Earthworms help to fertilise the soil by bringing nutrients closer to the surface.

Statistics
Earthworms vary in size from 90-300mm.

Physical description
Earthworms are made up of many small segments known as 'annuli'. These annuli are ridged and covered in minute hairs that grip the soil allowing the worm to move as it contracts its muscles. At about a third of the worm's length is a smooth band known as the clitellum. The clitellum is responsible for secreting the sticky clear mucus that covers the worm.

Distribution
Earthworms are widespread in Britain and Europe. They have been introduced to most parts of the world.

Habitat
They live in soil at depths of up to 2m.

Diet
Earthworms feed on decaying organic matter in the soil.

Behaviour
Earthworms move slowly underground feeding on decaying organic matter in the soil. They excrete digested material as worm casts and these can be seen as squiggly clumps of mud at the surface of the soil. These castings are very rich in nutrients because they contain minerals and nutrients that have been brought closer to the surface by the worms.

Reproduction
Earthworms are hermaphrodite and have both male and female reproductive cells. They cannot self-fertilise, however, and must find a mate to exchange sperm cells with. Earthworms reach sexual maturity at about four weeks old. This species comes to the surface to mate. Copulation, which may take up to an hour, involves two worms lying together with their heads pointing in opposite directions. While mating, the worms seem to shut out all other external stimuli and do not respond to light or touch. Large amounts of mucus are released by both individuals and while closely pressed against one another, sperm is exchanged. After this is complete the worms separate.

After mating the clitellum begins to secrete a substance which hardens to form a ring-like cocoon, into which the worm's own eggs and its partners sperm are placed. The 2mm cocoon eventually slips off the worm's head end and closes, becoming lemon-shaped. Fertilisation occurs inside the cocoon. This elaborate procedure is designed to prevent self-fertilisation.

Conservation status
Earthworms are not listed as endangered on IUCN Red List.

Notes
It is a commonly held belief that if you chop a worm in half you will end up with two live worms. This is not true. If you chop a worm in half it is possible that one half may recover and heal but you are most likely to end up with two halves of a dead worm.

Common earthworms (Lumbricus terrestris) are known in America and many parts of the world as 'nightcrawlers' and are frequently used as fishing bait.