Males are Home-Wreckers: Black Widow Spiders Eat Females' Webs

Males are homewreckers-at least when it comes to black widow spiders. Scientists have found that the male spiders actually destroy large sections of the female's web during courtship and wrap it up in their own silk to deter male rivals.

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

"The silk pheromones that female black widows produce are like scent-based personal ads," said Catherine Scott, the lead author of the new study, in a news release. "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."

As many as 40 male suitors may arrive at a female's web in one night. That's why males have developed ways to fend off competition. In this case, the researchers found that males actually cut female webs and buddle them up. This causes other males to be less likely to pursue those females.

"One possibility is that the female pheromone is concentrated in certain areas of the web, and males are bundling up those specific sections with silk, which stops the pheromone from being released," said Scott. "The males could also be adding their own pheromones, which rival males avoid. We didn't find evidence for a male silk pheromone in these experiments, but it's definitely something we want to investigate further."

The findings reveal a bit more about black widows. This, in turn, may tell scientists a bit more about the evolution of spiders and their mating behavior.

The findings are published in the journal Animal Behavior.

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