earthworm

The earthworm burrows through the soil by pressing its minute bristles into the walls of the tunnel and pulling itself along. The thickened segment, or saddle, towards the front of the body lies near the reproductive organs and secretes the egg cocoons.

Annelid worm of the class Oligochaeta. Earthworms are hermaphroditic and deposit their eggs in cocoons. They live by burrowing in the soil, feeding on the organic matter it contains. They are vital to the formation of humus, aerating the soil and levelling it by transferring earth from the deeper levels to the surface as castings.

Most North American earthworms belong to the genus Lumbricus. These are comparatively small, but some tropical forms reach over 1 m/3 ft in length. Megascolides australis, of Queensland, for instance, can be over 3 m/11 ft long.