Table Of Content1999. The Journal ofArachnology 27:503-512
MOVEMENT OF THE MALE BROWN TARANTULA,
APHONOPELMA HENTZI (ARANEAE, THERAPHOSIDAE),
USING RADIO TELEMETRY
Margaret E. Janowski-Bell’ and Norman V. Horner: Department of Biology,
Midwestern State University, Wichita Falls, Texas 76308-2099 USA
ABSTRACT. This study was designed to gain insight into the “migratory” life history component of
the male brown tarantula, Aphonopelma hentzi (Girard 1854), and to determine if radio telemetry could
successfully answer questions regarding the ecology oftheraphosids. Tarantulas were equipped with radio
transmitters and movement monitored using an antenna and radio receiver. Overall movement of males
was in all directions and randomness could not be excluded as a factor. Individual males movedrelatively
large distances, upto 1300 m, and significantdirectedness was onlyfoundinthreeindividuals. Inaddition,
notes on habitat, ecology and behavior are presented.
Many spiders disperse over large distances throughout the southwestern United States,
by ballooning, and this is well documented in Mexico, and possibly Panama. Baerg (1958)
the aranemorphs (Weyman 1993, 1995; Wey- also suggested that reduced inbreeding could
man et al. 1995). Mygalomorph spiderlings result from males moving large distances in
have been observed ballooning over short dis- search of mates.
tances (Bristowe 1939; Coyle 1983, 1985; Migration differs from dispersal in many
Coyle et al. 1985); and Coyle (1983, 1985) respects. Dispersal typically refers to the
concluded that ctenizid spiderlings could trav- movement of individuals in a population that
el significant distances if they launch from results in an increase in the mean distance be-
taller vegetation. However, immature tarantu- tween individuals (Andrewartha & Birch
las (Theraphosidae) are not known to balloon. 1954; Southwood 1981; Dingle 1996). Ac-
There is no mention in the literature of the cording to Danthanarayana (1986) and Dingle
large scale movement ofmale tarantulas. This (1996), migrants usually exhibit five basic be-
study was designed to determine the large havioral characteristics: 1) persistent move-
scale distance and direction traveled by the ment, 2) undistracted by the presence of re-
mature male tarantula, Aphonopelma hentzi sources promoting growth and maintenance
(Girard 1854), using radio telemetry. (Kennedy 1961), 3) “straightened out” move-
Mature males leave their burrows to search ment, 4) distinct leaving (Southwood 1962)
for mates from June to December (Baerg and arriving behaviors, 5) reallocation of en-
1928, 1958; Gertsch 1979; Minch 1979a). In- ergy specifically to support movement.
dividual males have been observed crossing In the United States Aphonopelma can be
highways, appear to be moving in the same
found west ofthe Mississippi River to the Pa-
direction, and resist being redirected (Baerg cific Coast and north into Arkansas, Utah, and
1958, 1963). Baerg (1958) stated that rarely Nevada (Baerg 1928; Gertsch 1979; Roth
are the movements ofhundreds ofindividuals
1993). They are typically found on hillsides
reported. Magnusson (1985) witnessed a co-
covered in sparse vegetation and mixed with
ordinated movement of89 male Cyclosternum
diverse desert growth (Baerg 1928, 1958;
sp. in Brazil. Mass movements could occur
Gertsch 1979). Tarantulas are usually noctur-
when weather conditions are ideal for travel
nal, but may be active fromlate afternooninto
(Baerg 1958). In addition, Baerg (1958) pro-
late morning when light levels are low (Baerg
posed a general “migration” of tarantulas
1958; Comstock 1975; Minch 1978).
' Currentaddress: 105 TuckerHall, DivisionofBi- Radio telemetry is an effective tool for col-
ological Sciences, University of Missouri-Colum- lecting data on organisms that are difficult to
bia, Columbia, Missouri 65211 USA. follow, observe or relocate (Mech 1983). His-
503
—
504 THE JOURNAL OF ARACHNOLOGY
torically, it has been used extensively to fol- to provide minimal physical contact the an-
low the movements of larger animals (Mech tenna was bent upward at a 45° angle.
1983). As technology decreased the size of Procedure. -Male tarantulas were
transmitters, this technique has been increas- equipped with transmitters from 2 September-
ingly applied to smaller invertebrates includ- 17 October 1994 and from 9-19 July 1995.
ing crayfish (Covich 1977), crabs (Gherardi et They were capturedin aclearplasticcontainer
al. 1987, 1988a, b, c; Gherardi & Vannini on predominantly open ground. Individuals
1989; Fletcher et al. 1990), snails (Bailey were examined to determine overall physical
1989; Tomiyama & Nakane 1993), and insects condition. Those lacking obvious physical ab-
(Hayashi & Nakane 1988, 1989; Riecken & normalities and exhibiting activity were
Raths 1996). Radio telemetry may provide weighed (to the nearest 0.1 g) using an Ohaus
unique insights into the ecology and behavior LS200 portable scale. The only exception was
of the larger arachnids. This technology is specimen #13-94, which was missing the third
used to study the brown tarantula, A. hentzi, left leg. Males ranged from 2.5-7.5 g. They
an ideal subject for radio telemetry due to its were anesthetized with carbon dioxide for 2
activity, abundance and size. min or until docile. Tarantulas were then
placed on a thick synthetic sponge with legs
METHODS
extended. Their legs were restrained by plac-
Study site.—The study was conducted on ing a second sponge which had been cut to
the W.T Waggoner Estate, 19.4 km WSW of expose the cephalothorax and abdomen over
Electra, Wilbarger County, Texas (33°58'N, the first sponge. String was used to hold the
two sponge pieces in place. Thisrestrainedthe
99°08'W). This area is part of the Rolling
spider and facilitated attachment of the trans-
Plains region of Texas, which is a subsection
mitter. To assist in the attachment of the con-
of the Great Plains region ofthe central Unit-
tact adhesive, the “hairs” (setae) were re-
ed States (Lewis 1962). It is characterized by moved from an area on the carapace, posterior
rolling-to-rough topography broken by inter-
to the eyes, by gently rubbing the area with a
mittent streams (Lewis 1962). Annual rainfall pair offorceps. A small amount ofwaterproof
for the area is approximately 76.2 cm, with contact adhesive was placed on the the cara-
May and September being the wettest months
pace and on the transmitter. After 5 min the
(Lewis 1962). The dominant vegetation is adhesive on the transmitter was pressed into
scrub mesquite (Prosopis), goat bush (Caste- the adhesive on the spider. This was allowed
ia), prickly pear cactus (Opuntia), turkey cac- to set for 20-40 min before the tarantula was
tus (Opuntia), little blue stem {Schizachyr- removed from the sponge and placed back
ium), mesquite grass (Bouteloua), and broom into the capture container. Equipped tarantulas
weed (Xauthocephalum). The southernportion (Fig. 1) were released at the exact site where
of the study site is dissected by a paved farm- they were collected within 2 h of capture.
to-market road running east to west. The area Tarantulas monitored in the fall of 1994
is broken by occasional dirt or gravel main- were observed a minimum of three days per
tenance roads. Past and current land use at the week, while those in 1995 were observedonce
site include oil production and cattle grazing. everyday, weather permitting. Locations of
Transmitters and receiver.—All radio te- spiders were marked and labeled using flag-
lemetry equipment was purchased from Wild- ging tape on adjacent vegetation. Direction
A
life Materials, Inc. (Carbondale, Illinois). traveled since the last observation was deter-
model TRX-IOOOS receiver was used with a mined by compass. Readings were corrected
folding three-element yagi directional anten- to reflect true north. Approximate distance
na. The frequency range used was 150.000- traveled between observations was obtained
150.999 Mhz. Each transmitter (SOPB-2011) using a tape measure or by pacing.
had a different frequency thereby identifying Seventeen Aphonopelma hentzi males were
individuals. Transmitters we9igXhe5dXa4pproxi- monitored in the Fall of 1994 for movement.
mately 0.6-0.8 g and were mm. Of these, seven individuals retained their
The flexible antenna, constructed of wire sim- transmitters for four or more days and were
ilar to guitar string, was 7.62 cm in length. To considered for data analysis. This yielded a
prevent possible chafing of the abdomen and total of 113 observations. Six additional males
JANOWSKI-BELL & HORNER—MOVEMENT OF MALE TARANTULAS 505
—
Figure 1. Aphonopelma hentzi male with attached radio transmitter.
were monitored in July 1995. These individ- samples when weight was considered {U — 0,
uals were checked for short-term movement P < 0.05). However, there was no difference
once every 24 hours. Four ofthese individuals between the samples when the rate {U = 10,
retained their transmitters for three or more P > 0.05) and inflection points per day (C/ —
days, and yielded—20 observations. 14, P > 0.05) were considered. Based upon
Identification. The tarantula population these data, the samples from both years were
studied was identified asAphonopelma hentzi. combined for statistical analysis except where
Representative specimens are on deposit in indicated.
the American Museum of Natural History,
RESULTS
New York. The study site lies outside the —
known distribution reported by Smith (1994) Movement.^ Figures 2-6 illustrate the
for three species in the region. As a result, a movement of males and give a brief descrip-
name could not be assigned to this spider us- tion of the habitat for each observation. The
ing Smith’s (1994) descriptions. The validity weight (x = 5.0 ± 1.5 g SE), total time ob-
of Smith’s species are in question (Prentice served, total path distance, rate (x = 53.8 ±
1997). Cokendolpher (pers. comm.) noted that 25.7 m/d SD), number of inflection (turning)
Smith failed to take individual variation into points per day (x = 0.64 ± 0.19 SD), point-
account. Therefore, the old name is applied to to-point distance (distance from the first ob-
the common tarantula of Texas and servation to the last observation), and point-
Oklahoma. Representative specimens fromthe to-point angles with 0° being north (angle
area were confirmed as A. hentzi by Dr. Rick from first observation to last observation) ((()
West, Research Associate, Royal B.C. Muse- = 253.6° ± 70.8° SD) for each male are pre-
um (West per—s. comm.). sented in Table 1. Male #12-94 traveled the
Statistics. The samples from each year farthest with regard to both point-to-point dis-
were compared using the Mann Whitney La- tance and rate (Fig. 4, Table 1). The most in-
test for unmatched pairs (Fowler & Cohen flection points per day was exhibited by #5-
1990). There was a difference between the 94 in 1994 (Fig. 6, Table 1) and #1-95 in 1995
506 THE JOUR^IAL OF ARACHNOLOGY
—
Table 1= Individual tarantula number, weight, days observed, total distance of path traveled, rate of
travel per day, number of inflection points per day, distance from first observation to last observation,
direction from first observation to last observation.
Point-
Total time Total Inflection Point-to-point to-point
Weight observed path distance Rate points distance angle
Spider # (g) (d:h:iniii) (m) (ro/d) per day (m) (degrees)
—
F94 4:18:35 148.8 31.2 0.60 102.1 236
5-94 7.0 24:00:00 1320.2 55.0 LOO 677.3 327
9-94 6.6 4:17:26 281.4 59.6 0.60 208.2 141
10-94 6.2 7:17:14 412.8 53.5 0.75 264.2 114
12-94 7.5 18:10:27 1750.2 94.9 0.72 1360.4 305
13-94 5.3 4:15:48 123.9 26.7 0.60 116.9 228
18-94 6.6 13:22:26 364.2 26.1 0.50 272.2 313
1-95 3—.6 9:22:09 815.6 82.2 0.80 324.6 98
2-95 3:00:34 211.1 69.9 0.66 188.3 215
3-95 2.6 2:22:50 222.2 75.8 0.66 176.3 243
6-95 4.2 3:22:55 69.2 17.7 0.25 14.1 6
(Fig. 5, Table 1). Male #6-95 traveledthe least a taunt abdomen was observed within the bur-
with respect to rate, inflection points per day row. There was no correlation between rate
and poinhto^point distance (Fig. 3, Table 1). (m/d) and the percentage of the transmitter
There was no correlation between tarantula weight to body weight (r^ = 0.104, w = 9, F
weight and rate (rg = 0.10, « = 9, F > 0.05). > 0.05). Three transmitters were known to
However, there was a marginally significant have been removed from spiders within bur-
correlation between rate and inflection points rows. These transmitters were tightly wrapped
per day (r^ = 0.68, « = 11, 0.02 < P < 0.05). in silk, and recovered just inside the burrow
Overall movement of individual males was or a few centimeters from the buixow en-
in almost all directions (Table 1). The Ray- trance.
leigh test [uses the mean vector (r) to deter- Microhabitat and refugia.—Males were
mine directedness (Batschelet 1981)] could found moving through a variety of habitats
not exclude randomness as a factor in the from relatively barren, rocky ground to areas
point-to-point movement of the combined ofdense vegetation. Tarantulas were observed
Psam=ple0.s5)froormobfotthheyesaarmspl(er =fro0m.231,99«4=(r11=, ctoenbteimtertaevreslianbgoevaesitlhyetghrroouungdh.tOhenegrmasaslemawnays
0m.e3n1t, owf=ma7l,eF#^=-904.5(5r).=H0o.w4e6,venr,=t2h6e,m0o.v0e0-1 observed hanging from vegetation several
m<alFe <#120-.09044;(r4)--0.3622,8.9w°=±1589,.7F°<SD0).0a0n1d; cenMtoismettemrasleasbowveerteheingarcotuinvde.during the day
nc!>es=s. T33h5e.4r°esu±lts49f.r7o°mSRDa)o’sinsdpiaccaitnedg tdeisrtec[tuesde-s ascnrdubretmhaicikneetdms).inSschreulbtetrheidckeentvsiwroenrmeen1t-s3 (me.gi.n,
height, 1-3 in diameter and dominated by
angular data to determine directedness (Bat-
mesquite (Prosopis), Other plants included
schelet 1981)] yielded similarresults with one
exception; #13-94 exhibited directedness (U goat bush {Castela), prickly pear cacti {Opun-
- 188, « = 5, F < 0.05; ^ - 247,1° ± 34.1°). tid), turkey cacti (Opuntid) and an understory
Performance of traesmitters*=-All trans- of dense grasses (Schizachyrium, Bouteloud).
mitters, except one, were recovered in work- Several small mammalburrows, outcroppings,
ing order at the end of the study. The trans- and large limestone rocks were also used for
mitter attached to #5-94 was recovered shelter during the day. One locale, character-
m
completely wrapped in silk within the en- ized by limestone slabs 0.5 in diameter and
trance of a tarantula burrow. There were abra- interspersed in dense grass, attracted three
sions and breaches on the epoxy coating of males within two days yielding a total of five
the transmitter and a very large tarantula with observations. The abundance of data obtained
JANOWSKI BELL & HORNER—MOVEMENT OF MALE TARANTULAS
507
1 A B
*!!
LEGEND
Capture site
*
Tarantula burrow
=r Predominately open ground
Mesquite thicket
Long, dense grass
NORTH
/ Slope
Goat bush thicket
Large limestone rocks
Intermittant creek
Washout
••• Rocky soil
Mammal burrow
Paved road
“Direction of movement
—
Figures 2-4. MovementofAphonopelmahentzimales. 2. Male#18-94hadthe lowestrateandnumber
of inflecmtion points per day in 1994; 3. Male #6-95 had the lowest rate and number of inflection points
per day 1995; 4. Male #12-94 had the highest rate in 1994
at this locale was not typical ofdata collected ture females. Males remained at these locales
during the rest of this study. from 1-3 days before continuing movement.
Seven males were found within burrows Female burrows were found by males within
with individuals that were assumed to be ma- thickets, in dense grass and on open ground.
THE JOURNAL OF ARACHNOLOGY
508
6
NORTH
LEGEND
Capture site
*
Tarantula burrow
rz Predominately open ground
A
Mesquite thicket
Long, dense gross
/ Slope
A
Goat bush thicket
Large limestone rocks
Intermittent creek
<; Washout
—<
Dead mesquite stump
••• Rocky soil
i)0 Cactus thicket
Crack in ground
O
Transmitter replaced
%
Mammal burrow
Direction of movement
—
Figures 5, 6. Movement ofAphonopelma hentzi males. 5. Male#1-95 hadthehighestrate andnumber
of inflection points in 1995; 6. Male #5-95 had the highest number of inflection points per day in 1994.
JANOWSKI-BELL & HORNER—MOVEMENT OF MALE TARANTULAS 509
Males probably visited more female burrows performance ofthe transmitters was excellent.
than detected due to the cover provided by The signal could be detected several hundred
dense vegetation. These “locales” or “sites” meters from the spider. In addition, the males
were not closely inspected for fear of dis- could be located easily when in burrows and
turbing the males and biasing movement re- under rocks. It was assumed the transmitters
sults. — would have a minimal effect upon the move-
Behavioral observations. On 2 Septem- ment ofindividual tarantulas. Maneuverability
ber 1994 male #1-94 was observed mating in small spaces was a concern, butthe antenna
m
with a female approximately 0.5 from the proved flexible enough to allow males to enter
entrance ofthe female’s burrow onbarren soil. and remain in burrows. Tagged males were
Upon approach the spiders separated and then observed crawling around or past residing fe-
the female quickly retreated into her burrow. males within the burrow.
The male was captured and outfitted with a Attachment of the transmitter to the taran-
transmitter. Male #5-94 was 45.7 cm from her tula was a problem. Many of the contact ad-
burrow for at least 18:54 h. hesives used did not maintain theirbond. This
On two separate occasions males were ob- resulted in several spiders losing their trans-
served moving in overlapping counter-clock- mitters within a few days and was the limiting
wise circles 60-90 cm in diameter. This is factor of this study.
similarto observations made by Shillington & Organisms use a hierarchical set of cues to
Verrel (1997). locate resources and exhibit behaviors appro-
Observations towards the end of the sum- priate for each level: habitat, patch, individual
mer indicated most males continually lost resource. (Bell 1991). It has been shown
body mass and ultimately possessed very (Baerg 1958; Minch 1979c; Shillington &
small abdomens. On the morning of3 October Verrel 1997) that male tarantulas are able to
1994 male #12-94 (Fig. 4) was found in the detect local “cues” provided by females in
open, positioned vertically with his abdomen the vicinity of their burrows. These have not
in the air. The last two pairs of legs were been shown to be directional, but do elicit lo-
stroking the antenna ofthe transmitter. His ab- cal search behavior described as “animated
domen was very small. In the evening he was circular motion” (Shillington & Verrel 1997),
found dead, legs curled under the shrunken and were observed in this study. Baerg (1928,
abdomen. Males #2-95 and #3-95 were also 1958), Gabel (1972), and Kotzman (1990)
found dead. However, males #1-95 (Fig. 5) have noted the clumped or patchy distribution
and 6-95 (Fig. 3) were recovered, transmitter of theraphosid burrows. Theraphosids are al-
removed, and released at the end of the 1995 most blind and cannot see beyond 2.5-5 cm
study period. (Baerg 1958). As a result, it is unlikely taran-
tulas use visual environmental cues when
DISCUSSION
searching forburrow patches. Bell (1991) pro-
The movement of male tarantulas has been posed several search strategies organisms may
a subject of speculation and interest to arach- adopt when lacking environmental cues while
nologists for many years (Smith 1994). Most searching for resource patches: random walk,
of what is known regarding the ecology of straight line, systematic movement pattern
male tarantulas has been obtained from stud- (spiral or parallel movement), kinesthetic-in-
ies regarding the ecology of female and im- put mapping or a combination of these strat-
mature individuals within the proximity of egies. The results of this study did not reveal
theirburrows (Minch 1978, 1979a, b, c; Kotz- a systematic movement pattern, and this may
man 1990; Shillington & Verrell 1997) or in be because observations were not at the ap-
the laboratory (Baerg 1938, 1963), with two propriate scale. Three large scale loops were
known exceptions (Baerg 1958; Sanderson observed among individuals considered for
1988 as cited by Smith 1994). This is the first data analysis (Figs. 5, 6). These imply male
study known to extensively document the tarantulas are conducting systematic searches
movement of male tarantulas. to locate mates within “colonies.” The move-
Radio telemetry proved to be useful anden- ment of searching males between “colonies”
abled us to obtain data that would have been may be a combination of random walks and
difficult to acquire using other methods. The straight line movements as indicated by the
510 THE JOURNAL OF ARACHNOLOGY
directedness expressed in only a few individ- males and males were courting and mating
uals. However, the lack of directedness may with them. Multiple matings with the same
be a function ofthe time individuals were foL female are probable given the length of time
lowed. males were in the presence of these females,
There was limited evidence to support the which ranged from one to several days. Males
axiom that male tarantulas are migrating us- also visited multiple females (Figs, 2, 4, 5, 6).
ing Dingle (1996) and Danthanarayana’s The data reflect fewer matings than probably
(1986) definition. Based upon their observa- occurred due to sampling and lack of detec-
tions of North American tarantulas, Baerg tion within thickets. Baerg (1958) suspected
(1963) and Minch (1978) report that males mating occurs primarily inside the burrow.
travel farther during the mating period than However, male #1-94 was observed mating
any other period of the life cycle. There was with a female approximately 0.5 m from her
some evidence that movement of individuals burrow entrance.
was directed. Later in the season males were
This study indicates radio telemetry is a
observed with notably smaller abdomens in- valuable technique for studying the move-
dicating energy may be reallocated specifi- ment of male Aphonopelma hentzi. Males
cally for movement. Male #12-94 (Fig. 4) were observed moving large distances, up to
moved 30% (537 m) of the total distance
(1750 m) in 9% (1 day, 16h, 25 min) of the 1300 m, over a significant period oftime, up
to 18 days, while searching for mates. Cur-
total time (18 days, lOh, 27 min). Baerg
rent research on the behavior and ecology of
(1928) and Minch (1979c) noted that males
movement in tarantulas includes: evaluation
die at the end of the mating season. Their
ofextensive movement, influence ofdifferent
observations noted that preceding death the
abdomen becomes shrunken, ability to ex- habitat types, effect ofhabitat fragmentation.
tend legs is lost, and overall sluggish behav- ACKNOWLEDGMENTS
ior occurs. There was little evidence for a
synchronized, directional movement of all We thank the WT. Waggoner Estate in Ver-
males sampled. As aresult, no definitive con- non, Texas for their hospitality, providing free
clusions can be drawn regarding the charac- access to their land, and furnishing living
terization ofthe movement ofmale tarantulas quarters on the ranch. Funds for the purchase
as migratory. Further behavioral studies of the radio-telemetry equipment and other
would serve to elucidate the characterization supplies for this project were provided by the
of this behavior. Administration and Biology Department at
Early summer males were smaller in size Midwestern State University, forwhich we are
and weight. As a group they were not signif- most appreciative. We are indebtedto Dr. Rick
icantly different with respect to their rate and West, Royal B.C. Museum, for species confir-
inflection points perday, and they behavedthe
mation. Becky Janowski Technical Services
same ecologically with regard to movement.
(http:5si.com/bechtech/) donated time and ser-
Further study is needed to determine if the vices to produce figures. We are indebted to
early males have overwintered as adults or
Pauline Janowski who generously furnished
simply molted earlier than the late summer
funds for extraneous expenses. David V. Bell
brood.
Males frequented scrub thickets, small and R.W. Whisnand II provided field assis-
mammal burrows and large limestone rocks tance, for which we are grateful. Appreciation
throughout the study. These habitats probably is expressed to James Carrel and James Cok-
provided protection from predators and al- endolpher for early reviews ofthis manuscript
lowed better thermoregulation during the day. and two anonymous reviewers from the Jour-
In addition, the locale characterized by lime- nal whose suggestions were beneficial.
stone rocks may have a high density ofmature This paper is dedicated to the memory of
females not observed due to burrows being Mr. Glen Collier, Waggoner Ranch Game
hidden by the rocks. Warden, who acted as a liaison between Mid-
Males were frequently found within taran- western State University and the Waggoner
tula burrows in the presence of other individ- Estate. He was an insightful, sagacious natu-
uals. These were presumed to be mature fe- ralist, photographer and friend.
JANOWSKI-BELL & HORNER—MOVEMENT OF MALE TARANTULAS 511
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