Of all the insane mating behaviors in the natural world—and boy, are there some weird ones—few are more gruesome than sexual cannibalism. This behavior is widely seen in insects and arachnids, and involves the female eating her mate after they copulate, and sometimes even before it.
The evolutionary benefits of lining up a fast meal post-fertilization are evidently numerous, given how many species participate in this behavior. But the finer biological mechanics of sexual cannibalism are still being figured out. Case in point: a study published today in The Proceedings of the Royal Society B claims to be the first to provide empirical proof that a high level of pheromone deception is at play in some these cases of fatal attraction.
The study’s author, Katherine L. Barry of Macquarie University in Australia, ran a series of experiments on the false garden mantis to determine how honestly they advertised their fecundity to males.
Female false garden mantis. Image: Donald Hobern.
She collected 24 female mantids from around the Sydney area and divided them into four feeding regimens: Very Poor, Poor, Medium, and Good. The females were placed in mesh containers that hid their appearance from introduced male mantids, but did not block the airflow of pheromones.
The idea behind the study was to test whether or not the very poorly fed females sent straightforward pheromone signals about their condition to the males, or whether they would lie about it by advertising that they were totally healthy. Interestingly, the females opted for the latter strategy.
“Very Poor females attracted significantly more males than any of the other female treatments,” wrote Barry in the study’s abstract, “even though these females were in significantly poorer condition.”
It's "an inherently honest signaling system with a subset of dishonest individuals."
“In addition, there was a positive correlation between fecundity and attractiveness if Very Poor females were removed from the analysis, suggesting an inherently honest signaling system with a subset of dishonest individuals,” she continued.
Though the study didn’t include direct detection of the pheromones released by the females, the assumption is that the Very Poor group must have pumped out a lot more sexy juice to compensate for their malnourishment. This strategy of lying about their health and fertility allowed those females to lure males in with promises of sex, only to unceremoniously devour them.
The results are surprising, given that similar tests on arachnids and insects revealed the females to be honest about their level of fecundity when attracting mates. “This is the first empirical study to provide evidence of sexual deception via chemical cues,” wrote Barry, “and the first to provide support for the Femme Fatale hypothesis”—ie. the strategy of false promising sex and delivering death instead.
Despite the chemical trickery, some males were still able to mate with the poorly fed females, even after the female starts eating them. Typically, the female starts by ripping off the male’s head as an appetizer, but due to a second brain in the male’s abdomen, the male is sometimes still able to headlessly copulate (shudder).
Let that be a lesson to all to complain about human mating rituals. It’s not unheard of for people to lie a little on the first date, but at least it doesn’t end up with pre-fornication beheadings.
I mean, unless you’re into that.