1969] 
Robinson — Predatory Behavior 
499 
the distinct impression, that, in at least some of these cases, the 
spider was ignoring newly arrived prey. 
In a sense, the conditions of this experiment were purely arbitrary, 
and may never even be approximated under natural conditions. (We 
have ? however, records of large numbers of social insects being 
caught in short periods.) The experiment does show that Argiope 
can compensate for its (for small prey) much less efficient web 
under certain conditions. We also believe that immobilization wrap- 
ping, and the subsequent possibility of quickly leaving the prey in situ 
is the key to this success. 
Conclusion 
We feel that it is possible to reconstruct the possible steps in the 
evolution of immobilization wrapping by considering the behavior of 
existing araneid spiders. This process eliminates the necessity to ex- 
trapolate from the behavior of spiders of other families which may 
be very distant from the line of araneid evolution. The explanation 
we propose below also accounts for the existence of several forms 
of attack behavior in some of the araneids which have developed 
attack by wrapping. We offer an adaptive function for each step in 
the process and envisage the evolution of complex predatory patterns 
in araneids to have been additive. 
We propose the following scheme: 
Stage i. All prey overcome by biting. Prey pulled from the web in 
the jaws and carried to the hub where post immobilization 
wrapping occurs. This stage is not found in any araneid 
whose predatory behavior is described but is represented 
in the behavior of Nephila and Argiope to small prey. 
Function of wrapping at the hub: to prevent loss of prey 
during subsequent attacks. 
Figure 2. An additive scheme illustrating the stages in the evolution of 
prey wrapping by araneids as proposed by the authors. The model for 
each stage is simplified, behavior prior to arrival at the prey is omitted 
and the spider’s capacity to interrupt a sequence before the cut out stage 
is not shown. The circles represent a behavioral unit and where more than 
one arrow leaves, or enters, a circle the behavior may be followed, or 
preceded, by the behaviors indicated. Stage 1 is hypothetical, but occurs 
as part of Stages 2 & 3. Stage 2 represents the prey capture sequences of 
Nephila clavipes, and with the omission of free wrap is a model of the 
behavior of some species of Micrathena and G aster acantha. Stage 3 occurs 
in Argiope spp. and Eriophora sp., and may be typical of most “advanced” 
araneids. 
