ferret, name for a domesticated polecat, Mustela putorius, common in the Old World. It has been used for centuries to hunt rats, mice, and rabbits. Domestic ferrets are found in many color types including albinos, brown, and black. The name is also applied to a related wild species, the North American, or black-footed, ferret, M. nigripes, which inhabits the Great Plains and is now extremely rare. Its range nearly coincides with that of the prairie dogs, which constitute most of its diet; it is often found in prairie dog burrows. The severe reduction of the prairie dog population by ranchers is probably partially responsible for the rarity of the black-footed ferret, although it was apparently not numerous when the West was first settled by Europeans. Ferrets are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Carnivora, family Mustelidae (weasel family).