Okay, curiousity got me.
Google search turns up this:
Although the praying mantis is known for its cannibalistic mating process in actuality it only occurs 5-31% of the time. Especially in laboratory conditions of bright lights and confinement, the female is more likely to eat the male as means of survival. "In nature, mating usually takes place under cover, so rather than leaning over the tank studying their every move, we left them alone and videotaped what happened. We were amazed at what we saw. Out of thirty matings, we didn't record one instance of cannibalism, and instead we saw an elaborate courtship display, with both sexes performing a ritual dance, stroking each other with their antennae before finally mating. It really was a lovely display". There is one species, however, the Mantis religiosa, in which it is necessary that the head be removed for the mating to take effect properly. Sexual cannibalism occurs most often if the female is hungry. But eating the head does causes the body to ejaculate faster.
Oh, and this too...
During one experiment, mantids were observed in copulation for an average of six hours.