Observations on Prey Capture and Anti-Predator Behaviors of Ogre-Faced Spiders (Deinopis) in Southern Costa Rica (Araneae, Deinopidae)

8 Pages·1996·6.9 MB·English

by  Richard M Getty

1996. The Journal ofArachnology 24:93-100
OBSERVATIONS ON PREY CAPTURE AND ANTI-PREDATOR
BEHAVIORS OF OGRE-FACED SPIDERS DEINOPIS
( )
IN SOUTHERN COSTA RICA (ARANEAE, DEINOPIDAE)
Richard M. Getty and Frederick A. Coyle: Department of Biology, Western
Carolina University, Cullowhee, North Carolina 28723 USA
ABSTRACT. Members of two apparently conspecific Deinopis populations from southern Costa Rica
perform backward (aerial) strikes (in response to vocalizations and vibrating tuning forks) and forward
strikes (to capture ambulatory prey). At daybreak these spiders quickly shift from foraging to cryptic
behavior. This cryptic behavior, which is described and illustrated in detail, involves camouflage on a
linear plant structure and/or stick mimicry. Body form, fringes ofsetae, palpal tarsus and claw shape, and
color pattern all enhance the effectiveness of these cryptic behaviors.
The so-called ogre-faced or net-casting spi- of another species, Deinopis longipes F. O.
ders ofthe genus Deinopis MacLeay 1839 are P.-Cambridge, in Panama. Coddington & So-
distinguished by remarkably large posterior brevila demonstrated that the backward strike
median eyes and an unusual prey capture is triggered by airborne vibrations, presented
strategy. A small, highly extensible, cribellate evidence consistent with Robinson & Robin-
capture web (a reduced orb-web) is construct- son’s conclusion that the forward strike is trig-
ed at nightfall, held at its four corners by the gered by visual stimuli, and predicted thatoth-
first two pairs of legs (Fig. 1), and actively er Deinopis species would be found to exhibit
manipulated to ensnare passing prey (Baum both types of capture behavior.
1938; Roberts 1954; Theuer 1954; McKeown Literature references to the cryptic behavior
& &
1963; Robinson Robinson 1971; Austin of Deinopis spiders during the daytime are
Blest 1979; Gertsch 1979; Coddington 1986; brief, in part because these behaviors are so
Coddington & Sobrevila 1987; Penney & effective (Baum 1938; Theuer 1954; Mc-
Whitehead 1995). Blest & Land (1977) have Keown 1963; Robinson & Robinson 1971;
shown how the posterior median eyes, possi- Austin & Blest 1979; Gertsch 1979). Three
bly the largest simple eyes of any land inver- such anti-predator postures have been ob-
tebrate, are specialized to concentrate light for served (pressed flat against a branch, suspend-
nighttime visual detection of prey; and Blest ed head downward in midair with legs ex-
(1978) has documented the spectacular and tended away from the longitudinal axis ofthe
enigmatic diurnal cycle of rapid destruction body in four tight pairs forming a cross, or
(at daybreak) and synthesis (at nightfall) of hanging head downward in midair with legs I
the photoreceptor membrane in these eyes. and II protracted and apposed in front and legs
Coddington & Sobrevila (1987) showed III and IV protracted and apposed behind the
that individuals of the Neotropical species body to form a single linear “stick”), but no
Deinopis spinosus Marx 1889 can perform one has described the form ofthese anti-pred-
two quite different stereotyped attack behav- ator behaviors or associated structural design
iors, a backward strike to capture aerial prey features in detail. Ackerman’s (1926) descrip-
and a forward strike to capture walking prey. tion oftwig/bud mimicry in Menneus camelus
In so doing, these authors resolved a contro- Pocock 1902 is, to our knowledge, the most
versy between Theuer (1954), who had de- detailed observation to date ofa deinopid anti-
scribed only backward strikes in D. spinosus predator tactic.
and Robinson & Robinson (1971), who ob-, Our brieffield study ofthe behavior oftwo
served forward strikes and were unable to Costa Rican Deinopis populations was de-
elicit backward (aerial) strikes in their study signed to achieve two main objectives: 1) de-
93
94 THE JOURNAL OF ARACHNOLOGY
ultimate males and the rest were probably
penultimate females. Two were collected from
each site and were examined by Brent Opell,
who concluded that both populations probably
represent the same undescribed species. These
four specimens have been deposited in the
Museum of Comparative Zoology.
When observing nocturnal behaviors, we
used headlights with lenses covered by one
(first night) or two (subsequent nights) layers
of red cellophane. In order to determine
whether this species performs the backward
(aerial) attack, we tested six of the spiders
with a tuning fork stimulus (256 Hz) after the
method of Coddington & Sobrevila (1987).
The tuning fork was positioned about 10 cm
A
behind the capture-ready spider. series of
ten stimuli, five vibrating (experimental) and
five not vibrating (control), were presented in
alternating sequence to each spider with about
10 sec between successive stimuli. To observe
the form and timing of the transition from
nocturnal foraging behavior to diurnal cryptic
behavior, we commenced observing a spider
at about 0400 h, almost one hourbefore dawn.
Still photographs were used to document
cryptic postures.
PREY CAPTURE BEHAVIOR
The postures of capture-ready spiders and
the form of the webs (Fig. 1) were virtually
&
identical to those described by Robinson
— Robinson (1971) for D. longipes. All capture-
Figure 1. Deinopis spider at Las Cruces in for-
aging posture above leaf surface. ready spiders were suspended above living or
dead (lying on the ground) horizontal leaves.
The capture web was held either parallel or
termine whether these spiders perform back- perpendicular to the leaf surface, usually
mm
ward strikes, and, if so, what stimuli trigger about 15-30 above it.
such strikes; and 2) describe in detail the di- The first author’s exclamation upon discov-
urnal anti-predator behavior of these spiders. ering the first spider triggered a backward (ae-
METHODS rial) strike, and the short series ofexcited vo-
calizations that followed triggered three more
We observed Deinopis from 5-12 March such strikes in quick succession. Subsequent
1995 along trails in second growth forest at observations of other individuals confirmed
two locations in Puntarenas Province, Costa that this species, like D. spinosus (Coddington
Rica: 1) the Las Cruces Field Station of the & Sobrevila 1987) and two species ofAustra-
&
Organization for Tropical Studies near San lian deinopids (Austin Blest 1979), re-
Vito, and 2) above Rio Sierpe Lodge near the sponds consistently with backward strikes to
mouth ofthe Rio Sierpe on the Osa Peninsula. hums and other vocalizations generated from
The nine spiders observed in this study, four a distance of up to 50 cm or more.
from Las Cruces (spiders A, B, C, and D) and In the tuning fork stimulus trials (Table 1),
five from Rio Sierpe (spiders E, F, G, H, and 30 of the 40 presentations of a vibrating fork
I), were discovered at night in their prey cap- triggered strikes (all of which were backward
ture posture (Fig. 1). Two (A and I) were pen- strikes) and none of the 40 presentations of a
GETTY & COYLE—BEHAVIOR OF COSTA RICAN DEINOPIS SPIDERS 95
—
Table 1. Results oftuning fork stimuluspresen- hopper) we encouraged to walk on the sub-
tations to Costa Rican Deinopis spiders. See text strate below two different spiders. Both prey
for description ofprocedure. were wrapped but only the roach was eaten;
the grasshopper was eventually released (re-
No. of stimulus jected). Two spiders were observed feeding
presentations
(in their foraging position) on prey items. Spi-
Non- No. of strikes der A was feeding on a 6-7 mm long beetle
Series Vibrat- vibrat- Vibrat- Non- and spider E was feeding on a worker leaf
# Spider ing ing ing vibrating cutter ant (Atta). The latter, and probably the
1 A 5 5 5 0 former, would have been captured by forward
2 A 5 5 5 0 strikes. We observed spider A use its pedi-
3 C 5 5 4 0 palps to bat at a small fly (about 2 mm long)
4 D 5 5 5 0 that hovered and landed on the beetle;jerking
56 HE 150 150 63 00 mbeovreemseponntssesoftolethgissIpraonbdabIlIealksloeptaopppaeraarsietde.to
7 I 5 5 2 0
DIURNAL ANTI-PREDATOR BEHAVIOR
We observed spiders shifting from noctur-
non-vibrating fork triggered a strike. These re- nal to diurnal behavior 12 times over the
sults, in conjunction with the responses to vo- course of our study. Spiders A-D were each
calizations described above, show that air- observed doing this twice and spiders E, F, G,
borne sounds and/or accompanying air and I once each. We recorded the duration of
currents are sufficient to stimulate the back- this shift (from the onset of web takedown to
ward strike, and support the hypothesis that completion of the cryptic posture) only five
this mode of attack serves to capture flying times (B = 3-4 min, E = less than 1 min, F
insects. Like Coddington & Sobrevila (1987), = 28 sec, G = about 30 sec, I = 1.5-2 min),
we observed habituation (and/or fatigue) of but recollect that none of the other seven ob-
this response; the first strike of a series was served shifts took more than 5 min except for
the most energetic strike (spiders A, D, and E the time that spider A was feeding on a beetle
each performed two strikes in response to the at the onset of dawn. Web takedown, which
initial vibrating stimulus) and later strikes consisted of consolidating the capture web
were less energetic than earlierones in agiven and at least some ofthe support elements, ap-
series (spiders E, H, and I failed to respond to plying this package of silk to the mouthparts,
the last 4, 2, and 3 presentations). Candidate and apparently digesting it, took from 20 sec-
sensory mechanisms which may permit Dei- 3 min. The spider then quickly climbed to its
nopis to detect these airborne vibrations in- daytime resting spot by following a silk guide-
clude trichobothria and slit sensilla, both of line and, with no more than a brief period of
which have been shown to play this role in localized orientation and settling activity, as-
other spiders (Barth 1982). Receptor ablation sumed a cryptic posture. There was little vari-
experiments could be used to test these hy- ation in the time of day when this shift took
potheses. place; the time when a spider assumed the
The aerial strike is very quick, and it is cryptic posture ranged from 0455-0527 h
therefore difficult to observe and describe its (mean and SD = 0509 h ±18) for the 11 in-
mechanics without high speed movie or video stances when a spider was not feeding on
cameras. In general, though, these strikes prey. The single exception involved spider A,
closely resembled the description and photos which moved to its daytime site at 0504 h but
&
presented by Coddington Sobrevila (1987). continued feeding in a partially cryptic pos-
The spider’s prosoma rotated backward, up, ture well past daybreak and became fully
and away from the substrate as its snare was cryptic at 0542 h, much later than its shift to
expanded by extension of legs I and II. a cryptic posture the following day (0455 h).
We observed two forward strikes like those Perhaps the environmental cue which trig-
&
described by Robinson Robinson (1971) gers this shift is the increase of light intensity
and Coddington & Sobrevila (1987), each in to a particular threshold level or rate of in-
response to insect prey (a roach and a grass- crease at dawn; we were able to first detect
96 THE JOURNAL OF ARACHNOLOGY
increasing light at about 0455 h each morning. protracted posteriorly and apposed along the
It is also possible that the foraging-to-crypsis sides of and beyond the tip of the abdomen
shift is a circadian rythym entrained by day- so that the spider became a long slender stick-
length. The only other potential cue perceived like unit (Figs. 2-11). Sometimes the spider
by us was the predictable and rather sudden “settled” into this posture with regular wave-
onset of bird and howler monkey vocaliza- like undulations of its legs and body; at other
tions at about 0515 h, but these events were times the shift to this posture was more sud-
too late to account for most of the observed den and direct. While a given spider often hid
shifts and no mechanism has been demonstrat- at the same location for at least two consec-
ed in spiders fordetecting such distant sounds. utive days, it did not necessarily adopt the
Typically, as in D. spinosus (see Theuer same posture on the same substrate (compare
1954), the hiding site is close to the foraging Figs. 2 and 3 to Fig. 10). This plasticity in the
site; the distance between these sites was re- cryptic behavior of individual spiders is con-
corded for five spiders and ranged from 25- sistent with Robinson’s (1985) suggestion that
80 cm (mean and SD = 58 ±21). Some site concealment is a “preadaptation to plant part
tenacity was observed during our short study. mimicry.” An individual which is positioned
Spiders A, B, and C each foraged and hid in as in Figs. 2 and 3, so that part of its body is
the same locations forthe three nights and two camouflaged on a stick and part is mimicking
days they were observed. Spider D likewise a stick, may illustrate an adaptive intermediate
used the same foraging and hiding sites during evolutionary step between pure concealment
the two days it was observed. Spiders E and and pure stick mimicry.
G both moved to new but nearby sites during Several anatomical design features contrib-
the second day ofobservation. Only spiders F ute to camouflage and stick mimicry in this
and I moved so far that they were not found species: 1) The long slender body and legs
afterthe first day ofobservation. The presence produce a sticklike form, 2) the flat and pos-
ofsilk strands anchoring otherwise unattached teriorly truncate carapace and anteriorly low
pieces of vegetation which served as hiding and truncate abdomen lower the body profile
substrates suggests that these spiders some- and help conceal the transition from carapace
times improve their hiding sites (Fig. 2). to abdomen, and 3) the fringes of long setae
Behavior, anatomy, and pigmentation all proximally on the prolateral surface ofthe first
contribute to the remarkable diurnal crypsis of femora and at the anterior median edge ofthe
this spider. Assumption of the cryptic posture carapace fill and thus hide much of the gap
at dawn always involved attachment to a sub- between the femora (Figs. 4-6). 4) The tip of
strate, usually a linear plant structure (twig, each palpal tarsus curves prolaterally and the
vine stem, or petiole), typically a dead palpal claws are long, features that help these
(brown) (Figs. 2-9), less often, a living (even claws grip and hold the body against cylin-
green) one (Fig. 10). Most commonly the spi- drical substrates (Figs. 2, 3, 7, 8). The spider’s
der aligned its whole body and legs parallel variegated light to darkbrown pigmentpattern
to and against the substrate and appeared to closely resembles the coloration ofmany dead
become part of that substrate (Figs. 5-9), a branches, vine stems, and petioles (Figs. 2, 3,
strategy of camouflage or concealment (Rob- 5-9).
inson 1973, 1985). Less often, much or nearly When its body or its substrate is touched, a
all of the spider was positioned well away cryptic spider typically increases its crypsis
from the attachment substrate (Figs. 2-4, 10), by pressing its legs more tightly together and
and the spider mimicked a dead twig, relying against the body, and, if positioned against a
on disguise rather than concealment (Robin- substrate, by flattening itself more tightly
son 1973, 1985). Attachment to the substrate against that substrate (Figs. 5-8). Such a pos-
was typically via silk (spinnerets to substrate) ture adjustment can effect a dramatic im-
(Figs. 2-4) and usually by leg and/or palpal provement in crypsis; sometimes it makes the
claws as well (Figs. 2-10). Most spiders were spider temporarily disappear from view!
oriented head down (Figs. 5-11), but one was When we tried to grasp one cryptic spider, it
inclined in a slight head-up position (Figs. 2- dropped several cm from the substrate and be-
4). Always legs I and II were protracted an- came sticklike while hanging free and mo-
teriorly and apposed and legs III and IV were tionless in midair from its dragline (Fig. 11).
GETTY & COYLE—BEHAVIOR OF COSTA RICAN DEINOPIS SPIDERS 97
—
Figures 2-4. Deinopis spider C at Las Cruces; three views of spider in cryptic posture. Spider is
attached by the claws of legs I and II, palpal claws, and dragline (see arrow in Figure 3) to undersurface
of dead piece of stem or petiole which is suspended from a vine by silk (see arrow in Figure 2); 2, 3,
Side view; 4, View from below (arrow points to gap between front femora, which is partly filled in by
fringes of long setae on femora and caput).
98 THE JOURNAL OF ARACHNOLOGY
—
Figures 5-8. Deinopis spiderE atRio Sierpe; fourviewsofspiderfacingdownwardsincrypticposture
on dead stem. 5, 6, Dorsal views; 5, Posture before stem is touched by observer; 6, Posture after stem is
touched; 7, 8, Side views; 7, Posture before stem is touched by observer; 8, Posture after stem is touched.
Arrows point tojunction between prosoma and opisthosoma.
The defensive effectiveness ofthese behav- ing a roughly 20 X 20 X 20 cm cubical search
ioral and structural design features against vi- space containing the spider. None of the four
sual predators is suggested by how much more people presented with this challenge succeed-
difficult it is to find these spiders in daylight ed. We suspect that the key selective agents
than at night. Despite careful searching, we responsible for the evolution and maintenance
were unable to find these spiders by day; this of this suite of cryptic defensive traits are to
matches the experience of other authors with be found among diurnal insectivorous wasps,
other deinopid spiders (Akerman 1926; Baum lizards, birds, and monkeys.
&
1938; Robinson Robinson 1971; Codding-
ACKNOWLEDGMENTS
ton & Sobrevila 1987; Penney & Whitehead
1995). On six occasions (three different spi- This research was conducted during aWest-
ders) we asked a person to locate one of our ern Carolina University (WCU) Tropical Bio-
subject spiders during the daytime after defin- diversity class field trip funded in part by
GETTY & COYLE—BEHAVIOR OF COSTA RICAN DEINOPIS SPIDERS 99
—
Figures 9-11. Deinopis spiders at Las Cruces in cryptic postures; all facing downwards. 9, Spider R
in longitudinal depression on stem; 10, Spider C hanging from slender vine and holding to leafedge with
anterior leg tarsi; 11, Spider D hanging motionless from dragline after being forced to drop from cryptic
posture on plant.
WCU. Course participants, especially Karen LITERATURE CITED
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We
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