[Animals] Female spiders play dead during sex so males don't have to worry about being eaten

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Researchers have determined the cause of an unusual behavior in funnel weaving spiders that involves the females curling up as if they're dead before having sex.

Female funnel weaving spiders engage a bizarre behavior to mate: They play dead during sex so males are less worried that they might be eaten when the deed is done, a new study shows. That, in turn, makes it easier for females to choose the best mates, by playing dead for appealing partners and fighting off the scrubs.

Some funnel weaving spiders (also called funnel weavers and funnel web spiders) — a family of fast-moving, slender spiders that build their webs in a distinctive funnel shape — are known to engage in sexual cannibalism, when females kill and eat the males after the pair has finished mating. Naturally, this makes sex a much less appealing for the males, which are literally risking their lives every time they want to hook up. 

To get around this, some species have developed an unusual behavior known as sexual catalepsy, in which the female curls up its legs and stays immobilized as if it had died. This allows males to go about their business without having to worry about becoming a post-sex snack for the female.   

Researchers have known about sexual catalepsy in spiders for some time, but until now, it has not been clear if the females are voluntarily immobilizing themselves for the benefit of the males or if the males have some control over the behavior, either through some behavioral trigger or via a chemical cue.

To understand what was going on, researchers conducted experiments on funnel weaving spiders from the species Aterigena aculeata to compare sexual catalepsy with similar behaviors to see if it was controlled by males or females. Results were published March 21 in the journal Current Zoology(opens in new tab).

Related: Male spiders drum out mesmerizing syncopated beats to woo mates

During the experiments, the team observed A. aculeata females during one of three scenarios: engaging in sexual catalepsy naturally during mating; playing dead, also known as thanatosis, after being shaken in a test tube; and being put to sleep by anesthesia, to mimic a potential male-produced chemical cue. 

Afterward, the spiders were frozen to death and their bodies were ground up so the researchers could analyze the chemicals being used to coordinate the spiders' actions. This allowed the researchers to look for physical and chemical similarities among the behaviors. 

If sexual catalepsy closely mimicked thanatosis, it was probably being controlled by the female. But if it was more similar to anesthesia, then it suggested that it was not in the female's control and could have been influenced by the male, study co-author Mark Elgar(opens in new tab), an evolutionary biologist at the University of Melbourne in Australia, told Live Science in an email.

The results showed that sexual catalepsy appeared almost identical to thanatosis. Individuals that had experienced both behaviors had chemical profiles much more similar than those that had been anesthetized. 

This finding strongly suggests that sexual catalepsy is controlled by females and acts as a way for them to choose their mates, Elgar said. "Mating occurs only when the female enters sexual catalepsy, so if she doesn't behave that way, then mating doesn't proceed," he added.

Although the females may appear to be dead during the mating process, the males are fully aware that they are faking. Shortly after mating has finished and the male has backed away, the female will get up and scurry away. 

Sexual catalepsy also occurs in several other species of funnel weaving spiders, but it is too soon to tell if the technique works the same way across the rest of the group, Elgar said. "It isn't clear yet whether it has consistently evolved as a female mechanism of mate choice or a male mechanism of protection against sexual cannibalism," he added.

Playing dead is not the only behavior spiders use to escape sexual cannibalism. In April 2022, researchers revealed that males from Philoponella prominens, a type of orb weaving spider, use a catapult-like mechanism in their legs to immediately launch themselves away from females after they finished mating. 

link: https://www.livescience.com/female-spiders-play-dead-during-sex-so-males-dont-have-to-worry-about-being-eaten