Rumors of the praying mantis' cannibalistic tendencies began when scientists observed their mating behavior in a laboratory environment. Entomologists would offer a captive female a potential mate, and would quite often be horrified to watch the female bite the head or legs off the smaller male. After the male had served his copulatory purpose, he was nothing more than a good meal to the female. For a long time, these observations of praying mantis sex in the lab were thought to be the way things were in the mantid world.
Once scientists started observing praying mantis sex in a natural setting, the story had a different ending, which is good for the males. When unconfined in laboratory terrariums, the majority of praying mantis mating ends with the male flying off, unharmed. By most estimates, sexual cannibalism by praying mantis females occurs less than 30% of the time outside the lab. Those are pretty good odds for the fellows. Praying mantis sex, it turns out, is really a rather romantic series of courtship rituals that typically ends satisfactorily and safely for both parties involved.
There is a decided advantage for the female, however, if she does decide to behead her lover. The praying mantis brain, located in his head, controls inhibition, while a ganglion in the abdomen controls the motions of copulation. Absent his head, a male praying mantis will lose all his inhibitions and consummate his relationship with wild abandon.
And what if she's hungry? For certain, a slow moving and deliberate predator like the praying mantis is not going to pass up an easy meal. If a male makes the unfortunate choice of a hungry female for a mate, he's probably going to be toast once they've mated.