Voluntary Cannibalism

Male redback spiders don't just accept being eaten by females — they actively facilitate it. During mating, the male performs a somersault that places his abdomen directly over the female's fangs.

This suicidal behavior actually benefits the male: - Males that are eaten copulate longer, transferring more sperm - Cannibalized males father about twice as many offspring as those that escape - Most males die shortly after mating anyway (they stop eating as adults) - Being eaten prevents the female from mating with other males

The male's sacrifice is almost inevitable. Females are about 100 times heavier than males and much more formidable. A male's only chance of reproductive success is to make the most of his one mating opportunity.

Males that survive their first mating attempt often go back for a second round — and are almost always eaten during or after. It appears evolution has determined that being consumed is simply the best reproductive strategy for male redbacks.

This extreme example of sexual cannibalism shows how natural selection can favor behaviors that seem counterintuitive from an individual survival perspective.