The corn field spider community

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Title:
The corn field spider community composition, structure, development and function
Physical Description:
xv, 207 leaves : ill. ; 28 cm.
Language:
English
Creator:
Plagens, Michael Joseph, 1954-
Publication Date:

Subjects

Subjects / Keywords:
Spiders -- Ecology   ( lcsh )
Corn -- Diseases and pests -- Florida   ( lcsh )
Genre:
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1985.
Bibliography:
Includes bibliographical references (leaves 190-206).
Statement of Responsibility:
by Michael Joseph Plagens.
General Note:
Typescript.
General Note:
Vita.

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Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 000527157
notis - ACU9242
oclc - 13297199
System ID:
AA00003407:00001

Full Text











THE CORN FIELD SPIDER COMMUNITY:
COMPOSITION, STRUCTURE, DEVELOPMENT AND FUNCTION

















By

MICHAEL JOSEPH PLAGENS


A DISSERTATION PRESENTED 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


1985




























Dedicated to my Parents





Joseph R. Plagens

and

Frances L. Plagens

















ACKNOWLEDGMENTS


During a three year research project, such as this,

many people along the way lend suggestions and aid towards

its successful completion. Foremost among these has been my

wife, Paula, who has supported me emotionally, logistically

and financially every step of the way.

Of course, my major professor, Dr. Willard H. Whitcomb,

was central in helping develop my goals and basic

understanding of crop spider ecology. One of his greatest

contributions to my success has been his ability to

encourage a sense of the importance and significance in the

time consuming research.

Learning the taxonomy of spiders was a long process; I

owe much to the individual tutoring provided especially by

Dr. G. B. Edwards, and also by Dr. David B. Richman.

Dr. Charles Dondale was indispensable for help in

identifying the linyphiid spiders.

I am thoroughly indebted to Mr. Jack Simmons, Mr. Ralph

Brown and the Haufler Brothers who kindly granted me access

to their crop fields. Dr. Edward V. Komarek was helpful in


iii











allowing me to study overwintering spiders at the Tall

Timbers Research Station. Dr. Matthew Greenstone lent

valuable advise and encouraged me to pursue the aerial

dispersal aspect of spiders.

Among the others who have made my job easier include

Helen Huseman who illustrated the corn plant and freely

provided much illustrative advise, T. Dave Gowan who

suggested computer hardware and software that greatly aided

the sorting of information, and finally my parents who were

always ready to provide encouragement and motivation.



















TABLE OF CONTENTS

Page
ACKNOWLEDGMENTS........................................... iii

LIST OF TABLES ........................................... vii

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

ABSTRACT ................................................xiii

CHAPTERS

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

II THE SPIDER FAUNA OF CORN FIELDS IN ALACHUA
COUNTY, FLORIDA. .................................... 3

Introduction ...................................... 3
Site Descriptions ................................. 7
Sampling Methods ................................. 12
Results and Discussion ........................... 15
Checklist and Description of the Species....... 15
Community Structure... .......................... 61
Spider Density ......... ........................ 91
Within Field Distribution ...................... 92
The Corn Field as a Habitat for Spiders ........ 96
Trophic Relationships ......................... 103
Conclusion ...................................... 118

III AERIAL DISPERSAL BY SPIDERS IN THE CORN FIELD
ECOSYSTEM ......................................... 120

Introduction .................................... 120
Site Descriptions ..... ...........................121
Methods and Materials ....... ..................... 123
Results .........................................126
Discussion ...................................... 138










IV WEED ASSOCIATIONS OF SPIDERS IN THE CORN FIELD
ECOSYSTEM .......................................... 146

Introduction .................................... 146
Site Descriptions................................ 148
Methods and Materials..... ...................... 149
Results ......................................... 151
Discussion ...................................... 162


V CORN STUBBLE AS AN OVERWINTERING SITE FOR
SPIDERS IN FLORIDA................................ 171

Introduction .................................... 171
Site Descriptions.. .............................. 172
Methods and Materials ............................ 172
Results ......................................... 173
Discussion ...................................... 175

VI CONCLUSION ........................................ 182

LITERATURE CITED ......................................... 190

BIOGRAPHICAL SKETCH ...................................... 207


















LIST OF TABLES


Table Page

2-1. List of weeds growing in sunny borders of
Archer, 1983 corn field ......................... 10

2-2. List of families and genera included in
each of the six defined spider guilds............84

2-3. Variance to mean ratios (measure of
aggregation) for samples of spiders from
corn fields in Alachua County, Florida........... 93

2-4. Spider predation on pests and occasional
pests as observed in corn fields in Alachua
County, Florida................................. 106

2-5. Spider predation on predaceous and accessory
insects as observed in corn fields in
Alachua County, Florida ....................108

3-1. Ballooning spider trap locations and number
of trap days accumulated at each location....... 125

3-2. List of ballooning spiders caught on sticky
wire traps in Alachua County, Florida........... 131

3-3 Relative ballooning frequencies for spiders
at three sites in Alachua County, Florida....... 142

4-1. Association of spiders with weeds growing in
Alachua County, Florida corn fields at
maturity and postharvest ....................... 152

4-2. Association of spiders with perennial weeds
and grasses growing in sunny borders,
pastures and fallow fields adjacent to corn
fields in Alachua County, Florida.............. 153


vii











Table Page

4-3. Association of spiders with trees growing in
fence rows and areas adjacent to corn fields
in Alachua County, Florida. ....................154


4-4. Association of spiders with weeds, shrubs
and saplings growing in shaded areas
adjacent to corn fields in Alachua County,
Florida. ......................................... 155

5-1. Overwintering spiders collected from corn
stubble in Alachua and Leon Counties,
Florida.......................................... 176

5-2. Overwintering predaceous insects collected
from corn stubble in Alachua and Leon
Counties, Florida............................... 178


viii


















LIST OF FIGURES


Figure Page

2-1. Distribution and typical web structures of
spiders occurring on the corn plant:
Theridiidae and Linyphiidae. ..................... 19

2-2. Stratification of the web building spiders
(Theridiidae, Linyphiidae and Araneidae) on
the corn plant................................... 31

2-3. Stratification of the horizontal plane orb
webs, Araneidae................................. 33

2-4. Stratification of the tangled space webs,
Theridiidae....................................... 35

2-5. Vertical stratification of Tetragnatha
laboriosa on the corn plant as a function of
body length...................................... 43

2-6. Principal species and percent rank abundance
of spiders in field corn at Archer, Florida,
1982, Field A .................................... 62

2-7. Principal species and percent rank abundance
of spiders in field corn at Archer, Florida,
1982, Field B .................................... 63

2-8. Principal species and percent rank abundance
of spiders in field corn at Archer, Florida,
1983 ............................................. 64

2-9. Principal species and percent rank abundance
of spiders in field corn at Orange Heights,
Florida, 1983....................................65

2-10. Principal species and percent rank abundance
of spiders in field corn at Archer, Florida,
1984 ............................................. 66











Figure Page

2-11. Principal species and percent rank abundance
of spiders in field corn at Gainesville,
Florida, 1984 .................................... 67

2-12. The major families of spiders collected in
field corn at Archer, Florida during 1982;
Field A and Field B.............................69


2-13. The major families of spiders collected, in
field corn during 1983 at Archer and Orange
Heights, Florida ................................. 70

2-14. The major families of spiders collected in
field corn during 1984 at Archer and
Gainesville, Florida .............................71

2-15. Species diversity of spiders as measured by
H' in six corn fields in Alachua County,
Florida........................................... 72

2-16. Stratification of spiders in the corn field
canopy during 1982 at Archer, Florida, Field
A and Field B .................................... 75

2-17. Stratification of spiders in the corn field
canopy during 1983 at Archer and Orange
Heights Florida................................. 76

2-18. Stratification of spiders in the corn field
canopy during 1984 at Archer and
Gainesville, Florida .............................77

2-19. Age structure of spiders in corn fields
during 1982 at Archer, Florida, Field A and
Field B.......................................... 80

2-20. Age structure of spiders in corn fields
during 1983 at Archer and Orange Heights,
Florida........................................... 81

2-21. Age structure of spiders in corn fields
during 1984 at Archer and Gainesville,
Florida........................................... 82











Figure Page

2-22. Guild structure of corn field spiders as a
function of phenological period during 1982
at Archer, Florida, Field A and Field B.........86

2-23. Guild structure of corn field spiders as a
function of phenological period during 1983
at Archer, Florida...............................87

2-24. Guild structure of corn field spiders as a
function of phenological period during 1983
at Orange Heights, Florida....................... 88

2-25. Guild structure of corn field spiders as a
function of phenological period during 1984
at Archer, Florida...............................89

2-26. Guild structure of corn field spiders as a
function of phenological period during 1984
at Gainesville, Florida.......................... 90

3-1. Trap used for studying aerial dispersal in
spiders.......................................... 124

3-2. Family proportions of ballooning spiders
captured from January, 1983 through July,
1984 in Alachua County, Florida .................127

3-3. Ballooning intensity of spiders by month at
Archer, Florida during 1983 and 1984 ............ 128

3-4. Ballooning intensity of spiders by month in
Alachua County, Florida at Orange Heights,
during 1983 and Gainesville during 1984......... 129

3-5. Size classes of ballooning spiders captured
on sticky wire traps in Alachua County,
Florida from January, 1983 through July,
1984............................................. 137

4-1. Temporal association of Peucetia viridans
with plants in and near the field corn
ecosystem in Alachua County, Florida............157

4-2. Temporal association of Metaphidippus
galathea with plants in and near the field
corn ecosystem in Alachua County, Florida..... 157











Figure Page

4-3. Temporal association of Hentzia palmerum
with plants in and near the field corn
ecosystem in Alachua County, Florida............159

4-4. Temporal association of Misumenops celer
with plants in and near the field corn
ecosystem in Alachua County, Florida............ 159

4-5. Temporal association of Chiricanthium
inclusum with plants in and near the field
corn ecosystem in Alachua County, Florida..... 161

4-6. Temporal association of Aysha velox with
plants in and near the field corn ecosystem
in Alachua County, Florida.................. 161

5-1. Cross section of corn stalk and leaf sheath
showing the protected cavity between them.......174

5-2. Cross section of corn cob with enclosing
husks showing the protected layers of air.......174


xii
















Abstract of a 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 CORN FIELD SPIDER COMMUNITY:
COMPOSITION, STRUCTURE, DEVELOPMENT AND FUNCTION

By

MICHAEL JOSEPH PLAGENS

August 1985

Chairman: Dr. Willard H. Whitcomb
Major Department: Entomology and Nematology

An agroecosystem approach was taken in analyzing the

the spider communities in Alachua County, Florida,

cornfields.

Visual examination of the corn plants detected 140

species and details of 40 species' microhabitat, prey and

reproduction. The most common were Pardosa milvina,

Achaearanea globosa, Misumeno.s celer, Tetrajnatha

laboriosa, Eperigone banksi, Metaphidippus galathea and

Uloborus glomosus.

Community structure and stratification are presented.

Guild dynamics was similar between fields and years.

Maximum species diversity was 61 species and H'=4.08. The

density of spiders ranged from 2.2 9.5/m2


xiii












Prey is recorded for 29 spider species. Solenopsis

ants are major prey of Achaearanea globosa and Eperigone

banksi. Parasitic hymenoptera are major prey for Araneidae.

Insects feeding on the copious pollen are chief prey for

spiders and divert predation away from major pests.

Aerial dispersal of spiders in the ecosystem was

studied using sticky wires which trap mostly spiders. The

seasonal phenology of the 15 families and 53 species trapped

revealed five dispersal strategies; spiders with widely

overlapping generations and several instars ballooning

throughout the year are dominant components of the aeronaut,

crop field, and weed faunas.

The principal spiders and their seasonal phenology on

the weeds of the ecosystem are presented. Most major

species are shared with crop fields and frequent movemenA

between plant species is characteristic. Oak trees in fence

rows are a major source of crop and weed spiders.

The overwintering ecology of spiders and predaceous

insects in the cornfield was examined; 24 species of spiders

and 25 predaceous insects were found in the cavities formed

by the leaf sheath and/or the imbricate bracts of the

shelled corn cob.

The determinates of crop field spider communities are

divided into those which affect the diversity of the pool of

dispersing colonists and the biological and ecological

factors which favor or exclude species which arrive in the

xiv










field. Cornfields are a tremendous sources of spiders,

parasitoids, and pests, and because corn is a major

worldwide crop, management of the agroecosystem and thus the

spider communities in cornfields is essential.















CHAPTER I
INTRODUCTION



Since the resurgence of research in biological control

in the early 1960's, and the pioneering work of Whitcomb,

Exline and Hunter (1963) the volume of literature on spiders

in crop fields has steadily increased. Luczac (1979) and

Riechert and Lockley (1984) provide useful reviews of this

material.

Most of the published studies list the species found

and their relative abundance on a particular crop in a

particular area, such as on cotton in Arkansas (Whitcomb et

al. 1963), Texas (Kagan 1943, Dean et al. 1982), California

(Leigh and Hunter 1969) and in Peru (Aguilar 1968); on

alfalfa in New York (Wheeler 1973), Virginia (Howell and

Pienkowski 1971) and California (Yeargan and Dondale 1974).

A few studies consider the seasonal dynamics of a

single spider (Plagens 1983) or groups of spiders (Lockley

et al. 1979). Culin and Yeargan (1983a,b) in a unique way

consider the dynamics and compare the spider communities

.found in soybean versus alfalfa. A central theme of

Luczac's (1979) paper was a contrast of the communities

occurring in different crops. Riechert and Lockley (1984)











focused on a theme concerned primarily with potential preda-

tor/prey relationships and their impact upon the effective-

ness of spiders as biological control agents.

However, the spider fauna of many of our most important

crops, particularly row crops, have yet to be considered.

In addition, basic questions concerning the mechanisms that

structure the communities and the potential for spiders to

affect control of pests or potential pests have received

scant attention. That habitat structure, microclimate,

habitat stability, prey availability and diversity can all

influence the composition and dynamics of a spider community

is generally accepted. But the relative importance of these

factors and their interactions are highly debatable given

the complexity of the systems and the dearth of information.

The following report explores as many aspects of the

spider community in a major crop, field corn, with the

intent of discerning the mechanisms which produce the

observed community structure. This knowledge is vital if we

are to manipulate the predator complexes of crop fields to

our benefit.













CHAPTER II
THE SPIDER FAUNA
OF CORN FIELDS IN ALACHUA COUNTY, FLORIDA


Introduction



Corn, Zea mays, is grown on some 30 X 106 hectares in

the United States and 163 X 106 ha. world wide (Corn

Refiners Assoc. 1982). Yet little information has been

published on the predaceous arthropods found in this major

crop. This is surprising, especially since pest management

in corn is so dependent on naturally occurring biological

control because of its low cash value and its importance in

underdeveloped areas of the world. Everley (1938a, 1938b,

1939a, 1939b, 1940) in a series of papers listed the

arthropods, including the spiders, that he had collected in

a rather casual manner from a small field of sweet corn in

Ohio. Dritschilo and Erwin (1982) studied the effect of

cultivation techniques on the abundance and diversity of

carabidae in an Iowa corn field, while Isenhour and

Yeargan (1981) studied the phenology of Orius in field

corn.











Luczac (1975, 1979) in her extensive research into the

spiders of crop fields mentioned the spiders of maize in

Poland, but this crop was a minor component in her study.

Work on spiders in similar crops includes that of Baily and

Chada (1968) in Oklahoma who conducted a thorough study of

spiders occurring in sorghum which is botanically related to

corn. A few studies of spiders occurring in cereal crops

have been conducted in Canada (Doane and Dondale 1979, Fox

and Dondale 1972) and Europe (Nyffeler 1982, Luczac 1979).

Altieri (1979) has made major contributions to the

understanding of how diversifying cropping systems can

influence the diversity and abundance of the natural ene-

mies. In field corn, he has shown that predaceous arthro-

pods were more abundant in plots intercropped with selected

weeds than in plots kept free of weeds. In addition, levels

of infestation by Spodoptera frugiperda were lower in the

weedy plots than in the weed free plots.

In Florida, corn is grown on approximately 130,000

hectares mostly in relatively small fields of 20 to 100

hectares (Komarek 1951). Most of the state's production is

concentrated in the panhandle region. A large percentage of

the crop is kept by the grower as feed for his own livestock

and is an integrated part of a farming system which normally

includes other summer crops such as sorghum, peanuts, to-

bacco, watermelons or soybeans, as well as livestock. Many

fields are double cropped with rye, winter wheat or winter








5


vegetables. And because we cannot consider a crop field to

be a closed system, but rather part of the total agro-

ecosystem, we must consider the role of the corn field both

as a source and as a sink for both pests and beneficial

insects.

The first step in understanding the role that spiders

play in the corn field ecosystem, as in any crop (Whitcomb

1980, Dean et al. 1982) is to determine the composition of

the community. In addition to this central goal, I hoped to

help answer several basic questions concerning the ecology

of crop spider communities:

(1) How are the various species distributed upon the

corn plant? Whitcomb et al. (1963) and LeSar and Unzicker

(1978) showed clearly that different strata in the crop

canopy are inhabited by different species. Do these strati-

fications relate to structural constraints, microclimate,

location of prey or a combination of these?

(2) How are the spiders distributed within the field?

That is, are there significant border effects on the density

and diversity of the spider community? Are some species

regularly or gregariously distributed in the field rather

than randomly? Pieters and Sterling (1974) found that

spiders were the least aggregated of the predaceous arthro-

pods in a Texas cotton field, while Bishop (1981) found just

the opposite in Australian cotton. Altieri and Todd (1981)

found that predaceous arthropods were more abundant in











soybean rows adjacent to weedy borders than in the field

center.

(3) By direct observation of predation in the corn

field, what species or classes of prey are taken by the

different spiders?

(4) How do the structure and size of the spider

community change during the season and how is this related

to the phenology of the corn crop?

(5) How does the nature of the surrounding vegetation

and land management influence the structure and development

of the spider community? Is there consistency in the struc-

ture of the spider communities from season to season even in

the same general area? Culin and Yeargan (1983a, 1983b)

found that the more perennially stable alfalfa tended

towards a more similar community structure from year to year

than did an adjacent soybean field which apparently started

with a new set of spider colonists of slightly different

species composition each year. They also suggested that the

nearby alfalfa field was contributing to the annual flux of

spiders into the new crop field. Dondale et al. (1979)

found consistency in the spider faunas of apple orchards

through the northeast United States and Canada.

(6) Which spiders in the corn field actually reproduce

there? LeSar and Unzicker (1978) stated that few if any

spiders can reproduce in Illinois soybean fields.











(7) And, finally, what factors, both biotic and abi-

otic, tend to limit or benefit the populations of spider

species and/or the community as a whole? Specifically, are

predation on spiders or competition with other predaceous

arthropods of importance in regulating spider populations?



Site Descriptions



A total of six corn fields were intensively studied

during the period of April 1982 through July 1984. Four of

these fields were located within a mile of each other near

Archer, situated in southwestern Alachua County. A fifth

field was located near Orange Heights at the eastern edge of

the county. The sixth field, just northwest of Gainesville,

was located near the county center. In the selection of the

fields, every effort was made to include the widest possible

range of adjacent habitats.

The Archer fields were part of the same farmers' opera-

tion where peanuts, watermelons, forage grasses and cattle

pasture were rotated with corn. The soil was a deep, well

drained and leached Candler Fine Sand (USDA 1980). Although

the nearby uncultivated habitat was primarily xeric hammock

of Quercus virginiana/Q. laurifolia (Live Oak/Laurel oak),

many years of cultivation had oxidized the organic matter in

the crop fields so that a sandhill habitat was resembled.

Burrows of the gopher tortoise were found in the fields, a











resident typical of sandhills in Florida. True sandhill

scrub of Quercus laevis (Turkey Oak)/ Pinus clausa (Sand

Pine) grow naturally within 8 kilometers of these fields.

Sprinkler irrigation is necessary, and during the hottest,

driest periods the pumps run continuously to keep the corn

adequately watered. Two adjacent fields were sampled during

1982 (AR82-A and AR82-B), and one each during 1983 (AR83),

and 1984 (AR84).

Field AR82-A had on its east border a fence row of

trees (Quercus spp. and Celtis laevigata) beyond which was

a 50 ha. fallow field which was periodically grazed by

cattle. The vegetation was composed primarily of herbaceous

plants that cattle avoid grazing: Sida rhombifolia, Cheno-

podium ambrosioides, Ambrosia artemisiifolia, Oenothera sp.

and Cassia spp. The north border had a 15 ha. enclosure

where hogs were kept; here there were patches of bare soil

and large areas of tall Amaranthus, Chenopodium, and Sida

rhombifolia. To the west and south were borders of trees

(again Quercus and Celtis) which divided the field from

adjacent corn fields.

This corn field to the south was AR82-B. The areas

east, south and west of this field were improved cattle

.pastures of Bahia Grass (Paspalum notatum). The only weeds

in these pastures were scattered clumps of Asimina spp.

(Paw-Paw). The field to the east also contained a










residence, and a border of trees. In addition, the field

also had two large laurel oaks growing within it, under

which were a variety of weeds, similar in species

composition to the weeds growing under the tree borders.

These were seedlings of trees such as Celtis and Quercus,

and herbs such as Ambrosia artemisiifolia, Callicarpa ameri-

cana, Solanum americana and Phytolacca americana.

In 1983 and 1984 the Archer fields were again very dry

and sandy, but the vegetation and adjacent habitat supported

different plant communities due to varying management and

use. The layout of AR83 was a large (50 ha.) continuous

field of corn; sampling was concentrated in the southwestern

corner of the field. Along the south border of the field

was a band, 20 meters in width, which supported a diverse

community of herbaceous and woody weeds. The most abundant

of these are listed in Table 2-1. Beyond this was an over

grazed horse pasture which was heavily infested with Eupato-

rium and Asimina. To the west was a border of large oak

trees and then a plantation of slash pine with a dense

understory of oak saplings. Several mature slash pines

were left standing within the corn field and were surrounded

by weed patches of Rubus and Ambrosia. The area north of

the field consisted of dense herbaceous weeds (Desmodium,

Indigofera, Cassia) surrounding a cattle pond. Beyond the

east end of the field was improved Bahia Grass pasture.

The 1984 Archer corn field (AR84) had a weedy (Rubus

and Asimina) bahia grass pasture to the south, a plantation








10







Table 2-1. Weeds growing in the south border of the Archer,
Florida corn field during May of 1983.


ASTERACEA
Heterotheca subaxillaris Lactuca graminifolia
Eupatorium capillifolium Ambrosia artemisiifolia
Gnaphalium obtusifolium Hieracium gronovii

ONAGRACACEA ROSACEAE
Gaura angustifolia Rubus sp.

POLYGONACEA FABACEA
Rumex sp. Arachis hypogaea

PHYTOLACCACEAE BRASSICACEAE
Phytolacca americana Lepidium virginicum

MALVACEAE POLEMONIACEAE
Sida rombifolia Phlox drummondii

SOLANACEAE AMARANTHACEAE
Solanum americanum Amaranthus hybridus

RUBIACEA SCROPHULARIACEAE
Richardia scabra Linaria canadensis

APIACEAE CYPERACEAE
Ptilimnium capillaceum Cyperus sp.

CAPRIFOLIACEAE
Triodanis perfolia Wahlenbergia marginata

VITACEAE
Vitis tomentosa Parthenocissus quinquefolia











of slash pine with dense oak undergrowth to the southwest

and north, peanuts planted in May to the west, a wide border

of xeric hammock (Quercus spp.) to the northeast and a

several hectare field of weeds on the southeast. This field

was also quite large (60 ha.) and sampling was concentrated

in the south end.

The field sampled in 1983, located near Orange Heights,

presented a radically different habitat. The soil,

classified as a Mulat Sand, was water logged for extended

periods and so a considerable quantity of black organic muck

was incorporated with the sand. Portions of the field were

too wet for farm equipment to be operated and planting was

delayed until April due to flooding. A pond at the center

of the field contained the remnants of a cypress dome:

Taxodium distichum (Pond Cypress), Nyssa aquatica (Tupelo)

and sedges. Completely surrounding the 40 ha. field were

slash pine plantations with an understory of Myrica ceri-

fera (Wax Myrtle) and Ilex glabra (Gall Berry). Cattle were

allowed to graze the rich flora of grasses and herbs under-

neath. This herbaceous flora included Eryngium prostratum,

Hypericum spp., Lobelia nuttallii, Polygala incarnata, Xyris

spp., Rhexia mariana and Sarracenia sp. Field corn was

rotated with soybeans, and vegetables such as cabbage, pole

beans, strawberries and sweet corn.

The last field, Gainesville 1984 (GN84), about 30 ha.

in size, was cut from terrain that had supported the diverse










southern mixed hardwood forest (Monk 1965) on Norfolk Loamy

Fine Sand. Relatively undisturbed sections of this vegeta-

tion type were located to the west, southeast, and east of

the field. Paved highways separated the field on the north

from a 15 ha. fallow field, and from the forest on the east.

The borders around the field were mostly quite wide (10 to

20m) and had scattered trees such as Pinus taeda (loblolly

pine), Quercus laurifolia, Q. nigra (water oak), Prunus ser-

rotina (black cherry), Liquidambar styraciflua (sweet gum),

Myrica cerifera and Prunus angustifolia (Chicksaw Plum).

Beneath these trees grew thickets of shrubs and tall herbs,

especially Rubus, Desmodium and saplings of trees. Beyond

the border on the southwest was another corn field of 20ha.



Sampling Methods



A sample, as defined in this study, consisted of a set

of continuous corn plants in one planted row. During the

1982 season this consisted of either 5 or 9 plants, while

all samples included 10 plants in 1983 and 1984. Spiders

were collected from the sample unit by careful visual

examination. First, the fast running Pardosa wolf spiders

were noted, and, if their identification was not certain,

they were captured in individually numbered snap cap vials

for later identification. Next, the soil was examined

closely for the delicate webs of Linyphiidae and Hahniidae










whose webs were often made visible by droplets of dew

(Whitcomb 1980) or pollen dust. These small, easily damaged

spiders were collected by aspirator. A small hand trowel

was used to uncover soil dwelling hunters from their burrows

in the soil.

The base of the corn plant warranted close attention.

Many spiders find a niche among the prop roots and lowest

leaves. Tapping of the leaves with a pencil was used to

dislodge spiders from the lower surface and pulling the

leaves away from the stem frequently revealed the hiding

spot for cursorial species. Moving up the plant, each leaf

was examined on the upper and lower surfaces. The corn silk

required special attention because spiders of at least three

families constructed their silken retreats deep within the

strands. The tassel was also examined closely after which

it was given a stiff rap that occasionally dislodged unde-

tected spiders. Once this systematic inspection was com-

pleted for each plant, the plants were shaken vigorously and

dropping spiders were collected; the efficiency of the

visual examination was confirmed by only infrequently

catching spiders by this. final method.

This sampling method allowed me to record for each

specimen, the precise location on the plant or soil that was

inhabited. It also allowed for many prey records and spec-

ific interactions to be observed. To accomplish this, care-

ful notes were taken and each specimen was numbered and











preserved separately until its specific determination was

certain. For juvenile specimens, identification was not

accomplished until I became familiar with the fauna and

could match them with their adult counter parts.

Sample sites within the fields were selected by making

a transect through the field from one of the borders. The

starting point was usually not more than ten rows from the

field edge, and each additional site was reached by moving a

given number of rows (consistent for any sampling date, and

between 10 and 30). This sampling scheme allowed me to

analyze the "border effect" on spider density and diversity.

The number of samples that could be taken on a given day was

largely a function of the size of the plants and the density

of spiders. Early in the season, as many as 20 sets of ten

corn plants could be examined as described above, whereas at

maturity, only three sets could be completed during the

sampling period, from 0730 hrs to 1130 hrs. For analysis,

the seasons' samples for each field were divided into three

periods based on the phenology of the corn plants: Growth,

Flowering, and Mature.

Identification of spiders was accomplished through the

use of family and generic keys (Kaston 1978, 1981), the

numerous published specific keys (listed separately under

each family) and by comparison with specimens in the well

curated Florida State Collection of Arthropods (FSCA). Dr.

G. B. Edwards, of the FSCA, verified the majority of the











identifications, while spiders of the family Linyphiidae

were identified by Dr. Charles Dondale of Agriculture

Canada. Voucher specimens of all collected species are

deposited in the FSCA. As mentioned above, juvenile spiders

could, for the most part, be determined by comparing them to

series of specimens from the same locality that included

adults. Obtaining such series usually required collection

of specimens before or following the crop period on nearby

weedy vegetation (Whitcomb 1980). Nevertheless, for some

closely related species that occurred together in the same

area, reliable identification beyond the generic level was

not possible, especially for very small specimens.



Results



Checklist and Description of the Species



The spiders collected in the corn field are here listed

by family. After a general discussion of the each family,

the species found are listed with their authors. Species

marked with two asterisks constituted at least 5% of the

spiders collected, in at least one of the six fields, during

at least one of the sampling periods. Those which made up

more than 1% are marked with one asterisk. Those species

which are marked with an asterisk or those which are of

particular interest are discussed separately.











Uloboridae. These spiders, like those discussed under

the next family, use a variety of silk which is much dif-

ferent than that of other spiders (Foelix 1982). The silk

adheres to the cuticle of insect prey by virtue of its

finely hackled threads which act like Velcro to ensnare tiny

projections and setae on the insect. This is in contrast to

the adhesive glue found on the sticky webs of other spiders.

The family was revised by Muma and Gertsch (1964). Two

species of this small family of spiders were found:



*Uloborus glomosus (Walckenaer)

Uloborus sp.



Uloborus glomosus builds a horizontal or tilted orb web

that has a bluish-grey cast due to the hackled silk. It

appeared in the field only after the canopy was well

developed and then in the lower third of the canopy. Very

small juveniles as well as adult females and males were

collected. These spiders were common at all three sites but

were never abundant.



Dictynidae. Although this is a large and diverse group

of rather small spiders (Chamberlin and Gertsch 1958), only

three specimens, representing two, as yet, unidentified

species were encountered:











Dictynidae:



Dictyna sp. A

Dictyna sp. B



Theridiidae. The comb-footed spiders, a large and

diverse group of spiders, were well represented in the corn

field by 15 species and 250 specimens. These spiders build

irregular space webs of strong, sticky silk that are espec-

ially designed to capture crawling insects. Figure 2-1

shows the vertical stratification and usual web placement

for the common species. Many of the generic keys have been

published by Levi (1955, 1957, 1963) and Levi and Levi

(1962). Exline and Levi published the revision of Argyrodes

(1962). The specimens collected were identified as



Achaearanea near rupicola (Emerton)

**Achaearanea globosa (Hentz)

Anelosimus studiosus (Hentz)

Argyrodes fictilium (Hentz)

Argyrodes sp. A

Argyrodes sp. B

*Coleosoma acutiventer (Keyserling)

*Latrodectus mactans (Fabricius)

Steotoda quadrimaculata

Steotoda erigoniformis











Theridion albidum Banks

Theridion crispulum Simon

**Theridion flavonotatum Becker

Theridion pictipes Keyserling

*Theridula opulenta (Walckenaer)

Tidarren sp.



Achaearanea globosa was one of the most characteristic

spiders of corn fields in Alachua County. It was common in

the 1983 Archer field, nearly absent from the 1982-A Archer

field and abundant in the remaining fields. A. globosa made

up 16% of the spiders collected during the flowering period

at the Gainesville field. This is a small spider, usually

less than 1.5mm in length as an adult female, but it is

easily recognized by the conspicuous black spot on the

dorsal surface of the abdomen.

A. globosa's web was nearly always in close proximity

to the ground (see Figure 2-4) and close to the stem of the

plant. As shown in Figure 2-1 it is placed either in the

leaf axil, or on the lower surface of a leaf near the base

and stretching down to the next lower leaf or to the soil.

The principal prey, as recorded many times during the study,

were ants, particularly Solenopsis spp. It reproduced

freely in the field. The index of.dispersion (Southwood

1978) for this spider increased during the flowering and

mature periods, reflecting the pockets of offspring and the























































Figure 2-1. Distribution and typical web structures of
spiders occurring on the corn plant. Theridiidae: 1. Ach-
aeranea globosa, 2. Coleosoma acutiventer, 3. Latrodectus
mactans, 4. Theridion flavonotatum, 5. Theridula opulenta.
Linyphiidae: 6. Eperiqone banks, 7. Frontinella
pyramitela, 8. Ceraticelus similis.










rarity with which it disperses by air (see Chapter III).

Prey of the young A. globosa consisted of the plentiful

psocoptera and collembola that multiply on the shed pollen

and dying corn leaves.

On several occasions I found series of empty A. glob-

osa webs and later found a Mimetus spider nearby feeding on

yet another spider in its web. Achaearanea spp. are fre-

quent prey as well in the nests of Scelephron (Hymenoptera:

Sphecidae, Rau 1935).

Anelosimus studiosus is one of the most curious

spiders in Florida by virtue of its sociality (Comstock,

1948). Rather than leaving the maternal web, offspring

remain to help enlarge the web and subdue larger prey. Two

such colonies were found in the corn fields at Archer. The

colony found in 1982 contained only a female and a dozen of

her offspring, but the web found in 1983 covered the entire

plant and contained an estimated 100 spiders. Most of these

were small juveniles. The corn plant itself had turned

brown, presumably due to the light-blocking web.

Argyrodes fictilium was only rarely encountered in the

corn fields, but was in two instances taken while it fed

upon another spider. Argyrodes spp. are believed to be

primarily kleptoparasitc (Exline and Levi 1962); that is

they live in the webs of larger spiders and feed unnoticed

on the larger spider's prey. Trail (1980), however, also

recorded A. fictilium as predatory in nature. The four











specimens that I collected were mature males and females

that might well have taken many spiders as prey before my

capturing them. In addition, I found a juvenile of another

species of Argyrodes preying upon Grammonota texana, a small

linyphiid spider. This suggests that the predatory behavior

of Argyrodes spp. may be more widespread than previously

recognized.

Coleosoma acutiventer is a bit larger than Achaearanea

globosa, and coal black in color with an elongate, oddly

shaped abdomen. It, too, was found preying on Solenopsis

ants and constructed its web close to the ground and the

plant stem, often in the axil of a leaf which had fallen

away from the corn plant. It was collected at Archer and

Orange Heights, but was common only at the Gainesville

field. Adult females protecting egg sacs and newly hatched

young were found at the Gainesville and Archer fields. As a

very curious observation, an adult male C. acutiventer was

found clutching a batch of eggs, yet no female specimens

were detected in the vicinity.

Latrodectus mactans, the black widow spider, was most

common at the Archer fields. No mature specimens of this

species were found in the corn field, although rather large

juveniles up to 10mm in length were collected just before

the crop was harvested. As its name suggests, this spider

is jet black, while its globular abdomen is variously marked

with red and/or yellow on the ventral surface. The silk is











very strong and studded with droplets of glue. When small,

the webs of this spider resemble A. globosa's but as the

spiders grow larger, they climb higher and higher up the

plant constructing a large web that extends to the soil

surface. As described in Kaston (1970), the vertical

strands of silk that attach to the ground are ideally suited

for the capture of strong crawling insects such as beetles

and ants. I recorded Solenopsis spp. as prey for Latro-

dectus mactans in the corn field. In the borders of the

Archer fields were piles of old lumber and boulders among

which there were numerous L. mactans including egg producing

females. These are the refugia and nurseries for the black

widow spiders that colonize the field.

Theridion flavonotatum was the only member of its genus

that was commonly encountered, and then only at the Gaines-

ville field where it comprised 5% of the spider community

when the crop was mature. Its irregular space web is con-

structed on the undersurface of middle canopy leaves. Unlike

the web of Theridula opulenta (discussed below), guy lines

do not extend down to the next leaf. As prey, I recorded

Cicadelidae, Aphidae, Ottitidae (leaf mining diptera), and

small parasitic hymenoptera. I found adult, reproducing

females on the corn plants by the time the corn plants

reached maturity.

During the study, I collected only six other specimens

of Theridion spp. Two of these, however, were with eggs











and/or young spiders in the web. Both of these species,

Theridion pictipes and T. albidum, are larger than T. flavo-

notatum. Their irregular webs included as many as 3 corn

leaves. A Theridion pictipes web was found with a half

dozen mummies of already consumed Solenopsis invicta, but

was itself being consumed by a pirate spider, Mimetus.

Theridula opulenta is an easily recognized spider with

its transversely oblong abdomen marked with two or four

yellow spots. The web of the adult spiders can vary in

structure, but in the corn fields of Alachua Co. the struc-

ture shown in Figure 2-1 predominated. The irregular top

portion captures insects that fly or crawl into the under

surface of the leaves. Additional strands of tough silk are

also attached to the next lower leaf. Here they can inter-

cept insects that walk over the surface of the leaf below.

The prey of these spiders, as recorded in this study, are

similar to that of Theridion flavonotatum but also include

ants as prey. Although present at all six fields, T.

opulenta was common only at the Gainesville field.



Linyphiidae. In many ways the Linyphiidae were the

most difficult family of spiders to deal with. Their size

is generally minute, with adults often measuring just a

millimeter in length. The webs too, are tiny, delicate and

inconspicuous. Countless species, many of which are poorly,

if at all, described in the literature are nearly impossible











for the uninitiated to identify. Many of the most important

genera have not been revised since the works of Bishop and

Crosby (1932) and Crosby and Bishop (1928, 1933). The

juveniles especially, are difficult to identify with any

degree of certainty, and many of the tiniest specimens in

the samples were surely overlooked.

Except for a few species (see Figures 2-1 and 2-3),

these spiders were closely associated with the soil and/or

the base of the corn plant, where moisture is higher and

their prey of collembola, psocoptera, and nematocerans are

concentrated. The abundance and diversity of linyphiidae

varied greatly between the six fields, apparently as a

function of the moisture level in the soil. These spiders

are avid ballooners (Glick 1939, Duffy 1956, Dean and

Sterling 1985 and see Chap III) and have been treated as a

distinct ecological group by researchers (e.g. Luczac 1979)

in crop spider ecology because they frequently arrive in the

fields as adults which can begin reproducing immediately.

Duffy reported that significant numbers of Linyphiidae can

survive cultivation while Thornhill (1983) has published a

comprehensive analysis of linyphiid in British sugar beet

fields. The species I collected are as follows:



Anibontes longipes Chamberlin & Ivie

*Ceraticelus similis (Banks)

Ceraticelus sp. A











Ceratinops crenatus (Emerton)

Ceratinopsis sutoris

**Eperigone banksi Ivie & Barrows

Erigone autumnalis Emerton

*Florinda coccinea (Hentz)

*Frontinella pyramitela (Walckenaer)

*Grammonota texana (Banks)

Meioneta micaria (Emerton)

**Meioneta spp. (4 species)

**Tennesseelum formicum (Emerton)

Genus et species indet. (ca. 7 species)



Ceraticelus similis is one of four species of Liny-

phiidae that was most frequently taken from the foliage

layer of the corn field. Its sheet web was constructed on

the under surface of corn leaves, particularly ones that had

curled and were in the lower third of the plant. The

spiders are orange-red, with a nearly spherical abdomen, and

measure 2mm or less at maturity. These spiders were

encountered with regularity at all six corn fields surveyed.

Eperigone banksi accounted for 200 of the 2300 spiders

collected from corn fields; only Pardosa milvina had a

larger representation. Although E. banksi was found in all

six fields, the greatest number of these were collected at

the Orange Heights field. At Orange Heights these spiders

were abundant even during the seedling and growth stages,










when they were aggregated in clumps of sod left partially

turned by the cultivator. Eventually these spiders and/or

there offspring spread out to colonize the whole field.

The web consists of a delicate sheet that employs tiny

weed seedlings, clumps of soil, or the lowest leaves and

prop roots of the corn plant as supports. This design is

used by many of the linyphiid species occurring in crops

(Thornhill 1983). E. banksi is up to 3mm in length as an

adult, and moves about on the undersurface of the web. Prey

that I observed being taken included collembola, psocoptera,

diptera, Cicadelidae and not infrequently Solenopsis.

Florinda coccinea was the largest of the linyphiidae

that I found in Alachua Co. corn fields, reaching 4mm in

length. It is easily recognized by its bright red color and

tubercled abdomen. It is a foliage level species, inhabi-

ting the lower third of the plant where it constructs a

sheet and lattice web that typically spans from the upper

surface of the leaf base to the stem and usually to a leaf

or stem of an adjacent plant. It was present in all six

fields, but was commonest at the Orange Heights and Gaines-

ville fields. No adult females were found in the corn

field, with the majority of collections being early to

middle instar juveniles. In adjacent habitat adults were

found at most times of the year, including winter.

Frontinella pyramitela was a commonly collected spider

at the AR82-B and Gainesville fields. It was also present











at the other fields. Most of the specimens were less than

3mm in length, none of which were adults. The common name

of this spider is "The Bowl and Doily Spider" after a

description of the web. It consists of a flat sheet of silk

over which is constructed a loosely woven lattice of space

webs. Small flying insects collide with these fine strands

and fall upon the silken net below. The spider maneuvers on

the underside of the web to the fallen prey and bites it

through the sheet. Thus, as I have recorded here, the major

prey are tiny diptera, hymenoptera, alate aphids and cica-

delids. This construction is similar to that of F. cocci-

nea's, but is situated higher in the plant at mid level.

Grammonota texana specimens were encountered at the

base of the corn plant, but also with regular frequency in

the canopy. When found on the plant itself, the web

occupied the space created by the leaf axil or a curled

leaf. The delicate sheet web did not have an overhead

lattice. This spider was present at all six corn fields,

but with greatest frequency at the Orange Heights and 1983

Archer fields where reproducing females were found. Preda-

tion by this species was not observed.

Meioneta spp., as a group, were collected in all six

fields, being common at the Orange Heights, Gainesville and

two of the Archer fields. However, they are difficult to

differentiate at the species level, even when adult

specimens are available. The webs of the five species are











similar, in that they were usually associated with the prop

roots and/or the lowest leaves. A sheet web is combined

with a course, overhead lattice composed of relatively

strong threads. The adult males of this species roam on

foot searching for females, and because they are very ant-

like in form and behavior they may achieve a certain amount

of protection.

Tennesseelum formicum was found with regularity at

moderate levels at all six fields, but was most common at

the AR82-A and Gainesville fields. Its web and the behavior

of the males is quite similar to Meioneta's. Although I did

not find any females with eggs, reproduction in the field

likely occurred since adults of both sexes were found as

well as patches of numerous juveniles.



Theridiosomatidae. This- is a small family of minute

spiders which are classified as members of the Araneidae by

some authors (Levi 1980). The tiny orb web is built close

to the ground in moist, protected situations. Its web

differs from typical araneid webs (Kaston 1965) by having an

indistinct hub; the radii meet at 3 or 4 points rather than

a single center. Also, the spider sits not at the hub of

its orb web, but rather at the end of a strand attached to

the hub. All but one of the five specimens representing

this family were found in the Orange Heights field. The

single species was










Theridiosomatidae:



Theridiosoma radiosa (McCook)



Araneidae. No other family of spiders had more

species or individuals than the Araneidae, the orb weavers.

Twenty-six species were recorded from the six Alachua County

corn fields. As would be expected, a wide range of size,

morphology, behavior, habitat selection and web structure

is found among this diverse fauna. Luczac (1975) also noted

the strong representation of Araneidae in corn fields.

Three basic variations of web orientation and con-

struction are used by the species found in the corn field.

The first of these types has the plane of the orb web paral-

lel to the ground. All of the species of this type that I

found in the corn fields have webs made of light, flexible

silk that yields to air currents, allowing the web to sway

up and down. Craig et al. (in press) suggest that this is

an adaptation for increasing the probability of capturing

nematoceran flies. The second basic design has the plane

perpendicular to the ground and constructed from relatively

tough, inflexible silk. The spider sits at the hub of such

a web during the day. The third design is also perpend-

icular to the ground, but has an additional component of a

retreat in the upper corner of the web where the spider

hides during the day. In some species that use this third
























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design, the web is consumed at daybreak and then rebuilt

each night. Within each of these design types, there is a

stratification of species within the canopy as depicted in

Figures 2-2 and 2-3. Interestingly, the araneids which are

at the hub primarily by night occur higher on the plant than

do species which stay at the hub both day and night.

Levi has published many of the keys useful for identi-

fying the species within this family (1971, 1975, 1976,

1977, 1980). Berman and Levi (1971) revised the genus

Neoscona. The orb weavers I collected from corn fields are

as follows:



Acacesia hamata (Hentz)

Acanthepeira sp.

Araneus miniatus (Walckenaer)

*Araneus pegnia (Walckenaer)

Araneus sp. indet.

Argiope aurantia Lucas

*Argiope trifasciata (Forskal)

Cyclosa caroli (Hentz)

**Cyclosa turbinata (Walckenaer)

*Eriophora ravilla

*Eustala anastera (Walckenaer)

Gasteracantha cancriformis (Linnaeus)

**Gea heptagon (Hentz)

Hyposinga prob. rubens (Hentz)











Araneidae--continued:



Larina direct (Hentz)

**Leucauge venusta (Walckenaer)

*Mangora gibberosa (Hentz)

Mangora spiculata (Hentz)

Mecynogea lemniscata (Walckenaer)

Micrathena sagittata (Walckenaer)

*Neoscona arabesca (Walckenaer)

Scoloderus cordatus (Taczanowski)

Tetragnatha caudata Emerton

**Tetragnatha laboriosa Hentz

Wagneriana tauricornis (0. P.-Cambridge)



Araneus pegnia, Eriophora ravilla, and Neoscona ara-

besca form the bulk of the third type of orb web builder

described above in which the spider hides in a retreat

within a curled leaf near an upper corner of the web.

Araneus pegnia was most common in the 1982 Archer fields

where adults were collected during the final stages of the

crop period. This spider was infrequently collected at all

fields studied in 1983 and 1984, including those at Archer.

Eriophora ravilla took the place of A. pegnia at the

1983 and 1984 fields. It was particularly common at Orange

Heights in 1983 and Archer in 1984. The majority of speci-

mens collected were small juveniles, 4mm in length or less.











Adults, which are large spiders nearly 12mm in length, were

collected in the months following harvest on nearby shrubs.

Neoscona arabesca, on the other hand, was collected at

all six fields but especially at the Archer fields in 1983

and 1984. Although most of the specimens collected were

again small juveniles, a number of adult females and males

were found by harvest time. The prey range that I recorded

for these three species was quite similar. Among the prey

recorded were small coleoptera such as Sitophilus and Cal-

lida spp., Braconidae, Agromyzidae (leaf mining diptera),

Ottitidae, Geocoris, Orius, and Cicadelidae. Mature spiders

have been observed to take moths, but are too small during

the growth and flowering stages when Spodoptera and Helio-

this are important.

Argiope trifasciata was common in both 1982 Archer

fields and present at the other four fields at low popula-

tions, but a number of large juveniles and an adult female

were collected. The web of these large spiders (up to 17mm)

was usually attached to the lower half of the plant, and

spanning two adjoining plants or even across the furrow.

The plane of the flat orb makes an angle of about 60 degrees

with the ground and has a characteristic zigzag stabili-

menta. A frequent component of the diet is grasshoppers

(Comstock 1948), but I also recorded coleoptera and cica-

delids.











Cyclosa turbinata was the most abundant araneid in the

1982 Archer corn fields but was only moderately common at

the other fields. The web of this species is markedly

characteristic and is also helpful in determining the prey

used. Rather than dropping the dried remains of consumed

prey out of the web, this spider incorporates them into the

web along the vertical axis. The spider is similarly

colored and shaped as this debris, and so is difficult to

spot as it sits upon it. By placing this clump of dead

insects in a dilute solution of bleach to dissolve the silk,

I was able to extract and identify the contents. Like many

spiders, Cyclosa has powerful gnathobases which effectively

crush the cuticle of prey so that for many prey items I was

able to determine only the family: Chrysomelidae, Sito-

philus, Dolichopodidae, Agromyzidae, Ottitidae, Braconidae,

Aphidae, Cicadelidae and alate Formicidae.

Eustala anastera, in its mature stages, which I found

only on adjacent shrubs and weeds, behaves like A. pegnia

and N. arabesca by hiding in a retreat by day. But as early

instar juveniles in the corn field, these spiders were

mostly found sitting at the hub by day. They reached their

greatest abundance on the corn plants late in the season as

the plants were entering senescence, constructing their webs

among the spikes of the tassel. Even when the plants were

dried and brown these spiders continued to use the tassels

for their orb webs.











Gea heptagon was consistently captured at all six corn

fields. This easily recognized spider has a black, five-or

seven-sided splotch on the dorsum of the abdomen from which

it gets its name. The web is vertical and nearly always in

the bottom third of the canopy (see Figure 2-2) with some of

the support strands attached to the ground. This spider's

web of tough silk was also frequently found suspended from

weeds and debris beneath the canopy.

Despite being the most common araneid in my collections

of corn field spiders, no adults of Gea heptagon were col-

lected, and only a few late instar juveniles. Adult speci-

mens were encountered in the corn field after harvest

beneath tall weeds, but also in the early spring before the

field was mown and harrowed. The prey I found in their webs

were mostly flying insects, but I also observed this spider

to take an ant that had blundered into one of the strands

attached to the ground.

Leucauge venusta became numerous in the corn fields at

the Archer and Gainesville fields in 1984 after the canopy

had developed sufficiently to shade the understory.

However, these spiders were mostly quite small,and so did

not reach maturity before the corn was harvested. Even as

the corn plants were entering senescence and thus allowing

more light to penetrate to the soil, these shade loving

spiders began to disappear. This is a reflection of this











spider's normal habitat in north Florida, the shaded under-

story of hammocks.

Its web of finely meshed, exceeding delicate silk, is

constructed parallel to the ground at about mid-level in the

canopy. The web sways freely in the breeze which helps it

intercept small flying diptera (Craig et al. in press) and

which may also allow it to be supported by the wavering corn

leaves.

Tetragnatha laboriosa was the most abundant of the

Araneidae which build a horizontal web, and the second most

abundant orb weaver over all. The greatest portion of the

specimens collected were quite small and in practice could

not be reliably separated from the other species of Tetra-

gnatha. But since adults of other species were not col-

lected in the vicinity of any of the corn fields, except for

swampy Orange Heights, I feel justified in assuming that

most of those collected in the corn field were in fact T.

laboriosa. As a group, Tetragnatha is normally found in

marsh or swamp habitats; T. laboriosa is the major excep-

tion.

I recorded a number of prey for this spider including

the alate forms of Aphidae and Formicidae, Cicadelidae,

Braconidae, Cecidomyiidae, and Agromyzidae. LeSar and

Unzicker (1978) in a study conducted in Illinois also made

considerable contribution to the biology and known prey

range of Tetragnatha laboriosa. There it was the most abun-











dant spider in soybean fields. Culin and Yeargan (1982)

also detailed the prey range for this spider in soybeans.

T. laboriosa showed an interesting stratification in

the crop canopy as a function of its size. The smallest

spiders, which are less than 1 mm in length occur more often

in the lower canopy, and the adults, which reach 7 mm, in

the upper canopy. The correlation between body length and

the height of the web in the canopy as shown in Figure 2-5

was significant (r=.54, p < .01, N=39). This was the only

spider which showed a significant correlation (negative or

positive) between body size and position in the canopy.



Agelenidae. The funnel web spiders, or Agelenidae,

were rare spiders in the corn field itself, but were quite

common in the wooded borders. Just four specimens were

collected, and these were near the border areas of the corn

field. A Cicadelidae and an early instar nymph of a

Gryllidae were seen to be taken as prey. Identification of

these spiders is based on adult characters of the genitalia

and so I am sure only of the genus:



Agelenopsis sp.



Hahniidae. The Hahniidae were another uncommon family

of spiders in Alachua County corn fields, but were nonethe-

less successful colonists in that they reached maturity





























S S S S S


S





S S S

S S


S S 55 S

S


* S 5


* S. S




* S S


55** 555 0


2 3 4 5 6 7


Lerngth mm



Figure 2-5. Vertical stratification of Tetragnatha labor-
iosa on the corn plant as a function of body length.


0 1











before harvest. These spiders are easily recognized by

having six spinnerets arranged along the posterior margin of

the abdomen and by the construction of their web. The tiny,

delicate sheet web is spun over the soil; the spider itself

hides under an earthen clod or among the prop roots of the

corn plant, running out over the top of the web to secure

prey. Specimens, up to 3mm in length, were captured at the

Archer and Gainesville fields only.



Mimetidae. The Mimetidae, unlike most spiders, do not

normally eat insects. Instead they prey on other spiders,

particularly web dwelling species, by stealthily climbing

into the host's web. Numerous long, curved spines on Legs I

and II are used by the mimetid to preclude an attack by its

prey until its own venom has taken affect. I frequently

found a trail of empty webs, particularly of Achaearanea

globosa, at the end of which I found Mimetus in the web of

its most recent victim. Surprisingly, Mimetus sp. was among

the common spiders at Archer in 1983; it was present but

rare at the other fields. At least two species of Mimetidae

were collected with specimens taken from all six fields:



Ero leonina (Hentz)

Mimetus sp.











Pisauridae. Only twelve specimens of Pisauridae were

collected from the corn field during the study. All of the

specimens were collected as early instar juveniles from the

lower surfaces of leaves in the lower half of the plant.

Two species were identified using the keys in Carico (1972):





Dolomedes sp.

Pisaurina sp. prob. mira (Walckenaer)



Lycosidae. The wolf spiders, family Lycosidae, are

the dominant group of hunting spiders on the soil in many

agricultural situations (Whitcomb et al. 1963). Most

species are active and hunt at night when reflective eyes

make the majority easy to find with a headlight. Pardosa

spp. however are most active during the daylight hours while

others are largely subterranean, such as Geolycosa, Lycosa

carolinensis and Lycosa lenta and so the populations of

these were probably underestimated by my sampling

techniques.

Identification of lycosids to the level of species

relies heavily on characteristics of the genitalia and so

juveniles cannot always be placed with confidence. Using

the keys of Dondale and Redner (1984) I was able to identify

adult Pardosa, and with practice, I was able to separate the

juveniles of the four Pardosa species; this was made easier










by comparison with juveniles reared from positively ident-

ified adults. Most members of the genus Lycosa were identi-

fied as L. lenta because it was the only identified adult

species found in the corn field at night by head light.

Identification of Pirata was aided by Wallace and Exline

(1978).

Fourteen species of lycosids were distinguished from

my collections in corn fields:



Allocosa floridana

Lycosa rabida Walckenaer

Lycosa carolinensis Walckenaer

Lycosa hellulo Walckenaer

*Lycosa lenta Hentz

Lycosa amophila

*Pardosa pauxila Montgomery (=georgae)

Pardosa littoralis Banks

**Pardosa milvina (Hentz)

**Pardosa parvula Banks saxatilisis)

Pirata allapahae Gertsch

Pirata sp. A

Pirata sp. B

Genus et sp. indet.



Lycosa lenta, as an adult, is a large nocturnal hunter

of the soil surface where I found it preying on other wolf











spiders and crickets. The majority of specimens collected

were taken at the Archer fields, all as early to middle

instar juveniles. All quantitative sampling was conducted

between 0730 and 1130 hours when L. lenta is usually inac-

tive and in hiding beneath dead corn leaves or under clods

of earth. Using a head light at night I could find L. lenta

adults at low densities, particularly in border areas and

along irrigation rows. I rarely found adults roaming in

under the corn canopy. As do all the Lycosidae, L. lenta

females carry the egg sac attached to the spinnerets until

the spiderlings emerge. The spiderlings crawl onto the

dorsum of their mother and then disperse over a period of

several days as she roams and hunts. Lycosa lenta fre-

quently prey on other lycosid spiders, either con- or heter-

ospecifics (Gowan, 1985).

Pardosa milvina, with 333 specimens collected during

the study, was the single most abundant spider in the corn

fields. All stages of this species were present in the

fields nearly throughout the year, but were scarcest at

planting and just after cultivations. Recolonization

occurred rapidly through ballooning and running over the

soil. Adult females can deposit spiderlings over a large

area as described above for L. lenta. Dense populations of

P. milvina were found in the cattle pastures (especially

over grazed ones with barren patches of soil) and in the











recently fallow fields that were integral parts of the

Archer and Orange Heights ecosystems.

The behavior of Pardosa milvina, as I observed it in

the field, was quite variable. Most specimens were

collected running over the soil, or among the basal leaves

and prop roots, but a significant number were found high on

the foliage, even on the corn silk. I recorded them to take

prey while on the plants, specifically corn leaf aphids

(Rhopalosiphum maizae), but they also take water that col-

lects in the leaf axils during the morning dew. Another

specimen was found hanging from the corn silk while in the

process of ecdysis; a number of exuviae were also found

similarly positioned.

Pardosa as a group seem to require a moist environ-

ment; this was dramatically demonstrated at the Gainesville

field. From the middle of May through the beginning of

June, just as flowering was about to start, a three week

long period of very dry weather nearly destroyed the crop

during which the population of Pardosa milvina plummeted

(see Figure 2-11). When rain returned, the crop quickly

recovered but the P. milvina did so only slowly. In this

case I believe that the absence of cattle pastures and

fallow fields was responsible for the failure of the popula-

tion to recover. Another facet of recolonization is that

Pardosa ballooned only rarely during May through August (see

Chapter III).











Pardosa pauxila and P. parvula were common to abundant

wolf spiders, notably during 1983. During the mature period

at the Archer field, P. parvula was the most frequently

captured wolf spider, while at Orange Heights Pardosa

pauxila was among the most commonly collected. The behavior

of these spiders was very similar to P. milvina's such as

climbing up into the plants to drink dew water and ecdysis

while hanging from the silk.



Oxyopidae. The lynx spiders, family Oxyopidae, are

largely diurnal hunting spiders which rely on a combination

of sight and acute tactile reception to capture prey. Silk

is used in construction of the egg sac and in ballooning,

but not for snaring prey. Identification of Oxyopidae is

aided by Brady (1964). One species made up the bulk of the

spiders in this family collected from corn fields:



Oxyopes salticus Hentz

**Peucetia viridans (Hentz)



Peucetia viridans, the green lynx spider, entered the

fields during April at the end of its ballooning period (see

Chapter III). It was one of the most common spiders when

the plants were small, and this population level that was

achieved in April remained relatively constant through the

season until senescence, when the spiders moved onto the













emerging weeds (see Chapter IV). The greatest numbers of P.

viridans occurred at the Archer fields but were virtually

absent at Orange Heights. They reached 7mm in length by

harvest time and so were the largest of the common species.

These are strong predators in the corn field preying on

Chrysomelidae, Scarabaeidae, Cucurlionidae, Diptera and

small bees.

Adult P. viridans, which appear in late July to

August, specialize on pollenators as prey. From the

blossoms of Eupatorium, Monarda, Indigofera hirsutum and

Bidens alba they catch numerous honey bees and even large

wasps. The spiderlings hatch in the late fall and become

soil surface wanderers until early spring (Whitcomb 1985)

when they can be found on spring weeds, low tree branches

and shrubs. They balloon frequently during this time (see

Chapter III) and remain in the first post emergence instar.

Soon after their arrival in the corn field they molt to the

second instar and cease to move through the air. Peucetia

viridans is an example of a spider that despite not reaching

maturity while a part of the corn field community can be an

abundant spider depending on the weeds that grow nearby.

-The presence of large areas of late summer weeds will

provide numerous offspring for next year's crop.











Gnaphosidae. Among the webless hunting spiders, the

Gnaphosidae are elongate, fast running, largely soil surface

hunters. Gnaphosa serricata, the only common species in

northern Florida corn fields, hides beneath the soil by day

and roams by night. Pitfall traps set in the corn field

efficiently captured these arachnids. I did not record any

predation by these spiders, but a spider wasp (Pompilidae)

was captured taking a penultimate female of G. serricata.

Gnaphosa serricata was the only one of the following species

for which more than one specimen was collected, and then

only from the drier Archer and Gainesville fields (Platnick

and Shadab, 1975):



Drassodes sp.

Drassyllus sp.

*Gnaphosa serricata (L. Koch)

Poecilochroa variegata (Hentz)

Genus et sp. indet.



Clubionidae. The sac spiders, family Clubionidae,

have some common and important species in agricultural

fields. These spiders have, for example, been recorded to

feed on the eggs of Heliothis (Peck and Whitcomb 1970) and

the larvae of other lepidoptera. Most species of Clubion-

idae hide by day in well concealed sacs constructed of silk.

The sacs can be in a rolled or torn leaf, in a folded blade











of grass, or deep in the corn silk. If the plant is vigor-

ously shaken, and sometimes only gently, the spider will

almost always emerge from the sac running at high speed for

some distance and then halt. If an empty sac is found

during a visual search it is wise to look about for the

spider which may be hiding nearby. Most species of Clubion-

idae are nocturnal, but several groups which apparently

mimic wasps and ants are active in full sunlight. The

driest corn fields at Archer had the highest numbers of

clubionids, while the wettest, Orange Heights, had few. All

of the Clubionidae make use of their acute tactile percep-

tion in the capture of prey. These species were found and

identified using Edwards (1958), Reiskind (1969), and

Platnick and Shadab (1974a, 1974b):



Castianeira sp. A

Castianeira sp. B

**Chiricanthium inclusum (Hentz)

*Clubiona abbotii L. Koch

Clubiona procteri Gertsch

Micaria sp.

Myrmecotypus lineatus (Emerton)

Phrurotympus minutus

Scotinella sp.

*Trachelas deceptus (Banks)

Trachelas similis O.P.-Cambridge)















Chiricanthium inclusum and its role in agricultural

fields was studied by Whitcomb et al. (1963) and Peck and

Whitcomb (1970) who found it to be an important predator in

cotton fields. But in Alachua County corn fields it was

common only at th4 Archer fields where it was among the top

ten most common spiders. From the time when the corn silk

emerged until it rotted off during the mature phase, C.

inclusum was found hidden deep in this silk. When the silk

was not available, it preferred leaves tattered by Spodo-

ptera frugiperda or in the recessed midrib on the lower leaf

surface. But on other plants these spiders normally tie

several nearby leaves together (or use ones already tied

together by pyralid larvae) and build their silken retreat

within. Thus, home sites for this spider on the corn plant

are marginal and could be a factor that limits this spider's

numbers in the corn field. Otherwise the corn plant should

provide adequate prey, such as lepidoptera, as evidenced by

my finding reproducing adults on the corn plants.

Clubiona abbotii and C. procteri are quite similar

even as adults, and so I have not attempted to separate the

juveniles. Five adults of C. abbotii were found; one of C.

procteri. Again, these spiders were absent from the Orange

Heights field and were only sporadically common at Archer.

Yet these spiders were among the most common species











captured as ballooners (see Chapter III). Only two nests of

this species were found in the corn silk; the remainder were

in the depression along the midrib on the lower surface of

the corn leaf or in the leaf axil. I did not record any

feeding by these species, but one female was found with an

egg sac.

Trachelas deceptus and T. similis are also not easily

distinguished as juveniles. Here five adults of T. deceptus

were identified and one of T. similis. Trachelas are gene-

rally robust spiders with the first pair of legs longer than

the others and with the cephlothorax and forward legs a deep

maroon color which fade to pale towards the posterior of the

animal. These spiders were regularly encountered only at

the Archer fields (both species), hiding deep in the leaf

axils, especially of the lowest leaves. I found no repro-

duction occurring and did not record any prey.





Anyphaenidae. In many ways the Anyphaenidae resemble

the clubionids and it can be troublesome for the novelist to

distinguish the two. The most important and reliable char-

acter is the placement of the spiracular slit on the venter

of the abdomen. In clubionids it is just anterior to the

spinnerets, while in the anyphaenids it is placed a half or

two thirds of the way anteriorly towards the epigastric

furrow. The spiracle is very faint and requires a good










microscope to see. Another character which is sometimes

useful is the notched trochanter (Roth 1964). Among the

species found only Aysha spp. was collected infrequently;

the others were rare. The silk retreats, which are also

similar to the clubionid's, were most frequently found in

the tassel. Again Aysha spp. were frequently caught on the

traps used to monitor aerial dispersal indicating that the

corn plants do not provide a suitable niche. Four species

were identified using the keys published in Platnick (1974):



Aysha velox (Becker)

Aysha gracilis (Hentz)

Teudis mordax (O.P.-Cambridge)

Wulfila saltibunda (Hentz)



Thomisidae. The crab spiders, family Thomisidae, are

so named for their elongated anterior legs and sideways

movement characteristic of true crabs. Thomisid spiders

position themselves at key positions on their substrate so

as to maximize the encounter rate with potential prey. For

many species this means sitting in the flower of a plant to

capture pollenators and other flower feeding insects.

Despite their cryptic coloration, species which frequently

hunt at the inflorescence of a plant are not restricted to

that position. They can also hunt from the growing term-

inals or leaf petioles (Plagens 1981). The identification











of the Thomisidae is greatly aided by the revision by

Gertsch (1939). Only one of the following five species

collected was common enough to warrant separate discussion:



Misumenoides formosipes (Walckenaer)

**Misumenops celer (Hentz)

Misumenops oblongus (Keyserling)

Xysticus sp. A

Xysticus sp. B



Misumenops celer was frequently the most abundant

foliage layer hunting spider. The majority of captures were

during the flowering and early mature periods when the

spiders were almost always captured on the inflorescences,

either the male tassel or the female silk. The age struc-

ture of this species was greatly skewed towards the smallest

instars which arrived by ballooning and then departed the

same way once the flowers stopped attracting prey (see

Chapter III). For these early juveniles, the principal

prey, as I recorded it, were thrips, followed by minute

diptera. Larger spiders were captured while feeding on

Orius, Geocoris, Agromyzidae and other hunting spiders

including conspecifics. Plagens (1981) found hymenopterous

parasitoids also to be a major part of this spider's diet.

Adult males and females were collected in the corn fields

but no females with eggs were found.













Philodromidae. For many years the family Philo-

dromidae was classified as a subfamily within the Thomisi-

dae. However, recent work on the ultrastructure of the eyes

combined with a host of other character differences has

convinced most arachnologists that they are correctly

separated (Homann 1971,1975). The hunting strategies differ

markedly also. Philodromids run very fast an legs provided

with adhering scopulae. They pursue prey for short distan-

ces after detecting their presence through vibrations and

are rarely found on or near the flowers. Many species are

found on the stems and bark of woody plants. I captured

just three specimens of this family in the corn field, but I

may well have missed some. They run to the other side of

the plant stem or leaf if they detect movement and can cling

to surfaces with surprising tenacity when the plant is

shaken. Identification was aided by Dondale and Redner

(1961, 1968).



Philodromus keyserlingi Marx



Salticidae. As sophisticated as the Araneidae are in

the construction of webs, so are the Salticidae in the

visual pursuit of prey. The eyes are certainly the most

sophisticated of any arthropod eye and rival the vertebrate

eye in their ability to detect form, color, movement,











orientation and distance (Homann 1971). Not only does this

aid them in locating prey, but also in the safe capture of

prey. By grasping prey such as caterpillars or ants at

precisely strategic points (Edwards et al. 1974) the prey's

defenses are rendered ineffective.

The Salticidae were common and well represented by

species at the Gainesville and Archer fields, but were

nearly absent from the Orange Heights field. Several

species are avid ballooners (Horner 1975 and Chapter III)

even as middle to late instars which can mature quickly on

abundant prey in their new surroundings and begin producing

offspring. Eighteen species of salticids from corn fields

were identified:



Corythalia canosa (Walckenaer)

Habronatus brunneus (Peckham & Peckham)

Habronatus trimaculatus Bryant

**Hentzia palmerum (Hentz)

Marpissa dentoides Barnes

Lyssomanes viridis (Walckenaer)

**Metaphidippus galathea (Walckenaer)

Peckhamia americana (Peckhams)

Phidippus apacheanus Chamberlin & Gertsch

Phidippus audax (Hentz)

*Phidippus regius C.L.Koch

Phidippus clarus Keyserling











Salticidae--continued:



Phidippus pulcherrimus Keyserling

Phidippus putnami (Peckhams)

Synageles sp.

Thiodina sp.

Zygoballus rufipes Peckhams



Hentzia palmerum was the second most abundant salticid

collected in the corn fields. The males of this species

have the chelicerae greatly elongated and porrect (directed

forward). Early juveniles through adults of this species

were found in the corn fields, particularly on the silks or

tassels. At Orange Heights, this spider was nearly absent

from the corn plants, but they became fairly common on the

weeds in that field by September (see Chapter IV). The prey

for this species consisted largely of soft bodied insects

such as agromyzids, aphids, Orius and thrips.

Metaphidippus galathea vied with Misumenops celer as

the most common foliage hunter. Like both M. celer and H.

palmerum these spiders concentrated their activity on the

inflorescences. Some arrived in the corn fields early

enough to mature and begin producing offspring. First

instar juveniles that emerge before the flowering is over

find abundant thrips and diptera in the silk and on the

tassels. Those that emerge later move to the emerging weeds











such as Indigofera, Cassia and Amborsia where they become

one of the most common species (see Chapter IV). Horner and

Starks (1972) found that M. galathea has a relatively short

life cycle, reaching maturity in 6 to 7 months. Female

spiders produced a mean 8.3 egg sacs over her life span.

Like salticids in general, Metaphidippus hunts primar-

ily by sight, taking an assortment of prey similar to

Hentzia's but it can adopt alternate hunting strategies. I

found M. galathea pulling diptera larvae from the rotting

frass left by corn ear worms.

Just two specimens of Metaphidippus were collected

from the corn plants at the Orange Heights field where it

was also less common than H. palmerum on the weeds following

harvest.

Phidippus regius is a member of a large genus of

common, large jumping spiders. These spiders produce large

quantities of offspring (Edwards 1980) that balloon fre-

quently (see Chapter III) and so it is not surprising that

they occur with regularity in the corn field. Some speci-

mens of this and the other five identified species reach the

middle instars. No adult Phidippus of any species were

collected. Like Hentzia and Metaphidippus these spiders

.were most frequently collected in the silk or on the

tassels. Prey included diptera and Cicadelidae. Muniappan

and Chada (1970) found P. audax to be a potential biological

control agent of green bugs (Aphididae) in sorghum.












Community Structure



Species Abundance. The rank abundances of the indi-

vidual species during the growth, flowering and mature

stages are presented for each of the six fields in Figures

2-6, 2-7, 2-8, 2-9, 2-10 and 2-11. Just one spider was

common in all six fields, namely Pardosa milvina. Four

spiders, Misumenops celer, Achaearanea globosa, Tetragnatha

laboriosa and Metaphidippus galathea, were common in five of

the six fields. Gea heptagon, Peucetia viridans, and Ulobo-

rus glomosus were common in four of the six fields while

eight species were common in three of the fields. Most

species which were common in one field were at least present

in the other fields. Thus, differences between fields were

mostly in the relative frequencies of the major species and

in the list of rarely captured species.



Spider Families. The family composition of spiders in

the six fields are presented in Figures 2-12, 2-13 and 2-14.

Even at this taxonomic division, there were considerable

differences between the six fields. This could be a reflec-

tion of the general strategies for surviving used by the

different spider families contrasting with the physical and

biotic conditions presented by the surrounding habitats.

The Lycosidae, for example are favored by the presence of













Major Species


Minor Species


RANK IN ABUNDANCE


Figure 2-6. Principal species and percent rank abundance of
spiders in field corn during three phenological periods at
Archer, Florida, 1982, Field A. Growth (A), Flowering (B),
Mature (C).


-iJ


DIL


1 5 1 15 21

B







I.l1*1

oiI j'itlI


-4.0

4-f
-3.0 .
o
2.
-2.0 -j
E
z


1 5


25 28








63





A

15 '- Major Species
0.6
10 m z Minor Species 0.4
5 4 0.2

0 -0
1 5 10 15 20 24 33


B
S4.0
o a na
U20 3.0 I5


S10 2.0
0. z
Q: 1.0 E


1 5 10 15 20 24 45


C
25 4.0

20 ,
Q 3.0
15 *0 0 2O ,,


.: 1.0

0 0
1 5 10 15 20 24 41


RANK IN ABUNDANCE


Figure 2-7. Principal species and percent rank abundance of
spiders in field corn during three phenological periods at
Archer, Florida, 1982, Field B. Growth (A), Flowering (B),
Mature (C).











M 0.8
30

2, Minor Species 0.6

20-
L = | Major Species 0.4


10 a0.2



0 0........
1 5 10 15 20 25

1.0
B
10 2 0.8

Sx a 0.6


0 5 z it 0.4

Sl -0.2

0 6 ar-- 02
1 5 10 15 20 39



S C 0.8
10 to

0.6
/~ 0.4



0.2

0 / 0
1 5 10 15 20 45

RANK IN ABUNDANCE


Figure 2-8. Principal species and percent rank abundance of
spiders in field corn during three phenological periods at
Archer, Florida, 1983. Growth (A), Flowering (B), Mature
(C).











2.0

40 r--
Major Species
1.5
30,
30 a Minor Species


20 1.0


10 0.5
10-0

0 ..... //-m 0
1 5 10 15 20 28


B
C-
30


20. 1u











4.0
30 62 2.0














oo
1 5 10 15 20 37
Figure 2-9. Principal species and percent rank abundance o.0

















spiders in field corn during three phonological periods at
30 C
4.0

20range Heights, Florida, 3.0


10l 2.0




1 5 10 15 20 37

RANK IN ABUNDANCE


Figure 2-9. Principal species and percent rank abundance of
spiders in field corn during three phonological periods at
Orange Heights, Florida, 1983. Growth (A), Flowering (B),
Mature (C).













40 0 .
q to 0.8
30 t
SMajor Species 0.6

20 Minor Species 0.4










1 S -0.8





0 002



1 5 10 15 20 45



2.0
-CC








1.0





Om0.5
0 ^111 0








1 5 10 15 20 55










RANK IN ABUNDANCE


Figure 2-10. Principal species and percent rank abundance
of spiders in field corn during three phenological periods

at Archer, Florida, 1984. Growth (A), Flowering (B), Mature
(C).










S






.2
I ?




L-K-


L Minor Species

I Major Species


10 15 20 24


1 5


10 15 20
RANK IN ABUNDANCE


Figure 2-11. Principal species and percent rank abundance
of spiders in field corn during three phenological periods
at Gainesville, Florida, 1984. Growth (A), Flowering (B),
Mature (C).


25 --


II


v











nearby cattle that produce habitat and prey for Pardosa spp.

The Linyphiidae are favored by wet conditions, like those

surrounding the Orange Heights field. And the visually

dependent Salticidae are favored by old field weeds and

shrubs where light and prey are plentiful.



Species Diversity. Species diversity, measured either

as H' or as the total number of species, reached its peak in

the corn fields just as the corn reached the mature stage.

The diversity measurements for all six fields and each

phenological period are presented in Figure 2-15. The

highest diversity measurement was in the mature stage at the

Gainesville field when I found 61 species and H'=4.08. As

would be expected the diversity is lowest when the corn

plants are small.

As the corn plants grow, many attributes of the

field's complexity emerge. A gradation of light, humidity

and wind is produced by the developing canopy. An array of

geometries for the web building spiders is created, as well

as an increasing variety and abundance of potential prey.

Also, the weeds begin to appear between the corn plants

providing sources of other potential prey as well as addi-

.tional structural supports. Robinson (1981) and others have

demonstrated the importance of geometry in determining

diversity and species composition.
























































Other Families





Figure 2-12. The major families of spiders collected in
field corn at Archer, Florida during 1982. Field A (Top)
and Field B (Bottom).





























Other Families


Figure 2-13. The major families of spiders collected in
field corn during 1983 at Archer, Florida (top) and Orange
Heights, Florida (Bottom).





















































Other Families


Figure 2-14. The major families of spiders collected in
field corn during 1984 at Archer, Florida (top) and Gaines-
ville, Florida (Bottom).












3




*---
2


r 1













ef
4









2
1











1


G F M G F M

Phenological Period
Figure 2-15. Species diversity of spiders as measured by H'
in six corn fields in Alachua County, Florida. Archer, 1982
Field A (A); Archer, 1982 Field B (B); Archer, 1983 (C);
Orange Heights, 1983 (D); Archer, 1984 (E) and Gainesville,
1984 (F). Phenological periods: G = Growth, F = Flowering,
M = Mature.











Stratification. Six layers within the corn field

canopy are here defined: (1) the soil surface, (2) the base

of the corn plant where it meets the soil, including the

prop roots, (3) the lowest third of the foliage, (4) the

middle foliage from the fifth to the ninth leaves (numbered

from the base), which includes the developing ear, (5) the

top foliage and tassel, and finally (6) the weeds beneath

the corn plants. The results of this breakdown are pre-

sented in Figures 2-16, 2-17, and 2-18.

The seasonal dynamics of each of these strata is a

function of each individual species' population dynamics.

But since several species may be dependent on the same

environmental and biotic variables, the strata dynamics can

reveal the nature of those variables. Thus, a number of

these variables were revealed through this analysis when

combined with general field observations.

Consider first the two lowest strata, that is those

spiders which inhabit the soil surface, and those that live

around the base of the corn plant. An important point here

is that a single species is not necessarily restricted to

any one strata, but rather the opposite is true; most

species were found in more than one layer. Excluding

Orange Heights, these strata have a small representation

during the growth stage and then a modest decline in numbers

by the flowering stage and finally a sharp increase through

the mature stage. There are at least three things that











contribute to this movement. The first of these factors is

the cultivation of the field. One of the main purposes of

cultivations is weed control. This is achieved by turning

the soil over and breaking it up so as to bury most of the

weeds, expose the roots of others and to allow the soil

surface to become dry and inhospitable for germinating weed

seeds. This process is detrimental to spider populations

at or near the soil surface by burying many of them direct-

ly, but also by burying their food supply, namely the

insects associated with decaying plant debris from the

previous season. Cultivation has a similar deleterious

effect on the Carabidae in crop fields (House and All 1981).

Second, the decay of plant debris in the soil, which

is delayed during the cool and damp winter, accelerates at

planting when warm conditions return, thereby increasing the

supply of detritivores available for the soil surface spider

community. This material is rapidly exhausted however, and

is not replaced until flowering, when great quantities of

corn pollen are shed, much of which falls to the ground.

The pollen feeds numerous Psocoptera and Collembola which

later feed and reproduce upon the dying corn leaves at

maturity.

The dynamics of these two lowest strata of spiders in

the Orange Heights field are radically different from that

in the other five fields largely because of the contrasting

edaphic conditions. Under wet soil conditions, like those
















15
a*:: Soil Surface

f:flfl::Base of Plant
Q" 10
Lower Foliage

m | Middle Foliage
E
z .. Li Upper Foliage


O Weeds

Growth Flowering Mature


B:
15



0 10




z 5



0
Growth Flowering Mature

PHENOLOGICAL PERIOD

Figure 2-16. Stratification of spiders in the corn field
canopy during 1982 at Archer, Florida, Field A (A) and
Field B (B).



























Growth Flowering Mature


10
C





Z
0






20



15
.-

0




10








5
0o



0


U
1000009


Growth Flowering


-.












00000


0000000000


'C.' 'SI.'








U


100000


Mature


PHENOLOGICAL PERIOD

Figure 2-17. Stratification of spiders in the corn field
canopy during 1983 at Archer, Florida, (A) and Orange
Heights, Florida (B).


Em







m


B
Soil Surface

Base of Plant

Lower Foliage

Middle Foliage

Upper Foliage

Weeds








77







A
15
15 Soil Surface

II.. O ]] Base of Plant
Lower Foliage


E --- Middle Foliage
Z 5 1111
z 5 Upper Foliage

^ Weeds

Growth Flowering Mature



B
15



-- 100






0 L


Growth Flowering Mature

PHENOLOGICAL PERIOD

Figure 2-18. Stratification of spiders in the corn field
canopy during 1984 at Archer, Florida (A) and Gainesville,
Florida (B).
o *















Florida (B) .











at Orange Heights, the effectiveness of cultivation in con-

trolling weeds is diminished considerably. Large clods of

soil and sod remain upright and unfragmented, weeds with

damaged root systems can regenerate, and the soil surface

remains moist and ideal for seedling regrowth. The general

ineffectiveness of weed control at Orange Heights is further

reflected in the greater numbers of spiders associated with

weeds. In addition, wet heavy soil is even more effective at

delaying the decay of plant debris during the winter thus

allowing an even larger production of detritivore prey with

the advent of warm temperatures and the aeration provided by

the cultivator.

Another major difference between the vertical

stratification of spiders at Orange Heights and the other

fields is a lag in the numbers of spiders inhabiting the

middle and upper foliage. In the immediate vicinity of the

Orange Heights field only a limited area was left as annual,

full sunlight weeds which could serve as nurseries for

spiders adapted to the high light and wind conditions

present in the upper corn field canopy. The increase in

upper and middle foliage spiders at maturity coincided with

the mowing of these weeds.

The lag in the upper foliage hunters at Orange Heights

was paralleled by much greater numbers of spiders in the

lower foliage. Sources for shade dwelling spiders were










abundant in the area as under story herbs and shrubs in the

slash pine plantations surrounding the field.

The stratification of the web building spiders was

presented in Figures 2-2, 2-3 and 2-4.

Age Structure. The age structures of the spiders

collected in the corn fields are presented in Figures 2-19,

2-20 and 2-21. At the Archer and Gainesville corn fields,

during each phenological period, juvenile spiders outnum-

bered the adults by 2:1 or 3:1, and the seasonal trends were

approximately parallel. Orange Heights on the other hand

saw more than half the spiders collected during the growth

period represented as adults, and just under half were adult

during the flowering and mature stages. This difference is

largely related to the proportion of the spiders belonging

to the family Linyphiidae.

Abundant Linyphiidae at Orange Heights were favored

for at least two reasons, both related to the wet soil

conditions. First the soil and weeds were disrupted less

than at the other fields because of the lower efficiency of

the cultivator. This permitted a greater number of these

largely soil surface dwelling species to escape destruction

and to find suitable habitat. Second, since the Linyphiidae

are generally favored by a damp microclimate, ballooning

spiders would be attracted by the favorable physical condi-

tions that would not appear in the other fields until after

the canopy had developed. Also, the Linyphiidae are favored
















15


A


=Adult Spiders

i--JuvenleSpiders


Growth Flowering Matu


B


=HAdult Spiders

=-I'Juvenile Spiders


5




Growth Flowering Mature


PHENOLOGICAL PERIOD

Figure 2-19. Age structure of spiders in corn fields during
*1982 at Archer, Florida, Field A (A) and Field B (B).
























Growth


CD
10
-0
E
z


Adult Spiders

1 Juvenile Spiders


Flowering Mature


Growth Flowering Mature


PHENOLOGICAL PERIOD


Figure 2-20. Age structure of spiders in corn fields during
.1983 at Archer, Florida (A) and Orange Heights, Florida (B).




















15



A 10
0



z 5



0






15


U Adult Spiders

-J Juvenile Spiders


Growth Flowering Mature


Growth Flowering Mature


PHENOLOGICAL PERIOD

Figure 2-21. Age structure of spiders in corn fields during
1984 at Archer, Florida (A) and Gainesville, Florida (B).











by the swampy conditions in the habitat surrounding the

Orange Heights field, and so were a major component of the

species pool available for colonizing the corn field.



Guild Analysis. A guild, as defined by Root (1973),

is a group of functionally similar species. The species

included in a guild should exploit a similar resource in a

similar way (Landers and MacMahon 1980). Of course the

breadth of a guild then will depend on the degree of overlap

between the guild species, since, it is assumed, that no two

species exploit exactly the same resource in exactly the

same way.

For this analysis six guilds were defined: (1) soil

surface hunters; (2) foliage hunters, diurnal; (3) foliage

hunters, nocturnal; (4) web spinners on the soil surface;

(5) web spinners around base of plant; (6) web spinners from

foliage layer. The families and genera that are included in

these guilds are listed in Table 2-2, and the results of

this analysis are shown in Figures 2-22, 2-23, 2-24, 2-25,

and 2-26.

Again, excluding the Orange Heights field, the dynam-

ics of these guilds through the season are remarkably

similar between fields and years, as seen in Figures 2-23,

2-25 and 2-26. This similarity can be a result of several

different phenomena. The similarity may simply be a result

of one or two dominant species in the "guild" that behave











Table 2-2. The guild definitions of spiders occurring in
the corn fields of north central Florida.


Lycosidae:


Salticidae:

Clubionidae:

Gnaphosidae:


SOIL SURFACE HUNTERS

Lycosa spp., Allocosa spp., Pirata spp.,
Pardosa spp.

Corythalia canosa, Habronatus spp.

Scotinella spp., some Casteniera spp.

Gnaphosa


FOLIAGE HUNTERS--DIURNAL

Oxyopidae: Peucetia viridans, Oxyopes salticus

Thomisidae: all species

Philodromidae: all species

Salticidae: all species except those listed above under
soil surface hunters



FOLIAGE HUNTERS--NOCTURNAL

Clubionidae: Chiricanthium inclusum, Clubiona spp.

Anyphaenidae: Aysha spp., Wulfila spp.



SOIL SURFACE WEBS

Linyphiidae: all species not listed under foliage layer
webs

Theridiidae: Steotoda spp.

Hahniidae: Neoantistea spp.












Table 2-2--continued


BASE OF PLANT WEBS

Linyphiidae: mostly the same species as occur in the soil
surface web guild

*Theridiidae: Latrodectus mactans, Achaeranea globosa,
sometimes Steotoda spp.

Hahniidae: occasionally Neoantistea sp.

Araneidae: Gea heptagon, occasionally other species.

Theridiosomatidae: Theridiosoma


Linyphiidae:


Theridiidae:



Araneidae:

Uloboridae:

Dictynidae:


FOLIAGE LAYER WEBS

Ceraticellus similis, Frontinella pyramitella,
Florinda coccinea, Grammonota texana

Theridion spp., Theridula opulenta, Coleosoma
acutiventer, Argyrodes spp. occasionally
Achaeranea globosa

most species

Uloborus spp.

Dictyna spp.