Wolf spiders weave a tangled web of birth control

August 29, 2017, 10:03 a.m.
Portrait of a wolf spider magnified 10 times
Photo: mandritoiu/Shutterstock

Birth control and monogamy can be controversial topics for us humans, and it seems wolf spiders feel the same way.

The sexual escapades of wolf spiders involve long-lasting mating sessions, sometimes with multiple partners at the same time. To reap the benefits of multiple partners, however, females from the species Schizocosa malitiosa have evolved to rid their bodies of large amounts of deposited sperm. The result? A clutch of eggs with many different fathers and more genetic variation.

These female wolf spiders store sperm for about a month before they fertilize a clutch of eggs. To see the the differences in the amount of sperm females used, researchers compared the levels found in females in the wild and dead females that they warmed up a little bit and induced males to copulate with in a lab. Icky, yes, but anything for science, we guess. (It also helped that playing dead is a common flirting technique among these wolf spiders.)

Female spiders in the wild would apparently reduce the amount of sperm deposited by a single male down to only 17 percent of what was observed in the lab. Scientists aren't sure how females are getting rid of it, though. They think the spiders could be absorbing it as nutrition, expelling it from their bodies or simply killing it off inside their bodies somehow.

The males of the species seem to be aware of this behavior, however. A 2006 study found that males sometimes surround their sperm with droplets of some kind that make the female less receptive to other males, perhaps in an effort to counter the female's free love approach to sexual reproduction.

It would appear that in the world of wolf spiders, all is fair in love and sex.

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