How some male mantises avoid getting their heads chopped off after sex

A female mantis with an abdominal wound from wrestling with a horny male. Credit: Biology Letters, Nathan Burke.

Mantises are famous in the animal kingdom for their extreme sexual cannibalism. If given the chance, females will often bite off the heads and eat other body parts of the male that they mate with. In the process, they acquire important nutrients that are incorporated into the eggs, thereby improving the odds that a male passes his genes — so not a totally unfair bargain. But some crafty males want to have their cake and eat it too.

In a new study, researchers documented how male springbok mantises (Miomantis caffra) manage to mate and escape cannibalism, finding that the insects dramatically improve their odds of surviving mating if they violently wrestle the females. Pinning down the female helps the male mate and come out unscathed, serving as both a mating and survival tactic.

Although female mantises are famous for exhibiting cannibalism of their mates, research suggests that females eat their mate just 13% to 28% of the time. Springbok mantises, however, fit the stereotype of a merciless fatal sexual encounter, killing their male spouses 60% of the time.

It then makes sense that the male springboks have had to evolve some sort of defence mechanism. Not having sex is, after all, not a solution either.

In order to learn how some males escape the particularly aggressive cannibalistic tendencies of the females, biologists at the University of Auckland in New Zealand organized gladiator-like showdowns between 52 male-female pairs.

Healed abdominal wound in a female. Credit: Biology Letters.

Within 12 hours of being placed in the same enclosure in the lab, 56% of the males initiated contact with the female. They did so very aggressively, leaping onto the females while rapidly fluttering their wings. About 90% of these contacts turned into violent albeit short-lived struggles. Lasting only 12.7 seconds on average, these struggles often resulted in the male inflicting a serious but non-fatal wound to the abdomen of the female using his serrated raptorial forelegs.

When the male managed to pin the female down, he stood a 78% change of escaping unscathed. The females won more than one-third of these wrestling matches, pinning down and cannibalizing the males in 35% of the cases.

However, not all winning showdowns resulted in a mating opportunity for the males. Coupling occurred only two-thirds of the time.

“When females win the struggle, they always cannibalize males. However, when males grasp females first, they dramatically increase the chance of mating. We also find striking evidence that, on some occasions, males wound females with their fore-tibial claws during struggles, resulting in haemolymph loss and scar tissue formation,” the researchers wrote in the journal Biology Letters.

The researchers believe that the reason why males evolved such harmful and aggressive behaviors is due to the even greater threat posed by the females. The males simply have to do whatever they can in order to both survive and replicate, and this dual strategy can lead to some pretty peculiar outcomes, such as two parents who are willing to kill each other during mating.

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