THE PREDATORY BEHAVIOR OF 
SOME ARANEID SPIDERS AND THE 
ORIGIN OF IMMOBILIZATION WRAPPING* 
By Michael H. Robinson, Heath Mirick and Olga Turner 
Smithsonian Tropical Research Institute, P.O. Box 2072, 
Balboa, Canal Zone (Panama.) 
The evolution of predatory behavior in web building spiders is 
a subject of considerable interest. Functionally the spider has to solve 
two problems immediately after prey strikes the web. It has to locate 
the prey and then to attack it in such a way that the prey is prevented 
from escaping and is subdued. The spider may then be confronted 
with further problems involved in freeing the prey from the web 
and in transporting it to a feeding or storage site. Spiders may attack 
solely by biting, may bite some types of prey and wrap others in silk, 
or may rely entirely on silk as an attack weapon. Silk may also be 
used, after the initial attack, at other stages in the process of prey 
capture. Eberhard (1967) has reviewed the possible stages in the 
evolution of the use of silk for attack. By comparing the uses of 
silk in the predatory behavior of several representatives of a number 
of families of web building spiders he arrived at the conclusion that 
immobilization by wrapping in silk is derived from post immobiliza- 
tion wrapping. We fully agree with his conclusions but feel that a 
comprehensive treatment of the subject requires a more detailed 
consideration of the uses of silk by araneid spiders. Araneids may 
use the wrapping process at four different (and in all probability, 
functionally distinct) stages in the prey capture sequence. Further- 
more, the behavioral components of the wrapping process are not 
necessarily common to all four cases. If these facts are considered, 
the picture of the evolution of wrapping behavior by web building 
spiders becomes more complex than Eberhard (ibid) assumed. 
This paper examines data on the predatory use of silk by Nephila 
clavipes (Linnaeus), Argiope argentata (Fabricius), A. savingnyi 
Levi and A. floridci Chamberlin & Ivie, as well as other araneid 
spiders. In addition, we report on an experimental investigation into 
the functional efficiency of two basic attack strategies used by these 
spiders. We finally propose a scheme by which complex predatory 
repertoires can be derived from simpler ones by an essentially additive 
process. 
* Manuscript received by the editor August 22, 1969 
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