1975] 
Tolbert — Avoidance Behavior in Orb Weavers 
47 
As previously mentioned, leaving the web site does occur in some 
instances. I have also observed “death feigning” by one adult female 
A. aurantia when I rapidly approached her web. The individual 
dropped into the vegetation and all legs were drawn in close to the 
body. The spider’s venter was exposed as it lay on its back and the 
spider remained motionless for several minutes. No color change 
such as that reported for Gea heptagon (Hentz) (Sabath, 1969) 
was detected. 
Response Threshold 
The response threshold is operationally defined here as the number 
of stimulus applications (model presentations) needed to elicit a re- 
sponse of any kind (one component or a sequence of components) by 
the spider. If 10 stimulus applications failed to produce a response, 
“no response” was recorded. 
Dorsal vs. ventral ?nodel presentations 
Intuitively it would seem that a spider approached from the ventral 
side would be safer from predators since the web constitutes a physi- 
cal barrier. Response threshold, in addition to response components, 
thus might differ with orientation of model presentation. When this 
parameter was tested for A. aurantia and A. trip as data, they exhibited 
significantly different response thresholds to ventral vs. dorsal pre- 
sentations of the model ( A . trifasciata n= 189, x 2 = 11.1, p< 
0.05 ; A. aurantia n — 95, x 2 = 17.2, p < 0.005). Both species were 
more responsive to the dorsal than the ventral model presentations. 
aurantia vs. trifasciata 
I found no significant difference in response thresholds (n — 284, 
x 2 — 10.5, p < 0.05) between the two species. Thus, while predator 
avoidance behaviors are utilized to different extents, the readiness to 
respond apparently does not differ in these two species. 
A ge differences 
A. trifasciata instars 4, 5, 6, 7 and adult females were tested for 
differences due to age. No significant difference (n = 176, x 2 = 
48.8, p < 0.05) among instars was revealed. 
Differences to repeated model presentations 
Finally I wanted to know if there were differences in the response 
thresholds in individuals undergoing successive trials. I applied four 
series of model presentations to the same individual with a 30 second 
pause at the end of each response sequence. There was no significant 
