The Strange Courtship of Black Widow Spiders

Male black widow spiders destroy large sections of the female’s web during courtship and wrap it up in their own silk, according to a recent article in Entomology Today. New research published in Animal Behaviour shows that this home-wrecking behavior does deter rival males, by making the female’s web less attractive to them.

Black Widow Spiders: Did You Know?

Surprisingly, the females don’t seem to mind the destruction. The authors of the study, from Simon Fraser University in Canada, say the males’ behavior could protect the female from harassment, thus enabling her to get on with her parenting duties.

The western black widow spider, Latrodectus hesperus, is native to western North America. Female black widows are around 15mm long and black, with a distinctive red hourglass-shaped mark on the abdomen. The male is much smaller, with a lighter tan color and a striped abdomen. Black widows build messy webs, which they use to communicate via vibrations and pheromones.

Catherine Scott, lead author of the study, said “The silk pheromones that female black widows produce are like scent-based personal ads. One whiff of the pheromone can tell a male about the age, mating history and even hunger level of the female. These complex chemical messages are just one part of the spiders’ communication system, and web reduction is a fascinating behavior that allows a male to interfere with a female’s message.”

Scary as it may sound, competition for females is fierce with as many as 40 male suitors arriving at a female’s web in just one night. Because of this, males have developed ways to fend off the competition, such as guarding females and applying mating plugs. The new study shows for the first time in the wild that destroying the female’s web is one such behavior, as it makes the web — and therefore the female — less attractive to other males.

It may seem strange that female black widows tolerate the destruction of their webs; they generally remain passive during web reduction. This could be because the behavior is helpful to the females, say the researchers. A female only needs to mate once to have all her eggs fertilized, but an intact web will keep sending out attractive pheromone signals to potential mates for another week. Web reduction could actually be saving the female from being harassed.

“Courtship in black widows is an hours-long affair, so several additional males may arrive at a web before the first male manages to copulate,” said Catherine. “By reducing the web, the male is not only reducing his chances of competing with other males, he might also be doing the female a favor. Web reduction may be giving her the opportunity to rebuild her web without pheromones and get on with reproduction, rather than wasting time and energy chasing away a parade of redundant male suitors.”

If you’ve seen Black Widow Spiders around your home or property, give Bug-N-A-Rug Exterminators a call at 910-754-9700 and we’ll come out for a home inspection.

Learn more about Black Widows and other Common Spiders that we help to deal with in our Spider Facts page.

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