THE WEASEL Mustela nivalis



Fur ginger to russet brown, cream below. Long slender body, short tail.
Head/body length: Males 194-217mm; Females 173-183mm.
Tail: males 42-52mm; females 34-43mm.
Weight: Males 106-131g, Females 55-69g.

General Ecology:

Widespread throughout Britain, weasels are our smallest and probably most numerous carnivores. However, they are absent from Ireland and most off-shore islands. They are found in a wide range of habitats which include urban areas, lowland pasture and woodland, marshes and moors. Weasels are less common where their small mammal prey are scarce, such as at higher altitudes and in dense woodland with sparse ground cover.

Weasels specialise in hunting small rodents and their numbers depend on the abundance of their prey. The weasel's small size enables it to search through tunnels and runways of mice and voles. Access to tunnels means weasels can hunt at any time of the day or year. They do not hibernate and can hunt even under deep snow. Additional prey such as birds, eggs and young rabbits may be taken, particularly if rodents are scarce.

Dens are usually nests of former prey taken over by weasels, and may contain the remains of food from several days meals. In cold climates the nests are often lined with fur from prey. A weasel's home range usually contains several dens and resting places that are visited at intervals.

Weasel home ranges vary in size according to the distribution and density of prey. Male and females live in separate territories, male ranges being larger. Resident animals of both sexes may defend exclusive territories at times when numbers are high and neighbours numerous. In spring males extend their range to seek mates.

Probably only one litter, of 4-6 young are born per season. Young are weaned at 3-4 weeks and can kill efficiently at 8 weeks. Family groups split up at 9-12 weeks.

Only one in 80-90 weasels survives to over 2 years old. They are small enough to be regarded as or confused with prey by almost all other predators; hawks, owls, foxes, cats and mink have been known to eat them.


Traditionally weasels have been considered enemies of gamebirds and Gamekeepers have exercised intensive predator control, trapping and killing many weasels along with other carnivores. Weasels do kill some gamebird chicks, but probably very few.

Weasels have no legal protection in Britain. Trapping probably has no long term effect: weasel populations are very resilient, and they naturally suffer high mortality. In bad rodent years many weasels starve and few of the survivors breed. Local populations often experience extinctions. However, weasels are extremely good at recolonising abandoned areas when conditions improve.

Frequent Questions:

What is the difference between a stoat and a weasel?
Stoats are larger and have longer tails which end in a black tip. Stoats may go white in winter, but weasels in Britain do not. (They do in northern Scandinavia).

I have seen a weasel running round and round in a circle, leaping about and somersaulting. What was it doing?
Weasels acting strangely in this way are said to be "dancing", either in play or as a clever trick to catch prey. This behaviour could be a response to extreme discomfort caused by a large parasitic worm commonly found in the nasal sinuses of stoats and weasels. The presence of these worms causes distortion of the skull bones and consequent pressure on the brain. This, along with the wriggling of the worms must result in extreme irritation, and may affect the weasel's behaviour.

Is it true that weasels form "gangs"?
Parties of weasels can be seen moving around together in early summer. These are usually family groups; a mother and her young, out on a hunting expedition. In a good breeding year these groups can be quite large. After 2 - 3 weeks, when they have got their permanent teeth and gained some experience of hunting, the young will set out on their own. Stories of aggressive gangs of weasels marauding the countryside have been perpetuated by fictional tales like The Wind in the Willows.

Further Information: