WARNING: May blow your mind-
..the female will mate with and devour up to seven males, whether she has laid her egg cases or not. The mating rites of mantises are well known: a chemical produced in the head of the male insect says, in effect, "No, don't go near her, you fool, she'll eat you alive." At the same time a chemical in his abdomen says, "Yes, by all means, now and forever yes."
While the male is making up what passes for his mind, the female tips the balance in her favour by eating his head. He mounts her. Fabre describes the mating, which sometimes lasts six hours, as follows: "The male, absorbed in the performance of his vital functions, holds the female in a tight embrace. But the wretch has no head; he has no neck; he has hardly a body. The other, with her muzzle turned over her shoulder continues very placidly to gnaw what remains of the gentle swain. And, all the time, that masculine stump, holding on firmly, goes on with the business! I have seen it done with my own eyes and have not yet recovered from my astonishment."
(Annie Dillard, Pilgrim at Tinker Creek)
A lesson there for all of us. By the way, if you need a little more help visualising, this might do the trick. A nasty, nasty business.