1977] 
Tolbert — Orb Weaving Spiders 
25 
vulnerable to predation, especially since they do not have the pro- 
tection a web affords (Tolbert, 1975). Some spiderlings probably 
starve during this time also (Tolbert, 1976). 
Spiderlings underwent a radical change in behavior toward con- 
specifics after dispersing from the communal tangle. As long as 
the spiderlings were on the communal tangle they were completely 
tolerant of one another and during hot sunny periods clustered very 
closely together. However, after a spiderling constructed an orb 
web it attacked and ate any prey that contacted the web. Litter- 
mates were invariably attacked and treated as prey items when they 
encountered or were placed on conspecific’s orb web. However, it 
is unnecessary for spiderlings of either Argiope species to engage in 
aerial dispersal before building an orb web. I have successfully 
reared both species in the laboratory after removing them from 
egg sacs. After building their first orb web and without the benefit 
of living on or building a communal tangle or engaging in aerial 
dispersal, Argiope spiderlings still attacked and killed littermates 
placed on their orb webs. 
Although Enders (1972) indicated he has observed unsuccessful 
ballooning attempts by mid-instar Argiope aurantia, my observa- 
tions indicate that only the emergent (first instar) disperses aerially. 
Summary 
Although both species are capable of all the behaviors in the 
ethogram (Figure 1), Argiope aurantia, possibly by virtue of their 
higher, more exposed egg sac locations, generally dispersed shortly 
after emergence from the egg sac. Argiope trifasciata produced 
communal tangles and engaged in preaeronautic behaviors on these 
structures before dispersing. 
In 1975, both spider species ballooned when their estimated body 
temperature exceeded 26° C, with most dispersal occurring when 
body temperatures were between 33° and 38° C. A vibrational stim- 
ulus occurring when spider body temperatures are above 26° C re- 
sulted in climbing behavior by the mass spiderlings on the com- 
munal tangle. Upon reaching the top of a promontory they either 
became airborne from that point or dropped on a dragline and 
ballooned from that position. Spiderlings ; ballooned at relatively 
low wind speeds (0.5 m/s). Multiple ballooning bouts were ob- 
served for some individuals. It is* hypothesised *1tet aerial dispersal 
serves to rapidly space spiderlings oveFiavailaWe' Habitats such that 
