Though sexual cannibalism has been observed throughout the animal kingdom, the practice does not have many immediately obvious benefits – especially for males, who invariably provide the meat in this deadly post-coitus snack. However, a new study appearing in the Proceedings of the Royal Society B reveals that by being eaten by their mates, male praying mantises actually “invest” in their young, making the ultimate sacrifice in order to ensure their bodies become recycled in the form of offspring.
It has previously been suggested that the benefits of being eaten immediately after sex may offset the drawbacks, as nutrients contained within the male body are directly incorporated into the female’s eggs, resulting in larger amounts of young. To test this idea, researchers fed crickets that had been radioactively labeled to praying mantises, which were then allowed to mate with one another.
Immediately after the mantises had completed their business, the researchers removed half of the males, saving them from being cannibalized, while the other half were left to be devoured by their voracious sexual partners.
Tracking the radioactive proteins ingested by the females after eating the males, the researchers noted that most were not absorbed by the bodies of the newly impregnated females, but were instead allocated directly to the eggs. This resulted in a significant increase in the number of eggs produced by these mantises.
While those that had not been allowed to cannibalize their mates produced an average of 258 fertilized eggs, females that ate their partners produced an extra 50.9. “Based on the numbers from our study,” say the study authors, “cannibalized males potentially gain the opportunity to fertilize an additional 50.9 eggs with their current mate but lose the opportunity to fertilize the 258 eggs” with another female.
Therefore, when re-mating opportunities are limited, the opportunity to fertilize these extra 60 or so eggs may be worthwhile, and could explain the “greater risk taking behavior by males and even self-sacrifice” seen in situations where access to females is restricted.
On the other hand, when many females are present, males are better off not getting eaten so that they can mate with as many partners as possible, and are therefore advised by the researchers to “be risk aversive". This may well explain why, in the wild, sexual cannibalism is not always a foregone conclusion among praying mantises, and only about 13 to 28 percent of mantis rendezvous end in a sexy supper.