argiopes to disappear during droughts.
Morphological differences between the eggs of spiders, or
differences in the sizes of the egg masses also affect hatching
success. At low humidities the egg mass of A. aurantia (which is TO
times larger than the egg mass of M. lemniscata) has a significant
advantage in hatching success when naked egg masses of the two
species are compared. This advantage disappears when the egg masses
of A. aurantia are reduced to the same size as those of
P4. lemniscata. Here, the egg masses of M. lemnimcata demonstrate
significantly greater hatching success, and these differences appear
to be related to a significantly denser layer of spherical granules
on the surface of the M. lemniscata eggs.
These morphological and size related advantages are exciting
for a number of reasons. All of the spider eggs so far observed
have a layer of mucoid granules on their chorions (Austin and
Anderson 1978, Grim and Slobodchikof 1978, 1980, Humphreys 1983),
and this layer has been previously suggested to function as a
barrier to water loss (Austin and Anderson 1978). The results of
this study provide the first evidence supporting this hypothesis.
Both the density of the spheres on the chorion and the size of
the egg mass function to reduce water loss, presumably by reducing
the area available for evaporation. This suggests that small egg
masses with dense sphere coatings and large egg masses with less
dense coatings may represent solutions for dessication control. I
looked at the relationship of sphere density to clutch size. Since


106
habitat (Fig. 7-1) or within one site (Fig. 7-2). In both cases,
there is no correlation at all between the level of host density and
parasitism (both p > 0.05), implying that some factor in the habitat
is interfering with this predator's foraging and reducing its
efficiency.
The average spider in 1983 produced a cocoon every 6.4 days (SD
= 3.2, n = 73), and produced a string containing 3.1 cocoons (SD =
1.6, n = 38). This is consistent with the average number of cocoons
found in strings in 1981 and 1982 (Table 7-2). Although the average
number of eggs in each of the sequentially produced cocoons varied,
the distribution of eggs among the cocoons showed a similar pattern.
In all three years, the first cocoon produced contained the greatest
number of eggs. In addition, egg number declined significantly in
the second and third cocoons of the string (all p < 0.05). The
fourth and subsequently produced cocoons in a string all contained
approximately the same number of eggs.
The wasp averaged 16 days to develop (l day in the egg stage; 5
days as larvae; 10 days as pupae), while M. lemniscata eggs averaged
20 days to develop to the spiderling stage (l6 days as eggs; 4 days
as deutova until molting). The three batches of eggs reared from
attacked cocoons took l6, 17, and 19 days, respectively, to develop
under identical rearing conditions. This suggests that the wasp is
obligated to attack the cocoon within the first few days of its
appearance.
Approximately 50-70% of the attacked cocoons collected during
December and March contained diapausing prepupae (Table 7-3) Wasps


88
Table 6-9. The effect of modification of the cocoon suspension
system and cover on the incidence of predator attack on the
spiderlings of Argiope aurantia. All cocoons were collected after
90 days, except for those in the bird damage group. They were
collected after 150 days.
Experimental
Modification
Sample
Size
Successful
Survival
No. Cocoons
Attacked
% Cocoons
Attacked
Control
23
20
3a
13.0%
Cover Removal
Control
15
Ik
lb
6.7%
Ground
Placement
19
2
17C
89.5%
Cover
Removal
21
20
ld
4.8%
Bird
Damage
23
15
8e
34.8%
Bird damage. Of the 3 cocoons, 2 had part of their cover
removed, and 1 had cover damage and the contents removed.
Bird damage.
Rodent (mice) or bird damage. Characterized by the cover
being shredded and the contents removed.
Bird damage. Contents removed from the cocoon.
Bird damage. Of the 8 cocoons, 2 were removed completely,
5 had 25-50% of their covers removed, and 1 had the cover
damaged and the contents removed.


A. aurantia to control the entrance of excess water and to limit
fungal attack.
In Chapter VI, I examine the architecture of the cocoons of
M. lemniscata and A. aurantia and its relation to the control of
predator and parasite attack. Although considered one of the
primary roles of cocoons (Austin and Anderson 1978, Robinson 1980,
Austin, In press), this function has not been examined for any
spider.
Many parasites locate their hosts in a stepwise manner using a
variety of chemical and physical cues (Salt 1935, Vinson 1975,
1976). A number of biotic and abiotic factors have been suggested
as disrupting these cues, thereby affecting the success of the
parasites (Hassell 1971, Hassell and May 1973, Vinson 1976, Morrison
and Strong 1980, Stiling and Strong 1982). However, host behaviors
such as the phenology of emergence and their effects on the temporal
\
and spatial distribution of the host have not often been considered
as factors affecting parasite success. In Chapter VII, I examine
the seasonal timing of reproduction, the length of the reproductive
season, the timing of cocoon production, and the resulting spatial
and temporal distribution of cocoons as methods used in conjunction
with cocoons to interrupt the foraging behavior of egg predators.
Chapter VII summarizes my major results and discusses their
relevance to the architecture of cocoons and to the diversity of
reproductive tactics displayed by orb-weaving spiders.


153
Schaefer, M. 1976. An analysis of diapause and resistance in the egg
stage of Floronia bucculenta (Araneae: Linyphiidae). Oecologia
25: 155-17^
Schaefer, M. 1977. Winter ecology of spiders (Araneida). Z. Ang.
Ent. 83: 113-134.
Scheffer, T.H. 1905- The cocooning habitats of spiders. Kansas Univ.
Sci. Bull. 3: 85-114.
Schildknecht, H., P. Kunzelmann, D. Krauss, and C. Kuhn. 1972. Uber
die Chemie der Spinnwebe, I. Arthropodenabvehrstoffe.
Naturwissenschaften 59". 98-99-
Schoener, T. 1971. Theory of feeding strategies. Ann. Rev. Ecol.
Sys. 2: 369-404.
Seligy, V.L. 1971. Postembryonic development of the spider
Enoplagnatha ovata (Theridiidae). Zool. J. Linn. Soc. 50: 21-31.
Sokal R.R., and F.J. Rohlf. 1969- Biometry. W.H. Freeman and
Company, San Francisco. 776 pp.
Stiling, P.D., and D.R. Strong. 1982. Egg density and the intensity of
parasitism in Prokelisia marginata (Homoptera: Delphacidae). Ecology
63: 1630-1635.
Tolbert, W.W. 1976. Population dynamics of the orb weaving spiders
Argiope trifasciata and Argiope aurantia (Araneae, Araneidae):
Density changes associated with mortality, natality, and migrations.
Ph.D. dissertation, University of Tennessee, Knoxville. 172 pp.
Tolbert, W.W. 1979 Thermal stress of the orb-weaving spider Argiope
aurantia (Araneae). Oikos 32: 386-392.
Trail, D.S. 1980. Predation by Argyrodes (Theridiidae) on solitary and
communal spiders. Psyche 87: 349-355*
Turnbull, A.L. 1973. Ecology of the true spiders (Araneomorphae).
Ann. Rev. Ent. 18: 305-348.
Variey, G.C. 194l. On the search for hosts and the egg distribution of
some Chalcid parasites of the Knapweed Gall-Fly. Parasitology
33: 47-66.
Vinson, B.S. 1972. Competition and host discrimination between two
species of tobacco budworm parasitoids. Ann. Entomol. Soc. Am.
65: 229-236.


151+
Vinson, B.S. 1975* Biochemical coevolution between parasitoids and
their hosts. Pages 14-36 in P.W. Price, ed. Evolutionary Strategies
of Parasitic Insects and Mites. Plenum Press, New York.
Vinson, B.S. 1976. Host selection by insect parasitoids. Ann. Rev.
Entomol. 21: 109-133.
Waage, J.K. 1979* Foraging for patchily-distributed hosts by the
parasitoid, Nemeritis canescens (Grv.). J. Anim. Ecol. 48: 353-371.
Washburn, J.O., and H.V. Cornell. 1979- Chalcid parasitoid attack on a
gall wasp population (Acraspis hirta (Hymenoptera: Cynipidae)) on
Quercus prinus (Fagaceae).Can. Entomol. Ill: 391-400.
Winston, P.W., and D.H. Bates, i960. Saturated solutions for the
control of humidity in biological research. Ecology 4l: 232-237.
Wise, D.H. 1982. Predation by the commensal spider, Argyrodes
trigonum, upon its host: An experimental study. J. Arachnol.
10: 111-116.
Witt, P.N. 1971. Instructions for working with web-building spiders in
the laboratory. Bioscience 21: 23-25.
Witt, P.N., C.F. Reed, and D.B. Peakall. 1968. A Spider's Web.
Springer-Verlag, Inc., New York. 107 pp.
Yoshikura, M. 1969 Effects of UV irradiation on the embryonic
development of a liphistiid spider, Heptathela kinmura. Kumamuto J.
Sci., B. 2: 57-108.
Zar, J.H. 1984. Biostatistical Analysis, 2nd ed. Prentice-Hall, Inc.,
Englewood Cliffs. 718 pp.


90
cocoons that had contacted the vegetation because of suspension
system failure (see Table 6-4). Second, the suspension system
functions to maintain the position of the cocoon within the proper
microhabitat or vegetational layer. Parasites (Moore 1977) and
pedestrian predators (Robinson 1980) may be distributed predictably
in the habitat, and cocoons that change position due to structural
failure may move into strata where they are available to new
predators or are generally easier to locate. Indeed, cocoons of
M. lemniscata suffered increased rates of predation from ants, while
those of A. aurantia were attacked heavily by small rodents (see
also Robinson and Robinson (1976)] when they were placed on the
ground. The importance of maintaining position is further
emphasized by the difference in average individual survival for
A. aurantia cocoons that were left in position in the vegetation
(59-98^), and for those that were placed on the ground (0-5%).
The literature suggests that parasitic flies are fairly common
in cocoons with loosely woven covers, but are not found often in
cocoons with hard or dense covers (Eason et al. 1967, Muma and Stone
1971, Austin, In press). The results of cover modification on
M. lemniscata cocoons supports this view. The triungulid larvae of
M. viridis had no trouble crossing the silk suspension line or
finding the correct line to the cocoon in the maze of the tangle web
(Hieber 1984). However, the dense cover prevented the larvae from
successfully entering the cocoon (see also Kaston and Jenks 1937).
The high percentage of unsuccessfully attacked cocoons with
chloropid fly eggs on them, and the significant increase in


61
fungal attack on the egg and spiderling stages of M. lemniscata and
A. aurantia. However, many predator groups have specialized on the
eggs of spiders, and it is probable that cocoons also function to
control their attacks. This possibility is considered in Chapter
VI.


CHAPTER III
THE "INSULATION" LAYER IN THE COCOONS OF ARGIOPE AURANTIA
Introduction
All spiders place their eggs in some form of silken cocoon
(Turnbull 1973). These structures must provide protection for the
eggs, create a proper microclimate for embryonic development,
hatching, and subsequent molting, and provide a safe retreat for the
spiderlings to overwinter until emergence in the spring. Because of
the lengthy development and overwintering period of some spiders
(Anderson 1978), many cocoons are exposed to severe temperature
extremes. Fluctuations in cocoon temperature have been shown to
have a direct effect on the development and survival of spider eggs
(Norgaard 1956, Schaefer 1976) and spiderlings (Norgaard 1956).
Several authors have observed spider behaviors which presumably
modify the thermal environment of the cocoon. These include burying
the cocoon (Levi and Levi 1969), shuttling the cocoon between
different microclimates (Norgaard 1951, Humphreys 197*0, and placing
it in protected microclimates. Others have suggested that a layer
of silk within some cocoons functions as insulation, modifying the
thermal environment experienced by the eggs or spiderlings (McCook
I89O, Kaston 1948, Turnbull 1973, Gertsch 1979). Schaefer (1976)
reported that the cocoons of Floronia bucculenta (Clerck)
(Linyphiidae) are capable of protecting the eggs from daily
12


38
and A. aurantia are relatively short (15-20 days and 20-30 days,
respectively), and even at low humidities this may not be long
enough to demonstrate the water retaining qualities of the cocoon.
In contrast, the eggs of F. bucculenta remain within the cocoon in
winter diapause for approximately l80 days. Since the eggs are net
particularly drought resistant (Schaefer 1976), they probably lose
water during this time. The significant effect of the cocoon on egg
survival, that Schaefer demonstrated, can probably be attributed to
his use of post-diapause eggs, from which enough water had already
been lost to make the effect of cocoon removal apparent.
The significant difference in hatching success between intact
and reduced A., aurantia egg masses without cocoons demonstrates that
clutch size can affect hatching success as well. Spider egg masses
are usually agglutinated, and as the mass gets larger, its surface
area to volume ratio declines as a greater number of eggs are
positioned completely within the mass. Presumably, this difference
also accounts for the difference in hatching success between intact
_M. lemniscata and A_. aurantia egg masses without cocoons at 0$ RH
(see Table 4-2).
The ability of intact M. lemniscata egg masses without cocoons
to maintain hatching success rates equal to those of the much larger
A. aurantia egg masses at humidities above 0f RH indicates that some
factor other than clutch size is also operating to control water
loss (see Table 4-2). A number of authors have suggested that a
layer of spherical mucoid granules (Austin and Anderson 1978) on the
chorions of spider eggs functions to control water loss by reducing


85
Table 6-7. The mean number of suspension line deltas and
oviposition holes of the ichneumonid Tromatobia ovivora rufpectus in
the upper, middle, and lower thirds of the cover of Argiope aurantia
cocoons. SD is in parentheses.
Sample
Upper
Middle
Lower
Size
Third
Third
Third
Suspension
Line Deltas
71
18.7 (6.2)
22.3 ( 9-2)
3.9 (3.7)
Ichneumonid
Oviposition Holes
8U
2.U (3.7)
9-5 (13.1+)
3.1* (5.0)


89
cocoons in the vegetation (98.4$). Predation by birds increased
during the latter part of the season, and while the numerical
increase was not significant, the average level of individual
survival was lower (j6.6$).
Laboratory Experiment
The mean percentage of success for T. ovivora rufopectus eggs
placed just under the cocoon shell was 62.5$ (SD = 13.8$, n = 4).
For the parasite eggs placed on the surface of the A. aurantia egg
mass the mean percentage of success was 85*4$ (SD = 11.2$, n = 3).
These two levels of success were not significantly different from
one another (0.10 > p > 0.05). Nevertheless, a trend is indicated
and a test with larger sample sizes would probably yield
significance.
Discussion
The suspension systems of the cocoons of both M. lemniscata and
A. aurantia function in two major ways. First, they keep the cocoon
isolated from contact with the surrounding vegetation and,
consequently, isolated from generalist pedestrian predators. The
low rates of attack by ants on the suspended cocoons of both spiders
suggest that few non-flying predators are willing or able to venture
out on the silk suspension lines. This is supported by the
significant rise in predation, particularly in the egg stage, for
M. lemniscata cocoons placed in contact with the vegetation. The
three field collected A. aurantia cocoons attacked by ants were also


Fig. 5-1. The rate of water loading in the laboratory for the covers of Mecynogea lemniscata
cocoons submerged in distilled water. The dots represent the mean volume of water absorbed per unit
area; the bars represent the SD; n, the sample size, equals 10.


Table 5-4. The effect of modification of the
cocoon suspension system and cover on the
incidence of fungal attack on the
spiderlings of Argiope aurantia 56
Table 6-1. Numbers of Mecynogea lemniscata
cocoons attacked by various predators for
the years 1981 to 1983 72
Table 6-2. The effect of modification of the
cocoon suspension system and cover on the
incidence of predator attack on the eggs
of Mecynogea lemniscata 74
Table 6-3. The effect of modification of the
cocoon suspension system and cover on the
incidence of predator attack on the
spiderlings of Mecynogea lemniscata j6
Table 6-4. Numbers of Argiope aurantia cocoons
suspended in the vegetation which were
successfully attacked by various predators for
the years 1981 to 1983 77
Table 6-5. The mean percentage of eggs which
survive in Argiope aurantia cocoons attacked
solely by various predators 8l
Table 6-6. Means for the variables cocoon
diameter, cocoon length, egg mass diameter,
egg mass length, distance to the egg mass,
and ovipositor length 84
Table 6-7. The mean numbers of suspension
line deltas and oviposition holes in the
upper, middle, and lower thirds of the
covers of Argiope aurant ia cocoons 85
Table 6-8. The effect of modification of the
cocoon suspension system and cover on the
incidence of predator attack on the eggs
of Argiope aurant ia 87
Table 6-9. The effect of modification of the
cocoon suspension system and cover on the
incidence of predator attack on the
spiderlings of Argiope aurant ia 88
vii


Eberhard, W.G. 1979* Rates of egg production by tropical spiders in
the field. Biotropica 11: 292-300.
Edgar, W.D. 1971. Aspects of the ecology and energetics of the egg sac
parasites of the wolf spider Pardosa lugubris (Walckenaer).
Oecologia 7: 155-163
Enders, F. 1974. Vertical stratification in orb-web spiders
(Araneidae, Araneae) and a consideration of other methods of
coexistence. Ecology 55: 317-328.
Evans, R.E. 1969* Parasites of spiders and their eggs. Proc.
Birmingham Nat. Hist. Soc. 21: 156-168.
Fisher, R.C. 1971. Aspects of the physiology of endoparasitic
hymenoptera. Biol. Rev. 46: 243-278.
Flanders, S.E. 1953. Variation in susceptibility of citrus-infesting
coccids to parasitization. J. Econom. Entomol. 46: 266-269.
Foelix, R.F. 1982. Biology of Spiders. Harvard University Press,
Cambridge. 306 pp.
Free, C.A., J.R. Beddington, and J.H. Lawton. 1977. On the inadequacy
of simple models of mutual interference for parasitism and predation.
J. Anim. Ecol. 46: 543-554.
Fulton, B.B. 1933. Notes on Habrocytus cerealellae, parasite of the
Angoumois grain moth. Ann. Entomol. Soc. Am. 26: 536-553.
Gertsch, W.J. 1979* American Spiders, 2nd Ed. D. van Nostrand
Company, Inc., New York. 274 pp.
Gilbert, L.E. 1971. Butterfly-plant coevolution: Has Passiflora
adenopoda won the selectional race with heliconiine butterflies?
Science 172: 585-586.
Grim, J.N., and C.N. Slobodchikoff. 1978. Chorion surface features of
some spider eggs. Pan-Pacific Entomol. 54: 319-322.
Grim, J.N., and C.N. Slobodchikoff. 1982. Spider egg chorion sphere
size and density. Ann. Ent. Soc. Amer. 75: 330-334.
Hall, D.G. 1937. The North and Central American spider parasites of
the genus Pseudogaurax (Diptera: Chloropidae). J. Wash. Acad. Sci.
27: 255-2231:
Hassell, M.P. 1966. Evaluation of parasite or predator responses. J.
Anim. Ecol. 35: 65-75


86
The location of the egg mass within the cocoon and the distribution
of drill holes suggests that the ichneumonid prefers to attack the
cocoon in this specific area.
For A. aurantia, egg predation due to the cocoon falling to the
ground was not statistically different from the control in terms of
the number of cocoons attacked (Table 6-8). However, the individual
survival of eggs in each cocoon was reduced substantially. All of
the cocoons on the ground discovered by predators suffered 100$ egg
mortality as compared to about 59.4$ mortality for cocoons remaining
in place in the vegetation. The cocoons on the ground that escaped
attack were buried by falling leaves and were presumably hidden from
predators. The level of predation on eggs in cocoons with modified
covers was also not significantly different from the Control group.
However, in all cases the cocoons were attacked by the chloropid fly
P^. signata, further suggesting that damaged cocoons appeal to this
egg predator. The lack of mantispids in the modified cocoons is
most likely related to the apparatus used to suspend the cocoons,
which prevented the larvae from locating the cocoons, and not
because of their inability to use them.
The effect of cover modification also had no effect on
predation in the spiderling stage when compared to the Control group
(both controls were not significantly different from one another)
(Table 6-9). Placement on the ground, mimicking suspension failure,
2
resulted in significantly greater predation (X = 24.37, df = 1, p
on the ground (5-9$) was also much lower then for spiderlings in


137
systems that isolate the cocoon from the substrate and effectively
reduce its accessibility to general pedestrian predators. Both
M. lemniscata and A. aurantia cocoons suffered significant increases
in egg and spiderling mortality when the cocoons contacted the
vegetation or fell to the ground and became accessible to arboreal
predators (ants) and terrestrial predators (ants, rodents, and
possibly birds). Those cocoons which remained in place were almost
never attacked by these groups (excepting birds; see Tolbert 1976),
underscoring the effective barriers that suspension systems make
against these predators.
If coevolution between spiders and their specialized egg
predators is responsible for the diversity of cocoon architecture
(Austin, In press), cocoons should demonstrate specific defenses
against these specialized attackers which reflect the manner in
which they attempt to introduce themselves or their eggs into the
cocoon. Overall, the results presented in Chapter VI demonstrate
that a dense cover is an adaptation to control actively searching
larval forms. The most striking example was the control exerted by
the cover of M. lemniscata cocoons against the mantispid egg
specialist Mantispa viridis. This parasite is an obligate cocoon
attacker (Redborg and MacLeod, In press), the larvae actively
locating and burrowing into cocoons. Parasitization rates rose
dramatically from 1-4% to approximately 63% when the cover of this
cocoon was damaged (see Table 6-2), suggesting that the larvae of
this species have no trouble in locating cocoons (Hieber 1984), but
are almost completely stopped by the cocoon cover. The large


124
73) is not significantly different from the rates Eberhard (1979)
found for M. lemniscata in Washington, D.C. (5*6 days, SD = 2.8, n =
15) and Central America (6.3 days, SD = 2.1, n = 20). Since climate
and the abundance of food vary at these sites, these factors are
probably not responsible for the observed timing of cocoon
production. All of these facts support parasite avoidance as the
selective pressure setting reproductive rates. However, the rate of
egg production could also represent some physiological limit
independent of food intake, or selection for rapid reproduction in
response to high levels of maternal predation. Adult female
M. lemniscata are preyed upon heavily in June by mud-daubing wasps
(Hieber, unpub.) and in July by kleptoparasitic Argyrodes spp.
(Araneae: Theridiidae) in the webs (see also Trail 1980, Wise 1982).
The phenology of reproduction may also be partially accounted
for by other factors. The shift to an early spring appearance has
been suggested as a way of taking advantage of abundant insect prey
in the habitat, while avoiding competition from other orb-weavers
which use the woodland habitat later in the season (Anderson 1978).


120
season when they are dispersed and have few cocoons, web-site
spacing has little or no effect on the probability of being
parasitized. Indeed, many of the cocoon strings attacked in the
experimental plot occured at spatially isolated sites (see Figure
7-4).
However, the change through time of the spatial distribution of
web-sites with cocoons 1-5 days old may act to reduce the
probability of a parasite successfully locating a useable cocoon.
The majority of wasp attacks occured between the 10th and the 23rd
of July. Just prior to this period (July 3-9), the percentage of
sites with useable cocoons was at the highest level for the season
(see Table 7-4). Sites with useable cocoons were also slightly
clumped in their distribution among all web-sites, which were also
slightly clumped. By the 15th of July, the reproductive pulse
started to taper off and the number of sites with useable cocoons
began to decline. More importantly, during this time period the
distribution of sites with cocoons 1-5 days old became random
compared to the slightly clumped distribution of all web-sites (see
Table 7-4). Many parasites locate their hosts through the use of
long-range chemical cues (Vinson 1975, 1976) and then use
short-range cues to determine the location and quality of the host
(Laing 1937, 1938, Eason et al. 1967, Vinson 1976). Since
long-range cues rarely provide information about the quality of the
host, the "switch" to a random distribution of hosts would lower the
probability that a parasite will find a cocoon since a response to
cues from an area of high cocoon density guarantees only a random


59
ground. In this location, the cocoons are in constant contact with
soil moisture. Argiope aurantia cocoons are relatively large (see
Figs. 2-1 and 2-2), and remain on the surface if they fall to the
ground. In this position, the area of the cocoon contacting the
soil is minimized, which probably allows the cocoon to dry out
between exposure to rain or submersion.
The spiderlings in M. lemniscata cocoons are also packed
together tightly, with no room to move about within the cocoon. In
addition, the flocculent silk layer in these cocoons is relatively
thin. Fungal infection, once established, can spread more easily to
all the spiderlings within the cocoon. The thicker flocculent silk
layer in the cocoons of A. aurantia provides protection from water
entering the cocoon, even when the cover is damaged. The large size
of these cocoons also allows the spiderlings to move about in the
cocoon, which may further reduce the probability of infection moving
through the mass. Indeed, in cocoons damaged naturally or modified
by me, the spiderlings are almost always appressed against the
cocoon cover opposite the site of the damage.
The differences between the overall levels of fungal attack on
the cocoons of these two spiders are also interesting. The cocoons
of M. lemniscata are covered by layers of discarded orb-web that
contains detritus composed primarily of prey remains. These remains
may provide a high quality medium for fungal spores to germinate on,
and from them, extend their hyphae into the cocoons. On occasion, I
have observed _M. lemniscata cocoons completely enswathed by a fuzzy
layer of grey or white fungus. I have also had M. lemniscata


133
CM
E
250-
o
200-

o
\
CO
4>

a?
150-
CL
CO

mmm
100-


CO
c
CD

a
CD
50-


4>

Cl
CO
0-
1 r
I 1
0 250
500 750 1000
Clutch Size
Fig. 8-1. The relationship between mean sphere density (spheres/
100 ym ) and clutch size for individual spiders from different
families.


Number of Eggs
68
Cocoon Diameter (cm)
Fig. 6-2. The relationship (Y = 1522.2X 1886.9; n = Ho) between
the diameter of Argiope aurantia cocoons and the number of
spiderlings (eggs) therein. The coefficient of determination (r^)
for the relationship is 0.90.


CHAPTER II
THE EXPERIMENTAL ANIMALS, THEIR COCOONS, AND THEIR HABITATS
Mecynogea lemniscata (Walkenaer),
the Basilica Spider
In northern Florida (at ny study sites), M. lemniscata emerges
in late March. Males mature in May and are found on the webs of
females from early June to early July. The females mature in late
May. Oviposition starts in mid-June and extends to mid-August with
a peak in mid-July. Females disappear from their webs by late
August.
The eggs of M. lemniscata take 16 days to eclose to the
deutoval stage at 25C and 70* RH. The deutoval stage lasts 4 days
until the molt to the first instar spiderling stage (Hieber 1984).
The spiderlings remain in the cocoon through the late summer, fall,
and winter, and emerge in mid- to late March the following year
after spending approximately 290 days in the cocoon (Anderson 1978).
The webs of M. lemniscata are placed in the shrub layer of
deciduous forests, approximately 1-2 m above the ground. The
cocoons are deposited at the web site, suspended above the domed
orb-web from a single support line (Fig. 2-la). The cocoons are
produced sequentially, and the strings may contain 1-10 cocoons (X =
3.1 cocoons, SD = 1.6, n = 38). The individual cocoons are small
(3-4 mm dia.) (Fig. 2-lb), and contain 8-30 eggs (X = 13.5 eggs, SD
= 6.3, n = 35) (Hieber 1984). The cocoon covering is olive-green in
5


91
successful attacks by P. signata larvae on A. aurantia cocoons
damaged by the attacks of other parasites suggests that the covers
of A. aurantia cocoons are also a barrier to attack by larvae. From
this, I concluded that the cocoon cover functions primarily to
prevent the access of actively searching mantispid and dipteran
larval stages. Austin (in press; citing an unpublished author)
points out that female wasps in the genera Tetrastichus and
Eurytomus (Eulophidae) oviposit into the topmost layers of cocoons.
The emerging first instar larvae then burrow through the cocoon wall
and attack the host eggs. If the Tetrastichus wasp in this study
utilizes a similar method of attack, the dense cover of
M. lemniscata cocoons cover may make entrance difficult for the
attacking larvae. Difficulty in entering the cocoon may account for
the relatively low rate of parasitization (see Table 6-1).
The greater success of mantispids in attacking A. aurantia
cocoons (5-14%) over M. lemniscata cocoons (0-4£) suggests that
A. aurantia cocoons do not present as difficult a barrier to
attacking larvae. This may be related to the structure of the
cocoon itself since the covers of A. aurantia cocoons are less
tightly woven than those of M. lemniscata (see Fig. 6-3). However,
the architecture of these two cocoons may also reflect broader
reproductive strategies. Adult female M. lemniscata are preyed upon
heavily by mud-daubing wasps (pers. ob.) and by kleptoparasitic
Argyrodes spp. (Araneae: Theridiidae) (see also Trail 1980, Wise
1982) in the early to middle part of their reproductive season.
They are therefore probably under some constraints to produce


1U9
Hassell, M.P. 1971 Mutual interference between searching insect
parasites. J. Anim. Ecol. 40: 473-486.
Hassell, M.P. 1978. The Dynamics of Arthropod Predator-Prey Systems.
Princeton University Press, Princeton. 246 pp.
Hassell, M.P., and R.M. May. 1973. Stability in insect host-parasitoid
models. J. Anim. Ecol. 42: 693-726.
Hassell, M.P., and R.M. May. 1974. Aggregation of predators and insect
parasites and its effect on stability. J. Anim. Ecol. 43: 567-594.
Heath, J.E. 1964. Reptilian thermoregulation: Evaluation of field
studies. Science l46: 784-785.
Hickman, V.V. 1970. The biology of the Tasmanian Chloropidae (Diptera)
whose larvae feed on spider's eggs. J. Entomol. Soc. Australia
(N.S.W.) 7: 8-33.
Hieber, C.S. 1984. Egg predators of the cocoons of the spider
Mecynogea lemniscata (Araneae: Araneidae): Rearing and population
data. Florida Entomol. 67: 176-178.
Horner, N.V., and K.J. Starks. 1972. Bionomics of the jumping spider
Metaphidippus galathea. Ann. Ent. Soc. Amer. 65: 602-607
Howard, L.O. 1892. Hymenopterous parasites of spiders. Proc.
Entomol. Soc. Washington 2: 290-303.
Humphreys, W.F. 1974. Behavioral thermoregulation in a wolf spider.
Nature 251: 502-503.
Humphreys, W.F. 1983. The surface of spider's eggs. J. Zool.
(London) 200: 305-316.
Jantzen, D.H. 1980. When is it coevolution? Evolution 34: 6ll-6l2.
Haston, B.J. 1948. Spiders of Connecticut. State Geological and
Natural History Survey No. 70, Hartford. 874 pp.
Kaston, B.J. 1970. Comparative biology of American black widow
spiders. Trans. San Diego Soc. Nat. Hist, lb: 33-82.
Kaston, B.J., and G.E. Jenks. 1937* Dipterous parasites of spider
eggs. Bull. Brooklyn Entomol. Soc. 32: I6O-I65.
Kaufman, W.C., D. Bothe, and S.D. Meyer. 1982. Thermal insulating
capabilities of outdoor clothing materials. Science 215: 69O-69I.


136
recently, Austin (in press) has considered cocoon architecture and
its relationship to predators and parasites. He suggests that the
cocoons of spiders function against two groups: l) oppurtunistic
scavenging predators (generalists), such as ants or beetles, and 2)
groups such as ichneumonid wasps, mantispids, and chloropid flies
(specialists) which are highly adapted for preying exclusively on
spider eggs. He further suggests that a coevolutionary "arms race"
(e.g., Krebs and Davies 1979) between spiders and the specialized
parasites and predators is responsible for the wide range of
structural diversity apparent among spider cocoons today. As such,
Austin's paper forms a convenient outline for discussing the results
of Chapter VI.
Predation pressure from generalists should show up as cocoon
adaptations which are generally distributed among a wide variety of
spiders, since generalist predators are distributed across habitats.
Austin (in press) suggests that the cocoon cover and maternal
guarding are adaptations against generalists, and should provide
high levels of protection. The results support this view.
Approximately 23% of the covers of the 185 A. aurantia cocoons
collected in 1982 were damaged by unknown predators (Table 6-U). In
many of these cocoons there was no damage to the egg or spiderling
mass, suggesting that the cover turned the attack away. Enders
(197M mentioned a generalist predator, a Chaulignatus beetle, that
attacks the cocoons of A. aurantia. He described damage similar to
ay observations. Other structures common to many cocoons may also
work against generalist predators. Many cocoons have suspension


8
Argiope aurantia Lucas,
the Black and Yellow Garden Spider
In northern Florida (at ray study sites), male A. aurantia
mature in July and are seen on the webs of females from
approximately mid-July to mid-August (see Levi 1968). Females
mature in late July to August (see Levi 1968). Oviposition starts
in early August and continues to October, with the greatest number
of clutches laid in mid-August to mid-September. Females disappear
from most study sites by late October.
Development to the deutoval stage (eclosin) takes
approximately 20-25 days in the laboratory at 25 C and 70-100# FJi
(see also Anderson 1978, Riddle and Markezich 1981). The deutoval
stage lasts approximately 6 days before the molt to the pigmented
first instar spiderlings. These spiderlings remain in the cocoon
until late April or early May of the following year when they
emerge.
Argiope aurantia builds its webs primarily in old field
vegetation, or in the vegetation at field edges. Its cocoons are
large brown spheres, 1-2 cm in diameter. Females deposit their
cocoons singly, away from the web site, suspended in the vegetation
0.5 to 4.0 m above the ground by a cloud of fine support lines
originating from "minute conical or pyramidal deltas" on the cocoon
surface (McCook 189O; pg. 75) (Fig. 2-2a). The cocoons are
multi-layered (Fig. 2-2b). The outer covering is usually composed
of a thin, stiff, parchmentlike material with a glazing applied to
it (almost like fiberglass), although it may occasionally be made of


121
Fig. 7-4* The spatial distribution of all the Mecynogea lemniscata
web-sites with cocoons in the 4 x H x 10 m experimental plot for
1983. The distribution of web-sites is slightly clumped ("R" =
0.77; see Table 7-M. Web-sites containing strings with attacked
cocoons are indicated with stars. The site with the open star had
two cocoons attacked in the string. The location of web-sites with
attacked cocoons is unrelated to their distance to other cocoons or
clumps of cocoons.


LITERATURE CITED
Anderson, J.F. 1978. Energy content of spider eggs. Oecologia
37: 41-57.
Askew, R.R. 1971. Parasitic Insects. Heinemann Educational Books,
London. 316 pp.
Austin, A.D. 1984. Life history of Clubiona robusta L. Koch and
related species (Araneae, Clubionidae) in South Australia. J.
Arachnol. 12: 87-104.
Austin, A.D. In press. The function of spider egg sacs in relation to
parasitoids and predators, with special reference to the Australian
fauna. J. Nat. Hist.
Austin, A.D., and D.T. Anderson. 1978. Reproduction and development of
the spider Nephila edulis (Koch) (Araneidae: Araneae). Aust. J.
Zool. 26: 501-518.
Auten, M. 1925. Insects associated with spider nests. Ann. Entomol.
Soc. Amer. 18: 240-250.
Bijl, van der, P., and A. Paul. 1922. A fungus Gibbellula haygarthii
n. sp. on a spider of the family Lycosidae. Trans. Roy. Soc. S.
Africa 10: 149-150.
Bristowe, W.S. 1941. The Comity of Spiders. The Ray Society, London.
560 pp.
Brower, L.P., and J.V. Brower. 1972. Parallelism, convergence,
divergence and the new concept of advergence in the evolution of
mimicry. Trans. Connecticut Acad. Arts Sci. 44: 59-67.
Burks, B.D. 1979* Symphyta and Apocrita (Parasitica). Pages 990-1002
in K.V. Krombein, P.D. Hurd, Jr., D.R. Smith, and B.D. Burks, eds.
Catalog of the Hymenoptera in America North of Mexico. I.
Smithsonian Institution Press, Washington, D.C.
Champlain, A.B. 1922. Records of hymenopterous parasites in
Pennsylvania. Pysche 29: 95-100.
Chapman, R.F. 1967. The Insects: Structure and Function. Elsevier
North Holland, Inc., New York. 819 pp.


93
clutches as quickly as possible. This may account for the small
clutch size of the spider. Since the probability of only producing
one or a few small clutches is high, these should be protected as
well as possible, particularly since successful predator attack on
M. lemniscata cocoons is always 100% fatal. In contrast,
A. aurantia is a large spider when mature, and few predators attack
it. This spider's reproductive season is timed with the early fall
peak, in orthopteran prey, and the relative abundance of food allows
the average spider to produce 1-3 huge clutches of 800-2000 eggs.
In the midst of abundant prey, allocating a percentage of the egg
mass to those predators using a larval attack might be less
expensive than the increase in time and energy involved in making a
cocoon totally impenetrable. The relativly low percentage of eggs
lost to attacking mantispids and chloropid flies (30-40%) in
comparison to those lost in a successful ichneumonid attack (90%)
suggests that this is a viable alternative (see Table 6-5).
The advantages of the cover as a physical barrier to attack
disappear when the cocoon is attacked by wasps with long
ovipositors. This is because the cover can be circumvented by the
ovipositor, and the predator's eggs, and ultimately its larvae, can
be placed near or on the host egg mass. The cover, however, may
still represent an obstacle to successful attack. Many wasps only
utilize hosts that are in a specific stage of development (Vinson
1976). The cocoon cover could limit information on the status of
the host to predators landing on the cocoon, thereby forcing them to
waste time or energy cutting a hole in the cover or inserting


72
Table 6-1. Numbers of Mecynogea leianiscata cocoons attacked by the
eulophid wasp Tetrastichus sp., the raantispid Mantispa viridis, and
ants/ unknown predators for the years 1981 to 1983- The cocoons
were collected in late August in 1981 and 1982 at the end of the
reproductive season, and in July, August, and December in 1983. The
percentages of attacked cocoons are in parentheses.
Year
Sample
Size
Total No.
Attacked
Eulophid
Wasp
Mantispid*3
Ants/
Unknown
1981
290
26
21 (80.8%)
0 (0%)
5
(19.2*)
1982
252
29
17 (58.6?.)
5 (17-2%)
7
(2k.1%)
1983
July
148
13
10 (76.9%)
2 (15-4%)
1
( 1.1%)
Aug.
97
l4
12 (85.7%)
0 (0%)
2
(14.3%)
Dec.
308
64
32 (50.Of.)
12 (18.8%)
20
(31.2%)
Cocoons contain either larvae, prepupae, and/or shed exuviae
with emergence holes.
Cocoons contain either a larva, a pupa, or a pupal case and
emergence hole.
Cocoons are characterized by a large chewed hole, and the
absence of the flocculent silk layer, pupal cases, pupae,
shed exuviae, or parasite.


l6
Fig. 3-l Cooling rates in still air in the laboratory for whole
and modified Argiope aurantia cocoons. The whole cocoons (squares)
contained spiderlings and the flocculent silk layer; the modified
cocoons contained only the flocculent silk layer (open circles), or
were empty (closed circles). The cooling curve for the whole
cocoons is Y = -0.208X + 2.73 (r = 0.95, n = 6); for the modified
cocoons with the flocculent layer Y = -0.824X + 2.85 (r = O.96, n
= 10); for the empty cocoons Y = -O.SlOX + 2.66 (r = 0.90, n = 8).
During cooling T = 8-9 C. The data points represent the range
for each set of experimental trials.


87
Table 6-8. The effect of modification of the cocoon suspension
system and cover on the incidence of predator attack on the eggs of
Argiope aurantia. All cocoons were collected after 30 days.
Experimental
Modification
Sample
Size
Successful
Survival
No. Cocoons-
Attacked
% Attacked
Attacked
Control
21
10
IIa
52. k%
Ground
Placement
10
2
8
80.0%
Cover
Removal
17
10
i
*1.2%
Of the 11 cocoons attacked, 8 were attacked by the chloropid
fly P. signata, 8 were attacked by the mantispid M. viridis,
1 by the phorid fly Megaselia sp., 1 by the ichneumonid
T. ovivora rufopectus, and 5 by birds.
Rodent (mice) damage. The cocoon covers were shredded and
the contents destroyed.
All 7 cocoons were attacked solely by the chloropid fly
P. signata.


139
egg mass, and the silk layer entraps emerging larvae as they move
toward the host eggs. Although not 100% perfect, the flocculent
silk layer substantially lowers the number of larvae which make it
to the host egg mass and is increasingly effective when the egg mass
is large. Under the best conditions, the principle predator of
A. aurantia cocoons, Tromatobia ovvora rufopectus, destroys only
90% of the eggs in a cocoon. In contrast, the predators of
M. lemniscata cocoons, which have small egg masses and a thin
flocculent silk layer, always destroy all of the eggs in an attack.
Many other araneids (e.g., members of the genera Araneus,
Gastercantha, Neoscona, and Nephila) utilize flocculent cocoons
without covers. These spiders also have relatively large egg
masses, suggesting that the combination of this layer and a large
egg mass may be a part of a set of adaptations for controlling
wasps. Austin (in press) points out that many scelionid wasps
cannot parasitize more than about 35% of some large host egg masses
because their ovipositors cannot reach further into the mass than
the upper two layers of eggs.
Chapter VI also demonstrates the integrated nature of the
various layers in defending the cocoon. For example, the suspension
system of A. aurantia cocoons fuctions to protect the eggs and
spiderlings from predators by keeping the cocoon away from contact
with the vegetation and off of the ground. Moreover, the suspension
lines on the cocoon are distributed in the areas of best fit between
the ovipositor of the ichneumionid predator and the distance to the
egg mass, presumably to interfer with oviposition.


115
Discussion
Explanations of parasitoid foraging suggest they locate hosts
through a series of steps mediated by one or more physical or
chemical cues. Such models have led to the prediction of
density-dependent parasite mortality of the host. Hosts should be
under heavy selection for behaviors which reduce or eliminate the
quality or number of useable cues available to the host to reduce
the probability of its success. For the Tetrastichus wasp, which
emerges from cocoons in the host habitat (the woods), a successful
search involves locating a string of M. lemniscata cocoons and
selecting a cocoon in the proper stage for attack. The low overall
levels of parasitism (7-9%) by this wasp in comparison with the
levels of parasitism demonstrated by other wasps using cocoons
(25-75%), and the lack of the predicted relationship between cocoon
density and the level of parasitism suggest that something is
interferring with this search process.
Mecynogea lemniscata (Walckenaer) (Araneidae) is the first
orb-weaver to emerge in the spring and its reproductive period is
shifted to the early summer, far earlier than the other orb-weavers
using the woodland habitat. Consequently, M. lemniscata starts egg
laying at a time when few other spiders are producing cocoons. This
limits the parasites in utilizing other spider hosts to build up
their numbers during the early appearance of M. lemniscata cocoons.
In addition, M. lemniscata is reproductively active for a 40 day
period. This short time interval limits the number of wasp


43
the suspension systems, the internal flocculent layers, and the
coverings of the cocoons of these spiders in protecting the eggs and
spiderlings from excess water, drowning, and fungal attack.
Materials and Methods
Laboratory Experiments
The abilities of the cocoon suspension system, the cocoon
cover, and the internal flocculent silk layer to limit the access of
water to, or into the cocoon were examined in the laboratory using
M. lemniscata or A. aurantia cocoons as appropriate. The
temperature and humidity in the laboratory during all the
experiments were 25 C and 50-60% RH, respectively.
To examine the function of cocoon suspension systems in
shedding water, M. lemniscata cocoon strings were hung between two
vertical supports by their silk suspension lines (see Fig. 2-1).
The angle of inclination of the suspension lines was set at 10, 20,
30, and 45 from the horizontal. At each of these angles, water
was applied to the suspension lines with a dropper, and its course
down the lines noted.
The ability of cocoons to shed water was examined by applying
1.00 ml of water with a syringe directly to hanging strings of
M. lemniscata cocoons. The runoff was collected, and the amount
retained by the cocoon string calculated. Both naked strings, and
those covered with a layer of silk and detritus (see Fig. 2-lc) were
tested in this manner. The abilities of both M. lemniscata and


123
Obviously, there are other factors which may also account for
the observed levels of parasitism and the lack of a
density-dependent relationship. It is possible that this
Tetrastichus species has other hosts, and that the eggs of
M. lemniscata represent either a secondary host, or one of several
alternatives used when they are accidentally discovered while
searching for the primary host. Indeed, wasps in this genus can be
quite catholic in the host preferences (Burks 1979)* However, the
presence of prepupae in cocoons collected late in the year, and the
close timing of wasp emergence with the onset of cocoon production
strongly suggest that the eggs of M. lemniscata represent a primary
host for this wasp. The observed patterns may also be partially
related to mutual interference (Hassell 1971) in response to
"trail-marking" substances (Price 1970a), or simply to variation in
the "toughness", and thus ease of entry, of the available cocoons in
the habitat (see Chapter VI).
The above discussion implies that the observed pattern of
reproductive phenology and rates of cocoon production are
adaptations which have evolved in response to parasite pressure.
Certainly the 7-9% level of parasitism represents sufficient
evolutionary pressure to select for such behaviors. The parasite
and the host also appear to be closely linked, as demonstrated by
the relatively constant levels of host density and parasitism, the
timing of parasite emergence with host emergence, and the timing of
the wasp attack with the peak availability of cocoons. In addition,
the rate of cocoon production in Florida (6.1* days, SD = 3.2, n =


97
The flocculent silk layer in the cocoons of M. lemniscata is
extremely thin and it seems unlikely that it provides much in the
way of a barrier to parasite larvae. However, this spider
periodically collapses its orb-webs as they become damaged or dirty,
and these collapsed webs are applied to the cocoons on the string.
This adds a thick external layer of silk and detritus to the cocoons
that may make it more difficult for the eulophid wasp, which is
relatively small, to gain access to the cocoon shell for drilling
(see Opell 1984). This layer may also work as a further barrier
against the mantispid larvae.
Obviously, the various layers of the cocoon may also interact
with each other to reduce successful parasite attack. The cocoon of
A. aurantia is suspended in the vegetation by a cloud of silk lines
which arise from suspension line deltas on the cocoon surface (see
Fig. 2-2a). If suspending the cocoon was the only purpose of these
lines, the majority of them should arise from the top of the cocoon,
with a few on the sides and bottom to provide stability and prevent
rotation. However, the greatest number of deltas are found in the
middle of the cocoon where the lines emanating from them would
contribute little to cocoon support. This is puzzling until the
position of the egg mass within the cocoon is considered. The egg
mass is closer to the cocoon cover in the upper part of the cocoon
because of its shape, and here the average ovipositor can reach it.
However, the egg mass is shielded at its top end by a cone of silk
and a thick cap of silk (the cup in which the eggs were initially
deposited) (see Fig. 2-2b), and the low number of ovipositor drill


71
the cover, and 2) on the host egg mass. Successful parasitism was
scored as the number of ichneumonid larvae found in the host egg
mass just prior to pupation.
The wasps were maintained in the laboratory at 23-25 C and
50-60% RH. They were provided with white refined sugar, a mixture
of honey and yeast, and water. Colony size was maintained by the
addition of new wasps collected from the field. Their eggs were
obtained by allowing a number of wasps to attack a cocoon produced
in the laboratory. The cocoon was then opened, and the white,
elongate wasp eggs were removed using a fine brush and forceps.
Known numbers of these eggs were then transferred to other
laboratory produced cocoons 1-3 days old, and placed in either of
the two test locations.
The cocoons were obtained from spiders held in the laboratory
in 50 x 50 x 10 cm cages (Witt 1971) or in 500 ml jars with screen
tops. Oviposition and cocoon construction in both of these
enclosures was normal.
Results
Field Experiments
The cocoons of M. lemniscata are attacked in the egg stage by
two major predators, a Tetrastichus sp. wasp (Eulophidae) and the
neuropteran Mantispa viridis Walker (Mantispidae) (Hieber 1984)
(Table 6-1). 3oth of these predators utilize all of the eggs in a
cocoon during their attacks. However, they attack the cocoons in


82
emerging larvae failed to gain entrance into the cocoon (no pupal
cases inside the cocoon). The remaining 42 cocoons were
successfully attacked and can be divided into two groups; 17 cocoons
attacked by the fly alone, and 25 cocoons attacked by the fly and
one or more other predators. Of the 17 singly attacked cocoons, 13
had eggs on the surface and a fewer number of pupae inside, 2 had
more pupae than eggs present, and 2 had pupae and no eggs present.
Of the remaining exhibiting multiple attacks, 11 had eggs on the
outside and inside of the shell and contained less (8 cocoons) or
more pupae (3 cocoons) than eggs. The other l4 cocoons had pupae,
but no evidence of eggs could be found because the cocoon and its
contents were heavily damaged.
The large number of cocoons attacked by P. signata in
conjunction with other predators suggests that shell damage may be
advantageous to this fly (see Table 6-4). Indeed, the average rate
of success (number of pupae/ number of eggs X 100) for the cocoons
attacked by the fly alone was 29.87 (SD = 30.2%) (based on the 13
cocoons which had visible eggs). The average rate of success for
the flies which attacked cocoons with other predators was 82.7% (SD
= 19-74%) (based on 11 cocoons; the 3 with more pupae than eggs were
counted as 100% successful). This level of success is significantly
greater (t = 10.05, df = 22, p < 0.001) than that achieved by
P. signata attacking cocoons alone.
It is difficult to determine whether the success rates for
mantispids and phorid fies attacking A_. aurantia cocoons are due to
an inability to locate the cocoons, or to the inability of the


15
temperature was relatively constant (12.9-13.6 C), and there was
no wind. All the cocoons used in this experiment were approximately
the same size, color, and mass. On a third day, the hourly changes
in ambient air temperature (YSI #405 probe, time constant of 0.60 s)
and in the internal (YSI #513) and surface temperatures (YSI #427)
of two cocoons in two different habitats (closed canopy under trees,
open canopy in an old field) were recorded for 24 h. Simultaneous
measurements of the sky and vegetation temperatures or enclosure
wall temperatures were made with a Stoll-Hardy HL4 radiometer during
all of the field experiments to measure the radiant heat load in the
respective test habitats.
Results
There were no significant differences between the slopes of the
cooling curves for the modified cocoons (Fig. 3-1). Both types of
modified cocoons showed cooling rates of approximately 11 C/ min.
In contrast, the whole cocoons cooled significantly more slowly than
the modified cocoons (F = 356.71, p < 0.001); the presence of
spiderlings (total cocoon weights 0.63 to 0.93 g; spiderling weights
O.56 to 0.83 g) decreasing the cooling rate to approximately 2.0
C/ min (Fig. 3-1).
Outdoors, in the artificial closed habitat, there were no
significant differences between the rates of cooling for the whole
cocoon (total weight 0.809 g; spiderling weight 0.682 g), and the
modified cocoons with and without the flocculent silk layer.


CHAPTER VI
THE ROLE OF THE COCOON IN LIMITING EGG AND
SPIDERLING PREDATORS
Introduction
A major portion of modern ecology is concerned with the
relationship between heterotrophic organisms and their food
supplies. Such interactions (e.g., predator vs. prey, host
vs. parasite) occur both in ecological time, and in evolutionary
time (Brower and Brower 1972, Dawkins and Krebs 1979) As such,
natural selection may be presumed to act within interacting
populations to optimize both the ability to acquire resources
(Schoener 1971, Pyke et al. 1977), and the ability to avoid becoming
the acquired resources of similarly-selected organisms of higher
trophic levels. Within this context, the strategy" of any host
organism should be to protect itself, or its offspring, from the
effects of predator or parasite attack through processes or
behaviors which limit the types and numbers of attackers that are
capable of using it. Ideally, the strategy should result in the
total exclusion of all the attackers. In reality, their effect is
only partially reduced due to the reciprocal nature of the
interaction over evolutionary time.
Spiders deposit their eggs in one or more discreet clutches.
These clutches can be extremely large (up to 2000 eggs; Kastcn
19^8). The individual eggs within the clutch are also
62


As a family, the orb-weaving spiders (Araneidae) are attacked
by a wide variety of specialized predators from a number of the
major insect groups (Eason et al. 1967, Askew 1971, Austin, In
press). The results of Chapter VI study suggest that a covered
cocoon with a thick flocculent layer (e.g., the cocoon of
A. aurantia) may be the best combination for discouraging the widest
variety of predators. However, many genera of araneids use
flocculent cocoons which small wasps and flies can apparently enter
with relatively little hindrance (see e.g., Muma and Stone 1971).
In addition, many spiders position their cocoons in what appear to
be locations that are higly accesible or easy to locate. This
suggests that many spiders are using methods that reduce the numbers
of predators and parasites that initially locate the cocoon.
One method of reducing the number of predators that will
potentially locate a cocoon is to limit the availability of the
cocoons in time (Chapter VII). This could involve shifts in the
oviposition season to times when parasites are less abundant, or a
shortening of the reproductive season. Mecynogea lemniscata
reproduces early in the summer at a time when few other spiders are
reproductive. Reproduction at this time could reduce the overall
numbers of parasites present in the habitat, as well as limit them
from building up large numbers because of the lack of alternative
hosts. Enders (197*+) has demonstrated the positive effects of such
a temporal shift in the reproductive period for Argiope trifasciata
Forskal (Araneidae). The reproductive season of M. lemniscata is
also relatively short, subsequently limiting the number of parasite


33
compared at each humidity. There was a significant difference at 0%
RH, underscoring the advantage of a large egg mass.
A different pattern of hatching success was revealed when
intact M. lemniscata egg masses without cocoons were compared to
reduced A. aurantia egg masses without cocoons at each humidity
(Table 4-2). The significant advantage previously demonstrated by
the whole A. aurantia egg masses at 0% RH disappeared, and hatching
success dropped significantly below that of M. lemniscata at 66% and
33% RH, presumably because of differences in the densities of the
the sphere layers covering the eggs of each species. There were no
significant differences at 100% RH, where dessication is obviously
not a problem.
The Effects of the Cocoons
Cocoon removal had no effect on the hatching success of
M. lemniscata at any experimental humidity (Table 4-2). Below 33%
RH, there were significant decreases in hatching success for egg
masses with and without cocoons. Molting success showed no
significant reduction with cocoon removal at any experimental
humidity (Table 4-3). Since few eggs hatched at 0% RH, however, the
percentage of total eggs which ultimately molted was small. The
cocoon did have a significant effect on spiderling survival. At all
the experimental humidities survival was greater with a cocoon
(Table 4-3). The field results support these findings (Table
4-4); only spiderling survival was significantly affected by removal
of the cocoon.


18
Fig. 3-2. Cooling rates outdoors for whole and modified Argiope
aurantia cocoons in an artificial closed habitat (l x 1 x 1 m
cardboard enclosure) over a 50 min period during an approximate
2.5 C change in ambient temperature. The whole cocoon (squares)
contained spiderlings and the flocculent silk layer; the modified
cocoons contained only the flocculent layer (open circles), or were
empty (closed circles). The cooling curve for the whole cocoon is Y
= 0.067X 1.57 (r = 0.99, n = l); for the modified cocoon with
the flocculent layer Y = O.O66X 1.6l (r = 0.99 n = l); for the
empty cocoon Y = O.O65X 1.50 (r = O.98, n = l). The curve for
the change in ambient temperature (stars) is Y = 0.060X 1.90 (r
= 0.99)* The temperatures of the top and sides of the enclosure
during this period were 4 C and 5 C, respectively.


73
different ways. Mantispa viridis deposits its eggs in the habitat,
removed from the host, and the emerging triungulid larvae actively
search out and burrow into previously constructed cocoons. These
larvae are obligate cocoon attackers, as opposed to the mantispid
larvae that ride on female spiders and attack the egg mass just
prior to cocoon construction (see Redborg and McLeod, In press, for
a review of Mantispid biology). The Tetrastichus wasp either
deposits eggs into the cocoon, or into the upper layers of the
cocoon cover where the emerging larvae burrow through the cocoon and
attack the egg mass (Austin, In press). Both the wasp and the
mantispid are never found together in the same cocoon. The cocoons
of M. lemniscata are also occasionally attacked by ants, which also
remove all of the eggs or spiderlings.
The single line suspension system of M. lemniscata cocoons
functions to prevent predation on the egg stage. Egg predation was
significantly greater than control for both the cocoons placed on
2
the branches (X = 47.40, df = 1, p < 0.001) and those placed on
the ground (X2 = 23.49, df = 1, p < 0.001) (Table 6-2). In both
cases, the principle predator appeared to be ants. Modification of
2
the cocoon cover also had a significant effect on egg predation (X
= 38.67, df = 1, p < O.OOl). In this case, however, the principle
predator was not ants, but the mantispid M. viridis. In no case did
the wasp attack any manipulated cocoons containing eggs, suggesting
that the position of the cocoon in the web or the integrity of the
cocoon cover are important to the wasp.


limited role in controlling temperature extremes from short-term
radiant loads.
The cocoons of both species play a significant role in
protecting the eggs and spiderlings from generalist and specialist
predators. The association between the various layers making up
these cocoons, and the specific methods used to gain entrance by
their predators strongly supports the notion of a co-evolved system.
However, the multiple functions of many cocoon components suggest
the architectural details have probably resulted from diffuse
evolutionary pressure from a number of simultaneously operating
factors, instead of as counter-adaptations to specific predators.
In general, these results support many of the previous
suggestions concerning cocoon function. Although specific functions
are related to specific components within the cocoon, there can be
great interspecific variation with relation to cocoon size and the
relative sizes or thicknesses of the component parts of the cocoon.
In addition, factors such as the size of the egg mass, the
ultrastructure of the eggs, the habitat used for oviposition, the
position of the cocoon within the habitat, and the reproductive
behavior of the spider may also influence the ability of any part of
the cocoon, or the whole structure, to limit the effects of any or
all of the suggested factors affecting egg and spiderling survival.
xii


99
and other vegetation. The cocoons of M. lemniscata are not attacked
by birds at all, even though they are visible in the habitat. This
may be for a number of reasons. First, they are extremely small and
probably do not give much return for the energy invested in
harvesting them. They are also very hard. In addition, they may be
covered with old web and prey remains, and appear as detritus to
visually hunting predators. Finally, they are hung away from
perches on their suspension lines and would be difficult to take
except while hovering.
In the preceeding discussion, I have dealt primarily with the
cocoon as a barrier to attack once the cocoon has been located by a
predator. However, the field evidence suggests that a number of
cocoons in the habitat are never found by T.. ovivora rufopectus or
P. signata. Failure to locate hosts may also explain the low
overall percentage of M. lemniscata cocoons attacked by the
Tetrastichus wasp. A number of factors may contribute to the
inability of a parasite to locate hosts, including the behavior of
the host itself. The spatial and temporal aspects of host
reproduction, and their effects on successful parasite foraging are
considered in Chapter VII.


31
Table 4-1. The distributions of sphere sizes found on the chorionic
surfaces of Mecynogea lemniscata and Argiope aurantia eggs. The
mean sphere sizes and mean sphere densities ( 1 SD; n in
parentheses) are given below the frequency column for each species.
Frequency
Sphere Size
Diam. (ym)
M. lemniscata A.
aurantia
0.40 0.79
9
2
0.80 1.19
57
17
1.20 1.59
104
117
1.60 1.99
47
26
2.00 2.39
12
2
2.1+0 2.79
3
0
2.80 3.19
1
0
3.20 3.59
2
0
3.60 3.99
0
0
4.00 4.39
2
0
4.40 4.79
0
1
4.80 5.19
1
2
5.20 5.59
1
0
5.60 5-99
1
0
6.00 6.39
1
0
6.4o 6.79
0
0
6.80 7.19
1
1
Mean Sphere
x = 1.56 0.79
x = 1.52 0.70
Size
(242)
(168)
Mean Sphere
X = 21.60 5.46
X = 17.00 4.22
Density
(10)
(10)


130
clutch size data are not available for the data of Grin and
Slobodchikoff (1980, 1982), I used clutch size data for conspecifics
of the same relative body size from the literature (see Table 8-1).
The relationship between sphere density and clutch size is
shown in Fig. 8-1. A Spearman rank correlation, which is
conservative in its treatment of the tail values, is not significant
(r = -O.36T, p = 0.035), falling just short of the 0.05 level of
acceptance. However, the data incorporate a substantial amount of
variation, and the analysis therefore represents a conservative test
of the relationship. The fact that a relationship emerges and
hovers around significance suggests that the relationship is real
and would show significance if species-level rather than
congeneric-level data were used.
Finally, the advantage of a large clutch size in controlling
temperature extremes and water balance points out that selection for
clutch size may be driven by abiotic factors. This is in direct
contrast to much of the vertebrate literature that lists primarily
biotic factors (e.g., food supply, parental efficiency, or
predators) as the major selective forces working on clutch size
(e.g., Lack 1954, i960, 1968).
The results presented in Chapter V indicate that the cocoon,
and in particular its suspension system, function to prevent the
eggs or spiderlings from drowning (see also Schaefer 1976, Reichert
1981). A strong suspension system appears to be particularly
important for small cocoons that have a high probability of being
worked into the soil and consequently drowned due to their constant


92
Fig. 6-3. The covers of the cocoons of Mecynogea lemniscata (A) and
Argiope aurantia (B) comparing the difference in the tightness of
the weaving. The scale line in each equals 120 ym. Both cocoons
were plated with 75 A of gold and observed using secondary
electrons.


Table 7-1. Densities of Mecynogea lean is cat a
cocoons, and the percentages of cocoons
attacked for the years 1981 to 1983 10p
Table 7-2. Mean numbers of Mecynogea lemniscata
cocoons per string, and the mean number of
eggs in each cocoon in the string for the
years 1981 to 1983 109
Table 7-3. A comparison of the contents of
attacked Mecynogea lemniscata cocoons 110
Table 7-^. The number and distribution in
space and time of all Mecynogea lemniscata
web-sites with cocoons, and of sites
with cocoons in the proper stage for
attack in the experimental plot for 1983 112
Table 8-1. The mean sphere density and median
clutch size for individual spiders from
different families 131
viii


Xi, The Research Society, and the Florida Entomological Society for
their generous financial support during ny graduate program.
Numerous other post doctoral associates and graduate students
in the Zoology Department have listened to my ideas and provided
helpful suggestions. Among these I would especially like to thank
J.B. Anderson, W.W. Henneman, J.R. Lucas, S.B. and B.J. Malcolm,
P.G. May, M.S. Obin, K. Prestwich, N.E. Stamp, and N.T. Wheelwright.
I also extend ny thanks to A.D. Austin and K.E. Redborg for
providing me with relevant manuscripts concerning my research.
I would like to separately thank ny office mate and friend
James A. Cohen (UVPD) for the countless stimulating discussions
concerning my work and biology in general, the lovebug
collaboration, and, in particular, for his influence on ny writing.
Jim, the "big chair" will always be open!
I would also like to separately thank Sherry M. Hieber for
putting up with the late nights, the wild talk, and the oftentimes
crazed behavior of this researcher. I could not have done this
without her support and love.
Finally, I would like to thank my parents, Bernie and Doris
Rieber, who have always told me I could be anything I wanted to be.
iii


TO
left suspended in place at the veb site. Female spiders treated
these modified cocoons normally. The laboratory reared cocoons of
A. aurantia were modified and attached to the arms of a support
system using alligator clips. The support systems were placed in
the vegetation where normally oviposited cocoons were hanging. They
held the cocoons approximately 1 m off of the ground (the average
cocoon height as determined by collecting).
Cover removal control. This group was to control for the
possible contaminating effects of the alligator clip used in the
apparatus to suspend A. aurantia cocoons. Clips were attached to
cocoons hanging normally in the habitat and the cocoons were
observed for any effect.
Control. Control cocoons were subjected to no structural
intervention. These cocoons controlled for handling effects in the
ground placement, vegetation placement, and cover removal groups.
Bird damage. These A. aurantia cocoons were subjected to no
mechanical modification. They were marked and collected after 150
days in the field to determine whether bird predation increases
later in the year after the plants lose their leaves (see also
Tolbert 1976). They were compared to the control group.
Laboratory Experiments
The role of the flocculent silk layer in the cocoons of
A. aurantia as a barrier to predator attack was tested in the
laboratory by placing the eggs of Tromatobia ovivora rufopectus
(Cresson) (ichneumonidae) at two depths in the cocoon: l) just under


Ill
began to emerge in the laboratory from the cocoons collected in
March as early as the 4th of May. However, the majority of wasps
completed development and emerged between the 24th of May and the
10th of June, 2 to 19 days before the spiders started egg laying in
the field.
In 1983, cocoon production started the 12th of June and
continued to approximately the 8th of August (Table 7-4).
Reproduction was not synchronized, and initially cocoons appeared
slowly in the habitat as the early laying spiders started
oviposition. For the majority of spiders, the oviposition period
ran from approximately the 25th of June to the 25th of July. Early
in this period cocoon production increased rapidly with the number
of cocoons nearly doubling every 6 days. Cocoon production peaked
around the 15th of July and then declined sharply as the majority of
the population finished reproduction. Production then continued at
a reduced rate until the late starting spiders finished egg laying
in early August.
As the number of web-sites with cocoons increased over the
season, their distributional pattern changed from one significantly
more dispersed than random early in the season (15-21 June), to
random (27 June), to a loosely clumped distribution where it
remained (3 July to the end of the season) (Table 7-4). The
distribution of web-sites with cocoons in the appropriate stage for
attack (1-5 days old) showed a similar pattern of change (Table
7-4). Early in the season the distribution of sites with cocoons of
this age changed from overdispersed (21 June), to random (27 June),


2k
mean a few degrees difference in internal cocoon temperature. This
difference may be important when the ambient temperature approaches
the upper critical temperature of the eggs or spiderlings.
The limited ability of the relatively large A. aurantia cocoons
to resist temperature fluctuations suggests that cocoons with
smaller masses of eggs or spiderlings will have more difficulty in
controlling temperature extremes. The non-functional role of the
flocculent silk layer as insulation further suggests that cocoons
may function to regulate other factors in the environment. Due to
the small size of the eggs and spiderlings, and their consequent
high surface area to volume ratio, it seems likely that cocoons may
play a role in limiting water loss. This role is explored in
Chapter IV.


LIST OF TABLES
Table 4-1. The distributions of sphere sizes
found on the chorionic surfaces of
Mecynogea lemniscata and Argiope
aurantia eggs 31
Table 4-2. Mean percentages of eggs successfully
hatched at the four experimental humidities
for intact Mecynogea lemniscata and Argiope
aurantia egg masses with and without cocoons,
and for reduced A. aurantia egg masses without
cocoons 32
Table 4-3* Mean percentages for molting success
and spiderling survival at the four
experimental humidities for Mecynogea
lemniscata egg and spiderling masses with
and without cocoons 34
Table 4-4. Mean percentages for hatching and
molting success and spiderling survival
in the field for the spiders Mecynogea
lemniscata and Argiope aurantia 35
Table 4-5* Mean percentages for molting success
and spiderling survival at the four experimental
humidities for Argiope aurantia egg and
spiderling masses with and without cocoons 37
Table 5-1 The effect of modification of the
cocoon suspension system and cover on the
incidence of fungal attack on the eggs of
Mecynogea lemniscata 52
Table 5-2. The effect of modification of the
cocoon suspension system and cover on the
incidence of fungal attack on the
spiderlings of Mecynogea lemniscata 53
Table 5-3 The effect of modification of the
cocoon suspension system and cover on the
incidence of fungal attack on the eggs of
Argiope aurant ia 55
vi


THE ROLE OF THE COCOONS OF ORB-WEAVING SPIDERS
By
CRAIG S. HIEBER
A DISSERTATION SUBMITTED TO THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1984

ACKNOWLEDGEMENTS
It is a pleasure to acknowledge the many friends and colleagues
who aided me in this work. My major professor, John F. Anderson,
has been a source of stimulation and encouragment. His comments on
ny work were always critical but fair, and he always emphasized the
importance of doing good, solid research. Most importantly, he
encouraged me to be as independent as possible while doing ny
research. To John I extend ny sincerest thanks. The other members
of my dissertation committee, Lincoln P. Brower, Jonathon Reiskind,
and Reese I. Sailer, and the additional colleague, David H. Evans,
who sat at my defense, all provided ready assistance during the
research phase and many helpful editorial suggestions, from which I
benefitted. I also recognize the advice or equipment provided by
Drs. L. Berner, P. Feinsinger, M.H. Greenstone, F.J. Maturo, and
B.K. McNab.
I was also fortunate to have the cooperation of a number of
people in positively identifying my egg predators. Thanks for this
service go to H. Townes (ichneumonids), American Entomological
Institute; Dr. M.E. Schauff (eulophids), Systematic Entomology Lab,
USDA; and Dr. L. Stange (mantispids), Division of Plant Industries,
FDACS. Further thanks go to Mr. and Mrs. H.M. Chitty, who
generously allowed me access to the Stardust Ranch for many of ny
experiments. I also acknowledge the Department of Zoology, Sigma

Xi, The Research Society, and the Florida Entomological Society for
their generous financial support during ny graduate program.
Numerous other post doctoral associates and graduate students
in the Zoology Department have listened to my ideas and provided
helpful suggestions. Among these I would especially like to thank
J.B. Anderson, W.W. Henneman, J.R. Lucas, S.B. and B.J. Malcolm,
P.G. May, M.S. Obin, K. Prestwich, N.E. Stamp, and N.T. Wheelwright.
I also extend ny thanks to A.D. Austin and K.E. Redborg for
providing me with relevant manuscripts concerning my research.
I would like to separately thank ny office mate and friend
James A. Cohen (UVPD) for the countless stimulating discussions
concerning my work and biology in general, the lovebug
collaboration, and, in particular, for his influence on ny writing.
Jim, the "big chair" will always be open!
I would also like to separately thank Sherry M. Hieber for
putting up with the late nights, the wild talk, and the oftentimes
crazed behavior of this researcher. I could not have done this
without her support and love.
Finally, I would like to thank my parents, Bernie and Doris
Rieber, who have always told me I could be anything I wanted to be.
iii

TABLE OF CONTENTS
ACKNOWLEDGEMENTS ii
LIST OF TABLES vi
LIST OF FIGURES ix
ABSTRACT xi
CHAPTER I INTRODUCTION 1
CHAPTER II THE EXPERIMENTAL ANIMALS, THEIR
COCOONS, AND THEIR HABITATS 5
Mecynogea lemniscata 5
Argiope aurantia 8
CHAPTER III THE "INSULATION" LAYER IN THE
COCOONS OF ARGIOPE AURANTIA 12
Introduction 12
Materials and Methods 13
Results 15
Discussion 20
CHAPTER IV THE ROLE OF SPIDER EGGS AND
COCOONS IN RESISTING WATER LOSS 25
Introduction 25
Materials and Methods 26
Results 29
Discussion 36
CHAPTER V THE ROLE OF THE COCOON IN
LIMITING EXCESS WATER AND
FUNGAL ATTACK 1+2
Introduction 1+2
Materials and Methods 1+3
Results 1+7
Discussion 5^
iv

CHAPTER VI THE ROLE OF THE COCOON IN
LIMITING EGG AND SPIDERLING
PREDATORS 62
Introduction 62
Materials and Methods 64
Results 71
Discussion 89
CHAPTER VII COCOON SPACING AND THE TIMING OF
PRODUCTION AS METHODS TO AVOID
EGG AND SPIDERLING PREDATORS 100
Introduction 100
Materials and Methods 102
Results 104
Discussion 113
CHAPTER VIII GENERAL DISCUSSION AND
CONCLUSIONS 125
General Discussion 123
Conclusions 143
LITERATURE CITED 146
BIOGRAPHICAL SKETCH 155
v

LIST OF TABLES
Table 4-1. The distributions of sphere sizes
found on the chorionic surfaces of
Mecynogea lemniscata and Argiope
aurantia eggs 31
Table 4-2. Mean percentages of eggs successfully
hatched at the four experimental humidities
for intact Mecynogea lemniscata and Argiope
aurantia egg masses with and without cocoons,
and for reduced A. aurantia egg masses without
cocoons 32
Table 4-3* Mean percentages for molting success
and spiderling survival at the four
experimental humidities for Mecynogea
lemniscata egg and spiderling masses with
and without cocoons 34
Table 4-4. Mean percentages for hatching and
molting success and spiderling survival
in the field for the spiders Mecynogea
lemniscata and Argiope aurantia 35
Table 4-5* Mean percentages for molting success
and spiderling survival at the four experimental
humidities for Argiope aurantia egg and
spiderling masses with and without cocoons 37
Table 5-1 The effect of modification of the
cocoon suspension system and cover on the
incidence of fungal attack on the eggs of
Mecynogea lemniscata 52
Table 5-2. The effect of modification of the
cocoon suspension system and cover on the
incidence of fungal attack on the
spiderlings of Mecynogea lemniscata 53
Table 5-3 The effect of modification of the
cocoon suspension system and cover on the
incidence of fungal attack on the eggs of
Argiope aurant ia 55
vi

Table 5-4. The effect of modification of the
cocoon suspension system and cover on the
incidence of fungal attack on the
spiderlings of Argiope aurantia 56
Table 6-1. Numbers of Mecynogea lemniscata
cocoons attacked by various predators for
the years 1981 to 1983 72
Table 6-2. The effect of modification of the
cocoon suspension system and cover on the
incidence of predator attack on the eggs
of Mecynogea lemniscata 74
Table 6-3. The effect of modification of the
cocoon suspension system and cover on the
incidence of predator attack on the
spiderlings of Mecynogea lemniscata j6
Table 6-4. Numbers of Argiope aurantia cocoons
suspended in the vegetation which were
successfully attacked by various predators for
the years 1981 to 1983 77
Table 6-5. The mean percentage of eggs which
survive in Argiope aurantia cocoons attacked
solely by various predators 8l
Table 6-6. Means for the variables cocoon
diameter, cocoon length, egg mass diameter,
egg mass length, distance to the egg mass,
and ovipositor length 84
Table 6-7. The mean numbers of suspension
line deltas and oviposition holes in the
upper, middle, and lower thirds of the
covers of Argiope aurant ia cocoons 85
Table 6-8. The effect of modification of the
cocoon suspension system and cover on the
incidence of predator attack on the eggs
of Argiope aurant ia 87
Table 6-9. The effect of modification of the
cocoon suspension system and cover on the
incidence of predator attack on the
spiderlings of Argiope aurant ia 88
vii

Table 7-1. Densities of Mecynogea lean is cat a
cocoons, and the percentages of cocoons
attacked for the years 1981 to 1983 10p
Table 7-2. Mean numbers of Mecynogea lemniscata
cocoons per string, and the mean number of
eggs in each cocoon in the string for the
years 1981 to 1983 109
Table 7-3. A comparison of the contents of
attacked Mecynogea lemniscata cocoons 110
Table 7-^. The number and distribution in
space and time of all Mecynogea lemniscata
web-sites with cocoons, and of sites
with cocoons in the proper stage for
attack in the experimental plot for 1983 112
Table 8-1. The mean sphere density and median
clutch size for individual spiders from
different families 131
viii

LIST OF FIGURES
Figure 2-1. A string of Mecynogea lemniscata
cocoons 6
Figure 2-2. The cocoon of Argiope aurantia 9
Figure 3-1. Cooling rates in still air in the
laboratory for whole and modified Argiope
aurantia cocoons l6
Figure 3-2. Cooling rates outdoors for whole
and modified Argiope aurantia cocoons in
an artificial closed habitat over a 50 min
period during an approximate 2.5 0 change
in ambient temperature l8
Figure 3-3. Heating rates in still air outdoors
for whole and modified Argiope aurantia cocoons
under radiant loads of 2 and 10 min duration 19
Figure 3-4. The relationship of internal cocoon
temperature to habitat position for two
Argiope aurant ia cocoons 21
Figure 4-1. The layer of spherical mucoid
granules on the chorionic surface of a
Mecynogea lemniscata egg and an Argiope
aurantia egg 30
Figure 5-1* The rate of water loading in the
laboratory for the covers of Mecynogea
lemniscata cocoons submerged in distilled
water 50
Figure 6-1. A schematic view of an Argiope
aurantia cocoon showing the four measurements
taken to determine the position of the egg mass
in relation to the cocoon cover 66
Figure 6-2. The relationship between the
diameter of Argiope aurantia cocoons
and the number of spiderlings (eggs)
therein 68
ix

92
Figure 6-3. The covers of the cocoons of
Mecynogea lemniscata and Argiope aurantia
comparing the differences in the
tightness of the weaving
Figure 6-b. The ovipositor of the ichneumonid
Tromatobia ovivora rufopectus showing
recessed pits along its length and
concentrated at the tip 95
Figure 7-1. The relationship between
proportional survival and cocoon density
for Mecynogea lemniscata cocoons in
four different sites 107
Figure 7-2. The relationship between
proportional survival and cocoon density
for Mecynogea lemniscata cocoons
within one site 108
Figure 7-3. The number of Meycynogea lemiscata
cocoons in a three-cocoon string available
to a Tetrastichus wasp or her emerging
progeny assuming an 11-day period for attack,
or a more conservative 5-day period 119
Figure 7-^. The spatial distribution of all
the Mecynogea lemniscata web-sites in
the experimental plot for 1983 121
Figure 8-1. The relationship between mean
sphere density and clutch size for
individual spiders from different
families
133

Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment
of the Requirements for the Degree of
Doctor of Philosophy
THE ROLE OF THE COCOONS OF ORB-WEAVING SPIDERS
By
Craig S. Hieber
December, 1984
Chairman: John F. Anderson
Maj or Department: Zoology
The cocoons of spiders are believed to function in protecting
the enclosed eggs and spiderlings from a number of biotic and
abiotic factors. It has also been suggested that the wide diversity
in cocoon architecture is the result of a "coevolutionary arms-race"
between spiders and predators of their offspring. However, few
studies have provided evidence to support these claims. This study
provides evidence for some of these suggested functions by comparing
the abilities of the cocoons of Mecynogea lemniscata and Argiope
aurantia to control or limit temperature extremes, dessication, and
attack by fungi and predators.
Results indicate that the cocoon of M. lemniscata limits
dessication and fungal attack on the spiderling stage. In contrast,
the cocoon of A. aurantia does not. Both cocoons probably play a
xi

limited role in controlling temperature extremes from short-term
radiant loads.
The cocoons of both species play a significant role in
protecting the eggs and spiderlings from generalist and specialist
predators. The association between the various layers making up
these cocoons, and the specific methods used to gain entrance by
their predators strongly supports the notion of a co-evolved system.
However, the multiple functions of many cocoon components suggest
the architectural details have probably resulted from diffuse
evolutionary pressure from a number of simultaneously operating
factors, instead of as counter-adaptations to specific predators.
In general, these results support many of the previous
suggestions concerning cocoon function. Although specific functions
are related to specific components within the cocoon, there can be
great interspecific variation with relation to cocoon size and the
relative sizes or thicknesses of the component parts of the cocoon.
In addition, factors such as the size of the egg mass, the
ultrastructure of the eggs, the habitat used for oviposition, the
position of the cocoon within the habitat, and the reproductive
behavior of the spider may also influence the ability of any part of
the cocoon, or the whole structure, to limit the effects of any or
all of the suggested factors affecting egg and spiderling survival.
xii

CHAPTER I
INTRODUCTION
All spiders place their eggs in some form of silken cocoon
(Turnbull 1973) For some, the cocoon is a relatively simple
structure consisting of a few threads (e.g., the Pholcidae) and is
used to move the egg mass about the web. In others, the cocoon
provides a more complete container for carrying the eggs while
hunting (e.g., the Lycosidae) or an additional level of protection
for spiders which actively guard their eggs (e.g., the Oxyopidae).
For many web-building spiders (e.g., the Araneidae), the cocoon is
an elaborate structure composed of a variety of layers and is
suspended in the habitat by different devices (McCook 1890, Scheffer
1905, Kaston 19^8, Turnbull 1973). In many araneids where active
care is non-existent, the cocoon represents the sum total of
maternal care given to the eggs and spiderlings by the female.
Many web-building spiders deposit large clutches of eggs
(Kaston 19^+8, Foelix 1982). Within the cocoon, the eggs undergo
embryonic development, hatch to the deutova stage, and molt to the
spiderling stage. The spiderlings can spend as long as 6 to 10
months in the cocoon overwintering until emergence in the spring
(Anderson 1978). This long time interval, the large clutch sizes,
and the absence of active maternal care have led to many suggestions
concerning the function of cocoons. These include providing
physical support for the egg mass (Christenson and Wenzl 1980),

2
protecting the enclosed eggs and spiderlings from thermal extremes
(McCook 1890, Kaston 1948, Turnbull 1973, Gertsch 1979), dessication
(Foelix 1962), fungal attack (Christenson and Wenzl 1980), drowning
(Reichert 1981), UV light (Yoshikura 1969), and predator and
parasite attack (Moore 1977, Austin and Anderson 1978, Robinson
1980, Austin, In press). Few studies, however, have examined the
cocoons' effectiveness in controlling these factors.
I present here the results of several studies bearing on the
functional roles that the cocoons of Mecynogea lemniscata
(Walckenaer) and Argiope aurantia Lucas (Araneidae) play in
protecting eggs and spiderlings from a number of biotic and abiotic
factors. I also present results on the significance of cocoon
timing and spacing, and how they interact with cocoon architecture
to reduce predation. Both of these spiders use cocoons with dense
covers (as opposed to the flocculent silk cocoon used by other
araneids). However, they inhabit different environments, construct
cocoons of different size and complexity, produce differing numbers
of clutches, reproduce at different times of the year, and are
attacked by different parasites. These differences are discussed in
detail in Chapter II.
In Chapter III, I examine the role that cocoons, and in
particular the flocculent silk layer within many cocoons, play in
controlling temperature extremes. Many authors have suggested that
the flocculent silk layer acts as insulation (McCook 1890, Kaston
1948, Turnbull 1973, Gertsch 1979) Published reports on this
function have been contradictory. Schaefer (1976) reported that

3
the cocoons of Floronia bucculenta (Clerck) (Linyphiidae) protect
the eggs from daily changes in ambient temperature. In contrast,
Austin and Anderson (1978) concluded that the flocculent silk cocoon
of Nephila edulis (Koch) (Araneidae) does not do so.
Chapter IV presents a comparative analysis of the capabilities
of the cocoons of A. aurantia and M. lemniscata to control water
loss. Although this is commonly assumed to be one of their major
functions (e.g. Brispowe 19^1, Foelix 1982), the data supporting
this view are contradictory. Schaefer (1976) showed that the cocoon
of F. bucculenta effectively controlled water loss from diapausing
eggs. However, Austin and Anderson (1978) demonstrated that the
flocculent silk cocoon of N. edulis had no effect on egg hatching
success. Casual observations by McEwon (1963) suggest that the
cocoon of an Australian Nephila species limits spiderling
desiccation.
Closely related to the problem of desiccation is the problem of
excess water which, if allowed to enter the cocoon, could dissolve
materials from the surface of the eggs and increase their
susceptibility to disease (Austin and Anderson 1978). Water
entering the cocoon could also carry pathogens (Christenson and
Wenzl I960) or could drown the eggs or developing spiderlings.
Although Reichert (1981) strongly suggests that the cocoons of
Agelenopsis aperta (Gertsch) (Agelenidae) protect eggs from
flooding, only Schaefer (1976) and Austin (1984) have demonstrated
such a role for a cocoon or brood nest, respectively. In Chapter V,
I compare the abilities of the cocoons of M. lemniscata and

A. aurantia to control the entrance of excess water and to limit
fungal attack.
In Chapter VI, I examine the architecture of the cocoons of
M. lemniscata and A. aurantia and its relation to the control of
predator and parasite attack. Although considered one of the
primary roles of cocoons (Austin and Anderson 1978, Robinson 1980,
Austin, In press), this function has not been examined for any
spider.
Many parasites locate their hosts in a stepwise manner using a
variety of chemical and physical cues (Salt 1935, Vinson 1975,
1976). A number of biotic and abiotic factors have been suggested
as disrupting these cues, thereby affecting the success of the
parasites (Hassell 1971, Hassell and May 1973, Vinson 1976, Morrison
and Strong 1980, Stiling and Strong 1982). However, host behaviors
such as the phenology of emergence and their effects on the temporal
\
and spatial distribution of the host have not often been considered
as factors affecting parasite success. In Chapter VII, I examine
the seasonal timing of reproduction, the length of the reproductive
season, the timing of cocoon production, and the resulting spatial
and temporal distribution of cocoons as methods used in conjunction
with cocoons to interrupt the foraging behavior of egg predators.
Chapter VII summarizes my major results and discusses their
relevance to the architecture of cocoons and to the diversity of
reproductive tactics displayed by orb-weaving spiders.

CHAPTER II
THE EXPERIMENTAL ANIMALS, THEIR COCOONS, AND THEIR HABITATS
Mecynogea lemniscata (Walkenaer),
the Basilica Spider
In northern Florida (at ny study sites), M. lemniscata emerges
in late March. Males mature in May and are found on the webs of
females from early June to early July. The females mature in late
May. Oviposition starts in mid-June and extends to mid-August with
a peak in mid-July. Females disappear from their webs by late
August.
The eggs of M. lemniscata take 16 days to eclose to the
deutoval stage at 25C and 70* RH. The deutoval stage lasts 4 days
until the molt to the first instar spiderling stage (Hieber 1984).
The spiderlings remain in the cocoon through the late summer, fall,
and winter, and emerge in mid- to late March the following year
after spending approximately 290 days in the cocoon (Anderson 1978).
The webs of M. lemniscata are placed in the shrub layer of
deciduous forests, approximately 1-2 m above the ground. The
cocoons are deposited at the web site, suspended above the domed
orb-web from a single support line (Fig. 2-la). The cocoons are
produced sequentially, and the strings may contain 1-10 cocoons (X =
3.1 cocoons, SD = 1.6, n = 38). The individual cocoons are small
(3-4 mm dia.) (Fig. 2-lb), and contain 8-30 eggs (X = 13.5 eggs, SD
= 6.3, n = 35) (Hieber 1984). The cocoon covering is olive-green in
5

B.
C.
4 mm
Fig. 2-1. A string of Mecynogea lemniscata cocoons suspended in the
vegetation (A), showing the relative size of the cocoons (B), and
with the external layer of silk peeled away to show the individual
cocoons underneath (C). The external layer of silk is composed of
old orb-webs applied to the cocoon string by the female spider.
This layer also contains detritus and prey remains.

7
color, extremely hard, and tightly woven. Internally, there is a
thin flocculent silk layer between the loose, non-agglutinated mass
of eggs and the cocoon cover. The eggs are not enclosed in a
membranous silk bag. The cocoons in a string are periodically
covered with the damaged orb-web when it is replaced by the spider,
giving the cocoon string an additional layer of loose dirty grey
silk, detritus, and prey remains (Fig. 2-lc).
The eggs in M. lemniscata cocoons are attacked by two principal
predators, the neuropteran Mantispa viridis Walker (Mantispidae) and
the hymenopteran Tetrastichus sp. (Eulophidae) [near T. banksii
Howard; see Hieber (1984)]. The eggs and spiderlings may also
occasionally be attacked by ants, particularly if the support line
breaks and the cocoons contact nearby vegetation or fall to the
ground.
Mecynogea lemniscata is found in the shrub layer of southern
deciduous forests (Levi 1980). In Florida, this spider prefers
mesic hammocks, but can occasionally be found in more open habitats
such as upland woods. In its preferred habitat, the humidity
remains relatively constant (7585% RH) during June and July (the
egg laying and molting period) due to the overhead vegetation. From
August on, the habitat dries and uhe RH may fall to 50$ between
rains. During the fall and winter, RH may fall as low as 30-40%.
The temperature in this habitat is somewhat buffered due to the
overhead vegetation which blocks the sun and it remains relatively
constant (25-29 C) during the summer. From fall on, the
temperature in the habitat follows the ambient temperature closely.

8
Argiope aurantia Lucas,
the Black and Yellow Garden Spider
In northern Florida (at ray study sites), male A. aurantia
mature in July and are seen on the webs of females from
approximately mid-July to mid-August (see Levi 1968). Females
mature in late July to August (see Levi 1968). Oviposition starts
in early August and continues to October, with the greatest number
of clutches laid in mid-August to mid-September. Females disappear
from most study sites by late October.
Development to the deutoval stage (eclosin) takes
approximately 20-25 days in the laboratory at 25 C and 70-100# FJi
(see also Anderson 1978, Riddle and Markezich 1981). The deutoval
stage lasts approximately 6 days before the molt to the pigmented
first instar spiderlings. These spiderlings remain in the cocoon
until late April or early May of the following year when they
emerge.
Argiope aurantia builds its webs primarily in old field
vegetation, or in the vegetation at field edges. Its cocoons are
large brown spheres, 1-2 cm in diameter. Females deposit their
cocoons singly, away from the web site, suspended in the vegetation
0.5 to 4.0 m above the ground by a cloud of fine support lines
originating from "minute conical or pyramidal deltas" on the cocoon
surface (McCook 189O; pg. 75) (Fig. 2-2a). The cocoons are
multi-layered (Fig. 2-2b). The outer covering is usually composed
of a thin, stiff, parchmentlike material with a glazing applied to
it (almost like fiberglass), although it may occasionally be made of

9
Fig. 2-2. The cocoon of Argiope aurantia suspended in the
vegetation (a), and in cut away view (B) showing the position of the
egg mass (em), silk cap (sc), silken cone and cord (scd), and
flocculent silk layer (fsl) within the cocoon cover (cv).

10
a soft, thick, feltlike material. The agglutinated egg mass of
800-2000 eggs (X = 978.7 eggs, SD = 1+19.2, n = 1+0) is suspended
within the cocoon from a thick silk cup, which in turn is attached
to a cone and cord of strong silk which fills the stalk of the
cocoon. The egg mass is covered by a fine membranous layer of silk,
and is separated from the cover by a thick flocculent silk layer
(see McCook 1890, pp. 79-80 for a complete description of the
internal structure of the cocoon).
The eggs and spiderlings in A. aurantia cocoons are attacked by
a number of general and specialized predators including the
hymenopterans Tromatobia ovivora rufopectus (Cresson)
(ichneumonidae) (Cresson 1870, Keobele 1887, McCook 1890, Howard
1892, Champlain 1922, Enders 197, Tolbert 1976), Pimpla aquilonia
aquilonia (Cresson) (ichneumonidae) (Davidson 1896), Chrysocharis
banksii and Chrysocharis pikei (Entodontimidae) (McCook 1890), and
Pediobius wilderi (Howard) (Entodontimidae) (McCook I89O) [this is
probably a hyperparasite attacking T. ovivora rufopectus]; the
dipterans Pseudogaurax signata (Loew) (Chloropidae) (Coquillet
1898), Pseudogaurax anchora (Loew) (Kaston and Jenks 1937, Eason et
al. 1967), and Megaselia sp. (Phoridae) (Kaston and Jenks 1937);
the neuropteran Mantispa viridis Walker (Mantispidae) (Enders 1974,
Tolbert 1976); the coleopteran Chauliognathus sp. (Cantharidae)
(Enders 1974); salticid spiders (Salticidae) (Enders 1974); and
birds (Enders 1974, Tolbert 1976).
Argiope aurantia prefers vegetation along water courses in
Florida (Levi 1968), and is common in roadside hedgerows bordering

11
drainage ditches. In these habitats, the relative humidity is
usually quite high (70-90% RH) in late August-September (the
egg-laying and molting period), although exposure to high levels of
insolation may cause periodic fluctuations of the RH over a wide
range. By late fall, the RH may drop to 30-40%. The temperatures
may be buffered somewhat by the vegetation in the summer, but are
usually relatively close to ambient, although they may be quite high
(35-40 C) in southern exposures. From fall on, the temperatures
in the habitat follow ambient air temperature closely.

CHAPTER III
THE "INSULATION" LAYER IN THE COCOONS OF ARGIOPE AURANTIA
Introduction
All spiders place their eggs in some form of silken cocoon
(Turnbull 1973). These structures must provide protection for the
eggs, create a proper microclimate for embryonic development,
hatching, and subsequent molting, and provide a safe retreat for the
spiderlings to overwinter until emergence in the spring. Because of
the lengthy development and overwintering period of some spiders
(Anderson 1978), many cocoons are exposed to severe temperature
extremes. Fluctuations in cocoon temperature have been shown to
have a direct effect on the development and survival of spider eggs
(Norgaard 1956, Schaefer 1976) and spiderlings (Norgaard 1956).
Several authors have observed spider behaviors which presumably
modify the thermal environment of the cocoon. These include burying
the cocoon (Levi and Levi 1969), shuttling the cocoon between
different microclimates (Norgaard 1951, Humphreys 197*0, and placing
it in protected microclimates. Others have suggested that a layer
of silk within some cocoons functions as insulation, modifying the
thermal environment experienced by the eggs or spiderlings (McCook
I89O, Kaston 1948, Turnbull 1973, Gertsch 1979). Schaefer (1976)
reported that the cocoons of Floronia bucculenta (Clerck)
(Linyphiidae) are capable of protecting the eggs from daily
12

13
fluctuations in ambient temperature. However, Austin and Anderson
(1978) found no significant differences in the hatching success of
spider egg masses, with or without cocoons, exposed to a range of
constant temperatures. They concluded that the flocculent silk
cocoons of Nephila edulis (Koch) (Araeidae) did not function to
protect the eggs from temperature extremes.
The cocoon of Argiope aurantia Lucas (Araneidae) is a
multilayered structure, with a flocculent layer of silk located
between the eggs or spiderlings and the cocoon cover (see
Fig. 2-2b). In late August-September, the cocoons are usually
placed in the upper strata of the vegetation where they may be
exposed to direct sunlight, wind, and the night sky, all of which
may alter the internal temperature of the cocoon throughout the
development and overwintering period. Here, I examine the the role
of the cocoon, and in particular the effectiveness of the flocculent
silk layer within A. aurantia cocoons, in buffering temperature
extremes. I also examine the role that cocoon positioning in the
habitat plays as an adjunct method of temperature regulation.
Materials and Methods
I used three types of cocoons: whole, nonparasitized cocoons
containing spiderlings, and two types of modified cocoons,
"insulated" and "non-insulated". The latter two types were created
by halving whole cocoons longitudinally with a razor blade and
removing either the eggs alone, or the eggs and the flocculent silk
layer. The halves of these modified cocoons were rejoined with

clear nail polish. These whole and modified cocoons were mounted on
thermal probes (YSI #513, time constant of 0.02 s), with the tip of
the probe in the approximate position of the egg or spiderling mass.
Cocoons were allowed to equilibrate to room temperature (T =
26 C) in a large cardboard enclosure, and then placed in a
styrofoam cooler packed with salted ice. The internal temperature
of the cocoon in the cooler was recorded every 30 s until it reached
the ambient temperature of the cooler (T& = 8-9 C). The cooling
trials were performed in a dark room to avoid radiant loading from
the overhead lights, and with the air conditioning off to minimize
the effects of convective cooling from air movement. The walls of
the cardboard enclosure and the cooler were monitered with banjo
probes (YSI #427, time constant of 1.10 s) taped to the inner
surfaces. The temperatures of these surfaces matched the ambient
air temperatures within each container. Only data from trials where
the ambient temperature in the cooler varied by no more than
0.5C were used for the calculation of the cooling curves.
In the field, the changes in internal temperatures of whole and
modified cocoons (using YSI #513 probes) in an artificial closed
habitat (l x 1 x 1 m cardboard enclosure) were recorded at one min
intervals for 50 min over an approximate 2.5 C drop in ambient air
temperature. On a different day, changes in internal temperatures
(YSI #513) of whole and modified cocoons exposed to 10 min radiation
loads, and to 2 min loads followed by 8 min of cooling were also
recorded. This experiment was conducted between 1100 and 1300 h
when the sun was at its zenith. During this time, ambient

15
temperature was relatively constant (12.9-13.6 C), and there was
no wind. All the cocoons used in this experiment were approximately
the same size, color, and mass. On a third day, the hourly changes
in ambient air temperature (YSI #405 probe, time constant of 0.60 s)
and in the internal (YSI #513) and surface temperatures (YSI #427)
of two cocoons in two different habitats (closed canopy under trees,
open canopy in an old field) were recorded for 24 h. Simultaneous
measurements of the sky and vegetation temperatures or enclosure
wall temperatures were made with a Stoll-Hardy HL4 radiometer during
all of the field experiments to measure the radiant heat load in the
respective test habitats.
Results
There were no significant differences between the slopes of the
cooling curves for the modified cocoons (Fig. 3-1). Both types of
modified cocoons showed cooling rates of approximately 11 C/ min.
In contrast, the whole cocoons cooled significantly more slowly than
the modified cocoons (F = 356.71, p < 0.001); the presence of
spiderlings (total cocoon weights 0.63 to 0.93 g; spiderling weights
O.56 to 0.83 g) decreasing the cooling rate to approximately 2.0
C/ min (Fig. 3-1).
Outdoors, in the artificial closed habitat, there were no
significant differences between the rates of cooling for the whole
cocoon (total weight 0.809 g; spiderling weight 0.682 g), and the
modified cocoons with and without the flocculent silk layer.

l6
Fig. 3-l Cooling rates in still air in the laboratory for whole
and modified Argiope aurantia cocoons. The whole cocoons (squares)
contained spiderlings and the flocculent silk layer; the modified
cocoons contained only the flocculent silk layer (open circles), or
were empty (closed circles). The cooling curve for the whole
cocoons is Y = -0.208X + 2.73 (r = 0.95, n = 6); for the modified
cocoons with the flocculent layer Y = -0.824X + 2.85 (r = O.96, n
= 10); for the empty cocoons Y = -O.SlOX + 2.66 (r = 0.90, n = 8).
During cooling T = 8-9 C. The data points represent the range
for each set of experimental trials.

IT
The internal temperatures of all three cocoons closely followed the
change in ambient temperature (Fig. 3-2).
Among the cocoons exposed to radiation loads for 10 min, there
was no significant difference between the rates of heating for the
modified cocoon with the flocculent silk layer and the cocoon
without it (Fig. 3-3). Both cocoons heated rapidly to an
equilibrium temperature of 22.5 C in approximately 5 min. The
rate of heating for the whole cocoons (total weights 0.9735 g and
0.9025 g; spiderling weights 0.7500 g and 0.7^00 g, respectively)
was significantly different from that for the modified cocoons (F =
26.ll, p < 0.0001; calculated for the first U min). These cocoons
heated to approximately 19.0 C in 5 min; an internal temperature
some 3.5 C cooler. Beyond this point, they heated at a slower
rate. An extension of this second, flatter heating curve suggests
that the whole cocoons would not reach the equilibrium temperature
of the modified cocoons until another 15 min had elapsed.
The whole and modified cocoons exposed to the 2 min loads
heated at the same rates as their counterparts in the 10 min group
(Fig. 3-3). The rates for the two groups of cocoons were
significantly different from one another as well (F = 7.^90, p =
0.03*+; calculated on the first 2 min). When the radiation load was
removed, the modified cocoons rapidly cooled to ambient air
temperature. The whole cocoons also cooled upon removal of the
load, but at a much slower rate (Fig. 3-3).
The absolute internal temperature achieved by whole cocoons in
the field depended on their location in the habitat. While the

18
Fig. 3-2. Cooling rates outdoors for whole and modified Argiope
aurantia cocoons in an artificial closed habitat (l x 1 x 1 m
cardboard enclosure) over a 50 min period during an approximate
2.5 C change in ambient temperature. The whole cocoon (squares)
contained spiderlings and the flocculent silk layer; the modified
cocoons contained only the flocculent layer (open circles), or were
empty (closed circles). The cooling curve for the whole cocoon is Y
= 0.067X 1.57 (r = 0.99, n = l); for the modified cocoon with
the flocculent layer Y = O.O66X 1.6l (r = 0.99 n = l); for the
empty cocoon Y = O.O65X 1.50 (r = O.98, n = l). The curve for
the change in ambient temperature (stars) is Y = 0.060X 1.90 (r
= 0.99)* The temperatures of the top and sides of the enclosure
during this period were 4 C and 5 C, respectively.

19
Fig. 3-3. Heating rates in still air outdoors for whole and
modified Argiope aurantia cocoons exposed to radiant loads of 2 and
10 min duration. The whole cocoons (open squares, 2 min; closed
squares, 10 min) contained spiderlings and the flocculent silk
layer; the modified cocoons contained only the flocculent layer
(stars, 2 min; open circles, 10 min), or were empty (closed circles,
10 min).^ The heating curve for the whole cocoons is Y = 0.50X +
13.4U (r = O.98, n = 2); for the modified cocoons with the
flocculent layer Y = 1.01X + lU.29 (r = 0.93, n = l); for the
empty cocoons Y = O.96X + 1U.U7 (r2 = 0.9^, n = l). The ambient
air temperature during the experiment ranged from 12.9 C to 13.7
C. The vegetation and sky temperatures during the experiment were
+15 C and -20 C, respectively.

20
cocoon (total weight 0.820 g; spiderling weight 0.724 g) in the
sheltered site (under overhanging vegetation) attained highs and
lows close to the ambient air temperature, the internal temperature
of the cocoon (total weight 0.991 g; spiderling weight 0.842 g) in
the exposed site (open field) fluctuated widely, attaining much
higher and lower values (Fig. 3-4). The surface temperatures of the
cocoons equaled the ambient temperature in the shade (T =
T ) and were greater than both ambient and the internal temperature
of the cocoons in the sun (T < T > T ).
a surf c
Discussion
Under laboratory conditions, the internal temperatures of whole
and modified A. aurantia cocoons exposed to sudden drops in ambient
temperature (from 2 C to 8-9 C) do not change instantaneously
(see Fig. 3-1), indicating that some part of the cocoon acts as
insulation. However, under these conditions the cooling rates for
cocoons with and without the flocculent silk layer are identical,
suggesting that it is the cover of the cocoon, and not the
flocculent layer, that creates the dead air space that acts as
insulation (Kaufman et al. 1982). This explains why Austin and
Anderson (1978) found that the coverless, flocculent cocoons of
N. edulis offered no protection to their egg masses; these cocoons
have little or no dead air space. The whole cocoons also cooled
four times more slowly than the modified cocoons (see Fig. 3-1).
Presumably, this additional thermal inertia is due to the mass of
the spiderlings, which are approximately 70% water (Anderson 1978).

21
habitat position for two Argiope aurantia cocoons. The solid lines
( ) are ambient temperatures, and the dashed lines ( ) are
internal cocoon temperatures. Over 2k h, the cocoon in the open
habitat (old field) was exposed to extended periods of direct
sunlight, andQfaced greater reflected radiation from the vegetation
(32 C to -15 C), and colder sky temperatures (2 C to -39 C)
bhan the cocoon in the closed habitat (old field edge under trees)
faced from the vegetation (25 C to -10 C), or from the sky (25
C to -17 C).

22
The cocoon, in combination with the egg or spiderling mass,
acts as a buffer against rapid temperature changes (Fig. 3-1) Such
rapid changes could result from exposure to the night sky
immediately after sundown, particularly in the winter (see
Fig. 3-4). However, most A. aurantia cocoons are placed within the
vegetation. In these protected locations, radiant heat loss to the
cold night sky is reduced by the warmer overhead vegetation. Under
these conditions, cooling is slower and follows the change in
ambient air temperature (see Fig. 3-2). Cold hardiness (Schaefer
1977, Riddle 1981) resulting from physiological solutions such as
freezing point depression (Kirchner and Kestler 1969) probably
protects the eggs or spiderlings from extremely cold temperatures.
Cocoons in open habitats but under a layer of vegetation, or in
closed habitats such as woods may still be exposed to periodic
"sunflecks" as the sun moves across the sky. These short lived, but
potentially intense, radiant loads could present a serious thermal
challenge to the cocoon. The field experiments indicate that the
cocoon and the mass of the eggs or spiderlings provide a significant
buffer against short-term loads (see Fig. 3-3), extending the
heating time to equilibrium by approximately 15 min. However, the
level of protection provided by a cocoon is directly related to the
ambient air temperature, the duration of the load, and the elapsed
time between consecutive loads. The radiant loading experiments
were conducted in the winter, when the ambient air temperature was
relatively low (12-14 C). Even with constant exposure to
insolation, low ambient temperatures such as these would result in a

23
low equilibrium temperature (Heath 1964) that is probably below the
danger level for the spiderlings in the cocoon. However, during the
early part of the reproductive season, when the ambient temperature
is relatively high, radiant loads may represent a more serious
problem. Under these conditions, a load of long duration could
raise the equilibrium temperature of the cocoon past the safe limit
for the eggs or spiderlings. Loads of short duration also pose a
problem if they occur in rapid enough succession. Under these
conditions, the internal temperature of the cocoon would "step" up
with each successive load due to the slow rate of heat loss from the
egg or spiderling mass (see Fig. 3-3), finally rising above the
lethal limit.
Other behaviors may play a role in insuring that the cocoon is
not exposed to lethal thermal loads. Argiope aurantia prefers to
oviposit beneath a layer of vegetation or among the leaves of
broad-leafed plants. Such sites would limit the number and length
of insolation bouts the cocoon encounters, particularly during the
late summer when oviposition occurs. The comparison of internal
temperatures from cocoons in open and closed habitats supports
maternal positioning of the cocoon as an important control measure
(see Fig. 3-4). Positioning the cocoon in a closed site rather than
in an open site resulted in a 10 C difference between the highest
internal temperature achieved (because of radiation loading), and a
4 C difference in the lowest temperature achieved (because of
exposure to cold night sky temperatures). Although spiderlings can
tolerate high temperatures (Tolbert 1979), proper site choice could

2k
mean a few degrees difference in internal cocoon temperature. This
difference may be important when the ambient temperature approaches
the upper critical temperature of the eggs or spiderlings.
The limited ability of the relatively large A. aurantia cocoons
to resist temperature fluctuations suggests that cocoons with
smaller masses of eggs or spiderlings will have more difficulty in
controlling temperature extremes. The non-functional role of the
flocculent silk layer as insulation further suggests that cocoons
may function to regulate other factors in the environment. Due to
the small size of the eggs and spiderlings, and their consequent
high surface area to volume ratio, it seems likely that cocoons may
play a role in limiting water loss. This role is explored in
Chapter IV.

CHAPTER IV
THE ROLE OF SPIDER EGGS AND COCOONS IN RESISTING WATER LOSS
Introduction
All spiders enclose their eggs in some form of silken cocoon
(Turnbull 1973)- Within these structures the eggs undergo embryonic
development, hatch to the deutova stage, and molt to the spiderling
stage. The spiderlings then spend from 6 to 10 months in the
cocoons until emergence in the spring. Dessication may be a problem
for these developmental stages. Many insects use cocoon-like
structures to limit dessication (Chapman 1967, Chauvin et al. 1979),
and this is commonly assumed to be the function of cocoons as well
(Bristowe 1941, pg. 421; Foelix 1982, pg. 200). Few data exist,
however, to support this view. Schaefer (1976) showed that the
parchmentlike cocoon of Floronia bucculenta (Clerck) (Linyphiidae)
increased the survival time of post-diapause eggs exposed to a RH of
32/i (at 5 C) from 37 to 68 days. Austin (1984) has demonstrated
that the silk nests containing eggs of Clubiona robusta L. Koch
(Clubionidae) increases humidity levels. The casual observations of
McEwon (1963) also suggest that the flocculent cocoon of an
Australian Nephila sp. (Araneidae) provides desiccation protection
for the spiderlings. Austin and Anderson (1978), however, have
showed that the flocculent silk cocoon of the congener N. edulis
25

26
(Koch) has no effect on the hatching success of spider egg masses at
different controlled humidities.
Some spider eggs are dessication-resistant as well (Schaefer
1976). This resistance may result from a layer of spherical
granules on the chorion surface (Austin and Anderson 1978, Grim and
Slobodchikoff 1978, 1982, Humphreys 1983). Overwintering
spiderlings within the cocoon can also attenuate water loss by
reducing their rates of metabolism (Schaefer 1976, Anderson 1978),
or by metabolizing lipids. Presumably, the cuticle of spiderlings
also impedes water loss (Lees 19*+7, Davies and Edney 1952).
I investigate here the role of the cocoon in controlling water
loss from the egg and spiderling masses of Mecynogea lemniscata
(Walckenaer) and Argiope aurantia Lucas (Araneidae) during egg
development, deutoval molting, and spiderling overwintering. I also
examine the effect of clutch size, and egg morphology (Austin and
Anderson 1978, Grim and Slobodchikoff 1978, 1982) on water loss.
Materials and Methods
The Cocoons and Their Habitats
The cocoons of _M. lemniscata and A. aurantia differ in size,
density of the cover, and internal construction. The preferred
habitats of the two spiders also differ, the habitat of
M. lemniscata being more consistently humid than that of A. aurantia
(see Chapter II).

27
Experimental Material
The cocoons and egg masses of A. aurantia were obtained from
spiders collected in the field and maintained at 24-25C and 60-J0%
RH in 500 ml jars in the laboratory. The M. lemniscata cocoons and
egg masses were obtained by daily censusing 100-150 marked
web-sites. The cocoons used in the experiments on spiderling
survival were collected in the field in late August (for
M. lemniscata), and during September-October (for A. aurantia).
Only undamaged, nonparasitized cocoons were utilized. The
experimental spiderling masses were obtained by removing the cocoon
cover and as much of the internal flocculent layer of silk as
possible.
Egg Surface Morphology
The surfaces of M. lemniscata and A. aurantia eggs were
photographed with a Hitachi S-415A SEM. They were prepared by
attaching them to SEM stubs with double-sided tape, and coating with
o
75 A of gold. The densities of the spherical granules (spheres) on
egg surfaces were measured by placing a grid system (4x4 lines)
over the electronmicrographs of five eggs of each species and
counting all spheres within 2 randomly chosen grid-squares. Since
the spheres on both species1 eggs are distributed essentially as
monolayers (Humphreys 1983), densities were expressed as the mean
number of spheres/ 100 ym Sphere diameters were determined
directly by measuring all the spheres within the 10 grid-squares.

28
Effect on Dessication
The effects of the sphere layer, clutch size, and the cocoon on
hatching success, molting success, and spiderling survival were
determined by rearing intact egg and spiderling masses without
cocoons (and appropriate controls) at 25-26 C in one liter jars
controlled at four different RH levels (0%, 33%, 66%, and 100%).
The controlled humidities were achieved by using dry anhydrous KOH
pellets (0% RH), and saturated salt solutions of 300+ g CaCl2/
100ml HO (33% RH), 100 g NaNO^/ 100 ml H20 (66% RH), and 15 g
KgSO^/ 100 ml H20 (100% RH) (Winston and Bates 19^0, Peterson
1964). The pellets and solutions controlling the humidities were
changed every two weeks. Since the egg masses of A. aurantia
contain more eggs than those of M. lemniscata (approximately 970 to
20, respectively), artificially reduced egg masses of 15-25
A. aurantia eggs were also reared under these conditions to control
for the possible effects of egg mass size on hatching success.
The effect of the cocoon was also tested under field conditions
by placing intact egg and spiderling masses (and appropriate
controls) in individual screen-covered vials within styrofoam-cup
housings. These housings protected the replicates from
precipitation, predators, and parasites, and were hung in the shade
in locations where females had previously constructed cocoons.
Hatching and molting success was calculated after 30 days.
Hatching success was the percentage of total eggs in which the
chorion ruptured and a deutova successfully emerged. Molting

29
success was the number of these deutova which successfully molted to
the first instar spiderling stage. Spiderling survival was
determined using separate masses, and was calculated after the
experiments had run for 90 days.
Results
The Sphere Layers
The spheres associated with the eggs of M. lemniscata and
A. aurantia are shown in Fig. 4-1. For both, the sphere diameter
ranged from 0.40 to 7*20 ym. The mean diameter in M. lemniscata
eggs was not significantly different from that of A. aurantia eggs
2
(Table 4-1). However, the mean sphere density (spheres/ 100 ym )
of M. lemniscata eggs was significantly greater (t = 2.11, df = 20,
p < 0.05) than that of A. aurantia eggs.
The Effect of Clutch Size and the Sphere Layer
No significant differences in hatching success at 100$ RH were
found between intact and reduced A. aurantia egg masses without
cocoons at each humidity (Table 4-2). Reduction of the egg mass,
however, did have a significant effect at 66$, 33$, and 0$ RH,
indicating that the size of the egg mass of this spider is important
to dessication control. There were no significant differences at
100$, 66$, and 33$ RH when the hatching success of intact
M. lemniscata and A. aurantia egg masses without cocoons was

30
Fig. h-1. The layer of spherical mucoid granules on the chorionic
surface of a Mecynogea lemniscata egg (A), and an Argiope aurantia
egg (B). The scale line in each case equals 15 ynu Both eggs were
plated with 75 A of gold and observed using secondary electrons.

31
Table 4-1. The distributions of sphere sizes found on the chorionic
surfaces of Mecynogea lemniscata and Argiope aurantia eggs. The
mean sphere sizes and mean sphere densities ( 1 SD; n in
parentheses) are given below the frequency column for each species.
Frequency
Sphere Size
Diam. (ym)
M. lemniscata A.
aurantia
0.40 0.79
9
2
0.80 1.19
57
17
1.20 1.59
104
117
1.60 1.99
47
26
2.00 2.39
12
2
2.1+0 2.79
3
0
2.80 3.19
1
0
3.20 3.59
2
0
3.60 3.99
0
0
4.00 4.39
2
0
4.40 4.79
0
1
4.80 5.19
1
2
5.20 5.59
1
0
5.60 5-99
1
0
6.00 6.39
1
0
6.4o 6.79
0
0
6.80 7.19
1
1
Mean Sphere
x = 1.56 0.79
x = 1.52 0.70
Size
(242)
(168)
Mean Sphere
X = 21.60 5.46
X = 17.00 4.22
Density
(10)
(10)

32
Table 4-2. Mean percentages of eggs successfully hatched ( 1 SD; n
in parentheses) at the four experimental humidities for intact
Mecynogea lemniscata and Argiope aurantia egg masses with and
without cocoons, and for reduced A. aurantia egg masses without
cocoons. Pair-wise comparisons between treatments are by
Mann-Whitney U Tests; pair-wise comparisons between humidities
within treatments are by nonparametric multiple comparison tests
(Zar 1984).
% Hatching Success
M. lemniscata
A.
aurantia
Relative
Humidity
Cocoon
No Cocoon/
Intact
No Cocoon/
Reduced
No Cocoon/
Intact
Cocoon
100 %
94.9
13.5%
(10)
98.3
3-1%
(8)
96.2
4.0%
(5)
99-7
0.5%
(8)
100%
(8)
**
#
66%
95.4
14.6%
(10)
97.4
4.6%
(10)
49.2
*** 36.8% **
(8)
94.3
11.3%
(8)
£
90.0
24.8%
(7)
33%
96.9
7.9%
(10)
88.7
15-5%
(10)
28.7
*** 32.3% **
(10)
87.9
7.0% **
(9)
96.6
5.8%
(7)
***
#**
0%
3.4
7.3%
(10)
3.6
8.3%
(10)
6.7
5.7% ***
(10)
70.4
22.8% *
(8)
88.2
17.5%
(8)
Kruskall-
Wallis H
29.43
25.80
17-70
21.70
8.29
"p"
< 0.001
< 0.001
< 0.001
< 0.001
< 0.05
(* P < 0.
05; ** p <
0.01; *** p
< 0.001)

33
compared at each humidity. There was a significant difference at 0%
RH, underscoring the advantage of a large egg mass.
A different pattern of hatching success was revealed when
intact M. lemniscata egg masses without cocoons were compared to
reduced A. aurantia egg masses without cocoons at each humidity
(Table 4-2). The significant advantage previously demonstrated by
the whole A. aurantia egg masses at 0% RH disappeared, and hatching
success dropped significantly below that of M. lemniscata at 66% and
33% RH, presumably because of differences in the densities of the
the sphere layers covering the eggs of each species. There were no
significant differences at 100% RH, where dessication is obviously
not a problem.
The Effects of the Cocoons
Cocoon removal had no effect on the hatching success of
M. lemniscata at any experimental humidity (Table 4-2). Below 33%
RH, there were significant decreases in hatching success for egg
masses with and without cocoons. Molting success showed no
significant reduction with cocoon removal at any experimental
humidity (Table 4-3). Since few eggs hatched at 0% RH, however, the
percentage of total eggs which ultimately molted was small. The
cocoon did have a significant effect on spiderling survival. At all
the experimental humidities survival was greater with a cocoon
(Table 4-3). The field results support these findings (Table
4-4); only spiderling survival was significantly affected by removal
of the cocoon.

34
Table 4-3 Mean percentages for molting success and spiderling
survival ( 1 SD; n in parentheses) at the four experimental
humidities for Mecynogea lemniscata egg and spiderling masses with
and without cocoons. Pair-wise comparisons between treatments are
by Mann-Whitney U Tests; pair-wise comparisons between humidities
within treatments are by multiple range tests (Zar 1984).
Of
Molting
Success
% Spiderling
Survival
Relative
Humidity
Cocoon
No Cocoon
Cocoon
No Cocoon
100%
100%
(8)
99-1
2.5%
(8)
100%
(13)
80.0
*** 25.1%
(6)
**
66%
100%
do)
100%
(10)
81.9
29.8%
(13)
56.2
** 28.8%
(14)
*
#**
22%
100%
(10)
100%
(10)
47.4
38.1%
(11)
1.0
*** 2.7%
(14)
**
0%
100%
do)
100%
(10)
6.8
13.7%
(14)
** 0%
(14)
Kruskall-
Wallis H
0.00
0.00
35-44
38.22
"p"
1.00
1.00
< 0.001
< 0.001
(* p < 0.05;
** p < 1
0.01; *** p < 0.001)

35
Table 4-4. Mean pecentages ( 1 SD; n in parentheses) for hatching
and molting success and spiderling survival in the field for the
spiders Mecynogea lemniscata (ML) and Argiope aurantia (AA).
Conditions in the field (60-80% RH and 24-32C) approximated the
laboratory conditions at 66% RH. The data are presented as
percentages, but were arc-sine transformed for the statistical
analyses (Sokal and Rohlf 1969).
Spider
% Hatching
Success
% Molting
Success
% Spiderling
Survival
Cocoon
No Cocoon
Cocoon
No Cocoon
Cocoon
No Cocoon
99-6
99.3
98.2
50.T
ML
1-9%
2.1%
100%
100%
12.1%
2T.o%
(19)
(IT)
(19)
(IT)
(21)
(10)
1 *#* 1
Cocoon
No Cocoon
Cocoon
No Cocoon
Cocoon
No Cocoon
99.8
99-8
93.3
91.8
AA
0.1%
0.4%
100%
100%
0.9%
2.9%
(10)
(10)
(10)
(10)
do)
(10)
*** F-test: F = 15.12, df = 29, p = 0.005.

36
The results for A. aurantia differed from those for
M. lemniscata. In the laboratory, cocoon removal had no significant
effect on hatching success at 100%, 66%, or 0% RH, although it did
significantly affect success at 33% RH (Table 4-2). Cocoon removal
had no significant effect on molting success at any experimental
humidity. However, at 33% and 0% RH the variances in the non-cocoon
cells were much larger, suggesting that an effect may have been
difficult to detect. Molting success fell off significantly below
66% RH with and without a cocoon (Table 4-5). The absence of a
cocoon also made no difference in spiderling survival at either 100%
RH or 66% RH (Table 4-5). However, below 100% RH spiderling
survival significantly declined with and without cocoons, and below
66% RH all the spiderlings died after 90 days regardless of the
treatment. The results from the field experiments support the
laboratory results at 100% and 66% RH (Table 4-4). Under field
conditions, cocoon removal had no significant effect on egg hatching
success, molting success, or spiderling survival.
Discussion
The results indicate that the enclosed cocoons of M. lemniscata
and A. aurantia do not affect water loss from the egg stage. These
findings are paradoxical, since they support the findings of Austin
and Anderson (1978) for a flocculent cocoon, but do not agree with
Schaefer's (1976) findings for a covered cocoon. This paradox may
be explained by the amount of time the eggs of these spiders spend
in the cocoon. The developmental times of M. lemniscata

37
Table 4-5. Mean percentages for Molting Success and Spiderling
Survival ( 1 SD; n in parentheses) at the four experimental
humidities for Argiope aurantia egg and spiderling masses with and
without cocoons. Pair-wise comparisons between treatments are by
Mann-Whitney U tests; pair-wise comparisons between humidities
within treatments are by nonparametric multiple comparson tests (Zar
1984).
% Molting % Spiderling
Success Survival
Relative
Humidity
Cocoon
No Cocoon
Cocoon
No Cocoon
98.8
93.7
100%
100%
100%
1.5%
8.2%
(8)
(8)
(7)
(5)
**
*#
99.1
61.5 1
63.5 1
66%
100%
2.0%
27.5%
19.6 %
(7)
(8)
(6)
(8)
***
#*
***
***
96.0
76.2
33%
4.2%
34.8%
0%
0%
(7)
(9)
(8)
(8)
84.4
56.1
0%
19-0%
48.0%
0%
0%
(8)
(8)
(9)
(9)
Kruskall-
Wallis H
22.40
11.09
27.18
27.99
"p"
< 0.001
< 0.01
< 0.001
< 0.001
(* p < 0.05; ** p < 0.01; *** p < 0.001)

38
and A. aurantia are relatively short (15-20 days and 20-30 days,
respectively), and even at low humidities this may not be long
enough to demonstrate the water retaining qualities of the cocoon.
In contrast, the eggs of F. bucculenta remain within the cocoon in
winter diapause for approximately l80 days. Since the eggs are net
particularly drought resistant (Schaefer 1976), they probably lose
water during this time. The significant effect of the cocoon on egg
survival, that Schaefer demonstrated, can probably be attributed to
his use of post-diapause eggs, from which enough water had already
been lost to make the effect of cocoon removal apparent.
The significant difference in hatching success between intact
and reduced A., aurantia egg masses without cocoons demonstrates that
clutch size can affect hatching success as well. Spider egg masses
are usually agglutinated, and as the mass gets larger, its surface
area to volume ratio declines as a greater number of eggs are
positioned completely within the mass. Presumably, this difference
also accounts for the difference in hatching success between intact
_M. lemniscata and A_. aurantia egg masses without cocoons at 0$ RH
(see Table 4-2).
The ability of intact M. lemniscata egg masses without cocoons
to maintain hatching success rates equal to those of the much larger
A. aurantia egg masses at humidities above 0f RH indicates that some
factor other than clutch size is also operating to control water
loss (see Table 4-2). A number of authors have suggested that a
layer of spherical mucoid granules (Austin and Anderson 1978) on the
chorions of spider eggs functions to control water loss by reducing

39
the free surface area through which water can pass (Austin and
Anderson 1978, Grim and Slobodchikoff 1978, 1982, Humphreys 1983)
The eggs of M. lemniscata have a significantly denser coating of
these spheres than do the eggs of A. aurantia (see Table k-l).
Although a direct comparison of the eggs of each of these species
with and without spheres is difficult (due to problems in stripping
the sphere layer from the eggs and still maintaining viability), the
comparison of intact M. lemniscata egg masses with reduced
A. aurantia egg masses strongly suggests that the sphere layer does
reduce water loss (Table 4-2). However, the drop in hatching
success at 0$ RH indicates that this barrier has limits in its
ability to control water loss at very low humidities.
Molting is a dangerous period of time for deutova with their
high surface area to volume ratio (Horner and Starks 1972). At
molting, with the breaking and subsequent shedding of the egg
chorion, dessication protection shifts back to the level of the
cocoon. In spite of this, removal of the cocoons of M. lemniscata
and A. aurantia demonstrate no effect on molting success (see Tables
4-3 and 4-5). However, the variances among the no-cocoon treatments
of A. aurantia at 33$ and 0% RH are high, which may make detection
of the cocoon's effect on molting success difficult. Presumably,
the main factor affecting molting success for these spiders is the
ambient RH at the oviposition site, although the greater molting
success of M. lemniscata at low humidities suggests that there may
be morphological or physiological differences in the abilities of
the deutova of these species to reduce water loss.

4o
The cocoon of A. aurantia also appears to have little effect on
spiderling survival. The lack of a cocoon effect on hatching and
molting success, and the significant drops in molting success and
spiderling survival below 66% RH suggest that other considerations
are more important to reducing desiccation. Field observations of
damaged A. aurantia cocoons suggest that the large clutch size of
this species may protect the eggs from dessication [which may also
explain McEwon's (1963) observation for the Nephila sp.1. However,
the RH within the habitat or microhabitat used for oviposition is
probably most critical for A. aurantia. Indeed, Levi (1968) notes
that of the Argiope species in Florida, A. aurantia prefers moist
habitats such as pond edges and stream borders, and is one of the
first Argiope species to disappear during drought years.
Removal of the cocoon does have a significant effect on the
spiderling survival of M. lemniscata at all experimental humidities
(see Table 4-1), and in the field under ambient conditions (see
Table 4-3). This spider is the first of the orb-weavers to become
active in the spring, emerging in late March. Growth is rapid.
Reproduction begins by late June and the adults die by early to
mid-August. This early emergence and rapid disappearance is
apparently a means of taking advantage of the abundant prey in the
habitat, while avoiding competition with other orb-weavers whose
populations increase rapidly by August (Anderson 1978). The
spiderlings then spend approximately 290 days in the cocoon until
they emerge the following March; 2 to 3 months longer than most
other orb-weavers (Anderson 1978). The cocoon is apparently part of

4l
a suite of adaptations for controlling water loss [including
depressed metabolic rates (Schaefer 1976, Anderson 1978), and
lipid-rich eggs (Anderson 1978)], and fits into the foraging/
reproductive strategy of this spider by providing a
desiccation-resistant refuge in which the spiderlings spend these
additional months overwintering.
A number of the egg and spiderling replicates of M. lemniscata
and A. aurantia held at 100% RH in the laboratory were attacked and
destroyed by fungus. Although these replicates were removed prior
to data analysis, in some cases there was still a significant
reduction in survival without cocoons at 100% RH (see Table 4-3 for
M. lemniscata spiderlings), a humidity where survival should be
unaffected by desiccation. This suggests that the covers of cocoons
may be related to resisting fungal attack (Christenson and Wenzl
1980), possibly by limiting the amount of water which can enter the
cocoon. Chapter V addresses this possibility, and considers the
cocoon as a barrier to fungal attack

CHAPTER V
THE ROLE OF THE COCOON IN LIMITING EXCESS WATER
AND FUNGAL ATTACK
Introduction
Although desiccation is a problem for developing spider eggs
and overwintering spiders, too much water may also cause adverse
effects. Water, entering the cocoon, could dissolve materials from
the egg surface and lower the resistance of the eggs to disease
(Austin and Anderson 1978). It could also drown the contents of the
cocoon (Schaefer 1976, Reichert 1981). Water may also introduce
fungal spores that are pathogenic to the eggs or spiderlings.
Christenson and Wenzl (1980) suggested that the cocoon of Nephila
clavipes (Linneaus) (Araneidae) protects against fungal attack by
reducing the chance of spores gaining access to the egg mass. A
role in protecting the eggs and spiderlings from fungi seems
reasonable, since both spiders (Bijl and Paul 1922, Nellist 1965)
and their eggs (Seligy 1971, Christenson and Wenzl 1980) are
attacked by fungus.
Both Mecynogea lemniscata and Argiope aurantia utilize a
covered cocoon (see Figs. 2-1 and 2-2), in contrast to the
flocculent silk type used by many other orb-weavers (McCook 189O,
Scheffer 1905, Kaston 19^8). Both spiders also utilize habitats
where high humidity during the egg laying period may promote fungal
attack (see Chapter II). In this chapter, I examine the roles of

43
the suspension systems, the internal flocculent layers, and the
coverings of the cocoons of these spiders in protecting the eggs and
spiderlings from excess water, drowning, and fungal attack.
Materials and Methods
Laboratory Experiments
The abilities of the cocoon suspension system, the cocoon
cover, and the internal flocculent silk layer to limit the access of
water to, or into the cocoon were examined in the laboratory using
M. lemniscata or A. aurantia cocoons as appropriate. The
temperature and humidity in the laboratory during all the
experiments were 25 C and 50-60% RH, respectively.
To examine the function of cocoon suspension systems in
shedding water, M. lemniscata cocoon strings were hung between two
vertical supports by their silk suspension lines (see Fig. 2-1).
The angle of inclination of the suspension lines was set at 10, 20,
30, and 45 from the horizontal. At each of these angles, water
was applied to the suspension lines with a dropper, and its course
down the lines noted.
The ability of cocoons to shed water was examined by applying
1.00 ml of water with a syringe directly to hanging strings of
M. lemniscata cocoons. The runoff was collected, and the amount
retained by the cocoon string calculated. Both naked strings, and
those covered with a layer of silk and detritus (see Fig. 2-lc) were
tested in this manner. The abilities of both M. lemniscata and

1+1*
A. aurantia cocoons to shed water were also examined in the field
during periods of rain.
To determine whether water actually penetrates the cocoon
cover, 10 samples of 2-3 dry M. lemniscata cocoons were submerged in
distilled water for time periods of 7, 15, 30, 60, 120, 240, and 480
min. Upon removal from the water, they were blotted on Whatman #1
filter-paper discs for 1 min to remove surface water, and weighed on
a Mettler AK l60 balance to the nearest 0.0001 gm. The 10 samples
were air dried for 2k hrs between each submersion. After the last
submersion bout (480 min), the 22 cocoons comprising the 10 samples
were opened and examined under a microscope for the presence of
water.
The volume of water absorbed by each cocoon sample was
calculated from the increased weight of the sample (l gm water = 1
2
ml = 1 cc). This was normalized to ml/ cm by dividing the volume
of water by the combined surface area of the cocoons in each sample.
A mean value was then calculated from the 10 values for each
submersion time.
The role of the flocculent silk layer in resisting water was
also tested. Here, flocculent silk from A. aurantia cocoons was
used. Uncompressed pieces of this layer were placed on glass slides
and drops of distilled water were applied to the silk. The pieces
were observed for approximately 10 min, and any wetting of the silk
through wicking was noted.

Field Experiments
The function of the cocoon suspension system and the cocoon
cover in limiting fungal attack and drowning were investigated by
modifying these components in the field, and assessing their effect
on egg hatching success and spiderling survival. The cocoons used
in these studies were either reared in the laboratory, or collected
in the field from marked web-sites. Only nonparasitized cocoons
were used.
The cocoons were assigned to the four experimental groups
listed below. The experiments using cocoons with eggs were run for
30 days; those using cocoons with spiderlings for 90 days. The
cocoons not associated with apparatus were marked by plastic
flagging attached to the vegetation.
Vegetation contact. The effect of cocoon suspension systems in
preventing fungal attack was examined by placing >1. lemniscata
cocoons in contact with the vegetation. This simulated partial
collapse of the suspension system, and placed limitations on the
cocoons drying normally. Placement was accomplished by cutting the
cocoon free, and tying it in place to the vegetation with its
support line. Access to the cocoons by terrestrial predators was
controlled by applying tack-trap to the branches below the cocoons,
and pruning the branches above the cocoon so they did not contact
the surrounding vegetation. Argiope aurantia cocoons were not
subjected to this treatment.

46
Ground placement. This manipulation also tested the function
of the suspension system, hut placed the cocoons in a wetter
microhahitat where drying was more difficult and the chance of
fungal attack or drowning was greater. Both M. lemniscata and
A. aurantia cocoons were placed on the ground in enclosures. For
A. aurantia cocoons, these were constructed of hardware cloth (1/4"
mesh), and were 10 x 10 x 10 cm in size. The enclosure for
M. lemniscata cocoons was similar in design, but was constructed of
aluminum window screen, and was 5 x 5 x 5 cm in size. These
enclosures allowed exposure of the cocoon to the elements, protected
them from large predators (although ants could still get in), and
prevented them from washing away during heavy rain storms. They
were placed below positions where cocoons had previously been
collected.
Cover removal. To determine the roles that the covers of
M. lemniscata and A. aurantia cocoons play in controlling fungal
attack, approximately 20-30% of their covers were removed. During
the cover modification, care was taken not to disturb the flocculent
silk layer (see Fig. 2-2b), or damage the eggs or spiderlings. The
cocoons of M. lemniscata were modified in place in their respective
strings. They were treated normally by the female spiders, which
remained at the web-site after the modification. The laboratory
produced cocoons of A. aurantia were modified, and attached by
alligator clips to the arms of a support system. The support was
placed in the vegetation in areas where cocoons where already

47
hanging. Tack-trap was applied to the support arms to limit the
access of terrestrial predators (primarily ants).
Cover removal control. This group functioned as a control for
possible contaminating effects of the alligator clips. The clips
were attached to the necks of cocoons hanging normally in the
habitat, and the cocoons were observed for any detrimental effects.
Control. A number of cocoons were subjected to no structural
intervention, and functioned as a control for the handling effects
in the vegetation placement, ground placement, and cover removal
experiments.
Results
Laboratory Experiments
The suspension lines of M. lemniscata cocoons are relatively
poor conductors of water. At all the inclinations tested, dry lines
were not easily wetted, and consequently tended to shed water.
Suspension lines could be wetted by rubbing them between wet
fingers, but even here water moved with difficulty. At the lower
angles of inclination (10 and 20), water applied to the wetted
line formed drops or beads and hung in place. At the higher
inclinations (30 and 45), water moved down the line toward the
cocoons. However, the suspension lines of M. lemniscata cocoons are
made of multiple strands of silk and contain "knots" and
incorporated debris. When water moving down the line got to these
points it built to a drop and fell from the line.

The cocoons of M. lemniscata also shed water well. Depending
on whether the cocoon string is naked, or covered with a layer of
old web and detritus (see Fig. 2-1), approximately O.85 to 0.95 ml
of the 1.00 ml of water applied to the cocoon string with a syringe
was shed immediately. Most of the remaining water forms a droplet
at the end of the last cocoon in the string, or remains in the silk
over-layer where it disappears by evaporation. Observations of
M. lemniscata and A. aurantia cocoons under rainy conditions in the
field yielded results similar to those observed in the laboratory.
The suspension lines of both species had beads of water hanging on
them and appeared not to conduct water toward the cocoons. Both
cocoons also shed drops of water from the bottom of the cocoon or
end of the cocoon string.
The ability of cocoons with covers to rapidly shed water
appears to be related to the slow rate at which their covers absorb
water (Fig. 5-1). Over a 2-hr period, the covers of averaged sized
2
M. lemniscata cocoons (0.5 cm in total surface area), absorb only
0.0014 ml of water. Even after 8 hrs of immersion, the amount of
water absorbed has increased to only 0.0020 ml.
The thickness of the covers of M. lemniscata cocoons vary
between 0.3 and 0.8 mm. The cover is not solid, rather it is a
matrix of fibers with included air spaces, similar to fiberglass
insulation. Assuming that approximately 50% of the cover is
airspace that can be replaced with water, the cover should be able
to hold between 0.0015 and 0.0039 ml of water. The 0.0020 ml of
water absorbed by the cocoon after 8 hrs of immersion is consistent

Fig. 5-1. The rate of water loading in the laboratory for the covers of Mecynogea lemniscata
cocoons submerged in distilled water. The dots represent the mean volume of water absorbed per unit
area; the bars represent the SD; n, the sample size, equals 10.

7130 60 120 240 480
2
ml Water/cm Cocoon Surface (xIOOO)
_ ro oj k cti
o b b b b
\
\
\
i
o
0 9

51
with these calculations, and suggests that it is the cover alone
which absorbs water before the excess is shed by the cocoon.
Examination of the cocoons under the microscope supports this. None
of the 22 cocoons had water inside them after k hrs of submersion.
The flocculent layer of A. aurantia cocoons was completely
non-wettable. Water applied to the silk simply formed beads and sat
upon the silk until it disappeared by evaporation.
Field Experiments
The incidence of fungal attack on M. lemniscata cocoons
containing eggs in the control group was 7*3% (Table 5-l)*
Chi-square tests between this group, and the Vegetation Contact,
Ground Placement, and Cover Removal groups revealed no significant
differences in the number of cocoons in the egg stage attacked by
fungus. This suggests that neither the cocoon cover, nor the cocoon
suspension system function to protect the eggs from fungal attack.
There was, however, a significant increase in egg mortality among
p
those cocoons placed on the ground (X = 12.39, df = 1, p < 0.005).
The eggs in these cocoons were all killed, presumably by drowning.
They were not covered with fungus.
The natural incidence of fungal attack on M. lemniscata cocoons
in the spiderling stage was 1.0% (Table 5-2). Contact with the
vegetation did not significantly increase the number of cocoons
attacked by fungus in this stage. However, there were significant
increases in the number of cocoons attacked by fungus among those
2
placed on the ground (X =9.93, df=l, p< 0.005). Cocoons with

52
Table 5-1 The effect of modification of the cocoon suspension
system and cover on the incidence of fungal attack on the eggs of
Mecynogea lemniscata. Cocoons in the "Other" category contained
eggs which were not attacked by fungi, but did not hatch due to
inviability or drowning. In many cases the eggs rotted. All
cocoons were collected after 30 days.
Experimental
Modification
Sample
Size
Successful
Hatching
Fungal
Attack
% Cocoons
Attacked
Other
Control
171
153
12
7.3%
6
Vegetative
Contact
21
13
3
14.3%
0
Ground
Placement
19
12
2
14.3%
5
Cover
Removal
13
12
1
7.7%
0

53
Table 5-2. The effect of modification of the cocoon suspension
system and cover on the incidence of fungal attack on the
spiderlings of Mecynogea lemniscata. Cocoons in the "Other"
category contained spiderlings which were not attacked by fungi, but
did not survive due to drowning. All cocoons were collected after
90 days, except for those placed on the ground. They were collected
after 45 and 90 days.
Experimental
Modification
Sample
Size
Successful
Survival
Fungal
Attack
% Cocoons
Attacked
Other
Control
239
236
3
1.7%
0
Vegetation
Contact
65
63
2
3.2%
0
Ground
Placement (45)
22
17
3
n.6%
2
(90)
12a
11
1
11.0%
0
Cover
Removal
37
32
5
15.6%
0
A number of cocoons were attacked by ants in this group and
could not be used for the analysis. This explains the low
percentage of fungal attack after the longer 90-day period.

54
modified covers also had significantly higher rates of fungal attack
2
(X = 13.03, df = 1, p < 0.005). In addition, spiderling mortality
due to other causes, probably submersion and subsequent drowning,
2
was significantly higher on the ground (X = 13*34, df = 1, p <
0.005).
The incidence of fungal attack on the cocoons of A. aurantia
was very low in both the egg stage (4.9%; Table 5-3), and the
spiderling stage (0%; Table 5-4). Chi-square tests between the
Control group, and the Ground Placement and Cover Removal groups
revealed no significant differences in the number of cocoons
attacked by fungus in either the egg stage or the spiderling stage.
The two Control groups were not significantly different from each
other.
Discussion
The suspension systems of both M. lemniscata and A. aurantia
cocoons are difficult to wet, and conduct water poorly.
Consequently, they act to discourage water from moving down the
lines to the cocoons. The covers of both cocoons shed water
effectively, and apparently absorb only a small amount. Presumably,
the flocculent silk layers of both cocoons are also difficult to
wet, and function further to limit the water from entering the
cocoon. All of these structures ultimately function to keep the
cocoon dry by channeling water away from it. However, the
connection between this function, and the prevention of fungal
attack is not clear. Modification of the cocoon cover and partial

55
Table 5-3. The effect of modification of the cocoon suspension
system and cover on the incidence of fungal attack on the eggs of
Argiope aurantia. Cocoon modification had no effect on egg
inviability or drowning. All cocoons were collected after 30 days.
Experimental
Modification
Sample
Size
Successful
Hatch
Fungal
Attack
% Cocoons
Attacked
Control
Ul
39
2
h.9%
Ground
Placement
12
10
2
20.0%
Cover
Removal
13
11
2
15. U*

5 6
Table 5-4. The effect of modification of the cocoon suspension
system and cover on the incidence of fungal attack on the
spiderlings of Argiope aurantia. No spiderlings were killed by
drowning in these experiments. All cocoons were collected after 90
days.
Experimental
Modification
Sample
Size
Successful
Survival
Fungal
Attack
% Cocoons
Attacked
Control
40
40
0

Ground
Placement
22
22
0

Cover
Removal
20
20
0
cL
Of the 22 cocoons, 2 had small patches of fungus on the
shell, but the contents were unaffected.

57
collapse of the suspension system of M. lemniscata cocoons is
unrelated to the incidence of fungal attack in the egg stage (see
Table 5-1) Even total failure of the suspension system did not
result in increased fungal attack, although cocoons placed on the
ground did suffer higher egg mortality due to drowning.
The integrity of the suspension system and cocoon cover was
important to M. lemniscata cocoons that contained spiderlings (see
Table 5-2). In this stage, total collapse of the suspension system
resulted in increased mortality due to drowning. The incidence of
fungal attack also increased with modification of the cocoon cover.
However, it is unclear whether the spiderlings were attacked by
fungus because of damage to the cover, or died for some other reason
and were subsequently attacked. Modifying the cocoon cover does
increase dessication problems for M. lemniscata spiderlings (see
Chapter IV), and this may have been the real cause of the increased
spiderling death. However, I have also had fungus attack
spiderlings in the laboratory under conditions of high relative
humidity (66-100/ RH) where dessication should not be a problem.
Christenson and Wenzl (1980) found that 17*5% of the cocoons of
N. clavipes were attacked in the egg stage by fungus. They cited
the loss of protection from the rain (removal of a leaf canopy above
the cocoon), and falling to the ground (support line failure) as
reasons why the flocculent silk cocoons of this spider failed.
Overall, the lack of any effect on the incidence of fungal attack
through manipulation of the covers and suspension systems of
M.* lemniscata and A. aurantia cocoons is surprising, particularly

58
since these components presumably perform the same functions as the
leaf layer and support system of N_. clavipes cocoons. These results
may be partially explained by differences in the cocoons of the
three species. The cocoons of M. lemniscata and A. aurantia have
dense covers, and layers of flocculent silk between the cover and
the egg mass. While the covers of both these cocoons are wettable,
the flocculent silk layer is not. The cocoon of N. clavipes is
composed primarily of a basket-like mesh, with little or no
flocculent layer between the eggs and the mesh. The eggs in
M. lemniscata and A. aurantia cocoons with damaged covers are still
protected from water (and fungal spores?) by their flocculent silk
layer (which was not damaged in this study). The mesh cocoons of
N. clavipes, which are also wettable, have no flocculent layer to
turn water away from the egg mass once their protective leaf canopy
is gone. Other explanations for this difference, such as a layer of
spherical granules on the surface of the eggs of these two species
which repel water (Austin and Anderson 1978, Grim and Slobodchikoff
1978, 1982, Humphreys 1983), or relatively short developmental
periods are not adequate, since all three spiders share these
traits.
The differences in the incidence of drowning between
M. lemniscata and A. aurantia cocoons in the egg and spiderling
stages (see Tables 5-2 and 5-*0 are probably related to differences
in the size of these cocoons, and the thicknesses of their
flocculent silk layers. The cocoons of M. lemniscata are small, and
are worked down into the soil by rain action when placed on the

59
ground. In this location, the cocoons are in constant contact with
soil moisture. Argiope aurantia cocoons are relatively large (see
Figs. 2-1 and 2-2), and remain on the surface if they fall to the
ground. In this position, the area of the cocoon contacting the
soil is minimized, which probably allows the cocoon to dry out
between exposure to rain or submersion.
The spiderlings in M. lemniscata cocoons are also packed
together tightly, with no room to move about within the cocoon. In
addition, the flocculent silk layer in these cocoons is relatively
thin. Fungal infection, once established, can spread more easily to
all the spiderlings within the cocoon. The thicker flocculent silk
layer in the cocoons of A. aurantia provides protection from water
entering the cocoon, even when the cover is damaged. The large size
of these cocoons also allows the spiderlings to move about in the
cocoon, which may further reduce the probability of infection moving
through the mass. Indeed, in cocoons damaged naturally or modified
by me, the spiderlings are almost always appressed against the
cocoon cover opposite the site of the damage.
The differences between the overall levels of fungal attack on
the cocoons of these two spiders are also interesting. The cocoons
of M. lemniscata are covered by layers of discarded orb-web that
contains detritus composed primarily of prey remains. These remains
may provide a high quality medium for fungal spores to germinate on,
and from them, extend their hyphae into the cocoons. On occasion, I
have observed _M. lemniscata cocoons completely enswathed by a fuzzy
layer of grey or white fungus. I have also had M. lemniscata

6o
cocoons that were stripped of their outer layer of silk (see
Fig. 2-lc) attacked by fungi in the laboratory. In contrast,
A. aurantia cocoons, which have a naked cover with an almost
lacquered surface finish, are never covered by fungus. In fact, it
is rare to find small patches of fungus on the covers of these
cocoons at all, even after they have been lying on the ground for 90
days (see Table 5-^)*
Spiders produce a variety of silks and associated materials in
a number of different glands located in their abdomens (Witt et
al. 1968, Mullen 1969, Foelix 1982). One of these, the aggregate
gland, produces the glue-like material found on the catching spiral
of orb-webs. Schildknecht et al. (1972) have demonstrated that this
glue-like material contains nitrates (KNO^), phosphates (KHgPO^),
and pyrrolidines (C^^NO^). They suggest that one of the
functions of these compounds is to protect the web from bacterial
and fungal attack. If spiders are protecting their webs from such
attack, it seems reasonable that they would protect their cocoons,
which represent a much greater expenditure of energy and time, as
well. Given that these compounds can be manufactured in the silk
glands associated with web building, it seems likely that the
tubiliform and aciniform glands associated with cocoon production
may also able to manufacture similar compounds, so they can be
applied to the covers of cocoons.
The preceeding Chapters III, IV, and V have both considered and
demonstrated the role of the cocoon, or its various parts, in
limiting the effects of temperature extremes, dessication, and

61
fungal attack on the egg and spiderling stages of M. lemniscata and
A. aurantia. However, many predator groups have specialized on the
eggs of spiders, and it is probable that cocoons also function to
control their attacks. This possibility is considered in Chapter
VI.

CHAPTER VI
THE ROLE OF THE COCOON IN LIMITING EGG AND
SPIDERLING PREDATORS
Introduction
A major portion of modern ecology is concerned with the
relationship between heterotrophic organisms and their food
supplies. Such interactions (e.g., predator vs. prey, host
vs. parasite) occur both in ecological time, and in evolutionary
time (Brower and Brower 1972, Dawkins and Krebs 1979) As such,
natural selection may be presumed to act within interacting
populations to optimize both the ability to acquire resources
(Schoener 1971, Pyke et al. 1977), and the ability to avoid becoming
the acquired resources of similarly-selected organisms of higher
trophic levels. Within this context, the strategy" of any host
organism should be to protect itself, or its offspring, from the
effects of predator or parasite attack through processes or
behaviors which limit the types and numbers of attackers that are
capable of using it. Ideally, the strategy should result in the
total exclusion of all the attackers. In reality, their effect is
only partially reduced due to the reciprocal nature of the
interaction over evolutionary time.
Spiders deposit their eggs in one or more discreet clutches.
These clutches can be extremely large (up to 2000 eggs; Kastcn
19^8). The individual eggs within the clutch are also
62

63
quite large when compared to eggs of other groups such as insects.
The eggs are lipid rich and represent a considerable amount of
energy (Anderson 1978). In addition, during the reproductive
season, clutches may occur in large numbers in the habitat and may
be relatively conspicuous. They therefore represent a potential and
highly desirable resource for many predators and parasites. Indeed,
insects from a number of groups have specialized on spider eggs
(Auten 1925, Eason et al. 1967, Evans 1969, Askew 1971, Austin, In
press).
All spiders deposit their eggs in some form of silken cocoon
(Turnbull 1973). For many spiders this structure represents the sum
total of maternal care bestowed on the eggs by the female spider.
The large and diverse number of predators attacking cocoons, and the
wide range in complexity of cocoon architecture (McCook 1890, Kaston
19^+8) have led to speculation that the primary function of the
cocoon is to protect the eggs and spiderlings from attack (Austin
and Anderson 1978, Robinson 1980). Austin (In press) recently
reviewed the literature on cocoon attack by egg predators, and
proposed that the wide diversity of cocoon types arose because
spiders have attempted to reduce the total number of predators that
can use their cocoons by forcing them to "specialize" on a
particular cocoon type. The predators have responded in
evolutionary time, and the relationships between cocoons and their
attackers that we observe today can be attributed to a
"coevolutionary arms-race" (Dawkins and Krebs 1979). While some
observations have been reported on parasite difficulty in entering

6k
cocoons (Kaston and Jenks 1937), there is still no evidence that
cocoons, or the various layers comprising them, function to turn
away or reduce the success of specific parasites or predators.
In this chapter, I investigate the roles that the suspension
systems, outer covers, and internal flocculent silk layers of the
cocoons of Mecynogea lemniscata Walckenaer and Argiope aurantia
Lucas (Araneidae) play in controlling the access of predators to the
eggs and spiderlings within. If the suggestions of various
researchers, and in particular Austin (in press), are correct, these
cocoons should demonstrate defenses which reflect the manner in
which their predators attempt to introduce themselves or their
offspring into the cocoon.
Materials and Methods
Population Data
The numbers and kinds of parasites and predators attacking the
cocoons of M. lemniscata and A. aurantia were determined by
collecting cocoons in the field and returning them to the laboratory
where they were opened and scored for parasites. Scoring was
relatively easy since each parasite leaves distinctive evidence in
the cocoon such as the type of hole in the cover, or remains such as
pupal cases, shed exuviae, or eggs. The M. lemniscata cocoons were
collected in late August in 1981 to 1983 after the eggs in the last
cocoons laid had hatched. A single sample of A. aurantia cocoons
was collected in late October in 1981. In 1982 and 1983
a

65
different 31 m of a 400 m stretch of roadside hedgerow was sampled
every two weeks. For each sample, all of the cocoons in the 31 m
section were collected. In 1982, the cocoons were collected from
August through November; in 1983, from August through October.
In addition to these data, specific information was also
collected regarding attacks on A. aurantia cocoons by ichneumonid
wasps and chloropid flies. For the ichneumonid attacks, these data
included two indices relating the distance of the egg mass to the
cocoon cover along the X and Y axis. These indices were calculated
by first measuring the following four variables: egg mass length,
egg mass width, cocoon length, and cocoon width (Fig. 6-1). These
values were then used in the following formulas:
Distance to the egg (Cocoon Width Egg Mass Width)
mass from the cocoon cover = and
(x-axis) 2
Distance to the egg (Cocoon Length Egg Mass Length)
mass from the cocoon cover =
(y-axis) 2
These two measures were compared to the average ovipositor length of
the ichneumonid to predict where the wasp might prefer to attack the
cocoon. The predicted preference was checked by examining the
shells of attacked cocoons collected in the field for the
distribution of ovipositor drill holes. Data on the number of
cocoons that the wasp attacked without ovipositing, and the
distribution of support line "deltas" (the structure on the cocoon
surface the support lines emanate from; McCook 1890) were also

66
Fig. 6-1. A schematic view of an Argiope aurantia cocoon
illustrating the four measurements; cocoon length (cl), cocoon width
(cw), egg mass length (eml), and egg mass width (emw) taken to
determine the position of the egg mass in relation to the cocoon
cover.

collected. For the chloropid fly attacks, the number of cocoons
successfully attacked (producing pupae), the number of cocoons
successfully attacked in conjunction with another predator, and the
number of cocoons unsuccessfully attacked (eggs laid on the cocoon
surface but no pupae produced) were recorded.
The relationship between the size of an A. aurantia cocoon and
the number of eggs it contained was established by measuring a
number of cocoon dimensions and counting the spiderlings in UO
2
cocoons. Figure 6-2 shows that there is a strong relationship (r
= 0.90) between the diameter of the cocoon and spiderling number.
This relationship was used to estimate the original number of eggs
in attacked cocoons. The percentage of eggs surviving the attack, a
measure of the damage caused by a given predator, was then
calculated by the following:
Percentage of Eggs No. of Survivors
Surviving = X 100.
Parasite Attack Estimated No. of Eggs
The relationship of cocoon size to egg number was not calculated for
M. leraniscata because all of the eggs in a cocoon are utilized when
attacked by its egg predators.
Field Experiments
The roles of suspension systems and cocoon covers in
controlling egg predator attacks were investigated by modifying
these components in the field and assessing the effects of their
change on egg hatching success and spiderling survival. The cocoons

Number of Eggs
68
Cocoon Diameter (cm)
Fig. 6-2. The relationship (Y = 1522.2X 1886.9; n = Ho) between
the diameter of Argiope aurantia cocoons and the number of
spiderlings (eggs) therein. The coefficient of determination (r^)
for the relationship is 0.90.

69
used for these modifications were either produced in the laboratory,
or collected in the field. They were assigned to the experimental
groups listed below. The cocoons in all the experimental groups
were marked either by flagged stakes placed beneath them, or by
flagging in the vegetation.
Vegetation contact. The function of cocoon support lines as a
deterrent to arboreal predators was examined by repositioning
cocoons so that they contacted the vegetation. This was done only
for M. lemniscata cocoons and was accomplished by tying cocoon
strings to branches with their suspension lines. This mimicked the
position of cocoons whose suspension systems had collapsed normally.
Ground placement. The role of the suspension system in keeping
cocoons off of the ground and away from terrestrial predators was
investigated by placing the cocoons of both species on the ground in
open-topped wire corrals. These corrals allowed cocoons to be
attacked but prevented them from being washed away in the rain. The
corral used for A. aurantia cocoons was constructed of hardware
cloth (1/4" mesh) and was 12.5 cm in diameter and 5 cm in height.
The corral for M. lemniscata cocoons was constructed of aluminum
window screen and was 5 cm in diameter and 5 cm in height. The
corrals were located below sites where cocoons had been collected
previously.
Cover removal. The function of the cocoon cover in limiting
predator attack was examined by removing approximately 25% of the
cocoon cover with a razor blade. Individual cocoons of
M. lemniscata were modified in the cocoon string and the string was

TO
left suspended in place at the veb site. Female spiders treated
these modified cocoons normally. The laboratory reared cocoons of
A. aurantia were modified and attached to the arms of a support
system using alligator clips. The support systems were placed in
the vegetation where normally oviposited cocoons were hanging. They
held the cocoons approximately 1 m off of the ground (the average
cocoon height as determined by collecting).
Cover removal control. This group was to control for the
possible contaminating effects of the alligator clip used in the
apparatus to suspend A. aurantia cocoons. Clips were attached to
cocoons hanging normally in the habitat and the cocoons were
observed for any effect.
Control. Control cocoons were subjected to no structural
intervention. These cocoons controlled for handling effects in the
ground placement, vegetation placement, and cover removal groups.
Bird damage. These A. aurantia cocoons were subjected to no
mechanical modification. They were marked and collected after 150
days in the field to determine whether bird predation increases
later in the year after the plants lose their leaves (see also
Tolbert 1976). They were compared to the control group.
Laboratory Experiments
The role of the flocculent silk layer in the cocoons of
A. aurantia as a barrier to predator attack was tested in the
laboratory by placing the eggs of Tromatobia ovivora rufopectus
(Cresson) (ichneumonidae) at two depths in the cocoon: l) just under

71
the cover, and 2) on the host egg mass. Successful parasitism was
scored as the number of ichneumonid larvae found in the host egg
mass just prior to pupation.
The wasps were maintained in the laboratory at 23-25 C and
50-60% RH. They were provided with white refined sugar, a mixture
of honey and yeast, and water. Colony size was maintained by the
addition of new wasps collected from the field. Their eggs were
obtained by allowing a number of wasps to attack a cocoon produced
in the laboratory. The cocoon was then opened, and the white,
elongate wasp eggs were removed using a fine brush and forceps.
Known numbers of these eggs were then transferred to other
laboratory produced cocoons 1-3 days old, and placed in either of
the two test locations.
The cocoons were obtained from spiders held in the laboratory
in 50 x 50 x 10 cm cages (Witt 1971) or in 500 ml jars with screen
tops. Oviposition and cocoon construction in both of these
enclosures was normal.
Results
Field Experiments
The cocoons of M. lemniscata are attacked in the egg stage by
two major predators, a Tetrastichus sp. wasp (Eulophidae) and the
neuropteran Mantispa viridis Walker (Mantispidae) (Hieber 1984)
(Table 6-1). 3oth of these predators utilize all of the eggs in a
cocoon during their attacks. However, they attack the cocoons in

72
Table 6-1. Numbers of Mecynogea leianiscata cocoons attacked by the
eulophid wasp Tetrastichus sp., the raantispid Mantispa viridis, and
ants/ unknown predators for the years 1981 to 1983- The cocoons
were collected in late August in 1981 and 1982 at the end of the
reproductive season, and in July, August, and December in 1983. The
percentages of attacked cocoons are in parentheses.
Year
Sample
Size
Total No.
Attacked
Eulophid
Wasp
Mantispid*3
Ants/
Unknown
1981
290
26
21 (80.8%)
0 (0%)
5
(19.2*)
1982
252
29
17 (58.6?.)
5 (17-2%)
7
(2k.1%)
1983
July
148
13
10 (76.9%)
2 (15-4%)
1
( 1.1%)
Aug.
97
l4
12 (85.7%)
0 (0%)
2
(14.3%)
Dec.
308
64
32 (50.Of.)
12 (18.8%)
20
(31.2%)
Cocoons contain either larvae, prepupae, and/or shed exuviae
with emergence holes.
Cocoons contain either a larva, a pupa, or a pupal case and
emergence hole.
Cocoons are characterized by a large chewed hole, and the
absence of the flocculent silk layer, pupal cases, pupae,
shed exuviae, or parasite.

73
different ways. Mantispa viridis deposits its eggs in the habitat,
removed from the host, and the emerging triungulid larvae actively
search out and burrow into previously constructed cocoons. These
larvae are obligate cocoon attackers, as opposed to the mantispid
larvae that ride on female spiders and attack the egg mass just
prior to cocoon construction (see Redborg and McLeod, In press, for
a review of Mantispid biology). The Tetrastichus wasp either
deposits eggs into the cocoon, or into the upper layers of the
cocoon cover where the emerging larvae burrow through the cocoon and
attack the egg mass (Austin, In press). Both the wasp and the
mantispid are never found together in the same cocoon. The cocoons
of M. lemniscata are also occasionally attacked by ants, which also
remove all of the eggs or spiderlings.
The single line suspension system of M. lemniscata cocoons
functions to prevent predation on the egg stage. Egg predation was
significantly greater than control for both the cocoons placed on
2
the branches (X = 47.40, df = 1, p < 0.001) and those placed on
the ground (X2 = 23.49, df = 1, p < 0.001) (Table 6-2). In both
cases, the principle predator appeared to be ants. Modification of
2
the cocoon cover also had a significant effect on egg predation (X
= 38.67, df = 1, p < O.OOl). In this case, however, the principle
predator was not ants, but the mantispid M. viridis. In no case did
the wasp attack any manipulated cocoons containing eggs, suggesting
that the position of the cocoon in the web or the integrity of the
cocoon cover are important to the wasp.

Table 6-2. The effect of modification of the cocoon suspension
system and cover on the incidence of predator attack on the eggs of
Mecynogea lemniscata. All cocoons were collected after 30 days.
Experimental
Modification
Sample
Size
Successful
Survival
No. Cocoons
Attacked
% Cocoons
Attacked
Control
175
153
22a
12.6%
Vegetation
Contact
2h
6
l8b
75.0%
Ground
Placement
26
12
iub
53.8%
Cover
Removal
32
12
20 C
62.5%
Of the 22 cocoons attacked, 2 were attacked by ants/ unknown
predators, 19 by the eulophid wasp Tetrastichus sp., and
1 by the mantispid M. viridis.
In both cases the cocoons were attacked by ants/ unknown
predators.
ATI 20 cocoons were attacked solely by the mantispid
M. viridis.

75
The effect of the suspension system in protecting M. lemniscata
spiderlings from predators was not as pronounced (Table 6-3). There
were no differences in predation between the Control group and
either the cocoons placed on the ground for 45 days or the cocoons
placed in contact with the vegetation. The cocoons placed on the
ground for 90 days, however, were preyed upon at significantly
p
higher levels (X =70.40, df = 1, p < 0.001). These results
probably reflect the generally lower densities of ants foraging on
the vegetation and ground late in the year (pers. ob.). Cover
removal also had no significant effect on spiderling predation when
compared to control, again because the the cocoons are inaccesible
on their support line.
The eggs of A. aurantia are attacked by four primary
predators; the wasp T. ovivora rufopectus (ichneumonidae), the
neuropteran M. viridis, and the flies Pseudogaurax signata (Loew)
(Chloropidae) and Megaselia sp. (Phoridae) (Table 6-4). Of these,
the two most common predators are the ichneumonid and the mantispid.
These are obligate egg predators and probably account for most of
the initial attacks in cocoons attacked by multiple predators. The
attack behavior of the mantispid has been previously discussed. The
ichneumonid T. ovivora rufopectus attacks A. aurantia cocoons by-
inserting its long ovipositor through the cover into the flocculent
layer. Its eggs are deposited on or near the host egg mass, and the
emerging larvae make their way to the host eggs and burrow into the
mass to feed.

76
Table 6-3. The effect of modification of the cocoon suspension
system and cover on the incidence of predator attack on the
spiderlings of Mecynogea lemniscata. All cocoons were collected
after 90 days, except for those placed on the ground. They were
collected after 1+5 and 90 days.
Experimental
Modification
Sample
Size
Successful
Survival
No. Cocoons
Attacked
Cocoons
Attacked
Control
259
239
20a
7.7%
Vegetation
Contact
77
71
6*
7.8%
Ground
Placement
(1+5)
19
17
2a
10.5$
(90)
32
11
20a
62.5 %
Cover
Removal
31+
32
2a
5.9%
a
All attacks were by ants/ unknown predators.

Table 6-4. Numbers of Argiope aurantia cocoons suspended in the vegetation which were successfully
attacked by the ichneumonid Tromatobia ovivora rufopectus, the mantispid Mantispa viridis, the
chloropid fly Pseudogaurax signata, the phorid fly Megaselia sp., and birds for the years 1981 to
1983. The percentages of attacked cocoons are in parentheses. The cocoons were attacked to a
lesser extent by ants [l cocoon (l.6%) in 1981, 2 cocoons (1.1%) in 1982], and moth larvae [3
cocoons (l.6%) in 1982]. Forty-two of the 185 cocoons (23.0%) collected in 1982 were also attacked
by unknown predators and showed varying degrees of cover damage. The cocoon sample for I98I was
collected in late October. In 1982 and 1983, the cocoon samples were collected approximately every
two weeks during the reproductive season (August to November).
Year
Sample
Size
Total No.
Attacked
Ichneumonid
Wasp
Mantispid^
Chloropid
FlyC
Phorid
Fly6
Bird6
1981
63
lbf
13 (81.2%)
1 ( 6.2%)
3 (18.8%)
2 (12.5%)
0
1982
185
89g
34 (38.2%)
27 (30.3%)
42 (47.2%)
4 ( 4.5%)
17 (19-1%)
1983
90
9h
2 (22.2%)
5 (55.6%)
1 (11.1%)
0
1 (11.1%)
Attack characterized by the presence of oviposition holes, eggs, larvae, and pupal cases.
Attack characterized by the presence of pupal cases and adults.
Attack characterized by the presence of eggs on the cocoon cover or in the flocculent silk layer,
larvae, pupal cases, and adults.

Attack characterized by the presence of larvae, pupal cases, and adults.
Attack characterized by a large percentage of the cocoon cover (> 10.0%) torn away, and the
partial or complete removal of the cocoon contents.
Of the 16 cocoons attacked, 11 were by the ichneumonid alone, 1 by the mantispid alone, and 1 by
the phorid fly alone. The remaining 3 cocoons were multiply attacked by the ichneumonid and
chloropid fly (2 cocoons), and the phorid and chloropid flies (l cocoon).
Of the 89 cocoons attacked, 24 were attacked by the ichneumonid (i) alone, 11 by the mantispid
(M) alone, IT by the chloropid fly (C) alone, 2 by the phorid fly alone (P), and 5 by birds (B)
alone. No cocoons were attacked by the moth (Mt) alone. The remaining 30 cocoons were attacked
by more than one predator in the following combinations: (l-M, 2 cocoons), (i-C, 4 cocoons),
(I-B, 1 cocoon), (M-C, 6 cocoons), (M-B, 1 cocoon), (C-B, 5 cocoons), (C-Mt, 2 cocoons),
(B-Mt, 1 cocoon), 1-M-C, 3 cocoons), (M-C-P, 1 cocoon), (M-C-B, 3 cocoons), and (C-P-B, 1
cocoon).
Of the 9 cocoons attacked, 2 were attacked by the ichneumonid alone, 5 by the mantispid alone,
1 by the chloropid fly alone, and 1 by birds alone.

79
The status of P. signata is less clear. This fly deposits eggs
on cocoon surfaces. The eggs hatch and the emerging larvae push
their way through the cover into the cocoon (Kaston and Jenks 1937,
Kessel and Kessel 1937, Hickman 1970). The literature suggests that
chloropid flies are obligate spider egg parasites (see Austin, In
press), a fact supported by the large number of A. aurantia cocoons
attacked by this fly in 1982. However, only 17 of 1+2 cocoons were
singly attacked by this fly (Table 6-4). The remaining cocoons were
attacked along with other predators (particularly mantispids), and
in many cases the fly deposited its eggs in the emergence holes of
these previous attackers. In addition, Hall (1937) lists this fly
as attacking the egg masses of the praying mantis. This suggests
that this fly is a facultative egg predator that attacks eggs in any
container, as well as utilizing dead or damaged eggs from other
attacks when located. The phorid is found alone in cocoons
approximately 50% of the time and it is probably an obligate egg
predator, attacking cocoons in the same manner as P. signata.
The observed levels of egg predation for T_. ovivora rufopectus,
P. signata, and M. viridis in this study are similar to the levels
of attack reported by Enders (1974) and Tolbert (1976) for
A. aurantia cocoons. The A. aurantia cocoons in this study were
also attacked by birds, ants, and moth larvae, although it is
unclear whether these attacks occured in the egg or spiderling
stage. The level of bird attack was lower (9%) than that found by
Tolbert (35-50%). Argiope aurantia cocoons containing spiderlings
are attacked by ants and other spiders (particularly salticids which

80
use damaged cocoons as retreats), and by small rodents if cocoons
fall to the ground.
The amount of damage done to the eggs in an A. aurantia cocoon
by each of the four primary predators varies greatly (Table 6-5).
The ichneumonid, on average, does the greatest amount of damage,
destroying approximately 90% of the host eggs. By themselves, the
chloropid fly and the mantispid attack roughly the same number of
cocoons. However, the average mantispid attack damages
approximately 20% more eggs than the average chlorpid attack. The
phorid fly destroys approximately 97% of the eggs in a cocoon.
Birds also damage the contents of the cocoon heavily (74%), but the
damage is usually done in the spiderling stage.
Tromatobia ovivora rufopectus was successful in attacking 34
cocoons in 1982 (see Table 6-4). However, an examination of the
covers of 167 cocoons collected that year (the other 18 covers were
to damaged to inspect) for ichneumonid oviposition holes indicated
that 92 cocoons were actually sampled by the wasps. Thus, 58
cocoons were sampled but had no eggs deposited in them, presumably
because they were in the wrong stage for attack (Vinson 1976). The
other 75 cocoons were either never found by the ichneumonids, or
were found and rejected based on criteria which did not require
insertion of the ovipositor to determine.
The number of cocoons containing pupal cases of _P. signata was
also not a valid measure of the total number of cocoons attacked by
this fly (see Table 6-4). Of the 69 cocoons in 1982 with attached
P. signata eggs, 27 (39*1%) were apparently unsuccessful in that

81
Table 6-5. The mean percentage of eggs which survive in an Argiope
aurantia cocoon attacked solely by the ichneumonid Tromatobia
ovivora rufopectus, the mantispid Mantispa viridis, the chloropid
fly Pseudogaurax signata, the phorid fly Megaselia sp., or birds.
SD is in parentheses.
No. Cocoons
Parasite Sampled
Percent Eggs
Surviving
Ichneumonid
Mantispid
Chloropid Fly
Phorid Fly
35
10.2
(13.7)
15
39-1
(27.6)
15
63.7
(35-6)
4
4.7
( 9.5)
16
26.4
(28.3)
Birds

82
emerging larvae failed to gain entrance into the cocoon (no pupal
cases inside the cocoon). The remaining 42 cocoons were
successfully attacked and can be divided into two groups; 17 cocoons
attacked by the fly alone, and 25 cocoons attacked by the fly and
one or more other predators. Of the 17 singly attacked cocoons, 13
had eggs on the surface and a fewer number of pupae inside, 2 had
more pupae than eggs present, and 2 had pupae and no eggs present.
Of the remaining exhibiting multiple attacks, 11 had eggs on the
outside and inside of the shell and contained less (8 cocoons) or
more pupae (3 cocoons) than eggs. The other l4 cocoons had pupae,
but no evidence of eggs could be found because the cocoon and its
contents were heavily damaged.
The large number of cocoons attacked by P. signata in
conjunction with other predators suggests that shell damage may be
advantageous to this fly (see Table 6-4). Indeed, the average rate
of success (number of pupae/ number of eggs X 100) for the cocoons
attacked by the fly alone was 29.87 (SD = 30.2%) (based on the 13
cocoons which had visible eggs). The average rate of success for
the flies which attacked cocoons with other predators was 82.7% (SD
= 19-74%) (based on 11 cocoons; the 3 with more pupae than eggs were
counted as 100% successful). This level of success is significantly
greater (t = 10.05, df = 22, p < 0.001) than that achieved by
P. signata attacking cocoons alone.
It is difficult to determine whether the success rates for
mantispids and phorid fies attacking A_. aurantia cocoons are due to
an inability to locate the cocoons, or to the inability of the

83
respective larvae to penetrate the cocoon cover. The large increase
in successful mantispid attacks on artificially damaged
M. lemniscata cocoons suggests that mantispid larvae are generally-
abundant and probably have no trouble locating cocoons, but have
difficulty penetrating the dense cocoon cover. This suggests that
the cover of A. aurantia cocoons is also responsible for the
relatively low rate of successful mantispid attack. Presumably, the
larvae of the phorid fly are also hindered by the cover, although
this is a rare parasite and the low numbers of successful attacks
may be a reflection of low numbers of searching parasites. It seems
likely that birds, once they find a cocoon, have little trouble in
exploiting it.
In A. aurantia cocoons, the egg mass is closest to the cocoon
cover at its top edge, farthest from the cocoon cover at its bottom,
and approximately the same distance as the average ovipositor length
from the cocoon cover in the middle of the cocoon (Table 6-6). The
cocoons are suspended in the vegetation by a cloud of lines
emanating from suspension line "deltas" on the surface of the cocoon
(see Fig. 2-2a). There are significantly more of these deltas, and
thus significantly more lines, in the middle third of the cocoon
surface than in either the upper (t = 4.k8, df = lUO, p < 0.001) or
lower third (t = 156.1+0, df = 1^0, p < 0.001) (Table 6-7). The
distribution of ichneumonid drill holes matches the delta
distribution; there are significantly more holes in the middle third
than in either the upper (t = U.9, df = 166, p < 0.001) or lower
third (t = 3.92, df = l66, p < O.OOl) of the cocoon (Table 6-7).

84
Table 6-6. Mean cocoon diameter, cocoon length, egg mass diameter,
egg mass length, distance to the egg mass (X-Axis), and distance to
egg mass (Y-Axis) for Argiope aurantia cocoons, and mean ovipositor
length for the ichneumonid Tromatobia ovivora rufopectus. The two
distance variables indicate the length of an ovipositor needed to
deposit eggs directly on the surface of the host egg mass. SD is in
parentheses.
Sample
Variable
Size
Mean
i (mm)
Cocoon Diameter
25
19.2
(2.2)
Cocoon Length
25
24.4
(2.4)
Egg Mass Diameter
25
10.2
(1.4)
Egg Mass Length
25
11.1
(1.4)
Distance to Egg Mass
from cover: X-axis
25
4.5
(0.7)
Distance to Egg Mass
from cover: Y-axis
25
6.7
(1.2)
Ovipositor Length
57
3.9
(0.5)

85
Table 6-7. The mean number of suspension line deltas and
oviposition holes of the ichneumonid Tromatobia ovivora rufpectus in
the upper, middle, and lower thirds of the cover of Argiope aurantia
cocoons. SD is in parentheses.
Sample
Upper
Middle
Lower
Size
Third
Third
Third
Suspension
Line Deltas
71
18.7 (6.2)
22.3 ( 9-2)
3.9 (3.7)
Ichneumonid
Oviposition Holes
8U
2.U (3.7)
9-5 (13.1+)
3.1* (5.0)

86
The location of the egg mass within the cocoon and the distribution
of drill holes suggests that the ichneumonid prefers to attack the
cocoon in this specific area.
For A. aurantia, egg predation due to the cocoon falling to the
ground was not statistically different from the control in terms of
the number of cocoons attacked (Table 6-8). However, the individual
survival of eggs in each cocoon was reduced substantially. All of
the cocoons on the ground discovered by predators suffered 100$ egg
mortality as compared to about 59.4$ mortality for cocoons remaining
in place in the vegetation. The cocoons on the ground that escaped
attack were buried by falling leaves and were presumably hidden from
predators. The level of predation on eggs in cocoons with modified
covers was also not significantly different from the Control group.
However, in all cases the cocoons were attacked by the chloropid fly
P^. signata, further suggesting that damaged cocoons appeal to this
egg predator. The lack of mantispids in the modified cocoons is
most likely related to the apparatus used to suspend the cocoons,
which prevented the larvae from locating the cocoons, and not
because of their inability to use them.
The effect of cover modification also had no effect on
predation in the spiderling stage when compared to the Control group
(both controls were not significantly different from one another)
(Table 6-9). Placement on the ground, mimicking suspension failure,
2
resulted in significantly greater predation (X = 24.37, df = 1, p
on the ground (5-9$) was also much lower then for spiderlings in

87
Table 6-8. The effect of modification of the cocoon suspension
system and cover on the incidence of predator attack on the eggs of
Argiope aurantia. All cocoons were collected after 30 days.
Experimental
Modification
Sample
Size
Successful
Survival
No. Cocoons-
Attacked
% Attacked
Attacked
Control
21
10
IIa
52. k%
Ground
Placement
10
2
8
80.0%
Cover
Removal
17
10
i
*1.2%
Of the 11 cocoons attacked, 8 were attacked by the chloropid
fly P. signata, 8 were attacked by the mantispid M. viridis,
1 by the phorid fly Megaselia sp., 1 by the ichneumonid
T. ovivora rufopectus, and 5 by birds.
Rodent (mice) damage. The cocoon covers were shredded and
the contents destroyed.
All 7 cocoons were attacked solely by the chloropid fly
P. signata.

88
Table 6-9. The effect of modification of the cocoon suspension
system and cover on the incidence of predator attack on the
spiderlings of Argiope aurantia. All cocoons were collected after
90 days, except for those in the bird damage group. They were
collected after 150 days.
Experimental
Modification
Sample
Size
Successful
Survival
No. Cocoons
Attacked
% Cocoons
Attacked
Control
23
20
3a
13.0%
Cover Removal
Control
15
Ik
lb
6.7%
Ground
Placement
19
2
17C
89.5%
Cover
Removal
21
20
ld
4.8%
Bird
Damage
23
15
8e
34.8%
Bird damage. Of the 3 cocoons, 2 had part of their cover
removed, and 1 had cover damage and the contents removed.
Bird damage.
Rodent (mice) or bird damage. Characterized by the cover
being shredded and the contents removed.
Bird damage. Contents removed from the cocoon.
Bird damage. Of the 8 cocoons, 2 were removed completely,
5 had 25-50% of their covers removed, and 1 had the cover
damaged and the contents removed.

89
cocoons in the vegetation (98.4$). Predation by birds increased
during the latter part of the season, and while the numerical
increase was not significant, the average level of individual
survival was lower (j6.6$).
Laboratory Experiment
The mean percentage of success for T. ovivora rufopectus eggs
placed just under the cocoon shell was 62.5$ (SD = 13.8$, n = 4).
For the parasite eggs placed on the surface of the A. aurantia egg
mass the mean percentage of success was 85*4$ (SD = 11.2$, n = 3).
These two levels of success were not significantly different from
one another (0.10 > p > 0.05). Nevertheless, a trend is indicated
and a test with larger sample sizes would probably yield
significance.
Discussion
The suspension systems of the cocoons of both M. lemniscata and
A. aurantia function in two major ways. First, they keep the cocoon
isolated from contact with the surrounding vegetation and,
consequently, isolated from generalist pedestrian predators. The
low rates of attack by ants on the suspended cocoons of both spiders
suggest that few non-flying predators are willing or able to venture
out on the silk suspension lines. This is supported by the
significant rise in predation, particularly in the egg stage, for
M. lemniscata cocoons placed in contact with the vegetation. The
three field collected A. aurantia cocoons attacked by ants were also

90
cocoons that had contacted the vegetation because of suspension
system failure (see Table 6-4). Second, the suspension system
functions to maintain the position of the cocoon within the proper
microhabitat or vegetational layer. Parasites (Moore 1977) and
pedestrian predators (Robinson 1980) may be distributed predictably
in the habitat, and cocoons that change position due to structural
failure may move into strata where they are available to new
predators or are generally easier to locate. Indeed, cocoons of
M. lemniscata suffered increased rates of predation from ants, while
those of A. aurantia were attacked heavily by small rodents (see
also Robinson and Robinson (1976)] when they were placed on the
ground. The importance of maintaining position is further
emphasized by the difference in average individual survival for
A. aurantia cocoons that were left in position in the vegetation
(59-98^), and for those that were placed on the ground (0-5%).
The literature suggests that parasitic flies are fairly common
in cocoons with loosely woven covers, but are not found often in
cocoons with hard or dense covers (Eason et al. 1967, Muma and Stone
1971, Austin, In press). The results of cover modification on
M. lemniscata cocoons supports this view. The triungulid larvae of
M. viridis had no trouble crossing the silk suspension line or
finding the correct line to the cocoon in the maze of the tangle web
(Hieber 1984). However, the dense cover prevented the larvae from
successfully entering the cocoon (see also Kaston and Jenks 1937).
The high percentage of unsuccessfully attacked cocoons with
chloropid fly eggs on them, and the significant increase in

91
successful attacks by P. signata larvae on A. aurantia cocoons
damaged by the attacks of other parasites suggests that the covers
of A. aurantia cocoons are also a barrier to attack by larvae. From
this, I concluded that the cocoon cover functions primarily to
prevent the access of actively searching mantispid and dipteran
larval stages. Austin (in press; citing an unpublished author)
points out that female wasps in the genera Tetrastichus and
Eurytomus (Eulophidae) oviposit into the topmost layers of cocoons.
The emerging first instar larvae then burrow through the cocoon wall
and attack the host eggs. If the Tetrastichus wasp in this study
utilizes a similar method of attack, the dense cover of
M. lemniscata cocoons cover may make entrance difficult for the
attacking larvae. Difficulty in entering the cocoon may account for
the relatively low rate of parasitization (see Table 6-1).
The greater success of mantispids in attacking A. aurantia
cocoons (5-14%) over M. lemniscata cocoons (0-4£) suggests that
A. aurantia cocoons do not present as difficult a barrier to
attacking larvae. This may be related to the structure of the
cocoon itself since the covers of A. aurantia cocoons are less
tightly woven than those of M. lemniscata (see Fig. 6-3). However,
the architecture of these two cocoons may also reflect broader
reproductive strategies. Adult female M. lemniscata are preyed upon
heavily by mud-daubing wasps (pers. ob.) and by kleptoparasitic
Argyrodes spp. (Araneae: Theridiidae) (see also Trail 1980, Wise
1982) in the early to middle part of their reproductive season.
They are therefore probably under some constraints to produce

92
Fig. 6-3. The covers of the cocoons of Mecynogea lemniscata (A) and
Argiope aurantia (B) comparing the difference in the tightness of
the weaving. The scale line in each equals 120 ym. Both cocoons
were plated with 75 A of gold and observed using secondary
electrons.

93
clutches as quickly as possible. This may account for the small
clutch size of the spider. Since the probability of only producing
one or a few small clutches is high, these should be protected as
well as possible, particularly since successful predator attack on
M. lemniscata cocoons is always 100% fatal. In contrast,
A. aurantia is a large spider when mature, and few predators attack
it. This spider's reproductive season is timed with the early fall
peak, in orthopteran prey, and the relative abundance of food allows
the average spider to produce 1-3 huge clutches of 800-2000 eggs.
In the midst of abundant prey, allocating a percentage of the egg
mass to those predators using a larval attack might be less
expensive than the increase in time and energy involved in making a
cocoon totally impenetrable. The relativly low percentage of eggs
lost to attacking mantispids and chloropid flies (30-40%) in
comparison to those lost in a successful ichneumonid attack (90%)
suggests that this is a viable alternative (see Table 6-5).
The advantages of the cover as a physical barrier to attack
disappear when the cocoon is attacked by wasps with long
ovipositors. This is because the cover can be circumvented by the
ovipositor, and the predator's eggs, and ultimately its larvae, can
be placed near or on the host egg mass. The cover, however, may
still represent an obstacle to successful attack. Many wasps only
utilize hosts that are in a specific stage of development (Vinson
1976). The cocoon cover could limit information on the status of
the host to predators landing on the cocoon, thereby forcing them to
waste time or energy cutting a hole in the cover or inserting

9k
their ovipositors into the cocoon to check on host condition. The
large number of cocoons which T_. ovivora rufopectus sampled without
ovipositing suggests that this wasp cannot determine host quality
without inserting its ovipositor into the cocoon (Dethier 19^7).
Indeed, this wasp has indentations along the tip of its ovipositor
similar to sensory pits described by other workers (Fulton 1933,
Salt 1937, Varley 1941, Fisher 1971) (Fig. 6-4).
In addition, many parasites use chemicals to mark previously
searched hosts so further time and energy are not wasted returning
to and exploring a nonproductive host (Salt 1937, Price 1970a,
Vinson 1972). These chemicals have a number of effects, including
the attraction of hyperparasites (DeBach 1944, Price 1970b, Vinson
1975, 1976). I have observed small circles of the hyperparasites of
T. ovivora rufopectus stroking the surface of A. aurantia cocoons
with their antennae and chewing into the cocoon. I have also found
the chewed entrance holes of the hyperparasites and female
byperparasites in approximately 29% of the cocoons that were
sampled, but not oviposited into, by this ichneumonid. These
observations strongly suggest that this hyperparasite is responding
to a marking chemical deposited by T. ovivora rufopectus during
oviposition. Attraction to such a chemical may partially explain
the relatively high rate of hyperparisitism (59-82%) on this wasp.
Increasing the general level of hyperparasites in the habitat by
forcing the parasites to mark cocoons would be particularly
beneficial if the spider host deposits more than one cocoon in a

95
Fig. 64. The ovipositor of the ichneumonid Tromatobia ovivora
rufopectus showing recessed pres along its length and concentrated
at the tip (in the box). These pits are similar to others that have
been described as having a sensory function. The scale line equals
20 um. The ovipositor was plated with 75 A of gold and observed
with secondary electrons.

9b
reproductive season. Indeed, communities of cocoon parasites may be
structured by their hyperparasites response to these chemicals
(Price 1980).
Successful avoidance of the cocoon cover by initial egg
positioning during oviposition, or through the damage done by other
predators does not guarantee, per se, that the attacking larvae will
have immediate unlimited access to the host egg mass. In many
cocoons there is a thick flocculent layer of silk between the egg
mass and the cocoon cover which must be crossed. In three field
collected A. aurantia cocoons in which oviposition had recently
occured, the flocculent silk layers contained the recently hatched
eggs of a predator and 20-30 small larvae which appeared dead (no
response to gentle prodding). Presumably these larvae died because
they ran out of energy or water, but it is conceivable that this
silk layer may actually damage the soft cuticle of the larvae much
like the trichomes of some plants damage attacking lepidopteran
larvae (see Gilbert 1971).
The presence of 8-10 large larvae in the egg masses of the
above-mentioned A. aurantia cocoons points out that the flocculent
layer is not a complete barrier. However, reducing the absolute
number of larvae that can reach the egg mass may be an adequate
defense when the egg mass is large. Although the result of the
laboratory experiment was not significant, the observed trend
further supports the idea of the flocculent silk layer as a barrier
to attack

97
The flocculent silk layer in the cocoons of M. lemniscata is
extremely thin and it seems unlikely that it provides much in the
way of a barrier to parasite larvae. However, this spider
periodically collapses its orb-webs as they become damaged or dirty,
and these collapsed webs are applied to the cocoons on the string.
This adds a thick external layer of silk and detritus to the cocoons
that may make it more difficult for the eulophid wasp, which is
relatively small, to gain access to the cocoon shell for drilling
(see Opell 1984). This layer may also work as a further barrier
against the mantispid larvae.
Obviously, the various layers of the cocoon may also interact
with each other to reduce successful parasite attack. The cocoon of
A. aurantia is suspended in the vegetation by a cloud of silk lines
which arise from suspension line deltas on the cocoon surface (see
Fig. 2-2a). If suspending the cocoon was the only purpose of these
lines, the majority of them should arise from the top of the cocoon,
with a few on the sides and bottom to provide stability and prevent
rotation. However, the greatest number of deltas are found in the
middle of the cocoon where the lines emanating from them would
contribute little to cocoon support. This is puzzling until the
position of the egg mass within the cocoon is considered. The egg
mass is closer to the cocoon cover in the upper part of the cocoon
because of its shape, and here the average ovipositor can reach it.
However, the egg mass is shielded at its top end by a cone of silk
and a thick cap of silk (the cup in which the eggs were initially
deposited) (see Fig. 2-2b), and the low number of ovipositor drill

98
holes in the top of the cocoon suggests that these structures are
hard to drill through (see Table 6-7). In the bottom third of the
cocoon, the egg mass is, on average, further from the cover than the
ovipositor can reach. An attack here would result in eggs being
deposited in the flocculent silk layer where the hatching larvae
have a high probability of becoming entrapped. The number of drill
holes is low in this end of the cocoon as well. The middle of the
cocoon represents the best fit between ovipositor length and
distance to the egg mass without interference from a mechanical
barrier, and the number of drill holes is greatest in the the middle
of the cocoon's surface (see Table 6-7). However, the distribution
of drill holes is identical to the distribution of support line
deltas. This suggests that the "suspension" lines are located to
interfere with the wasp during oviposition, either by making it
difficult to get to the cocoon surface in this area, or by making it
difficult to insert the ovipositor maximally, thereby causing eggs
to be deposited in the flocculent layer.
Given the relative size and strength of foraging passerine
birds, it seems unlikely that the cocoon of A. aurantia provides
much resistance to attack. However, many birds dislike coming in
contact with spider webs and the suspension system, and consequently
A. aurantia cocoons, might be avoided for this reason. Hiding the
cocoon might be a more appropriate measure against visually hunting
predators such as birds. However, there was no significant
difference between those cocoons attacked by birds and those not
attacked with regard to how well they were concealed by dead leaves

99
and other vegetation. The cocoons of M. lemniscata are not attacked
by birds at all, even though they are visible in the habitat. This
may be for a number of reasons. First, they are extremely small and
probably do not give much return for the energy invested in
harvesting them. They are also very hard. In addition, they may be
covered with old web and prey remains, and appear as detritus to
visually hunting predators. Finally, they are hung away from
perches on their suspension lines and would be difficult to take
except while hovering.
In the preceeding discussion, I have dealt primarily with the
cocoon as a barrier to attack once the cocoon has been located by a
predator. However, the field evidence suggests that a number of
cocoons in the habitat are never found by T.. ovivora rufopectus or
P. signata. Failure to locate hosts may also explain the low
overall percentage of M. lemniscata cocoons attacked by the
Tetrastichus wasp. A number of factors may contribute to the
inability of a parasite to locate hosts, including the behavior of
the host itself. The spatial and temporal aspects of host
reproduction, and their effects on successful parasite foraging are
considered in Chapter VII.

CHAPTER VII
COCOON SPACING AND THE TIMING OF PRODUCTION AS METHODS TO AVOID
EGG AND SPIDERLING PREDATORS
Introduction
Current evidence indicates that parasitoid species do not
search randomly, but rather are directed to their hosts through a
hierarchy of specific physical and chemical cues which function to
reduce and restrict the area and habitats searched and subsequently
increase the probability of finding a suitable host (Salt 1935,
Flanders 1953, Doutt 1959, Vinson 1976). In addition, behavioral
evidence suggests that parasitoids discriminate between areas of
high and low host density and allocate greater proportions of their
searching time to areas in which host density is high (Waage 1979).
This latter behavior has been termed "parasitoid aggregation" or
"non-random search" (Hassell and May 1973, 1971*, Hassell 1978).
Parasitoid aggregation should cause host mortality to be high
in areas where host density is high, while patches of low host
density, where the probability of parasitoid attack is low, should
represent refuges for the host (May 1978). Although true for some
insects (Hassell 1966, McClure 1977, Washburn and Cornell 1979),
negative correlations between host number and the level of
parasitoid attack (Hassell 1966, Morrison et al. 1980) or lack of
any correlation (Dowell 1979, Morrison et al. I98O) are more
frequent findings (Morrison and Strong 1980). When a
IOC

101
density-dependent pattern of parasitoid attack is not observed, some
factor has usually been suggested as acting to interfere with the
parasitoids' search. Suggested factors include tidal inundation of
hosts (Stiling and Strong 1982), temperature and humidity (Vinson
1976), heavy rain fall (Stiling and Strong 1982), differential
response to hosts at different densities (Hassell and May 1973),
insufficient numerical response, dispersal and/ or reduced search
efficiency due to mutual interference (Hassell 1971, Hassell and May
1973, 197*0, or "pseudo-interference" (Free et al. 1977).
Considerations of host behaviors such as the phenology of host
emergence or the timing of host production, and their effects on the
temporal and spatial distribution of the host or its reproductive
stages have not often been considered as factors affecting
parasitoid search, although an understanding of spacing and timing
in general are important to our overall understanding of host/
parasite interactions (Murdoch and Oaten 1975, Morrison and Strong
1980). In addition, this predicted relationship has not been tested
for any spider and its parasites, although spiders and their cocoons
can be heavily attacked (see Eason et al. 1967).
Here, I test the prediction of a positive relationship between
host density and the level of parasite attack for the cocoons of the
spider Mecynogea lemniscata (Walckanear) (Araneidae) and its primary
egg predator, the wasp Tetrastichus sp. (Eulophidae) [near
T. banksii Howard; see Hieber (1984)]. I then examine the early and
narrow reproductive season of this spider, the timing of cocoon
production, the spatial distribution of the cocoons within the

102
habitat, and the temporal appearance of the cocoons in space as host
behaviors that function to reduce egg predator success by making
hosts difficult to locate. Finally, I conclude that these behaviors
account, in part, for the low rates of parasitism and the observed
relationship between host density and the level of egg predator
attack.
Materials and Methods
This study was conducted from 1981 to 1984 in mesic,
flood-plain woods surrounding Lk. Alice on the campus of the
University of Florida, Gainesville, FL. Host density was determined
by collecting all the cocoons from areas of known volume. For 1981,
2
the sampling was done in one 800 m plot (10 x 20 x 4 m). In 1982,
2
four 200 m plots (7 x 7 x 4 m) were sampled to determine the
variation in host density within the habitat. During the sampling
of the 1982 plots, both currently produced cocoons and cocoons from
the previous year(s) were collected. In 1983, the sampling was done
2
in one 400 m plot. The sampling height of 4 m was chosen after I
observed that less than 5% of the cocoons in the population were
deposited above this height.
All the cocoon strings collected each year for the host density
determinations were brought into the laboratory and the individual
cocoons in each string were cut open and scored for parasite attack
(the presence of larvae, pupae, or shed pupal exuviae), or the
number of eggs or spiderlings they contained. The position of

103
parasitized cocoons within a string and the total number of cocoons
in each string were also recorded.
The relationship between host density and level of parasitism
among sites of high and low host density was determined from the
four plots sampled in 1982. For each plot the proportional survival
(S/N; number of unparasitized cocoons/ total number of cocoons) was
calculated and plotted against the cocoon density (N). The
relationship between host density and level of parasitism within a
2
site was determined by dividing the UOO m volume surveyed in 1983
into fifty 8 nr sub-volumes. The proportional survival in each of
the sub-volumes with cocoons was calculated and plotted against its
cocoon density. Density dependence is indicated by a negative slope
for such plots.
Developmental rates for the host and wasp were determined by
rearing spider eggs and wasp larvae in 2 dram glass vials stoppered
with cotton and maintained at 28 C and 70-60$ RH (ambient
conditions at the study site). The age of the host at the time of
attack was determined by rearing the remaining eggs from three
cocoons in which developing wasp larvae were found.
Additional collections of cocoons were made in mid-July [during
the peak of wasp attack (Hieber I98U)1 and late December in 1983,
and in early March in I98H (just before spiderling emergence) to
establish if the parasite overwinters in the cocoon as a prepupae,
and if so, when it emerges in the spring. Cocoons from these
collections were opened in the laboratory and scored for the
presence of wasp larvae, shed exuviae and larvae, or shed exuviae

alone. All the larvae from the March collection were held in 2 dram
glass vials at 60-75/ RH and 26 C until emergence.
The rate of cocoon production, and the temporal and spatial
distribution of the hosts were determined in 1983 by mapping the
web-sites (X, Y, and Z coordinates) in the U00 m volume and
recording the daily production of cocoons. These data, along with
the parasite attack data, were used to determine the overall spacing
pattern of the hosts, the spatial distribution of the hosts through
time [in both cases using a 3-dimensional nearest neighbor
approach; Clark and Evans (195^, 1979)1, and the location and time
of individual parasite attacks.
Results
The level of cocoon parasitism in the habitat remained
relatively constant at 7-9^ for all three years (Table 7-1) This
level is relatively low compared to the 25-75 levels suffered by
other spiders (Edgar 1971, Kessler and Fokkinga 1973, Enders 197^,
Tolbert 1976, Prakash and Pandian 1978). The cocoons are not
distributed evenly in the habitat. There is variation in both their
density across the habitat and within a single plot in the habitat,
presumably because of the heterogeneous distribution of young trees
and shrubs used by this spider for web supports.
Density dependence is indicated by a negative slope in plots of
proportional survival (S/N) against density (N). In this study,
there were no density-dependent relationships between the levels of
cocoon predation and cocoon density, either among sites in the

105
Table 7-1* Densities of Mecynogea leianiscata cocoons, and the
percentages of cocoons attacked by the^Tetrastichus sp. wasp for the
years 1981 to 19§3. In 1981, on 800 in volume was sampled; in
1982, four 200 m3 volumes; in 1983, one 400 mJ volume. The
experimental volume for 1983 was further divided to determine the
relationship between host density and the level of parasitism within
a site.
No.
Total
Cocoon
No.
%
Cocoon
No.
Density
Cocoons
Cocoons
Year
Strings
Cocoons
(in )
Attacked
Attacked
1981
83
290
.362
21
7.24
35
90
.450
6
6.67
1982
27
72
.360
5
6.9
27
55
.275
6
10.90
16
37
.185
1
2.70
1983
38
117
.292
11
9.40
8
22
2.750
2
9.09
6
21
2.625
2
9.52
3
10
1.250
2
20.00
3
9
1.125
1
11.11
3
9
1.125
0
0.00
2
10
1.250
1
10.00
2
6
.750
1
16.66
2
6
750
0
0.00
1983 by a
2
3
.375
1
33.33
Subvolume
1
6
.750
0
0.00
1
5
.625
1
20.00
1
5
.625
0
0.00
1
3
.375
0
0.00
1
1
.125
0
0.00
1
1
.125
0
0.00
1
1
.125
0
0.00
1
1
.125
0
0.00
a
Of the 50 subvolumes, 33 contained no cocoons at all

106
habitat (Fig. 7-1) or within one site (Fig. 7-2). In both cases,
there is no correlation at all between the level of host density and
parasitism (both p > 0.05), implying that some factor in the habitat
is interfering with this predator's foraging and reducing its
efficiency.
The average spider in 1983 produced a cocoon every 6.4 days (SD
= 3.2, n = 73), and produced a string containing 3.1 cocoons (SD =
1.6, n = 38). This is consistent with the average number of cocoons
found in strings in 1981 and 1982 (Table 7-2). Although the average
number of eggs in each of the sequentially produced cocoons varied,
the distribution of eggs among the cocoons showed a similar pattern.
In all three years, the first cocoon produced contained the greatest
number of eggs. In addition, egg number declined significantly in
the second and third cocoons of the string (all p < 0.05). The
fourth and subsequently produced cocoons in a string all contained
approximately the same number of eggs.
The wasp averaged 16 days to develop (l day in the egg stage; 5
days as larvae; 10 days as pupae), while M. lemniscata eggs averaged
20 days to develop to the spiderling stage (l6 days as eggs; 4 days
as deutova until molting). The three batches of eggs reared from
attacked cocoons took l6, 17, and 19 days, respectively, to develop
under identical rearing conditions. This suggests that the wasp is
obligated to attack the cocoon within the first few days of its
appearance.
Approximately 50-70% of the attacked cocoons collected during
December and March contained diapausing prepupae (Table 7-3) Wasps

Proportional Survival (S/N)
107
0.9
0.8 -
0.0
30 50 70 90
Cocoon Density (N)
Fig. 7-1. The relationship between proportional survival (S/N) and
cocoon density (N) for Mecynogea lemniscata cocoons in four
different sites. Proportional survival is not significantly
correlated with cocoon density (Y = -0.0004X + 0.959; r = -0.32, df
= 2, p > 0.05), indicating no density-dependent relationship between
predator foraging success and host density.

Proportional Survival (S/N)
108
1.0-
0.8-
0.6-
0.0
r 1 1 r
0 5 10 15 20 25
Cocoon Density (N)
Fig. 7-2. The relationship between proportional survival (S/N) and
cocoon density (N) for Mecynogea lemniscata cocoons within one site.
Proportional survival is not significantly correlated with cocoon
density (Y = -0.003X + 0.944; r = -0.19, df = 15, p > 0.05),
indicating no density-dependent relationship between parasite
foraging success and host density.

Table 7-2. Mean number of Mecynogea lemniscata cocoons per string, and the mean number of eggs in
each cocoon in the string for the years I98I-I983. The SD is in parentheses. The sample size (n) is
the number below each mean. The number in brackets is the number of times a cocoon in that position
in the string was attacked by the Tetrastichus sp. wasp for the sample collected that year.
Average Number of Eggs in Each Cocoon
Year
1981
1982
X No. Cocoons/
String
Cocoon
01
Cocoon
02
Cocoon
03
Cocoon
#4
Cocoon
#5
Cocoon
6
3.5 (1.3)
19.5 (6.6)
16.8 (5.5)
14.3 (6.2)
12.8 (4.1)
11.0 (3.7)
9.7 (5.5)
83
78
69
56
36
9
3
12]
[41
[6]
[31
[31
131
2.5 (1.2)
15.8 (6.1)
12.6 (4.6)
10.3 (4.3)
10.2 (4.6)
8.6 (4.4)
8.0 (0.0)
105
80
53
38
16
5
l
[41
[91
[41
[0]
[0]
HI
3.1 (1.6)
18.5 (5.6)
15.8 (5.3)
12.7 (5-9)
13.4 (5.7)
12.7 (5.4)
15.0 (0.0)
38
37
25
19
12
7
1
[0]
[2]
[41
[21
[2]
[1]
o
vo
1983

110
Table 7-3. A comparison of the contents of attacked Mecynogea
lemniscata cocoons. Cocoons were collected in the experimental plot
in August 1983, and from random locations earlier in July (during
the peak in wasp attack), in December, and in March 1984 (two weeks
before M. lemniscata emerged from overwintering). The presence of
prepupae or exuviae in a cocoon were used as indicators of wasp
attack.
Date
No.
Cocoon
Strings
Total
No.
Cocoons
No.
Cocoons
Attacked
No. Cocoons
with
Prepupae
No. Cocoons
with only
Exuviae
July
37
125
10 (8.0%)
8 (80.0%)a
2 (20.0%)
August
38
117
11 (9.4%)
5 (45.5%)b
6 (54.4%)
December
92
357
32 (9.0%)
13 (40.6%)c
19 (59.4%)
March
59
254
21 (8.3%)
13 (6l.9%)d
8 (38.1%)
All 8 cocoons contained only prepupae.
All 5 cocoons contained only prepupae.
Of the 13 cocoons containing prepupae, 6 (18.8%) contained
only prepupae, and 7 (21.8%) contained prepupae and shed
exuviae.
Of the 13 cocoons containing prepupae, 8 (38.0%) contained
only prepupae, and 5 (23.8%) contained prepupae and shed
exuviae.

Ill
began to emerge in the laboratory from the cocoons collected in
March as early as the 4th of May. However, the majority of wasps
completed development and emerged between the 24th of May and the
10th of June, 2 to 19 days before the spiders started egg laying in
the field.
In 1983, cocoon production started the 12th of June and
continued to approximately the 8th of August (Table 7-4).
Reproduction was not synchronized, and initially cocoons appeared
slowly in the habitat as the early laying spiders started
oviposition. For the majority of spiders, the oviposition period
ran from approximately the 25th of June to the 25th of July. Early
in this period cocoon production increased rapidly with the number
of cocoons nearly doubling every 6 days. Cocoon production peaked
around the 15th of July and then declined sharply as the majority of
the population finished reproduction. Production then continued at
a reduced rate until the late starting spiders finished egg laying
in early August.
As the number of web-sites with cocoons increased over the
season, their distributional pattern changed from one significantly
more dispersed than random early in the season (15-21 June), to
random (27 June), to a loosely clumped distribution where it
remained (3 July to the end of the season) (Table 7-4). The
distribution of web-sites with cocoons in the appropriate stage for
attack (1-5 days old) showed a similar pattern of change (Table
7-4). Early in the season the distribution of sites with cocoons of
this age changed from overdispersed (21 June), to random (27 June),

Table 7-4. The number and distribution in space and time of all Mecynogea lemniscata web-sites with
cocoons, and of sites with cocoons of the proper age (1-5 days) for attack, in the experimental plot
for 1983.
Date
June July August
15
21
27
3
9
15
21
27
2
8
l4
No. web-sites
with Cocoons
2
7
21
34
34
34
35
35
35
35
35
Average No.
Cocoons/ web-site
1.0
1.1
1.3
1.6
2.4
2.9
3.0
3.2
3.2
3.2
3.2
Total No. Cocoons
for all Web-sites
2
8
28
56
80
99
106
111
112
113
ll4
No. Web-sites with
Cocoons 1-5 Days Old
2
6
i4
22
23
12
6
5
1
1
0
% Web-sites with
Cocoons 1-5 Days Old
100%
85%
67%
64 %
66%
35%
17%
l4%
3%
3%
0%
112

"R" for all
Web-sites8, 2.51
"R" for Web-sites with
Cocoons 1-5 Days Old8 2.5
i.6o*
0.99
0.77*
0.80*
0.79*
1.43*
1.09
0.83*
0.80*
1.13
0.77* 0.77* 0.77* 0.77* 0.77*
0.74 0.4l*
The "R" values (a measure of dispersion), and their departures from random were calculated using
the procedures outlined in Clark and Evans (1954). R values run from R = 0 indicating maximum
aggregation, to R = 1 indicating a random distribution, to R = 2.15 indicating a perfectly uniform
distribution. The stared (*) R values indicate a pattern of web-site distribution significantly
different from random (p < 0.01).
The R values for June 15th are beyond the scale because there were only two web-sites at this
time. Their distribution cannot be tested for significant departure from random for this reason
as well.
113

114
to loosely clumped (3 July). In mid-July (9-21 July) the
distribution returned to random as cocoon production declined. Late
in the season (27 July), as cocoon production drew to a close, the
distribution of web-sites with cocoons 1-5 days old became
relatively clumped again.
There were 11 cocoons attacked in 10 different strings by the
Tetrastichus wasp in the experimental plot in 1983. These attacks
occured between the 6th of July and the 8th of August, with the
majority (9 of 11) occuring between the 10th and 23rd of July.
Attacks can occur earlier in the year (Hieber 1984). Assuming that
overwintering wasps attack cocoons soon after emerging in mid-June,
the peak in attack represents the emergence of the second generation
of wasps (l6 day developmental period; 32 days later) from cocoons
attacked in late June-early July.
The concentration of wasp attacks coincided with the end of the
peak in cocoon production. Just prior to this period, the ratio of
web-sites with cocoons 1-5 days old to all sites with cocoons was at
its highest {66%) for the season (see Table 7-4). Over the
approximate 15 day period of heaviest wasp attack, however, this
ratio dropped to 14% as cocoon production slowed down. At the time
of the first attack, the average spider had already produced 584%
(SD = 22.5, n = 27) of its 3.1 cocoons. This resulted in the wasp
attacks being concentrated primarily on the third cocoon in a
string. This pattern is similar for 198l and I982 as well (Table
7-2).

115
Discussion
Explanations of parasitoid foraging suggest they locate hosts
through a series of steps mediated by one or more physical or
chemical cues. Such models have led to the prediction of
density-dependent parasite mortality of the host. Hosts should be
under heavy selection for behaviors which reduce or eliminate the
quality or number of useable cues available to the host to reduce
the probability of its success. For the Tetrastichus wasp, which
emerges from cocoons in the host habitat (the woods), a successful
search involves locating a string of M. lemniscata cocoons and
selecting a cocoon in the proper stage for attack. The low overall
levels of parasitism (7-9%) by this wasp in comparison with the
levels of parasitism demonstrated by other wasps using cocoons
(25-75%), and the lack of the predicted relationship between cocoon
density and the level of parasitism suggest that something is
interferring with this search process.
Mecynogea lemniscata (Walckenaer) (Araneidae) is the first
orb-weaver to emerge in the spring and its reproductive period is
shifted to the early summer, far earlier than the other orb-weavers
using the woodland habitat. Consequently, M. lemniscata starts egg
laying at a time when few other spiders are producing cocoons. This
limits the parasites in utilizing other spider hosts to build up
their numbers during the early appearance of M. lemniscata cocoons.
In addition, M. lemniscata is reproductively active for a 40 day
period. This short time interval limits the number of wasp

116
generations to one or two, preventing a large build-up of predators.
The slow initial appearance of cocoons due to the asynchrony of the
hosts' reproduction further acts to keep predator numbers down by
limiting the number of cocoons initially available to the wasps
emerging from overwintering.
More importantly, the rapid rate of cocoon production (every 6
days) in relation to wasp generation time (every l6 days) allows the
spiders to produce 1-2 cocoons with high numbers of eggs prior to
the emergence of the first generation of wasps in late June-early
July. In addition, the number of eggs in the cocoons drops
significantly by the third cocoon. Thus, during the peak in attack
in mid-July, the majority of cocoons available to the wasps contain
less eggs (and less energy) than those produced earlier in the
season (see Table 7-2). Overwintering wasps result from cocoons
attacked during this peak period, and the reduction in egg number
(and energy) may act to reduce the numbers of wasps which emerge the
following year.
Many parasites are restricted in their attack to a specific
time in the hosts' developmental sequence (Vinson 1976). The eggs
of M. lemniscata take 16 days to develop to the deutoval stage. The
larvae of the wasp take 5 days to develop before pupation. If there
is no specific period of time during which attack must occur, the
wasp can initiate an attack any time during the first 11 days of
host egg appearance to have enough time for development (assuming
that the larvae cannot use deutova as food). When such a timing
scheme is plotted out for a string of three cocoons, each 6

117
days apart in age, there are always two cocoons on the string in the
proper age for attack (Fig. 7-3a). In addition, one or two other
cocoons on the same string are available for attack when the wasp's
progeny emerge 16 days later (mating takes place on the outside of
the cocoon).
The rearing data suggests, however, that the time period for
attack is less than this 11-day period. If a more conservative
5-day period is used as the limit for successful parasite attack, a
different picture emerges (Fig. 7-3b). With cocoons produced every
six days, there is only one cocoon in the string at any given time
in the proper condition for attack. In addition, the timing of
cocoon production insures that the emerging progeny barely overlap
with one cocoon instead of two. The average string contains only
three cocoons, and if the second or third cocoon is attacked, there
are no cocoons available for emerging progeny. Thus, the
interaction between cocoon production and egg development forces the
initally attacking wasp, or its subsequent progeny, to locate other
web-sites with strings containing useable cocoons. The low number
of multiply-attacked cocoon strings (3.1^ of 286 for 1981-1983)
supports the hypothesis that timing of cocoon production is a
barrier limiting individual parasite success.
In general, web-sites, and thus host cocoons, are slightly
clumped in their distribution (Table 1-h). Spiders which utilize
sites that are spatially isolated from other web-sites or clumps of
sites may therefore have an advantage in avoiding parasites.
Although the distance between web-sites may play a role early in the

Fig. 7-3. The number of Mecynogea lemniscata cocoons in a three-cocoon string available to a
Tetrastichus wasp or her emerging progeny assuming an 11-day period for attack (a), or a more
conservative 5-day period (b). The cocoons in each string are represented by individual bars. In
both cases the cocoons are produced every 6 days. The stippled area of each bar represents the
period of time (ll or 5 days) during which attack can occur; the stippled and open areas together
represent the total l6 days the host is in the egg stage; the solid areas represent the 4 day
deutova stage after eclosin. The first cross-hatched box indicates the number of cocoons that can
be initially attacked by the wasp. The second box indicates the possible cocoons on the same string
that can be attacked by emerging progeny.

Days
119

120
season when they are dispersed and have few cocoons, web-site
spacing has little or no effect on the probability of being
parasitized. Indeed, many of the cocoon strings attacked in the
experimental plot occured at spatially isolated sites (see Figure
7-4).
However, the change through time of the spatial distribution of
web-sites with cocoons 1-5 days old may act to reduce the
probability of a parasite successfully locating a useable cocoon.
The majority of wasp attacks occured between the 10th and the 23rd
of July. Just prior to this period (July 3-9), the percentage of
sites with useable cocoons was at the highest level for the season
(see Table 7-4). Sites with useable cocoons were also slightly
clumped in their distribution among all web-sites, which were also
slightly clumped. By the 15th of July, the reproductive pulse
started to taper off and the number of sites with useable cocoons
began to decline. More importantly, during this time period the
distribution of sites with cocoons 1-5 days old became random
compared to the slightly clumped distribution of all web-sites (see
Table 7-4). Many parasites locate their hosts through the use of
long-range chemical cues (Vinson 1975, 1976) and then use
short-range cues to determine the location and quality of the host
(Laing 1937, 1938, Eason et al. 1967, Vinson 1976). Since
long-range cues rarely provide information about the quality of the
host, the "switch" to a random distribution of hosts would lower the
probability that a parasite will find a cocoon since a response to
cues from an area of high cocoon density guarantees only a random

121
Fig. 7-4* The spatial distribution of all the Mecynogea lemniscata
web-sites with cocoons in the 4 x H x 10 m experimental plot for
1983. The distribution of web-sites is slightly clumped ("R" =
0.77; see Table 7-M. Web-sites containing strings with attacked
cocoons are indicated with stars. The site with the open star had
two cocoons attacked in the string. The location of web-sites with
attacked cocoons is unrelated to their distance to other cocoons or
clumps of cocoons.

122
chance of a site with a useable cocoon. The random distribution of
sites with 1-5 day old cocoons remains until late July when sites
with useable cocoons again show a clumped distribution (see Table
7-1+) However, by this time sites with cocoons 1-5 days old are
rare, and the probability of locating one against the background of
older sites with nonuseable cocoons is low.
The low probability of locating a cocoon due to these spatial
and temporal effects may be further reduced if visual cues are used
by this wasp for host location (Laing 1937). Approximately 50-64%
of the cocoon strings collected in each of the four plots in 1982
were from the previous year(s). These strings were still hanging in
position, and presumably represent nonproductive sites which would
have to be examined at a cost in energy and time.
The preceeding discussion suggests that the low overall levels
of parasitism in this system can be explained by the short
reproductive season, which limits the number of wasp generations,
and the timing of egg development and cocoon production, which
limits the number of cocoons attacked in any one string. Both have
the effect of forcing wasps to look for new strings of cocoons. It
also suggests that the lack of a density-dependent relationship can
be explained by the interaction between the short reproductive
season, the rapid rate of cocoon production, and the limited time
period for successful cocoon attack. These factors force wasps to
locate a constantly decreasing number of randomly distributed
useable cocoons among a rapidly increasing number of web-sites with
cocoons too old for successful attack.

123
Obviously, there are other factors which may also account for
the observed levels of parasitism and the lack of a
density-dependent relationship. It is possible that this
Tetrastichus species has other hosts, and that the eggs of
M. lemniscata represent either a secondary host, or one of several
alternatives used when they are accidentally discovered while
searching for the primary host. Indeed, wasps in this genus can be
quite catholic in the host preferences (Burks 1979)* However, the
presence of prepupae in cocoons collected late in the year, and the
close timing of wasp emergence with the onset of cocoon production
strongly suggest that the eggs of M. lemniscata represent a primary
host for this wasp. The observed patterns may also be partially
related to mutual interference (Hassell 1971) in response to
"trail-marking" substances (Price 1970a), or simply to variation in
the "toughness", and thus ease of entry, of the available cocoons in
the habitat (see Chapter VI).
The above discussion implies that the observed pattern of
reproductive phenology and rates of cocoon production are
adaptations which have evolved in response to parasite pressure.
Certainly the 7-9% level of parasitism represents sufficient
evolutionary pressure to select for such behaviors. The parasite
and the host also appear to be closely linked, as demonstrated by
the relatively constant levels of host density and parasitism, the
timing of parasite emergence with host emergence, and the timing of
the wasp attack with the peak availability of cocoons. In addition,
the rate of cocoon production in Florida (6.1* days, SD = 3.2, n =

124
73) is not significantly different from the rates Eberhard (1979)
found for M. lemniscata in Washington, D.C. (5*6 days, SD = 2.8, n =
15) and Central America (6.3 days, SD = 2.1, n = 20). Since climate
and the abundance of food vary at these sites, these factors are
probably not responsible for the observed timing of cocoon
production. All of these facts support parasite avoidance as the
selective pressure setting reproductive rates. However, the rate of
egg production could also represent some physiological limit
independent of food intake, or selection for rapid reproduction in
response to high levels of maternal predation. Adult female
M. lemniscata are preyed upon heavily in June by mud-daubing wasps
(Hieber, unpub.) and in July by kleptoparasitic Argyrodes spp.
(Araneae: Theridiidae) in the webs (see also Trail 1980, Wise 1982).
The phenology of reproduction may also be partially accounted
for by other factors. The shift to an early spring appearance has
been suggested as a way of taking advantage of abundant insect prey
in the habitat, while avoiding competition from other orb-weavers
which use the woodland habitat later in the season (Anderson 1978).

CHAPTER VIII
GENERAL DISCUSSION AND CONCLUSIONS
General Discussion
Spider cocoons range in complexity from a few threads
surrounding the egg mass (e.g., the Pholcidae) to large complex
structures composed of many layers (e.g., the Araneidae) (McCook
1890, Scheffer 1905, Kaston 19^8, Turnbull 1973). Cocoons are
believed to protect the eggs or spiderlings by reducing the
detrimental effects of a number of biotic and abiotic factors
(Turnbull 1973, Foelix 1982, Austin, In press). However, with few
exceptions, none of the roles attributed to cocoons have been
tested.
I examined the effects of cocoon architecture on two abiotic
factors, temperature extremes (Chapter III) and dessication (Chapter
IV), and on the biotic problems of fungal attack (Chapter V) and
predator attack (Chapter VI). Chapter VII is closely linked with
Chapter VI and examines the temporal and spatial strategies that
spiders have evolved to reduce the initial probability of a predator
locating a cocoon. The primary technique I used was to modify the
cocoons and relate these modifications to changes in egg hatching
success and spiderling survival. The direct connection between the
function of the cocoon or component parts and measures of fitness
avoids many of the problems found in other ecological or
125

126
behavioral studies (e.g., foraging behavior). In the latter, a
number of initial assumptions, often unrealistic, must be made
concerning what is being maximized and how it relates to fitness.
Many authors have suggested that cocoons, and in particular the
flocculent silk layers often found within cocoons, function as
insulation and protects the eggs and spiderlings from extremes of
temperature (McCook 1890, Kaston 19^+8, Turnbull 1973, Gertsch 1979)*
Chapter III supports this view, and indicates that the protection
provided may be directed primarily at controlling short-term
radiation loads (i.e., "sunflecks"). The limited level of
protection offered by the cocoon is due to the cocoon cover, which
creates an insulating layer of dead, and, to a greater extent, the
size of the egg or spiderling mass which provides thermal inertia.
The flocculent silk layer has no role in the insulation of the
cocoon.
The size of the cocoon and the spiderling mass must be
considered before these results are extended to all cocoons. The
cocoon and egg mass of A. aurantia are among the largest found
(Kaston 19^8, Foelix 1982). As such, the level of protection
against short-term thermal loads provided by this cocoon and its egg
or spiderling mass is probably close to some maximum value. Cocoons
without covers which cannot produce a layer of dead air (Kaufman et
al. 1982), or cocoons with smaller egg masses would show
proportionately smaller effects in attenuating thermal extremes.
The position of the cocoon in the habitat probably plays a more
effective role in controlling thermal extremes for most spiders.

127
Given the time that the eggs, and particularly the spiderlings,
of many species spend in the cocoon (Anderson 1978), it seems likely
that this structure functions to control water loss. This is the
most commonly held assumption about the function of cocoons (e.g.,
Foelix 1982). However, previous work relating the cocoon to
dessication control has been contradictory. Schaefer (1976)
demonstrated that the parchment-like cocoons of the linyphiid
Floronia bucculenta increased the survival time of post-diapause
eggs. However, Austin and Anderson (1978) could detect no role in
desiccation resistance for the flocculent silk cocoon of the araneid
Nephila edulis.
The results of Chapter IV demonstrate that the cocoon of
Mecynogea lemniscata has no effect on hatching or molting success
but does have a significant effect on spiderling survival. In
contrast, the cocoon of Argiope aurantia has no apparent effect on
hatching success, molting success, or spiderling survival. These
results indicate that the level of protection provided by cocoons to
eggs or spiderlings is related to the length of time these
developmental stages spend in the cocoon. The eggs Schaefer (1976)
used in his study were post-diapause eggs approximately l80 days old
(F. bucculenta overwinters in the egg stage). These eggs are
apparently not very resistant to desiccation, and the cocoon may
provide the protection necessary for the eggs to make it through
this long period. In comparison, the eggs of Nephila clavipes
(Christenson and Wenzl 1980), M. lemniscata, and A. aurantia all
hatch in approximately 16 to 30 days. This may be too short to

128
demonstrate a protective function provided by the cocoon. The
significant effect of the cocoon on the survival of M. lemniscata
spiderlings appears to be related to the exceedingly long time that
they spend in the cocoon overwintering (2-3 months longer than
orb-weavers). Overall, the results of this study and those of
Schaefer (1976) and Austin and Anderson (1978) show that covered
cocoons should be found in species that spend long periods of time
as eggs or spiderlings in the cocoon in developmental diapause or
overwintering, or where the habitat is extremly xeric for all or
part of the year.
The results also emphasize that physiological or morphological
differences in the abilities of deutova and spiderlings to limit
water loss may also be operating in conjunction with, or in place
of, the cocoon. With no cocoons present, the deutova of
M. lemniscata molted successfully at much lower humidities than
those of A. aurantia. The survival rate for M. lemniscata
spiderlings without cocoons was also higher than those of
A. aurantia at lower humidities. Both of these results suggest that
the deutova and spiderlings of M. lemniscata are better able to
handle desiccation.
Finally, the results suggest that the above mentioned
differences might be part of a behavioral solution for controlling
water loss. The limited survival of A. aurantia spiderlings with a
cocoon at low humidities points out that other considerations, such
as the RH humidity at the oviposition site, are more important for
this spider. Indeed, Levi (1968) notes that of the Argiope species

129
in Florida, A. aurantia prefers moister habitats and is one of the
first Argiopes to disappear during droughts.
Morphological differences between the eggs of spiders, or
differences in the sizes of the egg masses also affect hatching
success. At low humidities the egg mass of A. aurantia (which is TO
times larger than the egg mass of M. lemniscata) has a significant
advantage in hatching success when naked egg masses of the two
species are compared. This advantage disappears when the egg masses
of A. aurantia are reduced to the same size as those of
P4. lemniscata. Here, the egg masses of M. lemnimcata demonstrate
significantly greater hatching success, and these differences appear
to be related to a significantly denser layer of spherical granules
on the surface of the M. lemniscata eggs.
These morphological and size related advantages are exciting
for a number of reasons. All of the spider eggs so far observed
have a layer of mucoid granules on their chorions (Austin and
Anderson 1978, Grim and Slobodchikof 1978, 1980, Humphreys 1983),
and this layer has been previously suggested to function as a
barrier to water loss (Austin and Anderson 1978). The results of
this study provide the first evidence supporting this hypothesis.
Both the density of the spheres on the chorion and the size of
the egg mass function to reduce water loss, presumably by reducing
the area available for evaporation. This suggests that small egg
masses with dense sphere coatings and large egg masses with less
dense coatings may represent solutions for dessication control. I
looked at the relationship of sphere density to clutch size. Since

130
clutch size data are not available for the data of Grin and
Slobodchikoff (1980, 1982), I used clutch size data for conspecifics
of the same relative body size from the literature (see Table 8-1).
The relationship between sphere density and clutch size is
shown in Fig. 8-1. A Spearman rank correlation, which is
conservative in its treatment of the tail values, is not significant
(r = -O.36T, p = 0.035), falling just short of the 0.05 level of
acceptance. However, the data incorporate a substantial amount of
variation, and the analysis therefore represents a conservative test
of the relationship. The fact that a relationship emerges and
hovers around significance suggests that the relationship is real
and would show significance if species-level rather than
congeneric-level data were used.
Finally, the advantage of a large clutch size in controlling
temperature extremes and water balance points out that selection for
clutch size may be driven by abiotic factors. This is in direct
contrast to much of the vertebrate literature that lists primarily
biotic factors (e.g., food supply, parental efficiency, or
predators) as the major selective forces working on clutch size
(e.g., Lack 1954, i960, 1968).
The results presented in Chapter V indicate that the cocoon,
and in particular its suspension system, function to prevent the
eggs or spiderlings from drowning (see also Schaefer 1976, Reichert
1981). A strong suspension system appears to be particularly
important for small cocoons that have a high probability of being
worked into the soil and consequently drowned due to their constant

Table 8-1. The mean sphere density ( 1 SD), and median clutch size for individual spiders from
different families. The sphere density values are from Gim and Slobodchikoff (1982). The clutch
size data has
values used to
been taken from the literature. The numbers
calculate the median clutch size.
in brackets
are the
range of clutch size
Family
Genus and species
Sphere Density,-,
(spheres/ 100 ym )
Median
Clutch Size
Theraphosidae
Dugiesiella sp.
10.00
( 5.30)
812a
Theridiidae
Lactrodectus hesperus Chamberlin and Ivie
Steadota grandis complex Banks
Argyrodes baboquivari Exline and Levi
Theridion sp.
24.69
54.38
48.13
97.50
( 5.40)
(18.10)
(11.80)
(27.35)
196b
62 [37-951^
32 [15-49]
69 [ 19-442]e
Araneidae
Araneus normandii Thurell
Argiope aurantia Lucas
Mecynogea lemniscata (Walckenaer)
4.84
17.00
21.60
( 1.90)
( 4.20)
( 5.50)
700 [284-887]f
978 [350-2000]g
14 (830Is
Agelenidae
Barronopsis floridensis (Roth)
184.38
(24.20)
130h
Lycosidae
Lycosa santrita Chamberlin and Ivie
Lycosa sp.
Pardosa makenziana (Keyserling)
Pardosa yavapa Chamberlin
126.25
35.00
103.13
211.20
(30.30)
( 9.86)
(27.20)
(37.70)
207 [32-600H
207 32-600]
4l [12-106jf
4l 112-106jk
Clubionidae
Castineira luctifiera Petrunkevitch
89.38
(14.70)
l4m
Philodromidae
Philodromus sp.
78.75
(20.60)
30 [7-104]n
Salticidae
Phiddipus octopuctatus McCook
80.63
(14.60)
90 [43-166]p
131

a Gertsch (1979)
k Kaston (1970)
from Steatoda borealis (Kaston 19**8)
^ from Argyrodes trigona (Kaston 19**8)
e
from Theridion tepidariorum, T. differens, T. murarium, T. spirale, T. frondeum,
T. albidum, T. unimaculatum, T. punctosparsum, T. redimitum (Kaston 19**8")
f
from Araneus diadematus, A_. cornutus, A., sericatus, A. marmoreus, A. trifolium,
A. pima, A_. gemmoides TKaston 19^8)
g This study
from Agelenopsis pen [ n ] sylvanica, A_. naevia (Kaston 19^8)
^ from Lycosa carolinensis, L^. aspersa, L. rabida, L. punctulata, L^. avida,
_L. helluo, Ij. modesta, L^. gulosa, L. frondicola, Ij. avara (Kaston 19^+8)
from Pardosa distincta, P. moesta, _P. milvina, P. saxatalia, Fh floridana,
Fh rnochia, _P. lapidiana, J?. xerampelina (Kaston 19^*81
m Reiskind (1969)
0 from Philodromus praelustris, P. pernix, JP. imbecillus, Fh rufus, _P. aureolus
(Kaston 19^8)
P from Phiddlpus audax, V. purpuratus, ]?. clarus, P. princeps, IP. whitmanni,
P. insjgnarius (Kaston 19**8)
132

133
CM
E
250-
o
200-

o
\
CO
4>

a?
150-
CL
CO

mmm
100-


CO
c
CD

a
CD
50-


4>

Cl
CO
0-
1 r
I 1
0 250
500 750 1000
Clutch Size
Fig. 8-1. The relationship between mean sphere density (spheres/
100 ym ) and clutch size for individual spiders from different
families.

exposure to soil moisture. This is apparently not a problem with
large cocoons which are not moved down into the soil and therefore
dry out between rains.
The suspension systems and covers also retard water entry, but
the relation between this function and the prevention of fungal
attack is less clear. The covers of M. lemniscata and A. aurantia
cocoons do not control fungal attack in the egg stage. However, the
flocculent silk layers in both of these cocoons are difficult to
wet, and this layer was left intact during the field experiments.
This could account for the lack of any effect from cover damage.
Although the cover of M. lemniscata cocoons controlled fungal, attack
in the spiderling stage, the cover of A. aurantia cocoons did not.
The differences in the incidence of fungal attack in the spiderling
stage may also be related to the flocculent layer, to the time spent
in the cocoon, and cocoon size. It is also possible that the
observed differences in egg and spiderling survival between these
two cocoons have nothing to do with the size or presence of various
layers, but rather with the chemical composition of the structure
itself. Some spiders manufacture anti-fungal materials which are
applied to their webs (Scnildknecht et al. 1972). Such materials
may also be used to protect cocoons.
One obvious function of cocoons is to protect them from
mechanical shock or damage (Opell 1984). In many of ny fungal and
predator attack experiments, the cocoons of M. lemniscata tied to
vegetation, and those of M. lemniscata and A. aurantia placed on the
ground were dented or partially collapsed by the falling rain.

135
For some, the impact of the rain was enough to crush the cocoons and
kill the contents. This suggests that the cover and suspension
system of many cocoons function to cushion the contents by
deflecting falling rain and absorbing its shock, or to keep the
cocoons off non-yielding surfaces where the force of the rain may be
concentrated. Such a protective role also explains the increase in
fungal attack that N. clavipes cocoons suffered when their
protective leaf canopies were removed (Christenson and Wenzl 1980).
With no canopy above the cocoon, rain would not be deflected from
the cocoon nor would its velocity be diminished. In this condition,
water would be driven deep into the cocoon carrying fungal spores
with it. In contrast, the cocoons of M. lemniscata and A. aurantia,
even with some cover damage, might still be able to deflect much of
the rain striking the cocoon or reduce its velocity.
The importance of the leaf canopy to N. clavipes illustrates
the importance in selecting specific sites for oviposition. Many
spiders locate their cocoons in crevices, under bark, or in the leaf
litter (McCook 1890, Kaston 19^8, Turnbull 1973, Gertsch 1979),
presumably to avoid abiotic problems. If such sites are limiting,
covered cocoons, by creating protective microclimates, would allow
spiders to use a wider variety of potential habitats and web-sites.
The large and diverse number of predators and parasites
attacking spider cocoons, and the wide range in complexity of cocoon
architecture have led many to speculate that the primary purpose of
cocoons is to protect the eggs and spiderlings from attack (Austin
and Anderson 1978, Christenson and Wenzl 1980, Robinson 1980). More

136
recently, Austin (in press) has considered cocoon architecture and
its relationship to predators and parasites. He suggests that the
cocoons of spiders function against two groups: l) oppurtunistic
scavenging predators (generalists), such as ants or beetles, and 2)
groups such as ichneumonid wasps, mantispids, and chloropid flies
(specialists) which are highly adapted for preying exclusively on
spider eggs. He further suggests that a coevolutionary "arms race"
(e.g., Krebs and Davies 1979) between spiders and the specialized
parasites and predators is responsible for the wide range of
structural diversity apparent among spider cocoons today. As such,
Austin's paper forms a convenient outline for discussing the results
of Chapter VI.
Predation pressure from generalists should show up as cocoon
adaptations which are generally distributed among a wide variety of
spiders, since generalist predators are distributed across habitats.
Austin (in press) suggests that the cocoon cover and maternal
guarding are adaptations against generalists, and should provide
high levels of protection. The results support this view.
Approximately 23% of the covers of the 185 A. aurantia cocoons
collected in 1982 were damaged by unknown predators (Table 6-U). In
many of these cocoons there was no damage to the egg or spiderling
mass, suggesting that the cover turned the attack away. Enders
(197M mentioned a generalist predator, a Chaulignatus beetle, that
attacks the cocoons of A. aurantia. He described damage similar to
ay observations. Other structures common to many cocoons may also
work against generalist predators. Many cocoons have suspension

137
systems that isolate the cocoon from the substrate and effectively
reduce its accessibility to general pedestrian predators. Both
M. lemniscata and A. aurantia cocoons suffered significant increases
in egg and spiderling mortality when the cocoons contacted the
vegetation or fell to the ground and became accessible to arboreal
predators (ants) and terrestrial predators (ants, rodents, and
possibly birds). Those cocoons which remained in place were almost
never attacked by these groups (excepting birds; see Tolbert 1976),
underscoring the effective barriers that suspension systems make
against these predators.
If coevolution between spiders and their specialized egg
predators is responsible for the diversity of cocoon architecture
(Austin, In press), cocoons should demonstrate specific defenses
against these specialized attackers which reflect the manner in
which they attempt to introduce themselves or their eggs into the
cocoon. Overall, the results presented in Chapter VI demonstrate
that a dense cover is an adaptation to control actively searching
larval forms. The most striking example was the control exerted by
the cover of M. lemniscata cocoons against the mantispid egg
specialist Mantispa viridis. This parasite is an obligate cocoon
attacker (Redborg and MacLeod, In press), the larvae actively
locating and burrowing into cocoons. Parasitization rates rose
dramatically from 1-4% to approximately 63% when the cover of this
cocoon was damaged (see Table 6-2), suggesting that the larvae of
this species have no trouble in locating cocoons (Hieber 1984), but
are almost completely stopped by the cocoon cover. The large

138
numbers of unsuccessful fly attacks on A. aurantia cocoons, and the
apparent preference of Pseudogaurax signata for cocoons with covers
damaged by other predators provide further support for the idea of
covers as specialized layers to control certain predators.
Dense covers may also be effective against wasps with short
ovipositors. The Tetrastichus wasp probably attacks the cocoons of
M. lemniscata by ovipositing into the top layer (Austin, In press);
the first instar larvae then burrowing through the cocoon wall to
attack the eggs. Unless the eggs are initially deposited through
the extremely hard cover, the larvae probably have a hard time
penetrating the cocoon (see also Kaston and Jenks 1937) The old
web deposited on the cocoon string may act to hide the dense cocoon
cover and fool the wasps into ovipositing into what appears to be
the outer layer of the cocoon, or keep them elevated off of the true
cocoon surface so that their ovipositors cannot completely penetrate
the outer cover (Opell I98U).
Although the covers of cocoons may force some wasps to waste
time and energy drilling through the cocoon to determine host
quality or to mark previously visited cocoons (which provides cues
for hyperparasites), cocoon covers appear to be only secondarily
related to controlling wasps with long ovipositors (e.g., the
ichneumonids). However, the distance of the egg mass from the
cocoon cover and the layer of flocculent silk between the cover and
the egg mass appear to be adaptations directly related to
controlling such wasps (see also Austin, In press). The separation
makes it difficult for wasps to deposit eggs directly on the host

139
egg mass, and the silk layer entraps emerging larvae as they move
toward the host eggs. Although not 100% perfect, the flocculent
silk layer substantially lowers the number of larvae which make it
to the host egg mass and is increasingly effective when the egg mass
is large. Under the best conditions, the principle predator of
A. aurantia cocoons, Tromatobia ovvora rufopectus, destroys only
90% of the eggs in a cocoon. In contrast, the predators of
M. lemniscata cocoons, which have small egg masses and a thin
flocculent silk layer, always destroy all of the eggs in an attack.
Many other araneids (e.g., members of the genera Araneus,
Gastercantha, Neoscona, and Nephila) utilize flocculent cocoons
without covers. These spiders also have relatively large egg
masses, suggesting that the combination of this layer and a large
egg mass may be a part of a set of adaptations for controlling
wasps. Austin (in press) points out that many scelionid wasps
cannot parasitize more than about 35% of some large host egg masses
because their ovipositors cannot reach further into the mass than
the upper two layers of eggs.
Chapter VI also demonstrates the integrated nature of the
various layers in defending the cocoon. For example, the suspension
system of A. aurantia cocoons fuctions to protect the eggs and
spiderlings from predators by keeping the cocoon away from contact
with the vegetation and off of the ground. Moreover, the suspension
lines on the cocoon are distributed in the areas of best fit between
the ovipositor of the ichneumionid predator and the distance to the
egg mass, presumably to interfer with oviposition.

As a family, the orb-weaving spiders (Araneidae) are attacked
by a wide variety of specialized predators from a number of the
major insect groups (Eason et al. 1967, Askew 1971, Austin, In
press). The results of Chapter VI study suggest that a covered
cocoon with a thick flocculent layer (e.g., the cocoon of
A. aurantia) may be the best combination for discouraging the widest
variety of predators. However, many genera of araneids use
flocculent cocoons which small wasps and flies can apparently enter
with relatively little hindrance (see e.g., Muma and Stone 1971).
In addition, many spiders position their cocoons in what appear to
be locations that are higly accesible or easy to locate. This
suggests that many spiders are using methods that reduce the numbers
of predators and parasites that initially locate the cocoon.
One method of reducing the number of predators that will
potentially locate a cocoon is to limit the availability of the
cocoons in time (Chapter VII). This could involve shifts in the
oviposition season to times when parasites are less abundant, or a
shortening of the reproductive season. Mecynogea lemniscata
reproduces early in the summer at a time when few other spiders are
reproductive. Reproduction at this time could reduce the overall
numbers of parasites present in the habitat, as well as limit them
from building up large numbers because of the lack of alternative
hosts. Enders (197*+) has demonstrated the positive effects of such
a temporal shift in the reproductive period for Argiope trifasciata
Forskal (Araneidae). The reproductive season of M. lemniscata is
also relatively short, subsequently limiting the number of parasite

generations that can occur in a given reproductive season. This
could further act to keep the overall number of parasites available
for attack low.
Escape can occur within a much shorter time scale if the
predator or parasite is limited to attacking the host within a
narrow developmental period. Both the eggs of A. aurantia and
M. lemniscata appear to present such limitations. In addition, the
timing of M. lemniscata cocoon production is such that only one
cocoon on a given string is available to an attacking wasp or her
emerging progeny. The interaction between the developmental
constraints and the timing of cocoon production for M. lemniscata
leads to two important outcomes. First, it limits the number of
cocoons at any one site which can be attacked by a wasp. This
forces the wasp to move off and look for another site. Second, it
results in a spatially variable pattern of cocoon distribution over
time. During the peak in wasp attack, this interaction results in a
random spatial distribution of useable cocoons that the wasps must
locate against a constantly increasing background of older
non-attackable cocoons.
The suspension systems and cocoons of M. lemniscata and
A. aurantia function in controlling the access to the cocoon of a
number of generalized and specialized predators (Chapter VI). These
results and the limited control that the cocoon of A. aurantia
exerts on the abiotic factors examined (Chapters III, IV, and V)
suggest that the main function of most spider cocoons and their
associated structures is to control parasite and predator attacks.

142
The results of Chapter VI also support the idea that much of the
observed variation in cocoon architecture is related to limiting
such attacks (Austin, In press). Does this imply that cocoon
architecture is the result of coevolution to avoid predator and
parasite attacks? Intuitively this proposal seems logical. Many of
the cocoon layers function to limit access to specific predators.
In addition, whole families of predators (e.g., the mantispidae)
have specialized on spider eggs. Since the Neuroptera in general
are a relatively old group, this family level specialization
suggests that some relationships between spiders and their predators
and parasites have existed for long periods of time.
Coevolution in its strictest definition is at least a three
step evolutionary sequence involving two interacting gene pools in
which the traits of one population change in response to the traits
of another, followed by changes in the first population in response
to the changes of the second (Jantzen 1980). For example, a spider
evolves a cocoon which limits a particular predator from gaining
access to the eggs or spiderlings. In response, the predator
evolves a means of circumventing the defense. The spider then
counters the predators ability to circumvent the defense by evolving
another defense or improving upon the first. Chapter VI indicates
that cocoons do act as barriers to both generalist and specialist
egg predators. However, many of the cocoon layers which function as
barriers are not 100% effective in keeping out attackers, and in
many cases this inability to totally limit predators is related to
predator specialization (see also Austin, In press). It also

appears that the third criteria for coevolution, a counter-response
by the spiders, has evolved in the form of larger clutches and
thicker cocoon layers (Chapter VI), or temporal and spatial
reproductive behaviors (Chapter VII). Caution should be invoked,
however! The evidence presented here suggests that many of these
behaviors did not evolve exclusively as counter-adaptations to
specialized predators. For example, M. lemniscata shows a shift in
reproduction to the early summer, and a compressed reproductive
season, both of which limit the number of parasites available to
attack the cocoons. However, these behaviors may also be the result
of other factors, such as competition for prey with other
orb-weavers in the habitat (Anderson 1978). Even more important is
the duality of function displayed by many of the structural
"adaptations" against predator attack. This suggests that in many
cases, cocoons and their associated suspension systems probably
represent responses to a wide variety of factors which are operating
at the same time (diffuse evolutionary pressures), rather than from
a response to one single factor such as predation or parasitism.
Conclusions
The results of this study demonstrate that the suspension
system of M.. lemniscata cocoons protects the eggs and spiderlings
from drowning by keeping the cocoon off of the ground, keeps water
from gaining access to the cocoon, and isolates the cocoon from
generalist arboreal and terrestrial predators. It may also protect
the eggs and spiderling from physical damage. The cover of

M. lemniscata cocoons protects the spiderlings from dessication and
fungal attack, keeps water from entering the cocoons, and protects
the eggs and spiderlings from predators. The cover may also provide
some protection for the eggs and spiderlings from temperature
extremes and physical damage.
The suspension system of A. aurantia cocoons protects the eggs
and spiderlings by keeping water from the cocoon, isolates the
cocoon from generalist arboreal and terrestrial predators, and
inhibits oviposition by wasp predators. It may also provide some
protection from physical damage. The cover of A. aurantia cocoons
prevents water from entering the cocoon, creates a dead air space
which acts as insulation, and protects the eggs and spiderlings from
a number of specialized predators. The flocculent silk layer in
A. aurantia cocoons is unwettable and may function to repel water.
It also works to protect the eggs from predator attack and appears
to function against wasp egg specialists. It may also play a role
in protecting the eggs and spiderlings from physical damage and
fungal attack.
These results, in combination with the few other studies on
cocoon function (Schaefer 1976, Austin and Anderson 1978,
Christenson and Wenzl 1980), suggest that the primary function of
cocoons is probably to protect the eggs and spiderlings from
predators and parasites. These studies also suggest that the time
the eggs and spiderlings spend in the cocoon in diapause or
overwintering has a strong influence on the strucure of the cocoon
and should select for covered cocoons. Covered cocoons may also be

expected to be found among those spiders that suspend their cocoon
because of the possibility of damage.
The results of this study point out, however, that
interpretation of cocoon function is difficult because the various
layers can perform one or more functions depending on the size of
the egg mass, the morphology of the eggs, the ability of the eggs
and spiderlings to control dessication, the habitat used for
oviposition, and the number and kinds of predators in the habitat.
The results also show that spiders use various reproductive
behaviors resulting in spatial and temporal patterns of cocoon
distribution that may aid in protecting the eggs and spiderlings by
making cocoons difficult to locate. This study further suggests
that eggs and spiderlings may be protected from pathogens by
chemicals applied to cocoon covers. Finally, this study illustrates
the need for further work in the area of cocoon architecture and
function before the role of the cocoon and its place within the
reproductive strategies of spiders can be fully understood.

LITERATURE CITED
Anderson, J.F. 1978. Energy content of spider eggs. Oecologia
37: 41-57.
Askew, R.R. 1971. Parasitic Insects. Heinemann Educational Books,
London. 316 pp.
Austin, A.D. 1984. Life history of Clubiona robusta L. Koch and
related species (Araneae, Clubionidae) in South Australia. J.
Arachnol. 12: 87-104.
Austin, A.D. In press. The function of spider egg sacs in relation to
parasitoids and predators, with special reference to the Australian
fauna. J. Nat. Hist.
Austin, A.D., and D.T. Anderson. 1978. Reproduction and development of
the spider Nephila edulis (Koch) (Araneidae: Araneae). Aust. J.
Zool. 26: 501-518.
Auten, M. 1925. Insects associated with spider nests. Ann. Entomol.
Soc. Amer. 18: 240-250.
Bijl, van der, P., and A. Paul. 1922. A fungus Gibbellula haygarthii
n. sp. on a spider of the family Lycosidae. Trans. Roy. Soc. S.
Africa 10: 149-150.
Bristowe, W.S. 1941. The Comity of Spiders. The Ray Society, London.
560 pp.
Brower, L.P., and J.V. Brower. 1972. Parallelism, convergence,
divergence and the new concept of advergence in the evolution of
mimicry. Trans. Connecticut Acad. Arts Sci. 44: 59-67.
Burks, B.D. 1979* Symphyta and Apocrita (Parasitica). Pages 990-1002
in K.V. Krombein, P.D. Hurd, Jr., D.R. Smith, and B.D. Burks, eds.
Catalog of the Hymenoptera in America North of Mexico. I.
Smithsonian Institution Press, Washington, D.C.
Champlain, A.B. 1922. Records of hymenopterous parasites in
Pennsylvania. Pysche 29: 95-100.
Chapman, R.F. 1967. The Insects: Structure and Function. Elsevier
North Holland, Inc., New York. 819 pp.

Chauvin, G., G. Vannier, and A. Gueguen. 1979* Larval case and water
balance in Tinea pellionella. J. Insect Phys. 25: 615-619.
Christenson, T.E., and P.A. Wenzl. 1980. Egg laying of the Golden Silk
Spider, Nephila clavipes L. (Araneae: Araneidae): Functional analysis
of the egg sac. Anim. Behav. 28: 1110-1118.
Clark, P.J., and F.C. Evans. 195^. Distance to nearest neighbor as a
measure of spatial relationships in populations. Ecology
35: L45-U53.
Clark, P.J., and F.C. Evans. 1979* Generalization of a nearest
neighbor measure of dispersion for use in K dimensions. Ecology
60: 316-317.
Coquillet, D.W. 1898. On the habits of the Oscinidae and Agronyzidae
reared at the United States Department of Agriculture. U.S.D.A. Div.
Ent. Bull. 10 (N.S.): 70-79*
Cresson, E.T. 1870. Descriptions of new species belonging to the
sub-family Pimplariae found in America north of Mexico. Trans.
Amer. Ent. Soc. 3: 1^5-148.
Davidson, A. 1896. Parasites of spider eggs. Entomol. News
7: 319-320.
Davies, M.E., and E.B. Edney. 1952. The evaporation of water from
spiders. J. Exp. Biol. 29: 571-582.
Dawkins, R., and J.R. Krebs. 1979* Arms races between and within
species. Proc. Royal Soc. Lond., B. 205: ^89-511.
DeBach, P. 19^. Environmental contamination by an insect parasite and
the effect on host selection. Ann. Entomol. Soc. Am. 37: 70-7^
Dethier, V.G. 19^7* The response of hymenopterous parasites to
chemical stimulation of the ovipositor. J. Exp. Zool. 105: 199-207.
Doutt, R.L. 1959. The biology of parasitic hymenoptera. Ann. Rev.
Entomol. U: l6l-l82.
Dowell, R.V. 1979. Effects of low host density on oviposition by
larval parasitoids of the alfalfa weevil. J. N.Y. Entomol. Soc.
87: 9-lU.
Eason R.R., W.B. Peck, and W.H. Whitcomb. 1967. Notes on spider
parasites, including a reference list. J. Kansas Entomol. Soc.
LO: L22-43U.

Eberhard, W.G. 1979* Rates of egg production by tropical spiders in
the field. Biotropica 11: 292-300.
Edgar, W.D. 1971. Aspects of the ecology and energetics of the egg sac
parasites of the wolf spider Pardosa lugubris (Walckenaer).
Oecologia 7: 155-163
Enders, F. 1974. Vertical stratification in orb-web spiders
(Araneidae, Araneae) and a consideration of other methods of
coexistence. Ecology 55: 317-328.
Evans, R.E. 1969* Parasites of spiders and their eggs. Proc.
Birmingham Nat. Hist. Soc. 21: 156-168.
Fisher, R.C. 1971. Aspects of the physiology of endoparasitic
hymenoptera. Biol. Rev. 46: 243-278.
Flanders, S.E. 1953. Variation in susceptibility of citrus-infesting
coccids to parasitization. J. Econom. Entomol. 46: 266-269.
Foelix, R.F. 1982. Biology of Spiders. Harvard University Press,
Cambridge. 306 pp.
Free, C.A., J.R. Beddington, and J.H. Lawton. 1977. On the inadequacy
of simple models of mutual interference for parasitism and predation.
J. Anim. Ecol. 46: 543-554.
Fulton, B.B. 1933. Notes on Habrocytus cerealellae, parasite of the
Angoumois grain moth. Ann. Entomol. Soc. Am. 26: 536-553.
Gertsch, W.J. 1979* American Spiders, 2nd Ed. D. van Nostrand
Company, Inc., New York. 274 pp.
Gilbert, L.E. 1971. Butterfly-plant coevolution: Has Passiflora
adenopoda won the selectional race with heliconiine butterflies?
Science 172: 585-586.
Grim, J.N., and C.N. Slobodchikoff. 1978. Chorion surface features of
some spider eggs. Pan-Pacific Entomol. 54: 319-322.
Grim, J.N., and C.N. Slobodchikoff. 1982. Spider egg chorion sphere
size and density. Ann. Ent. Soc. Amer. 75: 330-334.
Hall, D.G. 1937. The North and Central American spider parasites of
the genus Pseudogaurax (Diptera: Chloropidae). J. Wash. Acad. Sci.
27: 255-2231:
Hassell, M.P. 1966. Evaluation of parasite or predator responses. J.
Anim. Ecol. 35: 65-75

1U9
Hassell, M.P. 1971 Mutual interference between searching insect
parasites. J. Anim. Ecol. 40: 473-486.
Hassell, M.P. 1978. The Dynamics of Arthropod Predator-Prey Systems.
Princeton University Press, Princeton. 246 pp.
Hassell, M.P., and R.M. May. 1973. Stability in insect host-parasitoid
models. J. Anim. Ecol. 42: 693-726.
Hassell, M.P., and R.M. May. 1974. Aggregation of predators and insect
parasites and its effect on stability. J. Anim. Ecol. 43: 567-594.
Heath, J.E. 1964. Reptilian thermoregulation: Evaluation of field
studies. Science l46: 784-785.
Hickman, V.V. 1970. The biology of the Tasmanian Chloropidae (Diptera)
whose larvae feed on spider's eggs. J. Entomol. Soc. Australia
(N.S.W.) 7: 8-33.
Hieber, C.S. 1984. Egg predators of the cocoons of the spider
Mecynogea lemniscata (Araneae: Araneidae): Rearing and population
data. Florida Entomol. 67: 176-178.
Horner, N.V., and K.J. Starks. 1972. Bionomics of the jumping spider
Metaphidippus galathea. Ann. Ent. Soc. Amer. 65: 602-607
Howard, L.O. 1892. Hymenopterous parasites of spiders. Proc.
Entomol. Soc. Washington 2: 290-303.
Humphreys, W.F. 1974. Behavioral thermoregulation in a wolf spider.
Nature 251: 502-503.
Humphreys, W.F. 1983. The surface of spider's eggs. J. Zool.
(London) 200: 305-316.
Jantzen, D.H. 1980. When is it coevolution? Evolution 34: 6ll-6l2.
Haston, B.J. 1948. Spiders of Connecticut. State Geological and
Natural History Survey No. 70, Hartford. 874 pp.
Kaston, B.J. 1970. Comparative biology of American black widow
spiders. Trans. San Diego Soc. Nat. Hist, lb: 33-82.
Kaston, B.J., and G.E. Jenks. 1937* Dipterous parasites of spider
eggs. Bull. Brooklyn Entomol. Soc. 32: I6O-I65.
Kaufman, W.C., D. Bothe, and S.D. Meyer. 1982. Thermal insulating
capabilities of outdoor clothing materials. Science 215: 69O-69I.

150
Kessel, E.L., and B.B. Kessel. 1937 The life history of Gaurax
araneae Coq., an egg predator of the black widow spider, Lactrodectus
mactans (Fabr.). Pan-Pacific Entomol. 13: 58-60.
Kessler, A., and A. Fokkinga. 1973. Hymenopterous parasites in the egg
sacs of spiders of the genus Pardosa (Araneida, Lycosidae).
Tijdschr. Entomol. il6: 46-6l.
Kirchner, W., and P. Kestler. 1969 Untesuchungen zur Kalteresistenz
der Schilfradspinne Araneus cornutus (Araneidae). J. Insect
Physiol. 15: 41-53
Koebele, A. 1887. Some of the bred parasitic bymenoptera in the
National Collection. Insect Life 3: 46l.
Lack, D. 1954. The Natural Regulation of Animal Numbers. Oxford
University Press, New York. 343 pp.
Lack, D. 1966. Population Studies of Birds. Oxford University Press,
New York. 341 pp.
Lack, D. 1968. Ecological Adaptations for Breeding in Birds. Methuen,
London. 409 pp.
Laing, J. 1937 Host-finding by insect parasites. I. Observations on
the finding of hosts by Alysia manducator, Mormoniella vitripennis,
and Trichogramma evanescens. J. Anim. Ecol. 6: 298-317
Laing, J. 1938. Host-finding by insect parasites. II. The chance of
Trichogramma evanescens finding its hosts. J. Exp. 3iol.
15: 281-302.
Lees, A.D. 1947. Transpiration and the structure of the epicuticle in
ticks. J. Exp. Biol. 23: 379-410.
Levi, H.W. 1968. The spider genera Gea and Argiope in America
(Araneae: Araneidae). Bull. Mus. Comp. Zool7 136: 319-352.
Levi, H.W. 1980. The orb-weaver genus Mecynogea, the subfamily Metinae
and the genera Pachygnatha, Glenognatha, and Azila of the subfamily
Tetragnathinae north of Mexico (Araneae: Araneidae). Bull. Mus.
Comp. Zool. 149: 1-74.
Levi, H.W., and L.R. Levi. 1969. Sggcase construction and further
observations on the sexual behavior of the spider Sicarius
(Araneae: Sicariidae). Psyche 76: 29-40.
May, R.M. 1978. Host-parasitoid systems in patchy environments: A
phenomenological model. J. Anim. Ecol. 47: 833-844.

151
McClure, M.S. 1977* Parasitism of the scale insect, Fiorinia externa
(Homoptera: Diaspididae), by Aspidiotiphagus citrinus
(Hymenoptera: Eulophidae), in a Hemlock forest: Density dependence.
Environ. Entomol. 6: 551-555.
McCook, H.C. 1890. American spiders and their spinning work. II.
Acad. Nat. Sci. Philadelphia. 479 pp.
McEwon, K.C. 1963. Australian Spiders. Sirius Books, Sydney. 287 pp.
Moore, C.W. 1977- The life cycle, habitat, and variation in selected
web parameters in the spider Nephila clavipes Koch (Araneidae). Am.
Midi. Nat. 98: 95-108.
Morrison, G., W.J. Lewis, and D.A. Nordlund. 1980. Spatial variations
in Heliothis zea egg density and the intensity of parasitism by
Trichogramma spp.: An experimental analysis. Environ. Entomol.
9: 79-85-
Morrison, G., and D.R. Strong. 1980. Spatial variations in host
density and the intensity of parasitism: Some empirical examples.
Environ. Entomol. 9: 149-152.
Mullen, G.R. 1969. Morphology and histology of the silk glands in
Araneus sericatus Cl. Trans. Am. Microsc. Soc. 88: 232-240.
Muma, M.H., and K.J. Stone. 1971- Predation of Gastercantha
cancriformis (Arachnida: Araneidae) eggs in Florida citrus orchards
by Phalacrotophora epeirae (insecta: Phoridae) and Arachnophaga
ferruginea (insecta: Eupelmidae). Florida Entomol. 54: 305-310.
Murdoch, W.W., and A. Oaten. 1975- Predation and population stability.
Adv. Ecol. Res. 9' 1-131.
Nellist, D.R. 1965. Some preliminary notes on the attack of spiders by
fungi. Flatford Mill Spider Group. Bull. #26.
Norgaard, E. 1951- On the ecology of two Lycosid spiders (Pirata
piraticus and Lycosa pullata) from a Danish Sphagnum bog. Oikos
3: 1-21.
Norgaard, E. 1956. Environment and behavior of Theridion saxatile.
Oikos 37: 41-57.
Opell, B.D. 1984. Eggsac differences in the spider family Uloboridae
(Arachnida: Araneae). Trans. Am. Microsc. Soc. 103: 122-129.
Peterson, A. 1964. Entomological Techniques. Edwards Brothers, Inc.,
Ann Arbor. 435 pp.

152
Prakash, R.N., and T.J. Pandian. 1978 Energy flow through dipteran
parasite and hymenopteran hyperparasite populations. Oecologia
33: 209-219.
Price, P.W. 1970a. Trail odors: Recognition by insects parasitic on
cocoons. Science 170: 5*+6-5^7.
Price, P.W. 1970b. Biology of and host exploitation by Pleolophus
indistinctus. Ann. Entomol. Soc. Am. 63: 1502-1509.
Price, P.W. 1980. Evolutionary Biology of Parasites. Monographs in
Pop. Biol.#15. Princeton University Press, Princeton. 237 pp*
Pyke, G.H., H.R. Pulliam, and E.L. Charnov. 1977. Optimal foraging: A
selective review of theory and tests. Quart. Rev. Biol.
52: 137-151*.
Redborg, K.E., and E.G. MacLeod. In press. The developmental ecology
of Mantispa uhleri Banks (Neuroptera: Mantispidae). Illinois Biol.
Monographs.
Reichert, S.E. 1981. The consequences of being territorial: Spiders, a
case study. Am. Nat. 117: 871-892.
Reiskind, J. 1969. The spider subfamily Castianeirinae of North and
Central America (Araneae, Clubionidae). Bull. Mus. Comp. Sool.
138: 163-325.
Riddle, W.A. 1981. Cold survival of Argiope aurantia spiderlings
(Araneae, Araneidae). J. Arachnol. 9: 3^3-3^5.
Riddle, W.A., and A.L. Markezich. 1981. Thermal relations of
respiration in the garden spider, Argiope aurantia, during early
development and overwintering. Comp. Biochem. Physiol.
9A: 759-765.
Robinson, M.H. 1980. The ecology and behavior of tropical spiders.
C.R. 8th Congr. Intern. Arachnol., Vienna: 13-32.
Robinson, M.H., and B. Robinson. 1976. The ecology and behavior of
Nephila maculata: A supplement. Smith. Cont. Zool. 218: 1-22.
Salt, G. 1935. Experimental studies in insect parasitism. III. Host
selection. Proc. Royal Soc. Lond., B. 117: ^13-^35.
Salt, G. 1937. The sense used by Tricogramma to distinguish between
parasitized and unparasitized hosts. Proc. Royal Soc. Lond., B.
122: 57-75.

153
Schaefer, M. 1976. An analysis of diapause and resistance in the egg
stage of Floronia bucculenta (Araneae: Linyphiidae). Oecologia
25: 155-17^
Schaefer, M. 1977. Winter ecology of spiders (Araneida). Z. Ang.
Ent. 83: 113-134.
Scheffer, T.H. 1905- The cocooning habitats of spiders. Kansas Univ.
Sci. Bull. 3: 85-114.
Schildknecht, H., P. Kunzelmann, D. Krauss, and C. Kuhn. 1972. Uber
die Chemie der Spinnwebe, I. Arthropodenabvehrstoffe.
Naturwissenschaften 59". 98-99-
Schoener, T. 1971. Theory of feeding strategies. Ann. Rev. Ecol.
Sys. 2: 369-404.
Seligy, V.L. 1971. Postembryonic development of the spider
Enoplagnatha ovata (Theridiidae). Zool. J. Linn. Soc. 50: 21-31.
Sokal R.R., and F.J. Rohlf. 1969- Biometry. W.H. Freeman and
Company, San Francisco. 776 pp.
Stiling, P.D., and D.R. Strong. 1982. Egg density and the intensity of
parasitism in Prokelisia marginata (Homoptera: Delphacidae). Ecology
63: 1630-1635.
Tolbert, W.W. 1976. Population dynamics of the orb weaving spiders
Argiope trifasciata and Argiope aurantia (Araneae, Araneidae):
Density changes associated with mortality, natality, and migrations.
Ph.D. dissertation, University of Tennessee, Knoxville. 172 pp.
Tolbert, W.W. 1979 Thermal stress of the orb-weaving spider Argiope
aurantia (Araneae). Oikos 32: 386-392.
Trail, D.S. 1980. Predation by Argyrodes (Theridiidae) on solitary and
communal spiders. Psyche 87: 349-355*
Turnbull, A.L. 1973. Ecology of the true spiders (Araneomorphae).
Ann. Rev. Ent. 18: 305-348.
Variey, G.C. 194l. On the search for hosts and the egg distribution of
some Chalcid parasites of the Knapweed Gall-Fly. Parasitology
33: 47-66.
Vinson, B.S. 1972. Competition and host discrimination between two
species of tobacco budworm parasitoids. Ann. Entomol. Soc. Am.
65: 229-236.

151+
Vinson, B.S. 1975* Biochemical coevolution between parasitoids and
their hosts. Pages 14-36 in P.W. Price, ed. Evolutionary Strategies
of Parasitic Insects and Mites. Plenum Press, New York.
Vinson, B.S. 1976. Host selection by insect parasitoids. Ann. Rev.
Entomol. 21: 109-133.
Waage, J.K. 1979* Foraging for patchily-distributed hosts by the
parasitoid, Nemeritis canescens (Grv.). J. Anim. Ecol. 48: 353-371.
Washburn, J.O., and H.V. Cornell. 1979- Chalcid parasitoid attack on a
gall wasp population (Acraspis hirta (Hymenoptera: Cynipidae)) on
Quercus prinus (Fagaceae).Can. Entomol. Ill: 391-400.
Winston, P.W., and D.H. Bates, i960. Saturated solutions for the
control of humidity in biological research. Ecology 4l: 232-237.
Wise, D.H. 1982. Predation by the commensal spider, Argyrodes
trigonum, upon its host: An experimental study. J. Arachnol.
10: 111-116.
Witt, P.N. 1971. Instructions for working with web-building spiders in
the laboratory. Bioscience 21: 23-25.
Witt, P.N., C.F. Reed, and D.B. Peakall. 1968. A Spider's Web.
Springer-Verlag, Inc., New York. 107 pp.
Yoshikura, M. 1969 Effects of UV irradiation on the embryonic
development of a liphistiid spider, Heptathela kinmura. Kumamuto J.
Sci., B. 2: 57-108.
Zar, J.H. 1984. Biostatistical Analysis, 2nd ed. Prentice-Hall, Inc.,
Englewood Cliffs. 718 pp.

BIOGRAPHICAL SKETCH
Craig Stephen Hieber was born into the midst of the
urban-industrial wasteland in East Orange, New Jersey in 1951* At age
15, after constant exposure to New York city television and radio, he
moved to Chester, in northern New Jersey, where he attended West Morris
High School. After graduation from high school in 1969, he studied
mechanical engineering at the University of Virginia for 2 years. In
1975, he received a B.S. in biology from Roanoke College. He then moved
to Vermont where there were no jobs but the scenery was beautiful. From
Vermont, he moved to North Dakota where he received an M.S. in biology
in 1979 from the University of North Dakota. After three years of -20
degree winters, he moved to Florida where he expects to receive a
Ph.D. in zoology in 1984 from the University of Florida. When he is not
studying the behavioral or physiological ecology of insects and spiders,
he devotes most of his time to general tool use, the restoration of
machinery and furniture, tropical fish, and his passion, bicycles.
155

I certify that I have read this study and that in my opinion it conforms
to acceptable standards of scholarly presentation and is fully adequate,
in scope and quality, as a dissertation for the degree of Doctor of
Philosophy.
Jofi F. Anderson, Chairman
Associate Professor of Zoology
I certify that I have read this study and that in my opinion it conforms
to acceptable standards of scholarly presentation and is fully adequate,
in scope and quality, as a dissertation for the degree of Doctor of
Philosophy.
Distinguished Professor of Zoology
I certify that I have read this study and that in my opinion it conforms
to acceptable standards of scholarly presentation and is fully adequate,
in scope and quality, as a dissertation for the degree of Doctor of
Philosophy.
¡^,^4J
-tfnathon Reiskind
Associate Professor of Zoology
I certify that I have read this study and that in ny opinion it conforms
to acceptable standards of scholarly presentation and is fully adequate,
in scope and quality, as a dissertation for the degree of Doctor of
Philosophy.
Reese I. Sailer
Graduate Research Professor of
Entomology and Nematology

This dissertation was submitted to the Graduate Faculty of the
Department of Zoology in the College of Arts and Sciences and to the
Graduate School, and was accepted as partial fulfillment of the
requirements for the degree of Doctor of Philosophy.
Dean for Graduate Studies and
Research
December, 1984



clear nail polish. These whole and modified cocoons were mounted on
thermal probes (YSI #513, time constant of 0.02 s), with the tip of
the probe in the approximate position of the egg or spiderling mass.
Cocoons were allowed to equilibrate to room temperature (T =
26 C) in a large cardboard enclosure, and then placed in a
styrofoam cooler packed with salted ice. The internal temperature
of the cocoon in the cooler was recorded every 30 s until it reached
the ambient temperature of the cooler (T& = 8-9 C). The cooling
trials were performed in a dark room to avoid radiant loading from
the overhead lights, and with the air conditioning off to minimize
the effects of convective cooling from air movement. The walls of
the cardboard enclosure and the cooler were monitered with banjo
probes (YSI #427, time constant of 1.10 s) taped to the inner
surfaces. The temperatures of these surfaces matched the ambient
air temperatures within each container. Only data from trials where
the ambient temperature in the cooler varied by no more than
0.5C were used for the calculation of the cooling curves.
In the field, the changes in internal temperatures of whole and
modified cocoons (using YSI #513 probes) in an artificial closed
habitat (l x 1 x 1 m cardboard enclosure) were recorded at one min
intervals for 50 min over an approximate 2.5 C drop in ambient air
temperature. On a different day, changes in internal temperatures
(YSI #513) of whole and modified cocoons exposed to 10 min radiation
loads, and to 2 min loads followed by 8 min of cooling were also
recorded. This experiment was conducted between 1100 and 1300 h
when the sun was at its zenith. During this time, ambient


54
modified covers also had significantly higher rates of fungal attack
2
(X = 13.03, df = 1, p < 0.005). In addition, spiderling mortality
due to other causes, probably submersion and subsequent drowning,
2
was significantly higher on the ground (X = 13*34, df = 1, p <
0.005).
The incidence of fungal attack on the cocoons of A. aurantia
was very low in both the egg stage (4.9%; Table 5-3), and the
spiderling stage (0%; Table 5-4). Chi-square tests between the
Control group, and the Ground Placement and Cover Removal groups
revealed no significant differences in the number of cocoons
attacked by fungus in either the egg stage or the spiderling stage.
The two Control groups were not significantly different from each
other.
Discussion
The suspension systems of both M. lemniscata and A. aurantia
cocoons are difficult to wet, and conduct water poorly.
Consequently, they act to discourage water from moving down the
lines to the cocoons. The covers of both cocoons shed water
effectively, and apparently absorb only a small amount. Presumably,
the flocculent silk layers of both cocoons are also difficult to
wet, and function further to limit the water from entering the
cocoon. All of these structures ultimately function to keep the
cocoon dry by channeling water away from it. However, the
connection between this function, and the prevention of fungal
attack is not clear. Modification of the cocoon cover and partial


151
McClure, M.S. 1977* Parasitism of the scale insect, Fiorinia externa
(Homoptera: Diaspididae), by Aspidiotiphagus citrinus
(Hymenoptera: Eulophidae), in a Hemlock forest: Density dependence.
Environ. Entomol. 6: 551-555.
McCook, H.C. 1890. American spiders and their spinning work. II.
Acad. Nat. Sci. Philadelphia. 479 pp.
McEwon, K.C. 1963. Australian Spiders. Sirius Books, Sydney. 287 pp.
Moore, C.W. 1977- The life cycle, habitat, and variation in selected
web parameters in the spider Nephila clavipes Koch (Araneidae). Am.
Midi. Nat. 98: 95-108.
Morrison, G., W.J. Lewis, and D.A. Nordlund. 1980. Spatial variations
in Heliothis zea egg density and the intensity of parasitism by
Trichogramma spp.: An experimental analysis. Environ. Entomol.
9: 79-85-
Morrison, G., and D.R. Strong. 1980. Spatial variations in host
density and the intensity of parasitism: Some empirical examples.
Environ. Entomol. 9: 149-152.
Mullen, G.R. 1969. Morphology and histology of the silk glands in
Araneus sericatus Cl. Trans. Am. Microsc. Soc. 88: 232-240.
Muma, M.H., and K.J. Stone. 1971- Predation of Gastercantha
cancriformis (Arachnida: Araneidae) eggs in Florida citrus orchards
by Phalacrotophora epeirae (insecta: Phoridae) and Arachnophaga
ferruginea (insecta: Eupelmidae). Florida Entomol. 54: 305-310.
Murdoch, W.W., and A. Oaten. 1975- Predation and population stability.
Adv. Ecol. Res. 9' 1-131.
Nellist, D.R. 1965. Some preliminary notes on the attack of spiders by
fungi. Flatford Mill Spider Group. Bull. #26.
Norgaard, E. 1951- On the ecology of two Lycosid spiders (Pirata
piraticus and Lycosa pullata) from a Danish Sphagnum bog. Oikos
3: 1-21.
Norgaard, E. 1956. Environment and behavior of Theridion saxatile.
Oikos 37: 41-57.
Opell, B.D. 1984. Eggsac differences in the spider family Uloboridae
(Arachnida: Araneae). Trans. Am. Microsc. Soc. 103: 122-129.
Peterson, A. 1964. Entomological Techniques. Edwards Brothers, Inc.,
Ann Arbor. 435 pp.


23
low equilibrium temperature (Heath 1964) that is probably below the
danger level for the spiderlings in the cocoon. However, during the
early part of the reproductive season, when the ambient temperature
is relatively high, radiant loads may represent a more serious
problem. Under these conditions, a load of long duration could
raise the equilibrium temperature of the cocoon past the safe limit
for the eggs or spiderlings. Loads of short duration also pose a
problem if they occur in rapid enough succession. Under these
conditions, the internal temperature of the cocoon would "step" up
with each successive load due to the slow rate of heat loss from the
egg or spiderling mass (see Fig. 3-3), finally rising above the
lethal limit.
Other behaviors may play a role in insuring that the cocoon is
not exposed to lethal thermal loads. Argiope aurantia prefers to
oviposit beneath a layer of vegetation or among the leaves of
broad-leafed plants. Such sites would limit the number and length
of insolation bouts the cocoon encounters, particularly during the
late summer when oviposition occurs. The comparison of internal
temperatures from cocoons in open and closed habitats supports
maternal positioning of the cocoon as an important control measure
(see Fig. 3-4). Positioning the cocoon in a closed site rather than
in an open site resulted in a 10 C difference between the highest
internal temperature achieved (because of radiation loading), and a
4 C difference in the lowest temperature achieved (because of
exposure to cold night sky temperatures). Although spiderlings can
tolerate high temperatures (Tolbert 1979), proper site choice could


Table 6-4. Numbers of Argiope aurantia cocoons suspended in the vegetation which were successfully
attacked by the ichneumonid Tromatobia ovivora rufopectus, the mantispid Mantispa viridis, the
chloropid fly Pseudogaurax signata, the phorid fly Megaselia sp., and birds for the years 1981 to
1983. The percentages of attacked cocoons are in parentheses. The cocoons were attacked to a
lesser extent by ants [l cocoon (l.6%) in 1981, 2 cocoons (1.1%) in 1982], and moth larvae [3
cocoons (l.6%) in 1982]. Forty-two of the 185 cocoons (23.0%) collected in 1982 were also attacked
by unknown predators and showed varying degrees of cover damage. The cocoon sample for I98I was
collected in late October. In 1982 and 1983, the cocoon samples were collected approximately every
two weeks during the reproductive season (August to November).
Year
Sample
Size
Total No.
Attacked
Ichneumonid
Wasp
Mantispid^
Chloropid
FlyC
Phorid
Fly6
Bird6
1981
63
lbf
13 (81.2%)
1 ( 6.2%)
3 (18.8%)
2 (12.5%)
0
1982
185
89g
34 (38.2%)
27 (30.3%)
42 (47.2%)
4 ( 4.5%)
17 (19-1%)
1983
90
9h
2 (22.2%)
5 (55.6%)
1 (11.1%)
0
1 (11.1%)
Attack characterized by the presence of oviposition holes, eggs, larvae, and pupal cases.
Attack characterized by the presence of pupal cases and adults.
Attack characterized by the presence of eggs on the cocoon cover or in the flocculent silk layer,
larvae, pupal cases, and adults.


"R" for all
Web-sites8, 2.51
"R" for Web-sites with
Cocoons 1-5 Days Old8 2.5
i.6o*
0.99
0.77*
0.80*
0.79*
1.43*
1.09
0.83*
0.80*
1.13
0.77* 0.77* 0.77* 0.77* 0.77*
0.74 0.4l*
The "R" values (a measure of dispersion), and their departures from random were calculated using
the procedures outlined in Clark and Evans (1954). R values run from R = 0 indicating maximum
aggregation, to R = 1 indicating a random distribution, to R = 2.15 indicating a perfectly uniform
distribution. The stared (*) R values indicate a pattern of web-site distribution significantly
different from random (p < 0.01).
The R values for June 15th are beyond the scale because there were only two web-sites at this
time. Their distribution cannot be tested for significant departure from random for this reason
as well.
113


122
chance of a site with a useable cocoon. The random distribution of
sites with 1-5 day old cocoons remains until late July when sites
with useable cocoons again show a clumped distribution (see Table
7-1+) However, by this time sites with cocoons 1-5 days old are
rare, and the probability of locating one against the background of
older sites with nonuseable cocoons is low.
The low probability of locating a cocoon due to these spatial
and temporal effects may be further reduced if visual cues are used
by this wasp for host location (Laing 1937). Approximately 50-64%
of the cocoon strings collected in each of the four plots in 1982
were from the previous year(s). These strings were still hanging in
position, and presumably represent nonproductive sites which would
have to be examined at a cost in energy and time.
The preceeding discussion suggests that the low overall levels
of parasitism in this system can be explained by the short
reproductive season, which limits the number of wasp generations,
and the timing of egg development and cocoon production, which
limits the number of cocoons attacked in any one string. Both have
the effect of forcing wasps to look for new strings of cocoons. It
also suggests that the lack of a density-dependent relationship can
be explained by the interaction between the short reproductive
season, the rapid rate of cocoon production, and the limited time
period for successful cocoon attack. These factors force wasps to
locate a constantly decreasing number of randomly distributed
useable cocoons among a rapidly increasing number of web-sites with
cocoons too old for successful attack.


CHAPTER VII
COCOON SPACING AND THE TIMING OF PRODUCTION AS METHODS TO AVOID
EGG AND SPIDERLING PREDATORS
Introduction
Current evidence indicates that parasitoid species do not
search randomly, but rather are directed to their hosts through a
hierarchy of specific physical and chemical cues which function to
reduce and restrict the area and habitats searched and subsequently
increase the probability of finding a suitable host (Salt 1935,
Flanders 1953, Doutt 1959, Vinson 1976). In addition, behavioral
evidence suggests that parasitoids discriminate between areas of
high and low host density and allocate greater proportions of their
searching time to areas in which host density is high (Waage 1979).
This latter behavior has been termed "parasitoid aggregation" or
"non-random search" (Hassell and May 1973, 1971*, Hassell 1978).
Parasitoid aggregation should cause host mortality to be high
in areas where host density is high, while patches of low host
density, where the probability of parasitoid attack is low, should
represent refuges for the host (May 1978). Although true for some
insects (Hassell 1966, McClure 1977, Washburn and Cornell 1979),
negative correlations between host number and the level of
parasitoid attack (Hassell 1966, Morrison et al. 1980) or lack of
any correlation (Dowell 1979, Morrison et al. I98O) are more
frequent findings (Morrison and Strong 1980). When a
IOC


appears that the third criteria for coevolution, a counter-response
by the spiders, has evolved in the form of larger clutches and
thicker cocoon layers (Chapter VI), or temporal and spatial
reproductive behaviors (Chapter VII). Caution should be invoked,
however! The evidence presented here suggests that many of these
behaviors did not evolve exclusively as counter-adaptations to
specialized predators. For example, M. lemniscata shows a shift in
reproduction to the early summer, and a compressed reproductive
season, both of which limit the number of parasites available to
attack the cocoons. However, these behaviors may also be the result
of other factors, such as competition for prey with other
orb-weavers in the habitat (Anderson 1978). Even more important is
the duality of function displayed by many of the structural
"adaptations" against predator attack. This suggests that in many
cases, cocoons and their associated suspension systems probably
represent responses to a wide variety of factors which are operating
at the same time (diffuse evolutionary pressures), rather than from
a response to one single factor such as predation or parasitism.
Conclusions
The results of this study demonstrate that the suspension
system of M.. lemniscata cocoons protects the eggs and spiderlings
from drowning by keeping the cocoon off of the ground, keeps water
from gaining access to the cocoon, and isolates the cocoon from
generalist arboreal and terrestrial predators. It may also protect
the eggs and spiderling from physical damage. The cover of


M. lemniscata cocoons protects the spiderlings from dessication and
fungal attack, keeps water from entering the cocoons, and protects
the eggs and spiderlings from predators. The cover may also provide
some protection for the eggs and spiderlings from temperature
extremes and physical damage.
The suspension system of A. aurantia cocoons protects the eggs
and spiderlings by keeping water from the cocoon, isolates the
cocoon from generalist arboreal and terrestrial predators, and
inhibits oviposition by wasp predators. It may also provide some
protection from physical damage. The cover of A. aurantia cocoons
prevents water from entering the cocoon, creates a dead air space
which acts as insulation, and protects the eggs and spiderlings from
a number of specialized predators. The flocculent silk layer in
A. aurantia cocoons is unwettable and may function to repel water.
It also works to protect the eggs from predator attack and appears
to function against wasp egg specialists. It may also play a role
in protecting the eggs and spiderlings from physical damage and
fungal attack.
These results, in combination with the few other studies on
cocoon function (Schaefer 1976, Austin and Anderson 1978,
Christenson and Wenzl 1980), suggest that the primary function of
cocoons is probably to protect the eggs and spiderlings from
predators and parasites. These studies also suggest that the time
the eggs and spiderlings spend in the cocoon in diapause or
overwintering has a strong influence on the strucure of the cocoon
and should select for covered cocoons. Covered cocoons may also be


142
The results of Chapter VI also support the idea that much of the
observed variation in cocoon architecture is related to limiting
such attacks (Austin, In press). Does this imply that cocoon
architecture is the result of coevolution to avoid predator and
parasite attacks? Intuitively this proposal seems logical. Many of
the cocoon layers function to limit access to specific predators.
In addition, whole families of predators (e.g., the mantispidae)
have specialized on spider eggs. Since the Neuroptera in general
are a relatively old group, this family level specialization
suggests that some relationships between spiders and their predators
and parasites have existed for long periods of time.
Coevolution in its strictest definition is at least a three
step evolutionary sequence involving two interacting gene pools in
which the traits of one population change in response to the traits
of another, followed by changes in the first population in response
to the changes of the second (Jantzen 1980). For example, a spider
evolves a cocoon which limits a particular predator from gaining
access to the eggs or spiderlings. In response, the predator
evolves a means of circumventing the defense. The spider then
counters the predators ability to circumvent the defense by evolving
another defense or improving upon the first. Chapter VI indicates
that cocoons do act as barriers to both generalist and specialist
egg predators. However, many of the cocoon layers which function as
barriers are not 100% effective in keeping out attackers, and in
many cases this inability to totally limit predators is related to
predator specialization (see also Austin, In press). It also


TABLE OF CONTENTS
ACKNOWLEDGEMENTS ii
LIST OF TABLES vi
LIST OF FIGURES ix
ABSTRACT xi
CHAPTER I INTRODUCTION 1
CHAPTER II THE EXPERIMENTAL ANIMALS, THEIR
COCOONS, AND THEIR HABITATS 5
Mecynogea lemniscata 5
Argiope aurantia 8
CHAPTER III THE "INSULATION" LAYER IN THE
COCOONS OF ARGIOPE AURANTIA 12
Introduction 12
Materials and Methods 13
Results 15
Discussion 20
CHAPTER IV THE ROLE OF SPIDER EGGS AND
COCOONS IN RESISTING WATER LOSS 25
Introduction 25
Materials and Methods 26
Results 29
Discussion 36
CHAPTER V THE ROLE OF THE COCOON IN
LIMITING EXCESS WATER AND
FUNGAL ATTACK 1+2
Introduction 1+2
Materials and Methods 1+3
Results 1+7
Discussion 5^
iv


152
Prakash, R.N., and T.J. Pandian. 1978 Energy flow through dipteran
parasite and hymenopteran hyperparasite populations. Oecologia
33: 209-219.
Price, P.W. 1970a. Trail odors: Recognition by insects parasitic on
cocoons. Science 170: 5*+6-5^7.
Price, P.W. 1970b. Biology of and host exploitation by Pleolophus
indistinctus. Ann. Entomol. Soc. Am. 63: 1502-1509.
Price, P.W. 1980. Evolutionary Biology of Parasites. Monographs in
Pop. Biol.#15. Princeton University Press, Princeton. 237 pp*
Pyke, G.H., H.R. Pulliam, and E.L. Charnov. 1977. Optimal foraging: A
selective review of theory and tests. Quart. Rev. Biol.
52: 137-151*.
Redborg, K.E., and E.G. MacLeod. In press. The developmental ecology
of Mantispa uhleri Banks (Neuroptera: Mantispidae). Illinois Biol.
Monographs.
Reichert, S.E. 1981. The consequences of being territorial: Spiders, a
case study. Am. Nat. 117: 871-892.
Reiskind, J. 1969. The spider subfamily Castianeirinae of North and
Central America (Araneae, Clubionidae). Bull. Mus. Comp. Sool.
138: 163-325.
Riddle, W.A. 1981. Cold survival of Argiope aurantia spiderlings
(Araneae, Araneidae). J. Arachnol. 9: 3^3-3^5.
Riddle, W.A., and A.L. Markezich. 1981. Thermal relations of
respiration in the garden spider, Argiope aurantia, during early
development and overwintering. Comp. Biochem. Physiol.
9A: 759-765.
Robinson, M.H. 1980. The ecology and behavior of tropical spiders.
C.R. 8th Congr. Intern. Arachnol., Vienna: 13-32.
Robinson, M.H., and B. Robinson. 1976. The ecology and behavior of
Nephila maculata: A supplement. Smith. Cont. Zool. 218: 1-22.
Salt, G. 1935. Experimental studies in insect parasitism. III. Host
selection. Proc. Royal Soc. Lond., B. 117: ^13-^35.
Salt, G. 1937. The sense used by Tricogramma to distinguish between
parasitized and unparasitized hosts. Proc. Royal Soc. Lond., B.
122: 57-75.