Lying For Sex, Spider Style

In order to mate, males of many invertebrate species must present a nuptial gift to the female before she will acquiesce and let their relationship move to the next step. Male nursery web spiders (Pisaura mirabilis) usually present an edible insect wrapped up in spider silk. But some guys are sneaky. They wrap up a useless gift, such as an inedible plant seed or the empty exoskeleton left after he’s eaten a fly. (And if his chosen female tries to steal his gift without mating with him, the spider can play dead, letting him stay near her for longer and continue the mating.)

But there’s a downside to a male’s sly behavior, scientists found in a new study published in BMC Evolutionary Biology. Offering a gift of any kind, either real or fake, was more likely to lead to a spider getting some nooky, but males that presented a yummy treat were able to spend more time mating, and more time transferring sperm, than the guys who tried handing over a counterfeit contribution. “The females are wise to the deception and terminate mating early for worthless gifts,” says the study’s lead author, Maria Albo of Denmark’s Aarhus University.

Females may detect the liars, but it turns out that lying doesn’t have any bad consequences when it comes to fathering baby spiders. “The final results show that the number of eggs hatching was lower if the female had not received a gift,” Albo says, “but there was little difference between females who had received an edible or inedible gift.” And because both strategies–giving a real gift and passing a fake one–result in a successful transfer of a male’s genes to the next generation, evolution apparently hasn’t favored one over the other.

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Sarah Zielinski is an award-winning science writer and editor. She is a contributing writer in science for Smithsonian.com and blogs at Wild Things, which appears on Science News.