i8o 
Psyche 
[June 
the araneids, so their attack behavior is intermediate between that 
of the diguetids and that of the araneids. 
The family Diguetidae is probably far from the evolutionary lines 
leading to the Araneidae and Uloboridae, but it is almost certain 
that some of the same selection pressures acted on animals in all of 
these lines as they became adapted to life in aerial webs. Thus it 
seems reasonable to suggest that the evolution of wrapping behavior 
in the orb weavers may have included steps similar to the behavior 
of the diguetids. This is not certain, however, as I have observed 
some spiders IHersalia sp. ( Hersiliidae) , Filistata arizonicus (Fili- 
statidae), and Oecobius sp. (Oecobiidae)] which perform immobiliza- 
tion wrapping and which live on (or near) the ground. The 
ancestors of the araneids and/or the uloborids may have had the 
ability to wrap prey even before they began to build aerial webs. 
In summary, the steps from post immobilization wrapping to im- 
mobilization wrapping are not large, and intermediate behavior can 
be found. The elicitation of wrapping in diguetids by the presence 
of new prey in the web suggests that wrapping may have originated 
as a post-immobilization process designed to free the spider for new 
attacks, and only later devolved into a means of attack. 
The possible stages of evolution of attack behavior, coupled with 
stages of web evolution (Kaston, 1966/ are summarized below. 
1. Prey is overcome by holding and biting, no trapping web is 
spun (Theraphosidae, Clubionidae, Salticidae, many others) 
2. Low-lying trapping webs are built, prey are subdued by holding 
and biting (Agelenidae, Plectreuridae) 
3. Aerial trapping webs are built, prey are overcome by holding 
and biting and are wrapped to prevent their loss during sub- 
sequent attacks (Diguetidae, Linyphiidae) 
4. Aerial trapping webs are built, prey are overcome by biting 
and wrapping (Araneidae, Theridiidae) 
5. Same as 4 except prey are overcome exclusively by wrapping 
(Uloboridae) 
References 
Baerg, William J. 
1958. The Tarantula, Univ. of Kansas Press, Lawrence, p. 15. 
Barrows, W. M. 
1915. The reactions of an orb-weaving spider, Epeira sclopetaria 
Clerk, to rhythmic vibrations of its web, Biol. Bull. 29: 316-32. 
