This fierce little carnivore is scarcely larger than the mice on which it preys. Its total body length seldom exceeds 20 cm (8 in.). Its short tail would add less than 4 cm (1.5 in.) to that.

The least weasel occupies most of Canada with the exception of the Maritimes, southern Quebec and Ontario, the Arctic and central and coastal British Columbia. It has broad circumpolar distribution through Europe, north Africa, Asia and North America.

Living almost exclusively on mice, shrews, and lemmings, they also use the fur of these animals to line their underground nests. The Inuit in particular look upon this small hunter with great respect, and the capture of one is considered a good omen.

Incredibly quick and agile, these tiny predators are seldom trapped except by accident. The coat, which is brown above with a white underside, turns completely white in winter throughout most of its North American range. The least weasel does not have a black tip on its tail. This trait distinguishes it from similar weasels such as ermine.