shrew, common name for the small, insectivorous mammals of the family Soricidae, related to the moles. Shrews include the smallest mammals; the smallest shrews are under 2 in. (5.1 cm) long, excluding the tail, and the largest are about 6 in. (15 cm) long. Light-boned and fragile, shrews have mouselike bodies and long, pointed snouts with tiny, sharp teeth. They are terrestrial and nocturnal, mostly living under vegetation; some occupy the burrows of other small animals. Their musky odor, produced by a pair of glands on their flanks, deters some of their potential predators.
Extremely active and nervous, they have a higher metabolic rate than any other animal. The heart of the masked shrew, Sorex cinereus, beats 800 times a minute, considerably faster than that of the hummingbird. Shrews must eat incessantly in order to stay alive; most will starve to death if deprived of food for half a day. They eat anything available, but prefer small animals; they are economically important as destroyers of insects and slugs that harm crops.
Shrews are easily startled and will jump, faint, or drop dead at a sudden noise. They are vicious fighters, killing and eating larger animals, such as mice, as well as other shrews. A belief that the shrew's bite is poisonous was dismissed for years as a folk tale, but has since been substantiated; the saliva of at least one species of shrew is lethal to mice and can cause considerable pain to humans. Shrews live about 15 months and reproduce rapidly, bearing up to four litters a year, with up to eight young in a litter.
Shrews are found in Europe, Asia, North and Central America, and N South America. There are more than 350 species, all rather similar, classified in about 30 genera. The subfamily of red-toothed shrews, with orange- or red-tipped teeth, includes both Old and New World species; the white-toothed shrews are confined to the Old World. A third subfamily, sometimes called African shrews, is found exclusively in sub-Saharan Africa.
The common shrews of the Northern Hemisphere belong to the red-toothed genus Sorex, with many species in North America and a few in Europe and Asia. The water shrew of Canada and N United States, Sorex palustris, is adapted to aquatic living and can actually walk on the surface of water for a short distance. There are other aquatic shrews, of several genera, in Europe and Asia.
The giant water shrew of Africa is not a true shrew but an insectivore related to the tenrec. The elephant, or jumping, shrews of Africa are insectivores of the family Macroscelididae; they resemble miniature kangaroos with trunks. The Oriental tree shrew is an insectivorelike primate. True shrews are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Soricomorpha, family Soricidae.