Front Cover
 Table of Contents
 Habitat preferences
 Foraging behavior and food
 Effects of human activity
 Population density and composi...
 Literature cited
 Back Cover

Group Title: Bulletin of the Florida State Museum
Title: The Ecology of the Stock Island tree snail Orthalicus reses reses (Say)
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00095797/00001
 Material Information
Title: The Ecology of the Stock Island tree snail Orthalicus reses reses (Say)
Series Title: Bulletin - Florida State Museum ; volume 31, number 3
Physical Description: p. 107-145 : ill., map ; 23 cm.
Language: English
Creator: Deisler, Jane
Florida Museum of Natural History
Publisher: Florida State Museum, University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 1987
Copyright Date: 1987
Subject: Orthalicus reses   ( lcsh )
Mollusks -- Ecology -- Florida -- Florida Keys   ( lcsh )
Genre: bibliography   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references (p. 143-145).
General Note: Cover title.
General Note: Abstract in English and Spanish.
Statement of Responsibility: Jane Deisler.
 Record Information
Bibliographic ID: UF00095797
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 15702451

Table of Contents
    Front Cover
        Page 105
        Page 106
        Page 107
    Table of Contents
        Page 108
        Page 109
        Page 110
        Page 111
        Page 112
        Page 113
        Page 114
        Page 115
        Page 116
        Page 117
    Habitat preferences
        Page 118
        Page 119
        Page 120
        Page 121
        Page 122
        Page 123
    Foraging behavior and food
        Page 124
        Page 125
        Page 126
        Page 127
        Page 128
        Page 129
        Page 130
        Page 131
        Page 132
        Page 133
        Page 134
        Page 135
        Page 136
        Page 137
        Page 138
    Effects of human activity
        Page 139
    Population density and composition
        Page 140
        Page 141
        Page 142
    Literature cited
        Page 143
        Page 144
        Page 145
        Page 146
    Back Cover
        Page 147
Full Text

of the
Biological Sciences
Volume 31 1987 Number 3





ENCES, are published at irregular intervals. Volumes contain about 300 pages and are not
necessarily completed in any one calendar year.

S. DAVID WEBB, Associate Editor
RHODA J. BRYANT, Managing Editor

Consultants for this issue:


Communications concerning purchase or exchange of the publications and all manuscripts
should be addressed to: Managing Editor, Bulletin; Florida State Museum; University of
Florida; Gainesville FL 32611; U.S.A.

Publication date: 30 January 1987

This public document was promulgated at an annual cost of $2280.00 or
$2.28 per copy. It makes available to libraries, scholars, and all interested
persons the results of researches in the natural sciences, emphasizing the
circum-Caribbean region.

Price: $2.30





A study to determine the life history and behavior of the Stock Island Tree Snail,
Orthalicus reses reses (Say) (Pulmonata: Bulimulidae), was conducted during May-August
1981 and August-October 1982 in the southern Florida Keys. A follow-up assessment of
these populations was conducted in July 1986. The activity of the snail was found to be
linked to rainfall patterns. Statistical analysis indicated that population size was not limited
by species of tree available for colonization. The diet of the snail was determined by
stomach content analysis and substrate examination and was found to consist of epiphytic
growths on tree surfaces. Reproductive events were observed and growth rate and sources
of mortality were examined. The density and composition of a population on Stock Island
were determined. Human activity was determined to have a negative impact on the Stock
Island populations. Comparative data for 0. floridensis and 0. reses nesodryas were
included where they were available.


Se efectu6 un studio de la historic natural y comportamiento del caracol
arboricola de la Isla Stock, Orthalicus reses reses (Say) (Pulmonata: Bulimulidae) en los
cayos del sur de Florida, entire mayo-agosto de 1981 y entire agosto octubre de 1982. Una
evaluaci6n, a continuaci6n, de estas poplaciones fue conducida en Julio 1986. Se
determine que la actividad del caracol esti en relaci6n con los patrons de precipitaci6n.

*The author is Curator of Natural History at the Corpus Christi Museum, 1900 N.
Chaparral, Corpus Christi, Texas 78401.

DEISLER, J.E. 1987. The ecology of the Stock Island Tree Snail, Orthalicus reses reses
(Say). Bull. Florida State Mus., Biol. Sci. 31(3):107-145.


El an lisis estadistico indic6 que el tamano de la poblaci6n no est limitada por el n6mero de
species de rboles disponibles para la colonizaci6n. La dieta del caracol se determine
mediante el an lisis del contenido estomacal y examen del sustrato. La dieta consiste de
crecimientos epifiticos sobre los arboles. Tambi6n se hicieron observaciones reproductivas
y se estudiaron las tasas de crecimiento y las principles fuentes de mortalidad. Asimismo,
se determine la densidad y composici6n de una poblaci6n en la Isla Stock. Finalmente, se
incluye datos comparativos acerca de 0. floridensis and 0. reses nesodrvas, en la media
de su disponibilidad.


INTRODU CTION ....................................... ..... ............. ..... ........... 108
ACKNOWLEDGEMENTS ................................................................. 112
ENV IRONM ENT .......................................... .................................. 112
Plant Associations ...................................... .................................. 112
H habitat Preferences ................................... .................................. 118
Clim ate ......................................................... ................................ 120
BEHAVIOR ..................................................... ........ ...................... 121
A activity Patterns ........................................ ................................... 121
Foraging Behavior and Food.............................................................. 124
R production ............................................. .................................... 127
DEMOGRAPHY .................................. ............................... 131
G growth R ates ....... ........ ............................... .................................. 131
M mortality ...................................................... ........ ....................... 135
Effects of Human Activity ............................. ................................. 139
Population Density and Composition.................................................... 140
CONCLUSIONS ........................................... .................................... 141
LITERATURE CITED ................................ .................................... 143


The genus Orthalicus is a group of large, arboreal pulmonate snails
in the family Bulimulidae. The genus is distributed primarily in tropical
Central and South America. The two species that occur in North America,
Orthalicusfloridensis Pilsbry (Fig. 1A) and 0. reses (Say) (Figs. 1B, C), are
restricted to southern Florida. The latter species is divided into two
subspecies: 0. r. reses (Say) (Fig. 1B) and 0. r. nesodryas Pilsbry (Fig. 1C).


O. r. reses, also known as the Stock Island Tree Snail, is the primary subject
of this study.
0. reses reses historically has been restricted to its type locality on
Stock Island, but apparently now it has been introduced into Key Largo and
mainland Florida (Fig. 2). Its restricted range and lack of columellar and
apical pigmentation serve to set it apart from 0. reses nesodryas. The latter
snail historically has been distributed over a broader range in the Florida
Keys, exclusive of Stock Island (Fig. 2). Both subspecies of 0. reses bear
distinctive flame-like vertical brown stripes on the shell. These color
characters separate them externally from 0. floridensis, which lacks this
pigmentation. 0. floridensis is also the only one of these snails to occur
naturally on the mainland of Florida (Fig. 2). The systematic relationships
of these animals have been examined in detail elsewhere (Deisler, in prep.).
The purpose of this study is to provide data on plant associations,
habitat preferences, foraging, and activity patterns of Orthalicus in Florida
and to determine the life history of the Florida species. This project focuses
on 0. reses reses, the Stock Island Tree Snail, in its type locality in the
southern Florida Keys because of its status as a threatened species. This
snail has been included on the U.S. Fish and Wildlife Service list because of
severe reduction in its population size and near elimination of its habitat.
One purpose of studying its life history is to develop a recovery plan. Past
studies (Craig 1972) have dealt primarily with 0. floridensis in its range on
the mainland of Florida. Data from this mainland taxon are probably not
applicable to populations in the Keys, as the much lower rainfall in the Keys
radically affects these tree snails. Nevertheless, comparative data for 0.
floridensis and 0. reses nesodryas will be included in this study wherever they
are known.
Very little information has been compiled on the life history,
behavior, and ecology of Orthalicus. Most authors on the subject deal
briefly with the appearance of the eggs, the estivation habits of the snail,
and the production of the shell varices (Binney and Bland 1869:216-218,
Binney 1885:439, Pilsbry 1899:102-103, 1912:443-444, 1946:29-31). Several
authors have commented on the effect of cold on these animals, specifically
on 0. floridensis (von Martens 1893:179, McGinty 1936:2, Clency 1940:122).
Two papers have dealt with growth rates in 0. floridensis (Simpson
1923:111-112, Craig 1972:16-20) and two on probable diet in that animal
(Pilsbry 1912:443, Craig 1972:16-20). Some of this ecological information
was extracted from studies of the related tree snail, Liguus fasciatus
(Miiller), and is not the result of direct study of Orthalicus (Pilsbry


2I I
20 MM

Figure 1. Shells of (A) Orthalicus floridensis Pilsbry, (B) Orthalicus reses reses (Say),
and (C) Orthalicus reses nesodryas Pilsbry.




a------- *-----
0 miles 1 ONRO E


0 miles 30

Figure 2. Distribution of O. r. reses (A = location of colonies on Stock Island,
Monroe County), O. r. nesodras A ,and O. floridensis .



I would like to express my gratitude for the assistance given to me by a number of
people at the University of Florida. I greatly appreciate the time and effort invested in this
project by Fred G. Thompson, under whose supervision this study was conducted. I am
also grateful for the encouragement given to me by Martha Crump and Jonathan Reiskind.
Stephen Bloom and Carmine Lanciani assisted me with statistical methods and computer
analysis. The following people assisted me with identifications: James Kimbrough and
Jack Gibson (mycology), Joseph Davis (phycology), Mike Thomas (entomology), and David
Hall and William Stern (vascular plants). I would especially like to thank Shirley Taylor,
Louisiana State University, for her timely identification of my crustose lichen samples.
I am grateful for the loan of material from collections of the Field Museum of
Natural History (FMNH), Chicago; The Museum of Comparative Zoology (MCZ), Harvard
University; and The Academy of Natural Sciences (ANSP), Philadelphia. I am deeply
appreciative for the assistance and hospitality offered to me by George M. Davis, Robert
Dillon, and Arthur and Cindy Bogan at the Academy of Natural Sciences, Philadelphia, and
Richard Houbrick at the National Museum of Natural History (USNM), Washington, D.C.,
when I visited those institutions.
I would particularly like to thank the people too numerous to list who gave of
their time and energy to help me in the field, including the staffs of the following
organizations who allowed me to examine the snail colonies in their localities: IFAS
extension office in Key West, Key Deer Wildlife Refuge on Big Pine Key, the National
Weather Service at the Key West Airport, the Fruit and Spice Park in Homestead, and
Monkey Jungle in Miami.
This research was supported by funding from the U.S. Fish and Wildlife Service
(Contract No. 85910-0759) and the Division of Sponsored Research, University of Florida
(DSR Seed Grant A-I-26), extended to Fred G. Thompson as the principle investigator.
Finally, this study could not have been undertaken without the aid of the late
Howard W. ("Duke") Campbell of the U.S. Fish and Wildlife Service, to whom I owe a great


Only one previous study has attempted to identify the host trees of
Orthalicus in Florida. Craig (1972) observed 0. floridensis feeding actively
on Forestiera segregata (Florida privet), Piscidia piscipula (Jamaica
dogwood), Carica papaya (wild papaya), Eugenia axillaris (white stopper),
and Ficus aurea (strangler fig). He ranked these plants in order of
preference but gave no criteria for the order. Craig also noted these snails
on Sansevieria thyrsiflora (African bowstring hemp), Hymenocallis keyensis


(Key lily), Rhizophora mangle (red mangrove), Conocarpus erectus
(buttonwood), and Agave decipiens (agave), but did not directly observe
them feeding.
During the current investigations both species of Florida
Orthalicus, 0. floridensis and 0. reses, were observed feeding and estivating
on a large variety of native and introduced trees (Table 1).
The occurrence of Orthalicus on host-tree species was examined at
three sites in 1981 to determine if the snails demonstrated a preference for
any of the tree species at those sites (Table 2). At each site the number of
trees of each species and the number of snails inhabiting each tree species
were counted. The percentage of the flora that each tree species
represented was calculated, as was the percentage of the total snail
population that was found on each tree species. The tree species were
classified by bark type: either rough or smooth.
At sites where the trees are approximately equal in size, the
percentages calculated for tree frequency and snail occurrence should be
similar if snail distribution is random. When graphed these points should
lie close to the line y = x (Fig. 3). Points lying above the line indicate tree
species inhabited by fewer snails than expected, while points lying below the
line indicate tree species inhabited by more snails than expected.
At site 1 the trees were similar in size, with trunk diameters
averaging 15 cm and tree height 4.5 m. The calculated percentages of snails
inhabiting a tree species conformed with the abundance of that tree species
in the flora. This can be seen graphically in Figure 4 but was not tested
statistically because of the small size of the samples. Figure 3A shows that
the points for site 1 fall fairly close to the line y = x, an indication that O.
reses reses does not show a strong preference for any of the host-free species
at this site.
A situation similar to that at site 1 prevails at site 3 where all of the
trees are also approximately the same size. The points in Figure 3C lie
extremely close to the line y = x, indicating a very strong correlation between
the frequency of a tree species and the number of snails that inhabit it. At
site 3 also, 0. r. nesodryas shows no preference for any particular tree
species present (Fig. 4).
Site 2 shows a pattern that is similar to those at sites 1 and 3, but
with more variation (Fig. 4). The two apparent exceptions to the random
distribution of snails on tree species are the unexpectedly high frequencies
on Ficus citrifolia (shortleaf fig) and Piscidia piscipula (Jamaica dogwood).
These exceptions may be explained by the exceptional sizes of trees of these
As snails are distributed over the surface of a tree, a larger tree
with more surface area can be inhabited by a greater number of snails.
Most of the trees at site 2 are approximately the same size, with a trunk
diameter of about 45 cm and height of roughly 6 m. The two exceptional


Table 1. Trees on which Orthalicus have been found in South Florida. Nomenclature is from Little (1979) and
identification from Long and Lakela (1971), Little (1979), and Tomlinson (1980). E = exotic species, N = native

reses reses
Tree species Common name floridensis reses nesodiyas

Annona globifera
A. reticulata E
Bischofia javanica E
Broussonetia papynfera E
Bumelia celastrina N
Bursera simaruba N
Byrsonima lucida N

Cassia sp.
Chrysalidocarpus lutescens E
Chtysophyllum cainito E
Citns aurantifolia E
Coccoloba diversifolia N
C. uvifera N
Conocarpus erectus
var. sericeus N
Delonix regia N
Eriobotryajaponica E
(=myrtoides) N
E. axillaris N
E. uniflora E
Ficus area N
F. citrifolia N
Gymnanthes lucida N
Jacquinia keyensis N
Lysiloma bahamensis
(=latisiquim) N
Malpigia glabra E
Mangifera indica E
Manikara bahamensis
(=Achras emarginata) N
Metopium toxiferum N
Monts rubra N
Murraya koenigii E
Piscidia piscipula N

Pisonia discolor N
Pithecellobium guadelupense N
Pouteria campechiana E
Psidium guajava E
Reynosia septentrionalis N
Roystonea sp. N
Schinus terebinthefolia E

Syzygium jambos E
Thrinax radiata
(=floridana) N

custard apple
paper mulberry
saffron plum
Key brysonima

areca palm
star apple
pigeon plum
sea grape
silver buttonwood,
button mangrove
Spanish stopper,
boxleaf stopper
white stopper
Surinam cherry
strangler fig
shortleaf fig
crabwood, oysterwood
joewood, cudjowood
wild tamarind,
Bahama lysiloma
Barbados cherry
wild dilly

red mulberry
curry leaf
Jamaica dogwood,
fish-poison tree
Guadeloup blackbead
darling plum
royal palm
Brazilian pepper,
Florida holly
rose apple
Florida thatch






x x
x x


Table 2. Percent occurrence of Orthalicus on host trees at three sites.

Number Percent Number Percent
Tree species Bark Trees Flora Snails Population

SITE 1: 0. reses reses, Stock Island, golf course, June 1981

Mctopium toxifermn s 11 22.45 5 20.00
Eugema sp. s 9 18.37 3 12.00
Pisonia discolor s 8 16.32 6 24.00
Thrinax radiata s 6 12.25 0 0.00
Biursera sinmanba s 4 8.16 3 12.00
Byrsonirna lucida s 3 6.12 4 16.00
Coccoloba diversifolia s 3 6.12 1 4.00
Ficus citrifolia s 2 4.08 2 8.00
Reynosia septentrionalis s 2 4.08 0 0.00
Schinus terebinthefolia r 1 2.04 1 4.00
TOTALS 49 25

SITE 2: 0. reses reses, Stock Island, county home, September 1982

Bursera sinmanrba s 4 23.53 15 26.79
Swietenia mahogany r 3 17.65 8 14.29
Ficus citrifolia s 1 5.88 10 17.86
Piscidia piscipula s 1 5.88 14 25.00
Coccoloba diversifolia s 1 5.88 5 8.93
Schinus terebinthefolia r 1 5.88 1 1.78
Pisidium guajava s 1 5.88 1 1.78
Pisonia discolor s 1 5.88 1 1.78
Delonix regia s 1 5.88 1 1.78
Melaleuca leucadendra r 1 5.88 0 0.00
Citrus aurantifolia s 1 5.88 0 0.00
Cordia dentata s 1 5.88 _f 0.00
TOTALS 16 36

SITE 3: 0. reses nesodryas, Johnston Key, July 1981

Conocaipus erectus r 7 36.84 5 27.78
Manilkara bahamensis s 4 21.05 5 27.78
Gymnanthes lucida s 3 15.79 3 16.67
Thrinax radiata s 2 10.53 2 11.11
Pithecellobium guadalupense s 1 526 1 5.56
Metopium atoiferum s 1 5.26 1 5.56
Pisonia discolor s _1 5.26 1 5.56
TOTALS 19 18


10 20
Snails as percent population

) rough-barked trees
* smooth-barked trees

Snails as percent population

Figure 3. Distribution of 0. reses on tree species at three sites in the Florida Keys.





IM 20"

e 15-





M- -w U I I -I- -

SSite 1 Site 2
Tree species as % flora Snails as %

Site 3

Figure 4. Percent occurrence of O. reses compared to percent occurrence of host-tree
species at three sites.


trees are much larger: Ficus citrifolia measures 1.2 m by 12 m and Piscidia
piscipula 0.75 m by 10.5 m. These trees have more surface area and
therefore have more snails inhabiting them.
Voss (1976:68) stated that bulimuline tree snails prefer trees with
smooth bark over those with rough bark, because smooth bark theoretically
allows the snails to expend less energy when crawling over the surface and
to gather more food because of fewer obstructions to the movement of the
snails or of their radulae. Hypothetically, it also seems reasonable that
smooth bark should be advantageous because it is easier for an estivating
tree snail to form a secure mucous seal on a smooth surface. Mortality
from dehydration or accidental dislodgement should be lower.
The first step in examining this situation is to test statistically the
hypothesis that tree snails prefer one type of bark over the other (Hi). With
the data for 0. reses from all three sites (Table 2), a Chi-squared test was
used to examine the distribution of snails on trees with rough bark in
comparison with the distribution of snails on trees with smooth bark (Fig.
5). The resulting X value, 0.012, indicates that the null hypothesis should
not be rejected. 0. reses reses shows no preference for either smooth-
barked trees or rough-barked trees. In view of these data, no further
experiments were performed to test hypothetical advantages conferred by
smooth bark.


Early authors reported merely that Orthalicus is found in trees (Say
1830:39, Binney 1858:39, 1885:439, Binney and Bland 1869:216-218) and
sometimes on "dyewoods" (von Martens 1893:179). Pilsbry (1912:443-444)
stated that Orthalicus has the same habits as Liguus. He reported that the
latter lives in dense, shady woods on well-drained soil, and that the snail is
never found on pines and mangroves but only on hardwood trees. Later
authors concurred with this, specifically reporting on 0. floridensis in the
Cape Sable area (Simpson 1923:111-115, McGinty 1936:2) and 0. reses
nesodryas on Key Vaca and Sugarloaf Key (Pilsbry and Grimshawe 1936:19).
Craig (1972:16-17) noted that O. flofidensis on Pavilion Key occurs
primarily in areas that are similar to true tropical hammock, and that it
usually avoids the mangroves on the leeward side of the island and the
growth near the beach. When occasionally found in these areas, it was
always in estivation.
Populations of Orthalicus appear to be most dense in the true
mainland hardwood hammock such as that found in the Pinecrest region of
the Everglades. In the Keys, Orthalicus is also found in hardwood


number of

trees with


number of
trees without


rough bark smooth bark row totals

2 (O-E)2
X 02_..0122145; d.f.=1;p= 0.05; H0 not rejected.

Figure 5. Chi-squared 2x 2 contingency table for bark-type preference in 0. reses (Siegal
1976:104-111). HO = 0. reses shows no preference for bark-type. Hi = Q. reses prefers one
bark-type over the other. O = observed values, E = (column total x row total) N, N =
column total sum = row total sum, d.f. = (rows 1) x (columns 1).


hammocks, but appears to be limited to the portions of the islands that are
relatively high, with minimum altitudes of 5-11 feet.
The hardwood hammock is not the only habitat in which Orthalicus
can be found in Florida. On the mainland, 0. floridensis is frequently found
in ornamental and fruit trees in parks and backyards in the southern
portions of Dade County. In some cases these populations can be traced to
introductions made as long as 30 years ago by local residents. The trees in
which the snails occur are generally more isolated than trees in a true
hammock and often are non-native species. An important limiting criterion
may be the use of pesticides on the host trees (Craig 1972:19).
O. r. nesodryas also can be found in trees planted as landscaping,
but such situations are rarer in the range of this animal. The relatively
recent development of the keys on which this animal occurs has eliminated
much of the native hammock habitat without enough elapsed time for
replacement landscaping trees to have attained the size needed to support
breeding colonies of the snail.
At its type locality, 0. reses reses is found in the scrubby remnants
of native hammock on the golf course on Stock Island. However, it occurs
with more frequency on the native and exotic trees planted in isolated
pockets between the fairways and in the parking area around the county
buildings. Museum collections indicate that 0. reses once was found in Key
West proper, but development, the presence ofRattus rattus (black rat), and
mosquito fogging may have combined to eliminate any populations on that
island. 0. reses reses also appears to have been introduced to two sites on
the mainland and one on Key Largo. The mainland sites consist of
hardwood hammock made up largely of Lysiloma bahamensis (wild
tamarind), and also some Ficus. The Key Largo site is mixed hardwood


Few comments appear in the literature on the climate inhabited by
Orthalicus species. Von Martens (1893:179) wrote that the snail was
confined to hot regions of America. McGinty (1936:2) reported that large
specimens of O. floridensis were killed by frosts at Cape Sable. On the other
hand, Clench (1940:122) noted that a colony of 0. floridensis introduced to
Sanibel Island north of its natural range survived 19 years of normal
temperatures for that area, but that an extremely low temperature might kill
them. Pilsbry (1946:37) reported that this colony was still present in 1945.
The typical climatic pattern for south Florida is one of a dry season
alternating with a wet season. The dry season extends from November to
approximately April or June and the wet season coincides with the warmer


months of the year. Rainfall data from the National Climatic Center shows
that timing of the seasons is the same in Key West and the mainland (Fig.
6). However, the total amount of rain for the year is less in Key West than
on the mainland, as is the amount of rain received in any given month.
Similar mean temperature patterns are shown for the two sites (Fig.
7). In each location, the coldest months are December, January, and
February, June through September the warmest. The mainland site
experiences the greatest extremes, with a 3-year range of -0.6-38.90C. The
3-year range for Key West is 5.0-33.90C. The range during the active season
in Key West is given by the Climatic Center as 15.6-33.90C over a 3-year
span, with the range for June-July being 28.7-33.90C. The latter compares
favorably with the values measured at the study site on Stock Island, which
were 29-330C for the same months. The temperature range for the active
season on the mainland is given by the Climatic Center as 18.3-38.90C,
somewhat higher than for Key West.


Individuals in the Stock Island colony of Orthalicus reses reses
began moving and feeding at various times during mid-June and early July
in 1982. During a 2-week dry period in mid-July the snails resumed
estivation. A mucus seal was formed, but was not as thick as those formed
in the winter.
During June and early July the snails moved primarily during actual
rainfall. They moved infrequently at night when it was not raining, and they
never moved during a dry day. In late August and September, however, the
animals remained extended for periods of up to 8 hours during daylight
hours, even when no rain was falling.
Evidently water is an important stimulus to activity. At 11:55 a.m.
on 7 July 1981, 250 ml of distilled water at 210C was slowly poured over a
snail in estivation. The water dissolved the mucus seal, and the snail
emerged from its shell within 9 minutes. When water was similarly applied
to each of five individuals that were withdrawn into their shells but not
estivating, the snails emerged from their shells and began to move within 25
seconds to 20 minutes. They continued moving and feeding for 5-21
minutes. A similar experiment on 12 September 1982 resulted in activity
lasting up to 8 hours.
In contrast, artificial darkness showed no effect. On 7 July 1981, at
the same time as the water experiments, artificial darkness was applied to
three snails. This was done by placing a light-colored box over their
perches. The temperature was monitored to ensure that it remained with





1979 1980 1981

Figure 6. Monthly rainfall at (A) Forty-mile Bend in the Tamiami Trail and (B) Key West
Airport. Expected values = 50-year average.


A 35 *36.1 36.1'



3" "A1.1"

L C,

B 35



*yearly maximum
Yearly minimum

1979 1980 1981

Figure 7. Average monthly temperature at (A) Forty-mile Bend in the Tamiami Trail and
(B) Key West Airport.


the normal daytime range (29-330C). The snails did not respond within a
period of 2 hours. Snails were seen to move within 2 hours after nightfall
on dry days.
The rate at which Orthalicus moves ranges from 38.1 cm to 95 cm
per hour, measured over 5-minute intervals in the range of 29-330C. Rapid
movement is generally in a straight line and occurs when heavy rainfall is
present or the tree surface is very wet after heavy rain. When the surface
over which the snail is moving begins to dry, movement becomes irregular
and slow. The snail frequently follows a curved path, with apparently
random changes in direction.
Movement from tree to tree is infrequent and was noted to occur
under two circumstances. Snails will occasionally cross from one tree to
another in the course of feeding if the branches of the trees are interlocked.
This was seen twice on the Stock Island golf course site over a period of 63
days. Snails were also seen to change trees after egg-laying. Most snails
returned to the tree they had been on before nesting, but three did not
return to their original trees and were found as far as 3 m away from the
bases of those trees. In one case, a snail climbed a bus bench instead of a
tree after nesting. Craig (1972:19) reported an instance of movement across
a lawn from trees apparently when food was lacking. This was not seen in
the Stock Island colonies.
Estivation generally begins in December, but can start earlier if
rainfall ceases. 0. floridensis on the mainland finds hollows in the host tree
either at the base of the trunk or in the crotch of a major branch. In large
populations as many as 20-30 individuals were found in one hollow. 0. reses
reses was also found estivating in hollows in the host tree as a general rule,
but Orthalicus often estivates anywhere in the tree, frequently in exposed
sites on the limbs. These are commonly attacked by predators and killed,
with the crushed shell often remaining glued to the tree. Other estivation
sites include the crevices between rocks in ornamental walls, the eaves of
houses, the underside of bird-baths and bird-feeders, the spaces under piles
of discarded sheets of plywood, and the hollows among above-ground roots.
Estivation continues until movement is stimulated by rainfall during the
following year, between May and August.


In June and July 1981, individuals of populations of 0. reses reses
fed during the day while it was raining, immediately after rainfall, and at
night. By late August and September feeding was seen all times of day and
night. Maximum activity was noted from late afternoon through the night


to mid-morning, and during rainfall. Mainland populations of Orthalicus
fed in this pattern as early as July in the Everglades-Pinecrest region.
Feeding activity is indicated by a series of muscular contractions in
the head. This reflects the movement of the buccal mass and the repeated
passage of the radula over the bark surface. Feeding snails often follow a
random twisting path that covers the entire bark surface. As noted above,
they move in a straight line if surface moisture is abundant.
Pilsbry (1912:444) reported that Liguus fed mostly or entirely on
minute fungi from the bark of trees, judged on the basis of stomach
contents, and that Orthalicus has the same habits as Liguus. Craig (1972:18)
examined the substrate on which individuals of 0. floridensis were feeding
and reported that the probable foods for 0. floridensis on Pavilion Key are a
variety of algae and fungi on tree surfaces. He made tentative
identifications of these growths on Piscidia piscipula (Jamaica dogwood)
and found that most of the fungi were common and widespread.
Examination of the stomach contents of 0. reses reses from Stock
Island reveals that the animals feed primarily on fungi, with some algae and
lichens. The stomach contents of O. r. nesodryas from Johnston Key are
similar, but the stomach contents of a mainland population of Orthalicus
showed a predominance of algae, reflecting a similar predominance of algae
on the trees at that time. Specific items identified from gut contents
included basidiospores, Aureobasidium-fungus, mycelial fragments, algae,
and large quantities of bacteria (J. Kimbrough, pers. comm.). The bacteria
could be normal gut contents or a result of the relaxation and preservation
procedure. They are probably not a food item.
Host trees were surveyed for possible food items. This was done
because of the difficulty of identifying gut contents after partial digestion.
Samples of tree bark were gathered and either incubated under moist
conditions for 5-10 days for identification of algae and fungi, or dried for
lichen identification.
A large variety of fungi, algae, and lichens were found on the
various host trees (Table 3). Some mixobacteria also were seen, as were
some mites, both of which may serve secondarily as food for Orthalicus.
Neither mites nor mixobacteria were found in the gut contents of the snails
examined. However, the snails show no sign of selective feeding behavior
and may occasionally consume bacteria and mites inadvertently.
None of the epiphytes identified is specific to any particular species
of tree, and many are widely distributed and common. It is unlikely that the
type of food-growths present should be a factor in the absence of snails
from otherwise suitable trees.


Table 3. Epiphytic growths found on the bark of host trees of Orthalicus reses reses.

Tree Species Fungi Lichens Algae

ulrserwa sim amha

l''rwI(n hI lci(ht

Coccoloba Ir'ifi'ra
C. tTdirsifolia

EiLgenia sp.

Ficus sp.

Piscidia piscipula

Ptsonia discolor

Swietenia mahogany*

Thiynax radiata

Morterella sp.

Orbidia sp.

Hysterium sp.
Graphis sp.*
Pertusania sp.*
Pertusaria sp.*
Staurolhela sp.*
Verticillium sp.*

Chaetoniumn sp.

Echinostelium nlinatumn
Macbridida decapillata
Licea tenera
Pestalotia sp.
Pertusaria sp.


Pestalotia sp.
Libertella sp.

SFungus represented as part of a lichen.
' Myxobacteria also found on this tree species.

Opegrapha sp.
Pyrenula sp.
Ttypethelium cf. eleuteriae
Phaeographis sp.
Phaeographina spp. (2)
Anthracothecium ochraceoflavum
Pyrenula sp.

Lecanora chlarotera

Arthopyrenia lyrata
Arthopyrenia sp.
Anthracothecium ochraceoflavum
Pyrenula sp.
Arthonia sp.
Arthonia rubella
Lecanora chlarotera
Lecanora chlarotera
Anthracothecium ochraceoflavum
Pyrenula sp.
Pyxine cocoes
Physcia crispa
Ocellulania sp.
Graphina sp.
Arthonia rubella
Arthothelium sp. (?)
Lecanora chlarotera
Arthonia rubella
Anthracothecium sp.
Anthracothecium ochraceoflavum
Arthonia sp.
Bacidia sp.

Coccoid green

Leptosira sp.

Leptoira sp.
Coccoid green

Coccoid green

Tolypothlix sp.
Entophysalis sp.
Leptosira sp.
Coccoid green

Coccoid green



Previous information about reproduction in Orthalicus concerns
only size, appearance, and number of eggs that the Florida species lay
(Binney and Bland 1869:216, 218, Binney 1885:439, Pilsbry 1899:102-103,
1946:29-31). Reproductive activities of Liguus fasciatus were recorded by
Pilsbry (1912:443-444, 1946:38), Davidson (1965:382, 387), and Voss
(1976:66), but were not known for Orthalicus.
In this study mating was observed in 0. reses reses on Stock Island
in mid-September 1982 and in August and September 1986 (F. Ford, pers.
comm.). Furthermore, snails that were not then mating were induced to
mate by applying either distilled water or tap water to them. Mating was
not so induced in July 1982, although application of water stimulated them
to move and to feed. It is possible that water, in the form of rainfall, could
be the cue that induces mating in physiologically ready individuals.
The means by which two snails find each other for mating was not
noted, nor was any sort of courtship behavior seen. Voss (1976:66)
observed that Liguus tree snails follow the mucus tracks of other snails, and
this is probably the means by which Orthalicus individuals find their mates.
Copulation was observed only in the trees. Fertilization in these
hermaphroditic snails was seen to be reciprocal and sequential. The events
involved in copulation were witnessed as follows: two 3-year-old snails were
found in coitus on a branch 14 feet above the ground in a large Jamaica
dogwood tree (Piscidia piscipula) at 10:45 a.m., 13 September 1982. Snail A
was clinging to the underside of the branch. Snail B was clinging to the
shell of snail A at a 450 angle, with the anterior portion of the body of snail
B twisted so that the genital pore was adjacent to the genital pore of snail A
(Fig. 8). Snail B was serving as the male. After 10 minutes the snails
separated slightly but remained clinging to the same locations, no longer in
coitus. They did not move for 5 minutes. Then coitus resumed with snail A
as the male. The two snails remained linked for 38 minutes. After
unlinking, the snails separated slightly as before and remained without
motion for the rest of the period of observation, which ended at 12:25 p.m.
that same day.
No other actual instance of copulation was witnessed, though
several pairs of snails were seen clinging to each other as if coitus had
occurred recently. This sort of positioning was not seen at any other time
during the active season. Additional occurrences of copulation events were
reported in this population during August and September 1986.
Nesting occurred in 1982 two weeks after the observed coitus.
Rain was frequent and heavy during this time, and both the tree bark and
the ground were very moist. In the colony of 25 adult snails under
observation on 24 September 1982, I saw 13 descend the tree trunks in


Figure 8. Mating in 0. reses reses on Stock Island evertedd genitalia indicated by arrow).


straight-line paths at a relatively rapid rate. There was no sign of cephalic
muscular contractions, showing that the animals were not feeding as they
As each snail reached the base of its host tree it either crawled
along the junction of the tree and the ground, hesitantly left the tree and
moved onto the leaf-mold, or moved rapidly from the tree to the soil
without hesitation. Some snails were seen to "test" the soil by pausing to
dig shallow nests, but moving on before completing construction or laying
eggs. Others went directly to areas of soft dirt and leaf-mold and proceeded
to dig a deep nest (40-50 mm deep).
Excavation of the nest was carried out first by the posterior portion
of the foot (Fig. 9A). It was twisted and flexed repeatedly in order to push
dirt aside. When the hole was approximately 20 mm deep, the snail turned
in place and withdrew its head and the anterior portion of its foot as far as
possible into the shell and continued to dig until most of the shell was below
the surface (Fig. 9B). At this point the nest was approximately 50 mm deep.
This procedure required a variable amount of time, from 1 to 12 hours. As
many as 14 snails from a population of 25 adults were seen nesting at any
one time.
Once the nest was deep enough so that only the apex of the shell
was above the surface of the soil, the snail began to lay eggs (Fig. 9C). The
actual process of egg-laying lasted from 24 to over 96 hours. It also
required enlargement of the nest as the egg mass becomes larger. The eggs
are oval and calcareous as reported for the genus in Florida by other
authors (Binney and Bland 1869:216, 218, Binney 1885:439, Pilsbry
1899:102-103, 1946:29-31). They are tan when newly laid and measure 6 by
5 mm.
Most snails remained in one nest for at least 48 hours and played
from 8 to 21 eggs. Most of these nests contained at least 15 eggs. A few
snails made more than one nest, depositing only a few eggs in each. Once
egg-laying had ended, the eggs were covered over by the efforts of the snail
to move back to the soil surface. In some cases a snail was not successful in
this effort and died while still in the nest.
Nests were located in areas of soft soil or leaf-litter, either directly
at the base of the host tree or up to 2 m from it. Nests were also located in
cavities beneath above-ground roots that were filled with leaf-mold.
Certain sites appear to be preferred for nesting. As many as six
different snails, three at a time, were seen to nest in a space measuring 10
cm on a side at the base of a Jamaica dogwood tree. This area consisted of
soft soil and leaf-mold that was kept damp by the presence of a large, over-
hanging root extension. This tendency for multiple use of the same nest site
makes it necessary to exercise caution in estimating maximum individual
clutch size in 0. reses reses.



Figure 9. Nidification and ovulation in 0. reses reses on Stock Island. (A) Preliminary
nest-building with posterior portion of foot. (B) Excavation with head and anterior portion
of foot. (C) Completed nest with snail in position for ovulation.


Most nesting snails were 2 to 3 years old. One snail with four
estivation varices was seen nesting and laying eggs. A single 1-year-old also
was seen nesting, but it died while still in the nest. It had laid at least 10
eggs before dying and had six more eggs inside its body at the time of death.
Several juveniles less than a year old were in the colony, but they were not
seen to descend to the ground at any time, although they were actively
crawling on the trees.
Young snails were seen hatching 19 June 1982, one day after the
first two consecutive days of measurable rain since February of that year. A
total of 21 hatchlings emerged from the soil at the base of a poisonwood
tree (Metopium toxiferum). It was not possible to determine if these young
snails were from the same clutch or not because of the tendency for 0. reses
adults to lay eggs in sites where other clutches already have been deposited.
However, the hatchlings emerged from the same spot at the base of the
tree, and only one nest was found. No unhatched eggs remained in the
nest, indicating 100 percent of the clutch hatched. In a second nest found
at the base of a Jamaica dogwood tree, 4 of 18 eggs hatched. Thus the
hatching rate appears to be extremely variable.
Immediately upon hatching, the young snails began climbing the
nearest tree and feeding. They had fragile, brown shells that were
transparent and showed no signs of pigmentation. The shells were 6-7 mm
long and consisted of approximately three whorls. The animals were grey
with some of the internal organs visible externally as darker parts of the
body. The first fecal pellets were produced about 6 hours after hatching.


Pilsbry (1899:102-103, 1946:29-31) was the first author to discuss
the formation of growth varices by Orthalicus. He noted that these dark
brown lines are due to resting periods induced by climate, when shell
growth is halted but pigment deposition is not. The spacing and number of
these varices are dependent on the rate of growth of the individual snail and
the frequency of the dry weather that induces estivation.
Varices are also affected by the duration of estivation. The darkest
and widest growth lines are produced by the long annual period of
estivation that occurs in the winter. It is possible to estimate the age of a
snail from the number of these major varices on the shell. Simpson
(1923:111-112, 115) used varices in this way to comment on the age
distribution of a population of 0. floridensis on Cape Sable.
Craig (1972:18-19) also used varices to determine age. He
conducted a statistical age-growth study on 0. floridensis on Pavilion Key.


He found that the largest number of major varices was seven and estimated
the maximum age of the species to be seven years. He compared the length
of the shell with the age estimated from the number of varices and
calculated a mean age of 3.36 for the population and determined a mean
shell height of 51.6 mm.
Using the number of major shell varices as the criterion, specimens
of 0. reses reses were separated by age class. The shell heights were
measured, and mean height for each age class was calculated. These values
were plotted on a graph with 95% confidence intervals indicated for each
class (Fig. 10). Figure 10 shows that shell height increases most during the
first growing season, with average amounts of growth as follows: 16.06 mm
the first year, 5.16 mm the second year, 4.5 mm the third year, 1.73 mm the
fourth year, 2.1 mm the fifth year, and 3.04 mm the sixth year. Individuals
varied greatly, which was reflected in the high values calculated for standard
deviation. Calculated mean age for these snails was 2.11 years and mean
shell height 43.06 mm.
Another way to examine growth rate is to look at the yearly rate of
shell deposition. Shells of 0. reses reses were sorted by varix number into
age classes and weighed. The average weights were calculated for each age
class and plotted with 95% confidence intervals for each class (Fig. 11). In
the first year the amount of shell produced is less than in most succeeding
years. However, the actual amount of shell production per year follows a
linear pattern, with average grams of shell material deposited as follows:
0.80 gm in the first year, 1.03 gm in the second year, 2.13 gm in the third
year, 0.30 gm the fourth year, 0.81 gm the fifth year, and 2.67 gm in the sixth
year. On the basis of the increase in shell weight, growth is constant from
year to year. The slope of the regression line for the weight values is 1.22,
representing an average yearly increase of shell material of 1.22 gm.
The large amount of variation within the age classes is due to
variation in individual growth rates. These rates were measured in the two
most common age classes in populations of 0. reses reses on Stock Island by
marking and recapturing individual snails during the active season. Juvenile
snails showed rates of shell height increase of 0.019-0.340 mm/day over a
53-day period in the summer. Snails with two varices (those in the third
growth season) showed rates of addition to the shell lip of 0.07-0.52 mm/day
over a concurrent 56-day period.
Variability in individual growth rates is most likely caused by
differential food intake. Snails that are estivating in sites protected from
direct rainfall start feeding later than those in more exposed positions.
Therefore they also begin to grow later in the season, reducing the yearly
measurement. Although individual metabolism also may be a factor,
causing variable efficiency in converting food energy to growth, exposure to
rainfall is probably the most important factor.


I 95% confidence interval








total n=213

S I I I l I I l

o I I I I I I I I I
0 1 2 3 4 5 6 7 8

Number of varices

Figure 10. Growth rate in 0. reses reses (mm of shell height added per year).


1 1
=95% confidence interval
total n=63

o i i I I I I
0 1 2 3 4 5 6 7 8
Number of varices
Figure 11. Growth rate in 0. reses reses (g of shell deposited per year).







Mortality in Orthalicus stems from a number of causes. Some of
these causes can be determined after death by the condition and location of
the shells. One cause of death that can be determined in this manner is
mammalian predation.
Predation by carnivorous or omnivorous mammals leaves
characteristic patterns of shell damage. These predators generally crush the
smaller and weaker upper whorls of the shell with their teeth. They also
may gnaw on the shell. The shells generally have little organic matter left in
them after a mammal has fed on the snail.
The raccoon (Procyon lotor) may be a frequent predator of
Orthalicus and has been reported to prey on Liguus fasciatus on
Lignumvitae Key (Tuskes 1981:167). Raccoons are present throughout the
range of Orthalicus in Florida and are active climbers that can reach tree
snails easily throughout the year. Experiments with naive animals showed
that raccoons manipulate Orthalicus and Liguus shells in preference to more
customary food items. They typically bite the upper whorls from the shells
and consume the entire soft body.
The southern opossum (Didelphis virginiana pigra) also feeds on
tree snails and, like the raccoon, is an active climber. This animal is more
numerous in the mainland range of Orthalicus than in the Keys, but has
been reported from Key Largo, Key Vaca, Big Pine Key and Key West
(Layne 1974:387).
The black rat (Rattus rattus) is a foreign species abundant
throughout South Florida and the Keys, including Key West (Layne
1974:390). Because it is smaller than either the raccoon or the opossum,
the black rat may be limited to preying on younger and smaller snails.
Thompson (1980:5) listed the Norwegian rat (Rattus norvegicus) as
a possible predator of 0. reses reses on Stock Island. However, this species
is apparently limited to the Miami residential area (Layne 1974:390). It
probably does feed on Orthalicus, but only where the ranges of the two taxa
coincide, which limits predation primarily to 0. floridensis, the only member
of the genus to occur naturally in Miami. The introduced colony of 0. reses
in Cox's Hammock, Goulds, also may be affected by the Norwegian rat.
The grey squirrel (Sciurus carolinensis) was seen feeding on Liguus
fasciatus, the other large arboreal snail in South Florida, in the Miami area
(Thompson, pers. comm.). Squirrels are known to augment their diet with
other arboreal invertebrates, such as beetles, ants, and caterpillars (Martin
et al. 1951:232). This animal is probably an occasional predator on
Orthalicus as well as Liguus where its range overlaps that of the snails. This
squirrel has been reported in South Florida throughout most of the
mainland range of 0. floridensis as well as on Key Largo, Plantation Key,


and Lower Matecumbe Key (Layne 1974:390). Sciurus is not found in the
southern Keys and therefore is not a factor in the mortality of 0. reses reses
on Stock Island.
The eastern woodrat (Neotoma floridana) is represented in South
Florida by the subspecies N. f. small, the Key Largo woodrat. It is found
only on Key Largo and Lignumvitae Key (L.N. Brown 1978:11-12). The
woodrat is reported to be primarily a vegetarian but occasionally has been
observed to eat snails and insects (Lowry 1974:258). It may be a predator
on tree snails, including 0. reses and Liguusfasciatus, but, like the woodrat,
it may be restricted to feeding on smaller and younger snails by size
limitations. The woodrat is also known as the packrat because of its
tendency to carry bright or shiny objects to its nest. Empty snail shells
sometimes found in woodrat nests may only represent this collecting
tendency and not true predation.
There are unsubstantiated reports by local residents that house cats
(Felis cats) feed on 0. reses reses on Stock Island (Thompson 1980:5).
There are a large number of semi-feral cats in the area where the tree snail
colonies are found. However, these cats refused snails offered them in place
of their regular food. The cats washed vigorously after contact with the
snails and showed signs of distaste. Therefore, it is doubtful that house cats
prey on the snails.
Birds, such as blue jays (Cyanocitta crsta semplei), contribute to the
mortality of tree snails and, like mammalian predators, leave characteristic
patterns of shell damage (Voss 1976:68, Tuskes 1981:167). The birds peck
at the shells of exposed animals, usually while the snails are in estivation.
These attacks leave distinct radiating cracks in the body whorl of the shell.
Sometimes the damage to the shell is enough to produce a depressed area
or even a hole. The birds are then able to attack the flesh of the snail.
Unlike mammalian attacks, however, such avian attacks leave a considerable
quantity of flesh in the shell. Sometimes the snails are uninjured by these
attacks despite the damage done to the shell, in which case some snails are
able to repair the shell, leaving a scar. Other snails appear to die of
dehydration following breakage of the shell.
Observers in Dade County have seen blue jays (Cyanocitta crista
semplei) attack 0. floridensis. On Stock Island, Monroe County, local
observers report that a large black bird that they termed a "crow" carried
out attacks on Orthalicus reses reses. It has not been possible to identify this
bird more specifically. However, the following avian species occurring in the
Key West area are potential predators: common grackle (Quiscalus
quiscula), red-winged blackbird (Agelaius phoeniceus), smooth-billed ani
(Crotophaga ani), and starling (Stumus vulgaris) (M. Brown, pers. comm.).
Bird-caused shell damage was found in the colonies of 0. reses reses on
Stock Island, but such damage and mortality was particularly high in a large
colony of 0. floridensis in Homestead. The density of the population at this


site forces many snails to estivate in exposed situations, where they are
vulnerable to avian attack.
Unlike mammalian and avian predation, attacks by the two known
invertebrate predators on Orthalicus do not damage the shell. It is
therefore difficult to estimate the impact that such predation has on the
tree snails.
The predatory gastropod Euglandina rosea is one of the
invertebrates known to feed on Orthalicus (Baker 1903:51, Voss 1976:68).
Euglandina is found throughout the range of the Florida Orthalicus. This
carnivore is often considered to be terrestrial, but it is frequently found in
the same trees inhabited by Orthalicus.
The second invertebrate predator known to feed on Orthalicus is
the larva of a click beetle, probably Aleus sp., identified by M. Thomas of the
Department of Entomology at the University of Florida. This sizeable larva
(25-35 mm long) lives in the leaf-mold and feeds on any organism with
which it comes in contact. A specimen was found actively consuming a
nesting 0. reses reses on Stock Island.
Ants are commonly found in trees throughout the range of
Orthalicus, but it is not known if they attack and feed on the snails. Eisner
and Wilson (1970:14) reported that ants do not consume the related snail,
Liguusfasciatus, because of what appeared to them to be the discharge of a
defensive fluid that repelled the ants. However, Tuskes (1982:168) reported
that fire ants (Solonopsis geminata) do attack Liguus. Ants were seen
walking over the shell and extended foot of 0. reses reses on Stock Island,
without harming the snail, as they moved up the tree on which it lived.
Ants also were seen consuming the flesh of dead and rotting specimens of
0. reses and 0. floridensis.
Flies of the family Sarcophagidae may contribute to mortality of O.
reses reses. Two species, tentatively identified at the University of Florida by
M. Thomas as Sarcodexia stemodontis and Helicobia rapax, were reared
from recently dead snails collected on Stock Island. Muma (1954:8-9)
reported four parasitic sarcophagids causing death in Drymaeus dormani
(Binney), a small bulimulid tree snail distributed in northern and central
Florida. Stegmaier (1972:237-241) reared seven species of sarcophagid flies
from snails collected in Dade County. He wrote that most flies in this
family are saprophagous rather than parasitic, but did not indicate which
mode of life was followed by S. stemodontis or H. rapax, both of which he
reared from Marisa coru-arietis (Linn6). Stegmaier reports that both
species of fly have been reared from a large variety of invertebrates in North
and South America, including a number of terrestrial pulmonate snails. It
was not determined whether the eggs of these flies were laid on the flesh of
0. reses reses before death of the snail or after.
The land hermit crab (Coenobita clypeatus) has been reported as a
possible predator on tree snails (Davidson 1965:386, Voss 1976:69). Hermit


crabs do occupy the shells of 0. floridensis on Big Pine Key, but this is not
proof of predation. These crustaceans will inhabit any suitable containers
they find, usually gastropod shells, but can include small bottles.
A number of other predacious invertebrates may feed on
Orthalicus, but have not yet been reported doing so. Muma (1967:3-10)
indicated that two species of scorpion present within the range of Orthalicus
were large and aggressive enough to pose a possible threat to nesting tree
snails. These scorpions are Centuroides keysi (36-73 mm) and C. gracilis (70-
110 mm). Muma (1967:21-25) also recorded several whip-scorpions within
the range of the Florida Orthalicus: Mastigoproctus giganteus (38-50 mm),
Tarantula marginemaculata (10.5-17 mm), and Paraphrynus raptator (=T.
fuscimana [Koch] [Franz 1982:130]) (17.5-24 mm). Like scorpions, these
arachnids are secretive ground-dwellers and therefore would pose a possible
threat to nesting snails. Large centipedes of the genus Scolupendra also may
be possible predators of nesting Orthalicus (F. Thompson and R. Franz,
pers. comm.).
Several "lightning bugs" from the family Lampyridae are present
within the range of the Florida Orthalicus and may prey on the snails (J.
Lloyd, pers. comm.). Several climbing species in the genus Pyractomena are
found in Key West, as well as representatives of the non-climbing genus
Photurus. Pyractomena is believed to be a snail specialist, while Photurus will
feed on snails if they are present but feeds on other prey more commonly.
A summary of the feeding behavior of several prominent snail-eating
lampyrids is presented by Mead (1961:106-109).
In an effort to estimate minimum predation rates, all empty shells
seen in populations of 0. reses nesodryas on Johnston Key and 0. reses reses
on Stock Island were collected. Of 327 0. r. nesodryas specimens collected,
80% of the shells were whole, indicating death due to invertebrate
predation, cold, dehydration, old age, disease, or some other factor that
does not damage the shell. Only 3% showed signs of mammalian predation,
with 0.6% showing predation of undeterminable type. However, 16% of the
shells showed scars of past injury that had been repaired and was not the
apparent cause of death.
In the more restricted population of 0. reses reses, only 35 empty
shells were recovered. Of these 63% showed no signs of damage, while
20% showed indications of death by predation (17% mammalian and 3%
avian). Shells that showed scars of injuries not causing death made up 17%
of the sample.
If these samples are representative, then predation rates vary
greatly from colony to colony, with up to 20% of mortality attributable to
vertebrate predation. Since the act of predation often crushes the shell
beyond recovery, this is a minimum estimate. Some larger predators, such
as raccoons, may remove their prey from the area entirely. Invertebrate
predation that does not damage the shell cannot be distinguished from non-


predatory causes of death, and therefore also may exceed estimated
predation rates. Predation by vertebrates and invertebrates must be a very
important factor in controlling populations of Orthalicus in South Florida.


Numerous museum lots (containing 30-60 or more specimens each)
of live-taken Orthalicus reses reses shells exist. Most of these were collected
during the 1930s and a few during the 1940s. Collection pressure was
severe at that time and appears to have had a negative effect on population
size. Not since the 1950s has it been possible to collect such sizeable lots,
because the animals were not present in sufficient density. This evident
decline in population density of the Stock Island snails also was effected
through habitat loss as a result of real estate development.
During the 1981-1982 surveys on Stock Island it could be seen that
the snail was undergoing loss of habitat. Redevelopment of the golf course
was planned, though not completed. The county land population was
isolated in a parking lot area where nesting snails were subject to great
mortality through crushing. In 1986, reports were received by the Nature
Conservancy that the snail population was declining. On 2-3 July 1986 my
field investigation confirmed a reduction in the population.
In June 1981 I observed 25 adults in the golf course population
(Table 2) and 6 adults in August 1982, and J. Young (pers. comm.) saw 3
adults in September 1986. No empty shells were discovered, with the
exception of one specimen collected in 1982 by a golf course employee. The
dearth of empty shells and the observations made by local residents indicate
that this reduction is possibly due to human collecting activities.
The county land population is faring better than the one on the golf
course, but it also is showing a reduction in numbers. In August 1981, 36
adults were seen living at that site (Table 2). Approximately the same
number were present in August 1982 when the observable population was
estimated to be 30-40 adults and 67 hatchlings and juveniles, or a total of
107 snails. However, in multiple independent surveys of the same site in
during June through August 1986, all surveyers reported 21-25 adult snails
and 1 hatchling (J. Young, K. Sunderland, A. Hooten, F. Ford, pers.
comm.). Two adult snails were seen in the Botanical Garden (M. Huckel,
pers. comm.), making a total of 28 snails observed in the area.
Human collecting of the live snails has been reported by a resident
of the area (H. Schiller, pers. comm). Approximately 10 specimens were
removed from a hibiscus bush (Hibiscus rosasinensis) early in 1986. Since
that time no specimens have been found on that host plant.


Habitat degradation is also a factor in the reduction of the county
land population. In several instances, cement and gravel have been dumped
at the base of host trees. This effectively destroys the nesting grounds for
both Orthalicus reses reses and Drymaeus multilineatus, by making the soft
leaf mold and dirt inaccessible. In addition, because many of the host trees
are located in the parking lot, vehicles are being parked on the dirt
immediately at the base of these trees, thereby packing the soil and making
it unsuitable for nesting. These vehicles also pose a potential threat to
those individuals who are able to nest, because they remain in the nest for
72-96 hours and are extremely susceptible to crushing.


On Stock Island there are generally 1-4 snails per inhabited tree. A
maximum of 13 snails was found in a large Jamaica dogwood tree (Piscidia
piscipula) approximately 10 m tall. Similar densities were found in a colony
of 0. reses nesodryas on Johnston Key.
Population densities on the mainland were higher. 0. floridensis in
the Pinecrest region of the Everglades generally was found in numbers of
30-40 snails per inhabited tree. Similar densities were seen in a colony of O.
floridensis in the Fruit and Spice Park in Homestead, Dade County.
Densities of approximately 4-8 snails per inhabited tree were seen in a
mixed colony of 0. floridensis, 0. reses reses, and Liguusfasciatus in Goulds,
Dade County.
Calculation of a Lincoln Index for the population of 0. reses reses
on the golf course on Stock Island is inappropriate because of the
disturbance of the habitat by man and because the snails do not represent a
randomly mixing population. A census of an area of 0.33 acres produced 17
snails, which is a crude density of 510 snails per acre of uniform habitat. If
the entire 20-acre course were so populated, it could support approximately
10,200 snails. But a survey of the area showed the snail to be highly
restricted in its distribution in the suitable habitat. Only two places appear
to be well-colonized at this time. The total population actually may number
fewer than 200 snails.
Among the factors that may affect population density are quantity
of food available, size and density of habitable trees, presence of suitable
nesting and estivation sites, and rates of predation. The results of human
activity include both directly and indirectly causes of mortality. Density is
also affected by the climate, including the quantity and regularity of rainfall,
and the frequency of freezing temperatures. The large numbers of
specimens in museum lots indicate that human collecting of adult snails may


be responsible to a great degree for the low densities seen on Stock Island
at the present time.
An attempt was made to establish the age distribution of 0. reses
reses on Stock Island (Fig. 12). A detailed count of all snails present,
including hatchlings, resulted in a total of 107 individuals. When the snails
were sorted by age class, the following percentages resulted: 66% of the
population were hatchlings or juveniles of less than 1-year old, 6% were 1-
year-olds, 14% were 2-year-olds, 11% were 3-year-olds, 3% were 4-year-
olds, and 1% were 5-year-olds. No snails were found during the survey that
were more than 5 years old.
Error is most likely to occur in the counts of the hatchlings,
juveniles, and 1-year-old snails. They are relatively small (6-35 mm
generally) and can be overlooked easily. Therefore, young snails may
comprise more of the population than this study indicates. The counts for
the adult (2 years old and older) snails are more certain and give results
that are consistent with those from tracking marked animals.
In general, reproduction was found to begin when snails had
attained 2 years of age. On this basis, reproductive individuals comprise
29% of the Stock Island population. No difference was noted in the
number of eggs laid by individuals of different age classes.
Simpson (1923:111-112) examined the age distribution of a colony
of estivating 0. floridensis on Cape Sable. He found that of a colony of
approximately 500 snails, very few were "adult" (with three growth varices),
5% were 2-year olds, and over 90% were 1-year olds. However he indicated
that this was an unusual distribution, with many more "yearlings" than
normal. No other studies have been conducted on the age distribution
within colonies of Orthalicus, although several have been carried out on the
related snail, Liguusfasciatus (Brown 1978:39-59, Tuskes 1981:166-167).


This study of the ecology of the Stock Island tree snail, Olthalicus
reses reses (Say), was undertaken to facilitate the development of a recovery
plan for this federally listed, threatened species. Little was known about the
life history and ecological requirements of 0. reses. Information about
these subjects was required in order to be able to reverse the reduction in
population size and enlarge the habitat required by the snail.
The results of this study indicate that Orthalicus reses reses is not as
specialized as has been thought. This snail is not limited by species of tree
available for colonization and can be found on both native and introduced
trees with either rough or smooth bark. It feeds, apparently without


3% n =107

Number of varices

Figure 12. Age class distribution of 0. reses reses on Stock Island.



discrimination, on epiphytic lichens, fungi, and algae on tree surfaces. 0.
reses most generally is found in hardwood hammock or remnants of such
hammock, but appears able to survive in landscaped areas of sufficient
maturity. Most nests are constructed in soft soil and leaf-mold, but some
have been found in lawns as well. Activity (feeding and reproductive
events) is stimulated by rainfall. However, 0. reses is capable of surviving
long periods (6-9 months) of drought routinely by estivating. The discovery
of two recently established colonies of 0. reses reses, one in the Everglades
and one on Key Largo, indicates that it is possible to transplant the snail
Several factors limit the population of 0. reses reses. These include
predation, destruction and degradation of habitat, and temperatures near or
below the freezing point. Vertebrate predation, which can account for up to
20% of mortality, can be reduced by trapping programs. Such a program
for trapping raccoons (Procyon lotor incautus) in the area has been planned
by Monroe County in an effort to reduce the decline of the county land
population on Stock Island (A. Hooten, pers. comm.). Destruction of
habitat can be limited by legal means. Degradation of the nesting grounds
on the county property is being reversed by the county through the
construction of protective, leaf-mould-containing nesting boxes at the base
of host trees in and near the parking lot. These are planned to reduce
vehicle-related problems, as well as to prevent the dumping of unsuitable
substrates on the nesting grounds. Curtailment of collecting by humans
would greatly increase the size of the type population on Stock Island.
The effects of habitat degradation can be ameliorated by the
establishment of transplanted colonies in areas unlikely to be disturbed by
man's activities. These areas can be only in the most southern portions of
the State of Florida, where the winter temperatures only rarely drop to the
freezing point. The minimum number of snails that could be transplanted
to form these colonies would be two sexually mature adults, i.e. snails of at
least 2 years of age. A search for suitable transfer sites has been undertaken
jointly by Monroe County and the State of Florida, with the cooperation of
the U.S. Fish and Wildlife Service (D. Wesley, pers. comm.). Further
studies on the life history of the Stock Island Tree Snail are being carried
out by the Florida Game and Freshwater Fish Commission in cooperation
with Monroe County (J. Hovis, pers. comm.).


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