1977] 
Tolbert — Orb Weaving Spiders 
23 
WIND SPEED (meters/second) 
Figure 6. Number of Argiope trifasciata ballooning as a function of windspeed. 
a normal resting attitude. Spiderlings did not disperse at wind- 
speeds of greater than 0.9 m/sec. (Figure 6). Richter (1971) showed 
that Pardosa purbeckensis had preferred windspeeds for dispersal 
which were related to their body sizes; larger spiders preferred 
greater windspeeds. All size classes, however, preferred wind veloc- 
ities between 0.35 and 1.70 m/sec. These values exceed those ob- 
served for Argiope trifasciata, which is a slightly larger spider than 
Pardosa purbeckensis . From their study of spiders on Frisian Is- 
land (the Netherlands) Van Wingerden and Vugts (1974) concluded 
that aeronautic behavior ceased when the wind velocity at 2 m above 
the substrate exceeded 3.0 m/sec. They also found in the same 
study that unstable air masses near the ground and at dispersal 
height served as stimuli to aeronautic behaviour. Disturbances 
(wind gusts) apparently function in a similar fashion for Argiope 
trifasciata . 
After a spiderling becomes airborne it will travel on wind cur- 
rents until deposited at a potential web location. The spiderling 
may then build a web, or move a short distance from the deposi- 
tion site (perhaps searching for a site of better potential for web 
construction), and then build a web (Figure 1). It might also re- 
balloon with or without “searching behavior.” Data on the relative 
