Testacella
(a diminutive of testa, a shell; in allusion to the small size of the shell). A genus of Slugs which must be regarded as beneficial in gardens, inasmuch as they feed exclusively on earthworms, following them into their burrows. The body is long and slender, so as to pass easily along the burrows. On the hinder part of the back is a small, depressed, ear-shaped shell, about 1/4in. long, which protects the rear of the animal when in the burrows. This external shell at once distinguishes these animals from the true Slugs, which do mischief in gardens. Two species are known in England. T. haliotidea is dirty-yellow, with brown specks, rarely pale yellow, sometimes entirely black; when extended, it is about three inches long. It is said to swallow the worms alive. This species is known to occur in many localities in the South of England, and has been found as far north as Kirkcaldy, in Fifeshire.
T. Maugei is a native of South-west Europe, but has naturalised itself near Bristol. It is dark brown, and the shell is larger than in T. haliotidea.