The key to a monogamous relationship is cannibalism – at least for wood-feeding cockroaches. This behaviour has evolved so these insects can keep partners around to help raise offspring.

Most cases of sexual cannibalism involve creatures like spiders eating their suitors after mating. Males are often the victims, and eating them could help females fatten up on nutrients for use during pregnancy. Some male spiders will even sacrifice legs to aggressive females during mating.

But males cannibalising females is …