The invasive brown widow spider is less often parasitized by egg sac parasitoids than native widow species

Abstract The brown widow spider ( Latrodectus geometricus , Theridiidae) is invasive globally. Of the 35 known widow spider species, the brown widow is the only one that has spread nearly worldwide, and its range continues to expand. Despite the species’ widespread success, it remains unclear which factors enable it to invade and thrive in new environments. Possible explanations include its preference for urban environments and superior defenses against natural enemies, particularly parasitoids. Egg sacs of widow spiders are commonly targeted by parasitoid wasps, which lay their eggs inside the sac, and their larvae consume the spider eggs. In the current study, we compared parasitism rates on L. geometricus egg sacs with three widow spider species that partially overlap in distribution with L. geometricus in Israel: a Mediterranean species, L. tredecimguttatus , and two desert species, L. revivensis and L. pallidus . We collected spider egg sacs from 20 sites across the country and incubated them until either spiderlings or wasps emerged. The results indicate that parasitism rates were indeed higher in egg sacs of the native species (~ 5–40%) than in those of L. geometricus (< 1%). The lower susceptibility of L. geometricus to parasitism may at least partially explain the success of the invasive spider relative to native widow spider species in the invaded range.