Least Weasel

Built for Tunnels

The least weasel is the smallest carnivorous predator in the world. It has a long, tubular body and short limbs, and it moves easily through leaf litter, underground tunnels and subnivean tunnels, which are the ones beneath the snow. It does not dig its own den. It uses dens abandoned by its prey or other burrowing animals.

Across its range a least weasel weighs 30 to 100 grams and measures 165 to 217 millimetres including the tail, and males are the bigger sex. Individuals from warmer climates tend to be bigger: populations in North Africa can weigh over 70 grams, while North American weasels average about 45 grams and about 190 millimetres. It is widespread across the Northern Hemisphere, native from Alaska through Canada and the northern United States, and in Europe outside Ireland.

Winter coat In northern populations the coat turns pure white in winter, but it always lacks the black tail tip that stoats and long-tailed weasels carry.

Eating Half Its Weight

The least weasel stores little fat, has very high metabolic demands and must eat very regularly to avoid starving. It can get through more than half its body weight in food every day, and more still in winter, and it is often out foraging day or night.

The menu is mostly rodents. Field voles, wood mice and bank voles make up much of the diet in southern populations, and when rodents are plentiful they can be almost 100 percent of it. In the Arctic, collared lemmings are vitally important for breeding success. When rodents are scarce, a weasel will switch to birds’ eggs, lizards, amphibians, small fish and invertebrates, and it will not turn down carrion.

A weasel often takes down animals bigger than itself, but each meal is only a few grams of meat. The leftovers are cached, hidden near the den entrance for later.

Born Ready

Kits are born hairless and helpless. Gestation lasts about a month. By about 47 days they can kill prey for themselves. Killing is an innate behaviour: captive kits with no experience of prey still kill it, though kits that stay with their mother have higher success rates.

Prey numbers have a dramatic effect on how many litters and young a female has. When prey is plentiful, as when Arctic lemming numbers boom, a litter can reach 15 kits and a female can have up to three litters in a year.

Musk and the War Dance

A weasel this size is prey for plenty of animals. Owls, falcons, eagles and hawks typically prey on adults, snakes and foxes often take the young, and larger weasels such as the stoat may also eat least weasels. Its answers are camouflage, hiding, biting and noise, and when cornered or startled it can discharge a foul-smelling fluid from its anal glands.

Sometimes it also performs the “weasel war dance”, a series of leaps and twists with an arched back and stiff limbs, often with bark-like calls. It is thought to perplex prey, but that is one hypothesis: there is no solid scientific evidence explaining it, and weasels have been seen dancing without an audience.

In captivity the oldest recorded least weasel reached 9.1 years. The International Union for Conservation of Nature rates the species Least Concern.