A new study finds that male praying mantises actually benefit from being cannibalized by their female sexual partners.
Researchers separated groups of male and female pairs and allowed them to mate. In one group the males were then removed; in the other, the females ate their partners post-coitus, as is their wont. The results show that the cannibalistic females produced more eggs and that those eggs contained a greater degree of the male genetic material than the eggs produced by females who didn't have the chance to devour their sexual partners.
In evolutionary terms, this benefits males because they are able to pass down a greater number of their genes. However, researchers found that male praying mantises still possess a Darwinian desire to avoid being eaten. "We can consider that an extreme form of paternal investment in offspring," study co-author William Brown, a biologist at the State University of New York at Fredonia, told Live Science.
Praying mantises are not the only creatures known to kill their sexual partners. Black widow spiders, common in the southwest, have been known to kill males after mating. Recently, female octopuses were observed by scientists strangling males during the act of mating. In the paper, "Wild Wunderpus photogenicus and Octopus cyaneaemploy asphyxiating 'constricting' in interactions with other octopuses" researchers Christine Huffard and Mike Bartick observed mating octopuses in the Fiabacet Island in Indonesia and witnessed the larger female octopus strangling the male.
As in the praying mantis study, Huffard and Bartick found that, "because this case of possible sexual cannibalism was post-copulatory, this male might have ultimately fertilized some of the cannibalizing female's egg." This means that, despite the seemingly counter-intuitive drive to kill a mate, it might actually be beneficial to the species in the long term.
A praying mantis is a carnivore and will fiercely hunt and stalk its prey. A Giant Asian Mantis, the type used in this study, can grow to be 5 inches long and will stalk and attack something half its size or larger. If all of this does not make you feel deeply unsettled, please enjoy this video of a giant mantis devouring two bees at one time.