The female mantis is one of the world's most notorious cannibals. Sometimes--but not all the time--she devours the male after he jumps on her back to mate, seen here.

Males know they're asking for trouble during mating, so if they boldly go there at all, they often try to leap onto her back from far away, and then escape when the deed is done. Even if she kills him, though, all is not lost: male mantises can famously continue to copulate hours after decapitation.