|MadSci Network: Zoology|
I have been unable to find exact references on this (although there may be some), but I can offer the following observations. Certainly not all pholcids (daddy-long-legs spiders- which are not true daddy-long-legs) attack other spiders. Those in the common genus Psilochorus appear to often be peaceful inhabitants of other spider's webs, including black widows. Dan Jennings, a retired arachnologist who still works on pholcids, tells me that this live and let live attitude of Psilochorus is not found in its larger cousins in the genus Physocyclus. These spiders actively seek out black widows and other web-building spiders, attack and kill them. From my own experience I can say that I have a shed full of Physocyclus and no black widows, although the latter can commonly be found around the yard. References: (Only for association of Psilochorus and other spiders) Gertsch, W. J. 1979. American Spiders. 2nd ed. Van Nostrand Reinhold, New York.
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