Weasels

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.