Defensive behavior of the black widow spider Latrodectus hesperus (Araneae: Theridiidae)

Summary

When threatened, the black widow spider, Latrodectus hesperus, emits an adhesive, viscous web, pulls the strand from its spinnerets with its fourth pair of legs, and spreads its appendages. This behavior positions the web over the delicate abdomen, increases the area of protection, and enables the spider to place the web onto the offender, if necessary.

In laboratory interactions, the viscous web protected black widows from mice (Peromyscus spp.). Mature female spiders, which had their spinnerets blocked and hence could not discharge the viscid silk, escaped less often than did black widows that were not experimentally altered.

The viscid silk is palatable to mice and it appears that the deterrent effect of the web is due solely to mechanical irritation.

The defensive behavior is elicited most often from mature females, which may suffer greater predation than other age groups. Males lose the ability to produce the defensive web at maturity and may shift their energy resources totally into reproductive effort.