Redback Spider

I'm sure most of you are aware that in some species of spider the female will devour the male after copulation. But did you know that some males not only do not fight against this cannibalization, they actively promote and facilitate it? The male Redback Spider performs a somersault after mating and literally jumps into the females mouth. But why? What possible evolutionary benefit could there be from enabling your mating partner to eat you?

Researchers discovered that the environment of these spiders was so hostile that it was highly unlikely that a male would be able to find another mating partner. Therefore it would be better for it to focus on ensuring that the female did not mate again. Mate guarding is a poor tactic for these spiders as the females are so much larger.

The researchers also found that if a female devoured her first mating partner she was much less likely to accept a second male. If she did not eat her first partner she would usually accept to solicitations of the next male that came along.

These two factors (hostile environment and female choice when full) means that promoting their own devouring actually confers an evolutionary advantage on these male spiders.