1977] 
Tolbert — Orb Weaving Spiders 
19 
when their body temperatures were above 26° C, and their preferred 
range was virtually identical to that of Argiope trifasciata (Figure 
5). Seventy-four percent of A. aurantia spiderlings dispersed when 
their body temperatures were between 33° and 38° C. A disturbance 
(gust of wind, striking the vegetation to which the communal tan- 
gle is attached, striking the tangle itself, and fanning the cluster of 
spiders directly) resulted in spiderling movement on the tangle. The 
nature of the disturbance seems to be vibrational and subsequent 
movement by spiderlings on the interlocking mass of silk threads 
of the communal tangle appeared to reinforce the initial disturb- 
ance. When a sufficient disturbance occurred and spider body tem- 
peratures were 26° C or higher, the spiderlings climbed to the top 
of any available object, usually vegetation. Spiderlings followed 
one another in mass to the top of a promontory where they pre- 
pared to disperse. Neither disturbance nor elevated temperature 
by itself was sufficient to trigger climbing behavior of A. trifasciata 
(Figure 1). By monitoring spiderling body temperatures on the 
communal tangle (spiderlings of eight Argiope trifasciata egg sacs 
in 1975), it was apparent that the spiderlings often experienced tem- 
peratures within their observed dispersal range (26° -42° C), but did 
not disperse. This was also evident by the time of residency on 
communal tangles during sunny periods (Table 1). Striking the 
vegetation near the tangle or fanning the cluster of spiderlings 
during times when body temperatures equalled or exceeded 26° C 
invariably induced climbing. Similar stimulation at body temper- 
atures of less than 26° C failed to produce climbing behavior. 
In April 1976, two additional clusters of A. trifasciata spiderlings 
were tested. Even when body temperatures exceeded 26° C and a 
vibratory stimulus was applied, these spiderlings could not be in- 
duced to climb and disperse. While these findings might simply be 
abberations or due to some genetic differences between populations 
between the two years, or to some microclimatic variables which 
were not examined, it seems likely that developmental differences 
between the spiderlings which emerged in May and those in April 
may account for the observed difference in behavior. 
A. trifasciata overwintered as eggs and the active spiderlings did 
not develop until April (Tolbert, 1976). A difference of as much 
as one month to six weeks in the developmental age of spiderlings 
could influence behavior. It is possible that the older spiderlings 
would be more prone to dispersal behavior than younger spider- 
