The Least Weasel, Mustela nivalis, is the smallest member of the weasel genus, Mustela and indeed the smallest living carnivore.
The least weasel is found throughout the northern parts of Europe, Asia and North America, except for Ireland and eastern Canada. It extends as far south as North Africa. It has been introduced into New Zealand. The North American population was formally classified as a separate species, Mustela rixosa, but it is now thought that the distinction cannot be maintained. They are generally found in farmlands, meadows, brushy areas and woodland edges.
Through much of its European range, the least weasel overlaps with the somewhat larger but otherwise similar Stoat.
Like all weasels, the least weasel is a slender animal with a long tail and short legs. This enables it to follow its prey, mostly small rodents into their burrows. They also kill hares, which can be more than 100 times their own size. Its fur is reddish-ginger, brighter than that of most other weasels, with white belly fur. In the northern parts of its range it moults to pure white in winter, as camouflage against the snow. It is rarely more than 9 in (23 cm) long. They are most active at night but weasels are sometimes seen during the day.
Least weasels are highly solitary, and even mating does not occur without a fight. Females can breed several times in a year when food is plentiful. Perhaps because of their small size, least weasels have an even greater reputation for ferocity than the other weasels.