Abdominal Spines on an Amazonian Spiny Spider (Micrathena schreibersi): A Defense Against Mud-Dauber Wasps (Sceliphron spp.) Attack?

Abstract

The conspicuous abdominal spines in females of Micrathena spiders have evolved independently in several species within the genus. Like other orb-web spiders, Micrathena species can serve as prey to parasitoid mud-dauber wasps, which paralyzes the spiders and inserts them into their nests to serve as food to their larvae. Based on this fact, some studies suggest that Micrathena spines evolved as an antipredator defense against the wasp. However, there is no direct evidence of how the spines could act to avoid the wasp behavior. Here, we present two distinct records involving an Amazonian species of spiny spider, Micrathena schreibersi, where the abdominal spines act as a mechanical barrier against mud-dauber wasps (Sceliphron spp.). These spines prevented the wasps from completely inserting the paralyzed spiders into their tubular nests, forcing the wasps to alter the opening shape to close it. In our second record, the wasp was not able to completely close the nest, leading to predation of her offspring by ants. We discuss the ecological implications of this potential defense trait for both species and propose future hypotheses to further elucidate how these spines may have evolved based on the foraging behavior of mud-dauber wasps.