46 
Psyche 
[March 
aurantia vs. trifasciata 
The responses of A. aurantia and A. trifasciata to dorsal presenta- 
tions and of A. aurantia and A. trifasciata to ventral presentations 
were analyzed separately. The two species differed significantly 
(n = 138, x 2 = 33.i, p < 0.005) from one another in their re- 
spective responses to dorsal presentations of the simulated predator. 
Switching sides of the web and this component followed by web 
flexing occur more frequently in A. aurantia than A. trifasciata. A. 
trifasciata either failed to respond or rebuffed the model with greater 
frequency than expected (compare figs. 4B and 5B). Responses to 
ventral presentations of the model were also significantly different 
(n = 138, x 2 = 38.3, p < 0.005) for the two species. Differences 
in web flexing accounted for over 75% of this variability and dif- 
ferences in this component alone were sufficient to produce a sig- 
nificant difference (p < 0.005) between the responses of the two 
species. A. aurantia web flexed significantly more often than A. 
trifasciata. 
Component differences of instars 
Since behavioral responses may change with the age or instar of 
the spider due to maturation, learning, perceptual abilities or other 
factors, juvenile instars 4, 5 and 6 and adult female (instar 10) 
A. trifasciata, were examined for possible differences in predator 
avoidance. When the simulated predator was presented dorsally there 
was a significant difference (n = 61, x 2 = 41.4, p < 0.005) in 
response components. Dropping and moving away from the hub were 
primarily juvenile responses while rebuff and failure to respond were 
adult responses (fig. 5). Juvenile responses also contained more 
components than adult responses. It should be noted that adult fe- 
male A. trifasciata are large enough to ward off the salticid species 
common in the area, since the salticid populations are primarily repre- 
sented by eggs and juveniles at this time; male salticids have died 
and females spend much of their time guarding eggsacs and young. 
This may account for some of the differences observed. Data were 
insufficient to compare ventral presentations statistically, but the rela- 
tive frequencies of occurrence of various components are shown in 
fig. 6. 
Both species are thus capable of a broad array of responses that 
enable them to escape predation on their relatively exposed webs. 
These responses may also be important in avoiding predatory wasps 
and other predators and parasites. It is not claimed that the responses 
discussed here represent the complete repertoire of the two species. 
