Mating Habits of Earthworms

The most obvious part of a worm’s reproductive system is the clitellum, the wide band near the head that’s thicker than the rest of the earthworm’s body. This is where the egg-holding cocoons get their start. Each worm also has male pores, situated between the clitellum and the head. These pores secrete sperm during mating. Female pores on the worm receive and store the sperm. Oviducts produce and release the eggs.

Despite that they produce both eggs and sperm, earthworms virtually always seek out a partner. Depending on species, they may mate on or near the surface of the earth, or may seek each other out further down inside the ground. Once two worms find each other they line themselves up side by side, with the head of one near the tail of the other. They press tightly together, and both worms excrete sperm packets from their male pores. The partner worms receive each other's packets and store them in their female pores.

Once they've transferred sperm packets, the worms go their separate ways. Each worm's clitellum secretes albumin, which forms into a cocoon as it slides down the outside of the worm. During this process, both the sperm and the eggs are encased in the albumin cocoon, at which point fertilization takes place. The cocoon starts to shrink, and the worm backs out of it, leaving the fertilized eggs inside. As soon as the worm is out, the cocoon seals itself.

The tiny cocoon, no bigger than a grain of rice, is shaped something like a tiny lemon. Once it drops off the parent worm, it remains in the soil for a few weeks or up to two months or more. When the eggs have developed, they’ll hatch; as many as 20 but as few as one or two threadlike babies will emerge. If environmental conditions aren’t suitable, the eggs can remain dormant for months or even years before they hatch.