mustelid

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mustelid

mammal

Also known as: Mustelidae

Written by Serge Lariviere

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Related Topics:: otter; badger; Melinae; Mellivorinae; Mustelinae

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mustelid, (family Mustelidae), any of about 62 species of ferrets, polecats, badgers, martens, otters, the wolverine, and other members of the weasel family. Historically, skunks were also included in Mustelidae, but genetic analyses suggest that they belong to a separate family of their own (Mephitidae). Mustelids are fur-bearing carnivores that inhabit terrestrial and aquatic regions throughout the world, except Australia, Antarctica, and most oceanic islands. Many mustelids, such as the American mink (Neovison vison), are trapped or raised commercially for their pelts.

Natural history

Most mustelids are fairly small. The least weasel (Mustela nivalis), which measures 11–26 cm (4–10 inches) long and weighs only 25 grams (0.9 ounce), is the smallest. The largest is the sea otter (Enhydra lutris) at about 1 meter (3.3 feet) long and a weight of 25–45 kg (55–99 pounds). The largest terrestrial mustelid is the wolverine (Gulo gulo), found in the northern United States and throughout Canada and northern Europe. It measures up to 1.2 meters in length and can weigh up to 20 kg (44 pounds) or more.

Many mustelids have a long tube-shaped body, short legs, and a strong thick neck with a small head. All possess well-developed anal scent glands. The five digits on each foot are equipped with sharp nonretractile claws. Males are usually larger than females; among some weasels, males are almost twice as large. A tubular body does not retain heat as well as a stockier body of the same weight and is therefore associated with higher metabolism. As a result, mustelids are very active and inquisitive in their constant search for prey.

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Most mustelids are strictly carnivorous, but a few include plant matter, mostly fruits or berries, in their diet. Dentition is characterized by strong canine teeth and sharp molars and premolars. Some mustelids have specialized diets. Clawless otters (genus Aonyx) specialize in crustaceans (especially crabs) and mollusks, whereas other otters (genus Lutra) are primarily fish eaters. Among the weasels (genus Mustela), specialization occurs even between the sexes, such that males, owing to their larger size, consume larger prey than females do.

Mustelids are mostly solitary except for Eurasian badgers (Meles meles), sea otters, and some northern river otters (Lontra canadensis). In solitary species, association between males and females during the mating season is brief. Mating occurs mostly in the spring, and, in many species, ovulation is induced during copulation. Delayed implantation of the fertilized egg occurs in many mustelids. Females raise the young alone. Only the least weasel produces two litters yearly; other species produce annually. In most mustelids, the young become sexually mature at about 10 months of age. Mustelids evolved from North American and Eurasian forms in the early Oligocene Epoch, some 30 million years ago.

Classification

Family Mustelidae
62 species in 23 genera belonging to 8 subfamilies, found worldwide except Australia and Antarctica.
- Subfamily Guloninae
  11 species.
  - Genus Eira (tayra)
    1 species.
  - Genus Gulo (wolverine)
    1 species.
  - Genus Martes (martens)
    8 species.
  - Genus Pekania (fisher)
    1 species.
- Subfamily Helictidinae
  5 species.
  - Genus Melogale(ferret-badgers)
    5 species.
- Subfamily Ictonychinae
  7 species.
  - Genus Galictis (grisons)
    2 species.
  - Genus Ictonyx (striped polecat and zorilla)
    2 species.
  - Genus Lyncodon (Patagonian weasel)
    1 species.
  - Genus Poecilogale (African striped weasel)
    1 species.
  - Genus Vormela (marbled polecat)
    1 species.
- Subfamily Lutrinae (otters)
  12 species.
  - Genus Amblonyx (small-clawed otter)
    1 species found in South and Southeast Asia and in New Guinea.
  - Genus Aonyx (small-clawed or clawless otter)
    1 species found in sub-Saharan Africa.
  - Genus Enhydra (sea otter)
    1 species found in North America.
  - Genus Hydrictis (spotted-necked otter)
    1 species found in South America.
  - Genus Lontra (river otters)
    4 species found in the Americas.
  - Genus Lutra
    2 species found in Africa and Eurasia.
  - Genus Lutrogale (smooth-coated otter)
    1 species found in southern Asia.
  - Genus Pteronura (giant otter)
    1 species found in South America.
- Subfamily Melinae (badgers)
  7 species.
  - Genus Arctonyx (hog badgers)
    3 species.
  - Genus Meles (Eurasian badgers)
    4 species.
- Subfamily Mellivorinae
  1 species.
  - Genus Mellivora (ratel, or honey badger)
    1 species.
- Subfamily Mustelinae
  18 species.
  - Genus Mustela (weasels, including the mink, ermine, and ferret)
    14 species.
  - Genus Neovison or Neogale (minks)
    4 species.
- Subfamily Taxidiinae
  1 species.
  - Genus Taxidea (American badger)
    1 species.

Serge Lariviere

weasel

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weasel summary

weasel

mammal

Written and fact-checked by The Editors of Encyclopaedia Britannica

Last Updated: May 10, 2025 • Article History

Related Topics:: Patagonian weasel; least weasel; African striped weasel; long-tailed weasel; tropical weasel

On the Web:: NC State University News - Why scientists are worried about weasels (May 10, 2025)

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weasel, any of various small carnivores with very elongated slender bodies. Most live in the Northern Hemisphere and belong to the genus Mustela, which in addition to weasels proper includes 17 species of ferrets and polecats as well as the mink and the ermine. Along with their tubelike bodies, weasels have small flattened heads, long flexible necks, and short limbs. The fur is short but dense, and the slim tail is pointed at the tip. Five toes on each foot end in sharp curved claws. The species can be differentiated by size, colour, and relative length of the tail.

Weasels are usually brown with white or yellowish underparts. In winter the coats of weasels living in cold regions turn white. Their pelts, especially that of the stoat (M. erminea), are known as ermine in the fur trade. The kolinsky (kolinski), also called the Siberian weasel (M. sibirica), is also much valued for its fur. The tail hairs are used to make artists’ paintbrushes.

Weasels are bold and aggressive predators. They generally hunt alone, feeding principally on mice, voles, rats, and rabbits, but they also take frogs, birds, and bird eggs. Because of their narrow bodies, weasels are able to pursue and capture rodents in their burrows and to chase them through holes and crevices, under dense herbage, up trees, or into water. Although proficient at catching mice, weasels are also notorious for raiding chicken coops. Because they cannot accumulate fat and thus must eat frequently, weasels often kill more prey than they can immediately consume and will store excess food for later use. This explains the carnage often seen after they discover captive domestic fowl.

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least weaselLeast weasel (*Mustela nivalis*) in the Bering Land Bridge National Preserve, Seward Peninsula, Alaska. The least weasel is the smallest living carnivore, measuring only 11–26 cm (4–10 inches) in length and weighing only 25 grams (0.9 ounce).

Male weasels mate with multiple females and do not provide parental care. Most species have a single litter per year, but the common, or least, weasel (M. nivalis) often has two. Sexual maturity is rapidly attained, and least weasels often breed at three months of age. Litter size varies from three to a dozen or more in some species. The young are born after a gestation period of anywhere from 35 days to more than 10 months, the latter because of delayed implantation of the fertilized egg.

The most-common and most widely distributed species are the stoat (called the short-tailed weasel in North America) and the least weasel. The range of both extends into polar regions. The stoat was introduced into New Zealand to control rabbits, but instead it became troublesome and now endangers many of the country’s native birds. The least weasel is the smallest living carnivore; the smallest subspecies inhabits North America. It measures 11–26 cm (4–10 inches) in length and weighs only 25 grams (0.9 ounce). Larger forms of the same species occur in Russia and adjacent countries, where they are somewhat longer and considerably heavier. The range of the stoat and the least weasel overlap, and in those areas the species can be differentiated by the stoat’s black-tipped tail. In North America the largest weasel is the long-tailed weasel (M. frenata); in South America it is the tropical weasel (M. africana). Both measure 25–30 cm (about 10–12 inches), excluding the 10–20-cm (4–8-inch) tail; weight is 85–350 grams (3–12.3 ounces). With most weasels, males are usually twice the size of females.

zorilleThe zorille (*Ictonyx striatus*), which is also known as the African striped polecat, is commonly found in agricultural areas. Its geographic range spans most of Africa south of the Sahara and outside the Congo basin.

Weasels belong to the family Mustelidae, and there are three weasel genera in addition to Mustela. The Patagonian weasel (Lyncodon patagonicus) is a larger mustelid of the South American Pampas. It is about 30–35 cm (12–14 inches) long, excluding the 6–9-cm (2.5–3.5-inch) tail. That weasel is grayish with dark brown underparts and a white stripe running across the forehead to the sides of the neck. The zorilles, or African striped polecats (two species of the genus Ictonyx), are somewhat smaller and are often found in agricultural areas. Their bodies are spotted black-and-white, and the tail, face, and back are striped. The African striped weasel (Poecilogale albinucha) is found in Africa south of the Congo Basin. Similar in habit to weasels of the genus Mustela, it is striped in light yellow and black, with black underparts and a long white tail.

This article was most recently revised and updated by Mic Anderson.