One of the most interesting aspects of earthworms is their sexuality. Earthworms are simultaneous hermaphrodites , meaning worms have both male and female reproductive organs. During sexual intercourse among earthworms, both sets of sex organs are used by both worms. If all goes well, the eggs of both of the mates become fertilized. You can imagine this is a highly efficient way of ensuring the survival of the species. Vermicomposters , people who raise worms and other organisms to compost , report that their earthworm populations typically double every 60 to 90 days [source: Werner ].

Though their serpentine locomotion might be off-putting to some, when roundworms do the deed, they're surprisingly graceful. A simple animal with only about neurons, C. But its reproductive system is quite complex. While the worm's mating behavior could be described as a reflex, "this is not a blind machine," Emmons said.

One morning I noticed two worms stuck together on the ground. Before I got a good eyeful, my dog rudely interrupted them and they hastily retreated into their burrows. Were they soil mates discussing Nietzsche or niches over a cup of dirt? Being hermaphroditic enhances the chances of finding a suitable mate for creatures like worms, with limited access to partners or the internet. And they may prefer a partner because mixing genes is a good way to hedge genetic bets in ever-changing environments.