Weasel (Mustela nivalis)

French: Belette D'Europe
Spanish: Comadreja
GenusMustela (1)
SizeFemale weight : 55 - 69 g (2)
Male weight: 106 - 131 g (2)
Male head-body length: 194-217 mm (2)
Female head-body length: 173-183 mm (2)
Male tail length: 42-52 mm (2)
Female tail length: 34-43 mm (2)

The weasel is classified as Least Concern (LC) on the IUCN Red List (7), and a species of conservation concern by the UK Biodiversity Action Plan, although not a priority species. Listed under Appendix III of the Bern Convention (3).

Britain's smallest native carnivore (2), the weasel (Mustela nivalis) has a long slender body, and a short tail. The fur is ginger to a rich chocolate-russet brown in colour, and the underparts are creamy-white (2). The narrow head is supported on a long neck, and the legs are short (1). The large eyes are black, and the ears are rounded (1). In northern parts of the range, weasels turn white in winter, but they do not do so in the UK (2).

The weasel is widespread throughout mainland Britain, and on large islands around the UK, but absent from Ireland (3). It also occurs throughout much of Europe, reaching into Asia as far east as Japan, as well as in North America (3).

Found in a range of habitats, the weasel favours good cover and plentiful prey, including woodland, grassland, sand dunes, mountains (3), urban areas, marshes and moors (2).

Weasels are active at any time of day or night, and intersperse periods of activity with a rest period (3). They feed mainly on small rodents, rabbits, birds and eggs (3), killing prey with a bite to the neck (1). Their small size enables them to enter the tunnels of mice and voles whilst hunting (2), and they often take over the nests of their prey, lining their dens with fur from prey during cold weather (2). A number of dens will be used within the home range. Males and females occupy separate territories, and defend these against members of the opposite sex (2). During spring, males move around in search of a mate (2). The male and female often fight prior to copulation, and the male grabs the female by the neck before he mates (1). A single litter of between 4 and 6 (2) naked, blind and deaf (1) kits is produced each year; the kits are weaned after 3 to 4 weeks and begin to hunt well by 8 weeks of age (2), often accompanying their mother to hunt in 'gangs' (2). By 9 to 12 weeks after birth the family group starts to split up (1).

Historically, weasels were believed to have magical powers, and were said to be able to bring their dead young back to life. It was also thought that they hypnotised their prey by dancing (4); in fact 'dancing' behaviour is thought to be a response to discomfort caused by internal parasites (2).

Populations of weasels are controlled because they take gamebird eggs and chicks (3). Likely threats include habitat loss and simplification, as well as predation by foxes. Agricultural changes have led in many areas to the loss or reduction of rough grasslands, which is prime habitat for the field vole, a key source of food for weasels (3). Evidence is building that rodenticides are having an effect on weasels and stoats, as they eat poisoned rodents (5).

Research is currently being carried out to determine whether the populations of weasels and stoats, our smallest carnivores are in decline (4). Weasels are not legally protected in the UK (2).

For more information on this species:

Information authenticated by Dr Pat Morris, with the support of the British Ecological Society

  1. Animal diversity web. (July 2002)
  2. The Mammal Society. Weasel Fact Sheet. (July 2002)
  3. The Environment Agency. (1998) Species and Habitats Handbook: Look-up chart of species and their legal status. The Environment Agency, Bristol.
  4. Macdonald, D.W. and Tattersall, F.T. (2001) Britain's mammals- the challenge for conservation. The Wildlife Conservation Research Unit, Oxford University.
  5. UK Safari (July 2002)
  6. McDonald, R.A., Harris, S., Turnbull, G., Brown, P. and Fletcher, M. (1998) Anticoagulant rodenticides in stoats (Mustela erminea) and weasels (Mustela nivalis) in England. Environmental Pollution103: 17-23.
  7. IUCN Red List (February, 2011)