weasel, name for certain small, lithe, carnivorous mammals of the family Mustelidae (weasel family). Members of this family are generally characterized by long bodies and necks, short legs, small rounded ears, and medium to long tails. All have scent glands, generally used for territorial markings but in some animals for defense. True weasels belong to the genus Mustela, with species found in Eurasia, N Africa, and the Americas. Weasels are very active and chiefly terrestrial but are able to climb trees. They prey on small animals by night, often killing more than they eat, and spend the day in dens made in holes in the ground, rock piles, or hollow stumps. Although they are notorious for destruction of poultry, the damage they do is far outweighed by their value as destroyers of rodents. Weasels are usually brown, with white underparts. Species living in snowy regions acquire white coats in winter and are then known as ermine. The most widely distributed weasel, Mustela erminea, is known in Europe as the stoat and in North America as the short-tailed weasel. It is about 16 in. (40 cm) long including the 5-in. (13-cm) tail; it has a white winter coat through much of its range and a characteristic black tail tip the year around. It ranges from the Arctic Ocean to central Asia, S Europe and the central United States. The much smaller M. nivalis, known in Europe simply as weasel, is found in Europe, N and central Asia, and N Africa. It turns white only in the extreme northern parts of its range. Among the New World weasels is the tiny least weasel, measuring only 7 or 8 in. (18-20 cm) in total length; it ranges from the N central United States to N Canada and Alaska. There are many other true weasel species, mostly in the Old World. Besides these, the genus Mustela includes the polecat, ferret, and mink. African animals of several genera in the weasel family are called striped weasels; they are characterized by conspicuous black and white markings and, in some cases, by the use of scent for defense. Among these is a skunklike animal with a powerful odor known as the zorilla. The weasel family also includes the marten, fisher, and wolverine, as well as the more distantly related skunk, badger, honey badger (or ratel), and otter. Weasels are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Carnivora, family Mustelidae.

Any of several genera (carnivore family Mustelidae) of voracious nocturnal predators found throughout the Americas, Africa, and Eurasia. Weasels have slender bodies and necks, small flat heads, short legs, clawed toes, dense short fur, and slim pointed tails. The size and relative length of the tail vary among species. Their total length is 7–20 in. (17–50 cm), and they may weigh 1–12 oz (30–350 g). The approximately 10 New World and Eurasian species of Mustela are reddish brown; in cold regions, their winter coat turns white, and the pelt, especially of the stoat (M. erminea), is called ermine. Weasels generally hunt alone, feeding on rodents, fish, frogs, and birds' eggs.

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