Weasel

Weasel facts at a glance

How big is a weasel?

An adult weasel measures 20 cm long — about 12% of the height of an average adult person (1.73 m) — and weighs around 100 g, a small fraction of an average adult’s body weight (70 kg).

What is a group of weasels called?

Explore more animal collective nouns and baby animal names .

Britain's smallest carnivore

The weasel holds the title of Britain's smallest carnivore and is one of the tiniest predatory mammals anywhere. Its long, slender body can be only 16–23 cm from nose to tail root and the smallest individuals weigh under 50 g. That tiny frame is an evolutionary trade-off: slenderness lets the weasel chase mice, voles, and shrews directly into their burrows — a pursuit no other British predator can follow. They can kill prey almost as large as themselves by biting repeatedly at the base of the skull.

Weasel vs stoat: the key differences

The weasel and stoat are closely related and frequently confused, but several features separate them reliably. The weasel is smaller and more compact, with a short tail that is plain brown all the way to the tip. The stoat is noticeably larger with a longer tail that always ends in a black tip — even in the white ermine winter coat that stoats in colder regions develop. In flight, stoats often bound with an arched back; weasels move in a lower, more continuous scurry. In Britain, weasels typically remain brown year-round.

Diet and hunting strategy

Weasels are specialist rodent hunters, eating mainly mice, voles, shrews, and small rats. Their high surface-area-to-volume ratio means they lose body heat rapidly and need to eat around a third of their own weight daily. When prey is abundant they cache food. They are also capable of killing rabbits much larger than themselves. In lean periods they take birds, eggs, and invertebrates. Weasels are active in short, intense bouts of hunting at any time of day or night.

Habitat and range

Weasels are found across Britain and Ireland and throughout much of the Northern Hemisphere — Europe, Asia, and North America (where the closely related least weasel and long-tailed weasel occur). In Britain they favour farmland with hedgerows and rough grassland where rodent populations are dense, using existing burrows, dry-stone walls, wood piles, and dense vegetation for shelter. Weasel populations fluctuate with rodent prey cycles.

Did you know? Weasel facts

• The weasel (Mustela nivalis) is the smallest carnivore in Britain and one of the smallest worldwide, with a body length of just 16–23 cm.
• The key tell is the tail tip: a weasel's tail is short and plain brown all the way to the tip, while a stoat's tail always ends in a black tip. The stoat is also noticeably larger. If size is hard to judge, check the tail tip — it is the most reliable single field mark.
• No. Weasels are tiny and extremely unlikely to bite a person unless cornered and handled. They are not aggressive toward humans and will flee given any chance. They are formidable hunters relative to their size, but pose no danger to people.
• In Britain, weasels generally remain brown year-round, though some develop small white patches. The white ermine winter coat is mainly associated with stoats, and even then only occurs reliably in populations in colder, snowier northern regions where camouflage on snow has a strong benefit.
• A group of weasels is called a pack or, more rarely, a confusion. However, weasels are primarily solitary; the main grouping is a mother with her young.
• Conservation: Least Concern (IUCN).

Diet & feeding

Weasel feeds primarily as a carnivore (mainly mice and voles). The weasel holds the title of Britain's smallest carnivore and is one of the tiniest predatory mammals anywhere. Its long, slender body can be only 16–23 cm from nose to tail root and the smallest individuals weigh under 50 g. That tiny frame is an evolutio

Adaptations

• The weasel holds the title of Britain's smallest carnivore and is one of the tiniest predatory mammals anywhere. Its long, slender body can be only 16–23 cm from nose to tail root and the smallest individuals weigh under 50 g. That tiny frame is an evolutionary trade-off: slenderness lets the weasel chase mice, voles, and shrews directly into their burrows — a pursuit no other British predator can follow. They can kill prey almost as large as themselves by biting repeatedly at the base of the skull.
• The weasel and stoat are closely related and frequently confused, but several features separate them reliably. The weasel is smaller and more compact, with a short tail that is plain brown all the way to the tip. The stoat is noticeably larger with a longer tail that always ends in a black tip — even in the white ermine winter coat that stoats in colder regions develop. In flight, stoats often bound with an arched back; weasels move in a lower, more continuous scurry. In Britain, weasels typically remain brown year-round.

Behaviour & ecology

• The weasel holds the title of Britain's smallest carnivore and is one of the tiniest predatory mammals anywhere. Its long, slender body can be only 16–23 cm from nose to tail root and the smallest individuals weigh under 50 g. That tiny frame is an evolutionary trade-off: slenderness lets the weasel chase mice, voles, and shrews directly into their burrows — a pursuit no other British predator can follow. They can kill prey almost as large as themselves by biting repeatedly at the base of the skull.
• The weasel and stoat are closely related and frequently confused, but several features separate them reliably. The weasel is smaller and more compact, with a short tail that is plain brown all the way to the tip. The stoat is noticeably larger with a longer tail that always ends in a black tip — even in the white ermine winter coat that stoats in colder regions develop. In flight, stoats often bound with an arched back; weasels move in a lower, more continuous scurry. In Britain, weasels typically remain brown year-round.
• Weasels are specialist rodent hunters, eating mainly mice, voles, shrews, and small rats. Their high surface-area-to-volume ratio means they lose body heat rapidly and need to eat around a third of their own weight daily. When prey is abundant they cache food. They are also capable of killing rabbits much larger than themselves. In lean periods they take birds, eggs, and invertebrates. Weasels are active in short, intense bouts of hunting at any time of day or night.

Communication

• Weasel uses scent, posture, and vocal signals to mark territory and coordinate social behaviour.
• Communication intensity often peaks during breeding seasons and territorial disputes.

Habitat & range

Farmland, hedgerows, grassland, woodland

Ecological role

Weasel acts as a predator that helps regulate prey populations and maintain balance in farmland, hedgerows, grassland, woodland.

Conservation status of the Weasel

Sources & references

This guide is compiled and reviewed against established zoological and conservation references. Key sources for the Weasel:

• IUCN Red List of Threatened Species

  Conservation status (Least Concern) reflects the IUCN Red List category for Mustela nivalis.

• iNaturalist — observations & photos

  Search citizen-science observations and community IDs for Mustela nivalis. Useful for range checks and recent sightings — not a substitute for formal Red List status.

• GBIF — occurrence data

  Global Biodiversity Information Facility species search for Mustela nivalis. Explore published occurrence records used in range research.

• IUCN Red List — Mustela nivalis.

  Conservation status (Least Concern) and population trends.

• Animal Diversity Web — Mustela nivalis. University of Michigan Museum of Zoology.

  Life history, morphology, and range.

• Wikipedia — Weasel.

  General taxonomy and overview (cross-check primary sources).

• Global Animal Guide editorial standards

  How we research, source, review, and update every guide for accuracy.