Predators and parasitoids of egg sacs of the widow spiders, Latrodectus geometricus and Latrodectus hesperus (Araneae: Theridiidae) in southern California

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...