h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

This entry, predictably, trost out the old factoid that female mantises tend to bite off their mates' heads. This is not really true. It occasionally happens in the wild, but not nearly as often as people think.

It does, however, happen much more often than natural when the mantises are made to mate in labs. A lab is a rather unfamiliar environment, which makes the bugs edgy. Hence, females are rather more eager to behead their prospective mates.