The brown widow spider, Latrodectus geometricus C. L. Koch 1841, is non-native to North America and has experienced an explosive range expansion in the first decade of the 21st century. Previously restricted to peninsular Florida, it is now well established in the southeastern United States and southern California. In southern California, brown widow spiders have become ubiquitous around urban homes and are well known to the general public because of their high numbers and distinctive spiked egg sacs. Several insects attack egg sacs of the native western black widow, L. hesperus Chamberlin & Ivie 1935, as either parasitoids or egg predators. We investigated whether and to what degree these insects would attack brown widow egg sacs. We dissected 3,739 brown widow egg sacs finding evidence of the chloropid fly, Pseudogaurax signatus (Loew 1876) in 2.0% and wasp parasitoids in 0.4% of the sacs. For comparison, we also dissected 263 western black widow egg sacs with P. signatus showing a higher level of predation (6.1%). Other brown widow sac inhabitants included larvae and adults of dermestid beetles, psocids, and lepidopterans, which are probably scavengers or incidental occupants. The overall impact of the recorded predators and parasitoids is too low to explore the possibility of a biological control program. Additionally, due to the relatively low number of predators/parasitoids in brown widow egg sacs and the entanglement of small arthropods on the outer surface, we speculate that the spiked egg sac surface might serve as an effective barrier to most predators and parasitoids.
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Vol. 40 • No. 2