D3446: Flexible foragers: Candy-striped spiders prey on sleeping insects

Enoplognatha ovata is a medium-sized theridiid spider introduced to North America from Europe, and common on the West Coast. Much-studied because of its striking colour polymorphism, its natural history has attracted little interest. Indeed, we assumed these candy-striped spiders to be uninteresting ourselves until we began to observe their remarkably flexible predation behaviour during nocturnal observations of black widow spiders on Vancouver Island, BC. By day, candy-striped spiders engage in the web-based ambush predation typical of theridiids. They build inconspicuous tangle-webs on flowering plants and capture crawling or flying arthropods that touch their silk, and they also occasionally engage in araneophagy and kleptoparasitism in neighbouring spiders’ webs. By night, however, we found that the candy-striped spiders leave their webs to climb nearby vegetation and launch sneak attacks on sleeping insects, particularly bees and wasps. This marauding behaviour allows the spiders to capture even well-defended prey many times their own size. Here we present data from 14 days of sampling at our field site, documenting the diversity and abundance of prey taken by spiders using each foraging tactic. Candy-striped spiders appear to be extremely effective predators of a broad range of arthropods, and at our field site their diet is dominated by flower-visiting insects. The extent of this introduced predator’s impact on the mortality and behavior of pollinators in North America remains to be determined.