Sexual Cannibalism: Some Males Lose Their Heads for Sex

Some males are ‘dying’ to have sex…literally! In praying mantises, soon after mating or during mating, the female starts devouring its partner, head first! Many spider males are in the same peril, so, in order not to fall victims to their sweeties, they deliver a large fly to their partners, which will keep them occupied.

In the end, males are just a source of protein for the hungry egg-developing females. Mantises mate in autumn, and the males would soon die after mating anyway (like females, too, after laying the egg packs), so why wasting a juicy piece of meat?

Mantises surely have been used as inspiration for creatures of "Star Wars" and "Alien." These predatory insects, related to termites and cockroaches, push the predatory instinct beyond feeding.

The female starts devouring the male’s head, as she would do with any prey, because this way the male or the prey are immobilized (with the destruction of the cerebral ganglions or brain). Anyhow, the male is smaller than the female. It seems that male's abdominal movements of delivering sperm turn more powerful. This is possible because the copulatory movement is under the control of the abdominal ganglions.

What are the advantages for the male? It seems that the sexual cannibalism doubles the copulating time, boosting the chances of the male to fertilize the eggs. That's because the cannibal female may copulate with several males, and that who pushes his sperm deeper may have an increased chance.

Is this a suicidal act of the male? Rather not, as he primarily has sex on his mind. It seems that males are not that willing to sacrifice themselves. Males mounting on hungry females stay there for a longer period, and it seems that males actively avoiding cannibalism have a chance to evade a bloody-ended monogamy, copulating more females.

Females usually cannibalize their mates when they finish their "job" and dismount, thus males avoiding to be turned into a snack will wait for the right time, and this prolongs the act. In the end, it seems that fit males have higher chances to escape.

Some say that sexual cannibalism is not a natural behavior, and that the animals are usually stressed in the lab or by the field observers, as these insects have good visual abilities and see the humans well.

Some researches that eliminated human disturbance (the insects were observed in vacant rooms) and the hunger factor (the females were fed very well) revealed that some mantis males displayed courtship behavior and females were less interested in seeing them as meal.

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