A small, carnivorous mammal of the genus Mustela (family Mustelidae). Weasels are up to 20 cm long and slender with short legs, and usually with reddish-brown fur on the back and a white underside. They feed on small animals, especially rats and rabbits, but also poultry. In the UK the term describes the least weasel (M. nivalis), which is the species found in the UK. In US usage it refers to any of the 17 species in the genus. Weasels are found worldwide except in Antarctica, Australia, and some islands.