
The common earthworm (Lumbricus terrestris) is an abundant species, which has an important role in the aeration and fertilization of soil. It is the largest British earthworm and has a reddish-brown back, a yellowish underside and an often-prominent orange red 'saddle' region known as the 'clitellum', close to the reproductive organs. Although this earthworm has a cylindrical body, the tail region may become flattened. The body is segmented and has visible rings known as ‘annuli’; each segment bears small hairs known as 'chaetae', which help the worm to move through the soil.