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The stoat (Mustela erminea), also known as the ermine or short-tailed weasel, is a species of Mustelid native to Eurasia and North America, distinguished from the least weasel by its larger size and longer tail with a prominent black tip. Its range has expanded since the late 19th century to include New Zealand, where it is

A Stoat in its winter coat, showing its teeth


North America, Europe, and Asia




Many small animals

Combat Status

Defeated by the Striped Polecat

held responsible for declines in native bird populations. It is classed by the IUCN as Least Concern, due to its wide circumpolar distribution, and the fact that it does not face any significant threat to its survival.[1] It is listed among the 100 "world's worst alien invasive species"

Physical Description[]

The stoat is entirely similar to the least weasel in general proportions, manner of posture and movement, though the tail is relatively longer, always exceeding a third of the body length,[20] though it is shorter than that of the long-tailed weasel. The stoat has an elongated neck, the head being set exceptionally far in front of the shoulders. The trunk is nearly cylindrical, and does not bulge at the abdomen. The greatest circumference of body is little more than half its length.[21] The skull, although very similar to that of the least weasel, is relatively longer, with a narrower braincase. The projections of the skull and teeth are weakly developed, but stronger than those of the least weasel.[22] The eyes are round, black and protrude slightly. The whiskers are brown or white in colour, and very long. The ears are short, rounded and lie almost flattened against the skull. The claws are non-retractable, and are large in proportion to the digits. Each foot has five toes. The male stoat has a curved baculum with a proximal knob which increases in weight as it ages.[23] Fat is deposited primarily along the spine and kidneys, then on gut mesenteries, under the limbs and around the shoulders. The stoat has 4 pairs of nipples, though they are only visible in females.[23]

The dimensions of the stoat are variable, but not to the extent as the least weasel.[24] Unusually among the Carnivora, the size of stoats tends to decrease proportionally with latitude, in contradiction to Bergmann's Rule.[6] There is pronounced sexual dimorphism in size, with males being 1.5-2.0 times the weight of females.[16] On average, males measure 187–325 mm in body length, while females measure 170–270 mm. The tail measures 75–120 mm in males and 65–106 mm in females. In males, the hind foot measures 40.0-48.2 mm, while in females it is 37.0-47.6 mm. The height of the ear measures 18.0-23.2 mm in males and 14.0-23.3 mm. The skulls of males measure 39.3-52.2 mm in length, while those of females measure 35.7-45.8 mm. Males weigh 258 grams, while females weigh less than 180 grams.[24]

The stoat has large anal scent glands measuring 8.5 x 5 mm in males and smaller in females. The glands produce a strong musky odour produced by several sulphuric compounds. Scent glands are also present on the cheeks, belly and flanks.[23] Epidermal secretions, which are deposited during body rubbing, are chemically distinct from the anal scent glands, which contain a higher proportion of volatile chemicals. When attacked or aggressive, the stoat excretes the contents of its anal glands, producing a strong, musky odour, which is distinct from that of least weasels.[25]


The winter fur is very dense and silky, but quite closely lying and short, while the summer fur is rougher, shorter and sparse.[20] In summer, the fur is sandy-brown on the back and head and a white below. The division between the dark back and the light belly is usually straight, though this trait is only present in 13.5% of Irish stoats. The stoat moults twice a year. In spring, the moult is slow, starting from the forehead across the back toward the belly. In autumn, the moult is quicker, progressing in reverse direction. The moult is initiated by photoperiod. The moult period starts earlier in autumn and later in spring at higher latitudes. In the stoat's northern range, it adopts a completely white coat (save for the black tail-tip) during the winter period.[23] Differences in the winter and summer coats are less apparent in southern forms of the species.[26] In the species' southern range, the coat remains brown, but is denser and sometimes paler than in summer.