Male Brown Widow Spiders Prefer Having Sex With the Females Who Are More Likely to Eat Them

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Male brown widow spiders seek to mate with older, less-fertile females that are more likely to eat them after sex. Lara Sandomirsky

The animal kingdom is home to all manner of weird and wonderful sexual behaviors. From the tiny Australian marsupial that has so much sex in a period of a few weeks that it dies of exhaustion to the Japanese snow monkeys that like to rub their genitals against deer, nature knows no bounds when it comes to the act of procreation.

Now, new research, published in the journal Animal Behaviour, has revealed the bizarre—and slightly morbid—sex lives of brown widow spiders, Latrodectus geometricus.

In this species, the males can either mate with immature but fertile females—which are capable of producing viable offspring—or more mature, less-fertile females, which often cannibalize their partners after copulation.

The researchers from Ben-Gurion University of the Negev, the Hebrew University of Jerusalem and the Volcani Center in Israel found that male brown widow spiders prefer to mate with older, less-fertile females over younger individuals, despite the fact that they are 50 percent more likely to be eaten.

To obtain their findings, the scientists collected male and female brown widow spiders from central and southern Israel, placing individuals of both sexes together in situations where the males had a choice of whether to approach immature or mature females. Then they observed what happened.

"We originally thought the males would prefer the subadult females, as they are more fertile and far less likely to cannibalize them, but we were surprised to discover that was not the case," Shevy Waner from the Hebrew University of Jerusalem said in a statement.

The researchers could find no evolutionary benefit for the males choosing to mate with the older females. The males' choice produces fewer offspring overall because the mature females are less fertile, and it also means that they cannot go on to procreate with another female because they are often eaten.

This led researchers to suggest that the older females were seducing the males through seemingly unscrupulous means.

"One possible explanation is that older females are manipulating the males by using strong [pheromone] signals to attract them, a hypothesis that remains to be tested," Warner added.