Sea worms mate in the following way: at mating time, males and females swarm together. Suddenly the females turn on the males and bite their tails off. The tails contain the males’ testes and sperm. When they are swallowed and acted upon by the females’ digestive juices, they fertilize her eggs.

When leeches mate, the leech playing the male role (leeches are hermaphrodites and can assume either sex) clings to the body of the female and deposits a sac of sperm on her skin. This sac produces a strong, flesh-deteriorating enzyme that eats a hole through the female’s skin and fertilizes the eggs within her body.

Only female bees work. Males remain in the hive and literally do nothing, their only mission in life being to fertilize the queen bee on her maiden flight. For this purpose literally thousands of males are hatched, out of which only one or two mate with the queen. After they have served their function, the males are not allowed back into the hive but are left outside, where they starve to death.