136 
Psyche 
[September 
would be the ‘apparent’ bulk of the prey beneath the spider during 
the prey-removal process. Our aims proved to be extraordinarily 
difficult to achieve and the results, although suggestive, are not 
convincing. In an attempt to manipulate the bulkiness of a series 
of presentations of butterflies ( Anartia sp.) we trimmed the wings 
of half of them down to small (5mm long) stubs. We then matched 
the weights of pairs of intact and mutilated specimens and presented 
the pairs, successively, in random order to the spiders. Only the 
intact insects elicited any free wrap behavior, and only 24% of 
these were so treated. This result is not statistically significant. If 
the number of free wrap occurrences is compared not with the total 
number of presentations of intact butterflies, but with that number 
less the number wrapped in situ or subjectively scored as presenting 
below average bulk on removal from the web, the result is signifi- 
cant. However this depends on our subjective assessment of the 
bulk and is unsatisfactory. 
These results do not enable us either to accept or reject, with 
confidence, the hypothesis that the free wrap response is related to 
the bulkiness of the prey after its removal from the web. We 
have yet to design an adequate test for this. 
Discussion 
A number of features of the predatory behavior of Nephila clavipes 
are of interest from the comparative standpoint. The most im- 
portant of these, in our view, are the total reliance of the species 
on biting, as an attack strategy, and the fact that the spider does 
not store prey in the web at the capture site. Both these features 
represent marked differences from the behavior of araneids belonging 
to the genera Argiope, Araneus and Eriophora. Reliance on attack 
(immobilization) wrapping, as the principal means of attack, prob- 
ably extends to a much greater number of araneid genera. 
These aspects of the predatory behavior of N. clavipes have been 
discussed in some detail by Robinson, Mirick & Turner (1969). 
These authors suggested that “advanced” spiders would obtain at 
least two advantages from the addition of immobilization wrapping 
to their behavioral repertoire. They would be enabled to attack 
large and/or dangerous prey without closing to the potentially 
dangerous contact distance involved in biting, and also could achieve 
a considerable economy in time spent at the capture site in subduing 
the prey. The bite & back off attack behavior, that we have de- 
scribed for N. clavipes , immediately suggests to the observer that 
it is a danger-avoiding device. Our experiments on the stimuli that 
