The Ermine has a very elongated slender body with short legs and a medium length tail. Body length ranges from 17-24 cm. The coat is brown and white with prominent black from tip to tail. The coat changes color in winter.

M. erminea is primarily noctural with a diet consisting of small rodents, birds, eggs, frogs and insects. The short-tailed weasel is swift, agile and has a keen sense of hearing and smell.

Adult males are dominant over females and young. Females are polyestrous but produce only one litter per year. Mating generally occurs in late spring or early summer. Litter size averages 6 young.

The Ermine is found in many habitats from tundra to deep forest but prefers areas with vegetative or rocky cover. Mustela erminea occurs in circumboreal, tundra and forested regions of Palearctic. Afghanistan, Algeria, Austraia, Belarus, Belgium, Posnia and Herzegovina, Canada, China, Croatia, Czech Rep., Denmark, Estonia, Finland, France, Germany, Great Britain, Hungary, Ireland, Italy, Japan (C Honshu), Kazakhstan, Kyrgyzstan, Latvia, Lithuania, Luxembourg, Mongolia, Netherlands, New Zealand (introduced), Norway, Poland, Romania, Russia, Serbia and Montenegro, Slovakia, Slovenia, Spain, Sweden, Switzerland, Tajikistan, USA (C California, N New Mexico, N Iowa and Maryland).