The stoat moves in a sinuous manner when pursuing its prey. It is extremely quick over the ground considering its small size, and is also a strong swimmer that is able to colonize offshore islands.  

  The stoat is built long and slender, making it one of the few species able to follow burrowing animals into their own homes. It partly compensates for this shape by having short legs, small ears, and thick fur in winter. Stoats may grow up to 30 cm long, with males much larger than the females.

  The stoat's coat is a rich red-brown with tan or off-white belly; the tail has a black tip. In winter, the coat is thicker, and in warmer areas it remains brown. However, in cold snowy regions its color changes to white, although the black tip to the tail remains.  

  This white fur is known as "ermine", a term originating either from the Latin phrase "Armenius mūs" ("Armenian mouse") or from a word common to the Germanic and Baltic languages, hence the scientific name.

  At this stage, where the animal is known as a "stoat", it may be referred to as ermine, or as being "in ermine".

  The winter ermine has been used in art as a symbol of purity or virginity. The white fur was highly prized, and used in the clothes of the Lord Chief Justice of England. The furs would be sewn together, the tail-tips making a pattern of black dots on a white ground. A version of this pattern is used in heraldry as ermine tincture.

Both the animal and the heraldic tincture are symbols of Brittany.

  In all seasons the stoat has a black tip to its tail. 

  The black tip probably serves as a sign to predators, which would include almost any carnivore large enough to eat a stoat (e.g. wolves, foxes, and some birds of prey). This kind of coat is very similar to the coat of the long-tailed weasel (Mustela frenata), a related animal of about the same size which also changes into white in the northern part of its range, and it is easy to confuse these kinds of weasels.

  The alternative North American name for the stoat, the "Short-tailed weasel" arose because its tail length distinguishes it from the long-tailed weasel. In general it is found farther north. Both species can be distinguished from the weasel because the weasel lacks a black tip on its tail.

 Geographical range

  Stoat is native to the area between the 40th parallel (north) and the beginning of the Arctic Circle, which encompasses most of northern Eurasia and North America.

  Stoats have been introduced to New Zealand and Australia to control a rabbit overpopulation. But the problem remained unsolved. They were also brought to Terschelling Island to control water voles (water rats).

  Ermines can swim up to 1.5 kilometres (0.93 mi) across seawater.

Diet

  The stoat is a carnivore. It eats insects, small mammals up to the size of a rabbit, birds and their eggs and young. It also eats small reptiles and fish. It is a very skillful tree climber and can descend a trunk headfirst, like a squirrel.

  The stoat is capable of killing animals much larger than itself. When it is able to obtain more meat than it can eat it will often stores the extra food for later. When this is the case, it will often kill by breaking the prey's neck without marking the body, presumably so its cache does not spoil easily.