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Weasel (Mustela nivalis)

What weasels lack in size, they more than make up for in appetite.

Scientific name: Mustela nivalis

Family: Mustelidae

Appearance

Weasels have chestnut brown fur, with white-cream underparts and a slim, long body with a typical length of 20-27cm, including the tail. Even the largest weasel is unlikely to weigh much more than 190g, while females can be as small as 50g.

It can be difficult to distinguish weasels from their close relative the stoat. Weasels are smaller – around two-thirds the length and half the weight - but the most obvious difference is the tail. A weasel’s tail is short and wholly brown, while a stoat’s is noticeably longer with a black tip.

Where and how to spot

Weasels are found across Britain (they are absent from Ireland) and will occupy a wide variety of habitats, provided there is cover to hide in and sufficient numbers of their small rodent prey. An extremely high metabolism means they are active day and night, but small size and a preference for sticking to thick cover make them hard to see. If you’re lucky, you may catch a glimpse of one of these micro-predators darting across your path in search of its next meal.

Feeding

The weasel is a small rodent specialist, primarily feeding on voles and mice. Its small, slender build means it can often follow rodents into tunnels and burrows that other predators can’t reach. Weasels will also take birds and their eggs and can even hunt rabbits, despite being only a fraction of their size.

Behaviour and breeding

Solitary, weasels only come together to mate. They will have a litter of around four to six young, known as kits, from April to August. A second litter may be produced if enough prey is available. Weaning occurs after around three to four weeks and the kits are independent after roughly two to three months. A weasel will rarely live any longer than two years. The species’ small size means it is occasionally killed by larger predators such as foxes and birds of prey.

Threats

Gamekeepers may trap weasels due to possible predation of gamebird eggs and chicks. The species is considered widespread and common, but there are concerns the UK population may be declining, with the loss of hedgerows (a favoured weasel habitat) possibly a contributing factor.

You might not know

• Rural folklore states that weasels are capable of squeezing themselves through a wedding ring!

• A weasel needs to eat roughly one-third of its body weight per day.

• The weasel is one of the world’s widest ranging carnivores, occurring across most of the northern hemisphere.