A worm crawls by lengthening its front part and pushing through the soil, then pulling the hind part up. A worm's body wall has two kinds of muscles that it uses to crawl. Circular muscles surround the worm's body and can make the body shrink or spread out. Longitudinal muscles run the length of the body and can shorten or lengthen the worm. Setae (bristles) prevent the worm from slipping.

The earthworm has no lungs or gills. It breathes through its thin skin, which is in contact with the air between the particles of soil. When it rains, these air spaces fill with water, and earthworms then must either come to the surface or drown. If the weather becomes too dry and warm, a worm will die. Earthworms feed on dead plant material that is found in the soil. This is why some people say an earthworm eats its way through the soil.

An earthworm has both male and female reproductive organs, but each worm must mate with another worm to form eggs. After mating, eggs are laid in a cufflike structure that surrounds the body of the earthworm. The clitellum, a few large annuli of the body, produces this cuff for the eggs. As the earthworm moves, the cuff slides along the body and over the head. It closes completely around the eggs to make a sacklike cocoon. After several weeks in the cocoon, the young earthworms hatch.

Scientific Classification. Earthworms are in the family Lumbricidae of the segmented worm phylum, Annelida. The scientific name for one common species is Lumbricus terrestris.