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Species of weasels

Weasels, ermines, and stoats are various species of small carnivores in the family Mustelidae, which also includes the otters, badgers, martens, minks, skunks, and wolverine. Species of weasels occur in North America, northern South America, northern Africa, Europe, Asia, and Southeast Asia.

Weasels have a long, lithe, almost serpentine body, and short legs. This body shape is highly adaptive for pursuing their prey of small mammals through small holes and along narrow passages. Weasels are very active, inquisitive animals, and they can run remarkably quickly and nimbly when they are chasing their prey.

Weasels have a very soft and dense fur, and although these animals are quite small, they are commonly trapped as furbearers. Northern species of weasels develop a thick, white coat in the wintertime, and these especially A long-tailed weasel (Mustela frenata). Photograph by Judd Cooney. Phototake NYC. Reproduced by permission.
valuable furs are known as ermine. Ermine is mostly used as a fine trim for coats and robes, or to make neck-pieces and stoles.

All of the weasels are terrestrial animals, occurring in a wide range of habitats, including tundra, various types of forests, and grasslands. Weasels are voracious carnivores, and they are capable of subduing animals substantially larger than themselves. They will often climb trees to hunt squirrels.

When they are faced with a super-abundance of food, weasels sometimes go on a lustful killing spree. A weasel in a chicken-house, for example, will kill a much larger number of birds than it could ever hope to eat. However, in more natural circumstances, these animals will attempt to cache their excess food. Weasels that learn how to kill chickens can be quite a problem, but they can be selectively killed. There is no need to kill weasels indiscriminately as perceived pests, especially considering the large numbers of small rodents that they kill, thereby providing a valuable service to farmers.

Weasels are generally solitary animals. However, the young stay with their mother until they learn to hunt for themselves. Young weasels engage in rough-and-tumble play, important in learning some of the physical skills that are necessary in hunting. Weasels are usually most active at night, although they often hunt during the day as well.

The ermine or stoat (Mustela erminea) is a circumboreal species, occurring widely in conifer-dominated boreal forests and tundras in northern North America, Europe, and Asia. The ermine is a ferocious predator. Although only some are 11.8 in (30 cm) long and weigh no more than 3.5 oz (100 g) (this is the weight of an adult male; females are about half as heavy), this carnivore can hunt and subdue animals as large as rabbits and hares weighing several kilograms. The winter coat of northern populations of this weasel is a well-camouflaged white, except for the black-tipped tail, while the summer pelage is tawny brown above, and yellow-white beneath.

The ermine has delayed implantation. This is characterized by mating in the summer, but the fertilized embryos remaining dormant in the uterus after they are fertilized, and not implanting and developing as embryos until three to four weeks prior to birth, which occurs the following spring or early summer. In this species the total post-fertilization gestation period is 200-340 days.

The long-tailed weasel (Mustela frenata) occurs from the southern half of North America to northern South America. Like the ermine, the long-tailed weasel has a white coat in winter, and delayed implantation.

The least, dwarf, or pygmy weasel (Mustela rixosa) of North America is the smallest of any of the predatory mammals (that is, order Carnivora). This species only attains a length (body plus tail) of 4.9 in (12.5 cm), and a weight of 1.47 oz (42 g). Because of its diminutive size, this species feeds mostly on mice, voles, and other small mammals. Also because of the small size of the least weasel, it must feed voraciously in order to maintain its weight and body temperature. This is because very small animals have a large ratio of body surface to mass, and they therefore lose heat quickly. In fact, the least weasel must eat an amount of small mammals equal to more than one-half of its own body weight each day. Like many other species of weasel, the dwarf weasel has a white coat in winter, and a brown coat in summer.

The common or Old World weasel (Mustela nivalis) is closely related to the least weasel, and these are sometimes considered to be geographic variants of the same species. The Old World weasel is a diminutive species that occurs in forests of Europe, northern and central Asia, and northern Africa. This species does not display delayed implantation. The Old World weasel has been introduced to New Zealand in a misguided attempt to control introduced rats and mice, but it has caused great damages through its depredations on native species of birds.

The alpine weasel (M. altaica) occurs in montane forests and alpine tundra of mountains in Asia. The yellow-bellied weasel (M. kathiah) and Siberian weasel (M. sibirica) are additional Asian species. The Java weasel (M. lutreolina) and bare-footed weasel (M. nudipes) are tropical-forest species of Southeast Asia.

Other species in the genus Mustela are relatively large in comparison with the true weasels. These include the rare and endangered black-footed ferret (M. nigripes) of the shortgrass prairies of western North America, the polecat or ferret (M. putorius) of northern Africa and Eurasia, the mink (M. vison) of North America, the Eurasian mink (M. lutreola) of Europe and Asia, and a tropical weasel (M. africana) of northern South America.



Grzimek, B. (ed.). Grzimek's Encyclopedia of Mammals. London: McGraw Hill, 1990.

King, C. The Natural History of Weasels and Stoats. London: Academic Press, 1989.

Nowak, R.M. (ed.). Walker's Mammals of the World. 5th ed. Baltimore: Johns Hopkins University Press, 1991.

Wilson, D.E., and D. Reeder. Mammal Species of the World. 2nd ed. Washington, DC: Smithsonian Institution Press, 1993.

Bill Freedman


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—A flesh-eating animal.


—A biogeographic distribution that includes the conifer-dominated boreal forests of both North America and Eurasia.

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