4 8 
Psyche 
[March 
difference in either A . aurantia (n = 18 spiders, x 2 = 5.04, P < 
0.05) or A. trifasciata (n = 8 spiders, x 2 = 4.03, p < 0.05) for 
dorsal or ventral model presentations. The spiders apparently ex- 
hibited neither habituation to the stimulus nor increased sensitivity 
under these test conditions. 
Response Duration 
Since the duration of several response components could vary with 
the particular test situation, I analyzed the variability of the web 
flexing response in this context since it is an easily measured com- 
ponent. Response levels were grouped into four categories: 0-10, 
11-30, 31-120 and >120 seconds. These levels were chosen such 
that the expected values would be large and the test thereby more 
rigorous (Conover, 1971). Response duration of web flexing to 
dorsal vs. ventral presentations of the model were not significantly 
different (p < 0.05) for either A. aurantia (n = 56) or A. trifas- 
ciata (n = 45). The mean web flexing duration was 39.71 zb 10.52 
and 44.27 zb 12.72 seconds respectively, for the two species. Thus 
the apparent variability existed in the ranges of response duration, 
but was not associated significantly with the test situation. 
Discussion 
In this study, barrier webs and stabilimenta were found to com- 
plement the predator avoidance behaviors of A. aurantia and A. 
trifasciata. It is interesting that these two closely related species with 
sympatric populations should also employ barrier webs and stabili- 
menta to such markedly different extents. Recall that A. aurantia 
switched sides of the web with much greater frequency when ap- 
proached dorsally or touched on the dorsum than A. trifasciata. This 
behavioral difference may be related to the more extensive use of 
stabilimenta by this species. A. trifasciata, on the other hand, has a 
thinner hub which more easily permits viewing the spider, and use 
of other predator avoidance behaviors or web structures, such as 
barrier webs, may better enhance survival. It is also noteworthy that 
A. aurantia web flexed to a significantly greater extent when the 
simulated predator was presented ventrally than A. trifasciata. Web 
flexing, in addition to adding motion to the potential predator’s at- 
tack problem, might give the stabilimentum some shock value. Web 
flexing and the stabilimentum may act synergistically as a threat 
stimulus. Salticids are known to respond to a wide variety of shapes 
and patterns (models) as though they were prey items. If the models 
