The common earthworm (Lumbricus terrestris) is a large, reddish worm species widely distributed around the world (along with several other lumbricids). In some areas where it is an introduced species, some people consider it a serious pest for outcompeting native worms.

Through much of Europe, it is the largest naturally occurring species of earthworm, typically reaching 20–25 cm in length when extended (though in parts of southern Europe, the native species are much larger). In September 2012, a specimen was found in Souhwest China measuring roughly 50 cm in length. In May 2016 a worm was found that was about 61 cm long. It has an unusual habit of copulating on the surface at night, which makes it more visible than most other earthworms.