a family of small or medium-sized predatory mammals. The fur is thick and fluffy, with a fine, soft undercoat. These animals generally have an elongated and flexible body and a bushy tail. The claws are not retractile, and in many species the digits are webbed. Special anal glands release a fetid secretion. Mustelids are distributed throughout the world except for Australia, the antarctic, Madagascar, Iceland, and some small islands. There are five subfamilies, with 28 or 30 genera. Sixteen species, making up eight genera, are found in the USSR.
Short-tailed, or snow, weasels (Mustela nivalis), polecats, and martens—all of the subfamily Mustelinae—are active predators. Feeding primarily on mammals and birds, they have molars with sharp cutting ridges. These species are terrestrial, and some are good tree-climbers. Badgers of the subfamily Melinae have digits with strong claws adapted for digging burrows. Feeding on animal and vegetable food, they have molars with broad, flat crowns that serve for grinding food. The common otter and the sea otter, which are both of the subfamily Lutrinae, are aquatic mammals, with well-developed swimming webs. These otters feed on fish, mollusks, and other aquatic animals.
Almost all mustelids are commercially valued for their fur (especially sable and sea otter).