Why do black widows eat their mates? Is there an evolutionary advantage?

The Wild File: Black Widows

Western black widow     Photo: Photograph by Paul Ollig/NPS

Western black widow

Western black widow

A. They don't at least, not with any more enthusiasm or frequency than other arachnids. Like most spiders, the black widow is a web builder, and the females are larger than the males. Also like most spiders, widows are predators that eat only living things. (Hence their much-fussed-about poison, a neurotoxin that can cause mild paralysis in mammals, including some humans.) So if a male comes poking around the web at mating time and his lady is hungry, there's a chance he'll provide her with more than sperm. If the male scores a well-fed widow, he'll probably escape. An exception to this rule: the Australian redback, a member of the black widow genus. The male redback has developed a taste for rough, sacrificial sex, flipping his bare abdomen into the hungry female's mouth during mating. Researchers at the University of Toronto discovered why: A male who offers himself to his mate scores more time in the sack, increasing his chances of passing on genes.

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