Praying mantis (or mantids as the plural is known) are a large group of carnivorous insects found throughout most of the warmer parts of the world. Most species are also cannibalistic in that given a chance they may eat other mantids they come across.
Praying mantis have unique front legs lined with fine barbs which they use to catch their prey. A praying mantis will normally stand motionless in a plant waiting for a passing insect whereupon they will strike with their front legs, impaling the unfortunate insect. Slow motion cameras have shown that the praying mantis actually moves so quickly when striking that it cannot be seen by the human eye.
Praying mantis feed mainly on insects such as flies and beetles though larger species may tackle proportionately larger prey items such as small birds, amphibians or mammals. Scientists have shown that the praying mantis decides whether to catch a pray item based on the overall volume of the animal and that mantids are only able to spot prey items when they move.
Studies on praying mantids show that while some females do indeed eat their mate after breeding this happens in only around 20% of cases. In the rest the male mantis, which is quicker and lighter, escapes unharmed. Scientists have long debated the reasons for the female eating the male however general agreement is that it makes evolutionary sense for the female mantis to eat as much as possible.
Once mating has occurred the male has successfully passed on his genes to the next generation and the more the female now eats, the greater her chances of survival and the more eggs she will be capable of laying. Consequently eating the male once the act is complete makes perfect sense.
It should be noted that in those situations where the female does eat the male she generally starts with the head and male praying mantis has been shown to be perfectly capable of continuing the act of mating even after losing his head.