What Do Weasels Eat? Least Weasel Diet and Hunting

The main foods of the least weasel

The least weasel is a specialist predator of small rodents. Over most of its range, voles and mice make up the bulk of its diet, and its whole body is built to catch them.

In Britain, the field vole is often the single most important prey. In years when field voles are abundant, they can make up around half of all the weasel’s meals. When voles are scarce, weasels turn more to birds and eggs, and many females fail to breed.

How weasels hunt in burrows

The least weasel’s long, narrow body and tiny head let it squeeze through any hole about 2.5 cm (1 in) wide. That means it can follow a vole or mouse into its own tunnel system, where the prey has nowhere to run. Few other predators can do this.

A hunting weasel moves in quick bounds, darting in and out of holes, along hedgerows and stone walls, and through long grass. It finds prey mainly by smell and hearing, and often stands upright on its hind legs to look around. It kills small rodents with a fast bite to the back of the skull or neck. Larger prey may be held with the feet and bitten repeatedly.

Weasels also move into the burrows of the animals they eat. The nest chamber is often lined with grass and the fur of former residents.

Hunting under the snow

In winter, voles and lemmings live in a hidden world of tunnels under the snow, called the subnivean zone. There, close to the ground, the temperature stays near freezing even when the air above is much colder. Owls and foxes must listen for prey and plunge into the snow to catch it, but the least weasel simply goes in after it.

In the Arctic and boreal forests, weasel numbers rise and fall with lemming and vole populations. When rodents boom, weasels breed quickly and become common; when rodents crash, many weasels starve. In the far north the weasel turns white in winter, which helps it hide when it does come to the surface.

How much does a weasel eat?

A least weasel needs about 30–35% of its body weight in food every day. For a small weasel that is roughly one or two voles. In very cold weather, or when a female is feeding kits, it may need even more.

There are two reasons. First, a long, thin body has a lot of surface area compared with its volume, so it loses heat fast. A weasel’s body shape is great for chasing prey into tunnels but costly in the cold. Second, weasels store very little fat, because extra bulk would stop them fitting into burrows. They solve the problem by eating often and by hunting in many short bursts, day and night, with rests in a warm nest in between.

Surplus killing and caching

When prey is easy to catch, a weasel may kill more than it can eat at once. Biologists call this surplus killing. It is not wasteful, because the weasel usually carries the extra prey back to its nest or to a hidden store and eats it later. Caches of several dead voles or mice have been found in weasel nests.

This habit acts as insurance against bad weather or a sudden drop in prey. When food is very plentiful, a weasel may eat only the most nutritious parts, such as the brain, and leave the rest.

Males, females and prey size

Male least weasels are much bigger than females, and they eat slightly different food. Males have larger home ranges, travel more and take a wider range of prey, including more young rabbits and larger rodents. Females are small enough to follow voles and mice much deeper into narrow tunnels, so they depend more on rodents.

The larger stoat takes more rabbits and bigger prey than either sex of least weasel. Where the two species live together, the weasel concentrates on small rodents. To compare their diets in detail, see what do stoats eat?, and for more on the weasel’s tiny size, read what is the smallest carnivore?.

Myths about what weasels eat

Myth: weasels suck blood. Weasels do sometimes lick blood from a wound, which may be the source of the story, but they eat meat, not just blood.

Myth: weasels are pests on farms. In the past, gamekeepers and farmers killed weasels for taking eggs and chicks. Today many farmers value them because a single weasel can eat hundreds of voles and mice in a year, rodents that would otherwise damage crops and stored grain.