The Predatory Behavior of Some Araneid Spiders and the Origin of Immobilization Wrapping

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 rom escaping and is subdued. The spider may then be conronted 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 a.ttack weapon. Silk may also be used, after the initial attack, at other stages in the process o prey capture. Eberhard (967) has reviewed the possible stages in the evolution of the use of silk or attack. By comparing the uses of silk in the predatory behavior o 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 immobilization wrapping. We fully agree with his conclusions but eel 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, unctionally distinct) stages in the prey capture sequence. Furthermore, 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 w.eb building spiders becomes more complex than Eberhard (ibid) assumed. This paper examines data on the predatory use o silk by Nephila clavipes (Linnaeus), Argiope argentata (Fabricius), A. savingnyi Levi and A. florida Chamberlin & Ivie, as well as other araneid spiders. In addition, we report on an experimental investigation into the unctional efficiency o 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.