Least weasel

Name and taxonomy

Carl Linnaeus named the least weasel in 1766, in the twelfth edition of Systema Naturae. The species name nivalis comes from the Latin word for snow, because northern animals turn white in winter. The type locality is Västerbotten in Sweden. Around 18 subspecies are recognised, and they fall into three groups by size. The tiny pygmaea and rixosa forms live in the far north and in North America. The large boccamela weasels live in Transcaucasia, Central Asia and North Africa, and the nivalis group sits between them.

Some zoologists once split the species into four, and others separated the Egyptian weasel. A 2016 study found the Egyptian weasel to be a population of nivalis after all. In Britain it is simply the weasel, and in North America the least weasel, to set it apart from the long-tailed weasel. Other English names include little weasel and common weasel.

Evolution and relatives

The family Mustelidae includes stoats, polecats, otters and badgers, and the genus Mustela holds the true weasels. The least weasel is the least specialised member of the genus, with a skull that keeps juvenile proportions even in large races. Mustela praenivalis, a Middle Pleistocene species of Europe, is the weasel's direct ancestor. The line began 5 to 7 million years ago, when open grassland replaced northern forest and small burrowing rodents multiplied. The weasel's ancestors were larger, and they shrank to follow the rodents underground.

The modern species probably arose in the Late Pleistocene. Its small size and long body let it work under snow and in burrows through the Ice Age. It probably crossed to North America over the Bering land bridge about 200,000 years ago. Fossils of the species are known from Denisova Cave in Siberia. Its closest relative in Europe is the stoat, which is larger and has a black tail tip.

Appearance

The body is thin, long and very flexible, with a blunt head no wider than the neck. The eyes are small, dark and bulging, and the ears are short and round. The legs are short, and the tail is less than half the body length and carries no black tip. The feet have five toes with sharp, dark claws and hairy soles. Summer fur is short and rough, brown to chocolate on top and white below, with a straight line between the two. A brown spot often sits at the corner of the mouth.

Size varies more than in almost any other mammal, and North African weasels can weigh four times as much as Arctic ones. Head and body length is 11.4 to 26 centimetres, with a tail of 1.2 to 8.7 cm. Males average 13 to 26 cm and females 11.4 to 20.4 cm. In the biggest races a male can be 1.5 times as long as a female. Males weigh 36 to 250 grams and females 29 to 117 g, though most adults fall between 30 and 100 g. In the north and at high altitude the winter coat is pure white, dense and silky.

Habitat and range

The least weasel lives right around the northern world. Its range covers all of Europe except Ireland, and North Africa from Morocco to Tunisia. It also spans much of Asia, including Japan, and northern North America from Alaska across Canada. People have introduced it to New Zealand, Malta, Crete, the Azores and São Tomé. GBIF holds records from 72 countries.

The weasel uses fields, open woodland, scrub, rocky ground, tundra, taiga, parks and gardens. It lives up to about 3,000 metres in mountains. What matters is cover, because the weasel hunts by ambush and hides from owls and foxes. It does not dig, and it sleeps in the burrow of a mole, a vole or a rat. The nest chamber, about 10 centimetres across and up to 15 cm below ground, is lined with grass and the fur of its prey. A weasel keeps several dens in its territory and uses each for a short time.

Diet and hunting

Small rodents are the main food: voles, mice, hamsters, gerbils and lemmings. In England the field vole is the favourite, and in a good vole year it makes up to 54% of the diet. When rodents are scarce, the weasel turns to birds, eggs, lizards, frogs, fish and insects, and females may not breed. Young rabbits are important in spring, and a weasel can kill a rabbit that outweighs it five to 10 times over. In rare cases weasels have killed hares and capercaillie.

The weasel follows prey down tunnels and under snow, where its narrow body fits. It kills a vole with a bite to the back of the skull or the neck. A large prey animal dies of blood loss or shock. The weasel eats about 35 grams a day, around a third of its body weight, and it can eat more than half in winter. Because it kills more than it can eat, it caches the rest near the den. When food is plentiful it may take only the brain.

Behaviour and social life

Least weasels live alone outside the breeding season. A male holds an exclusive range that overlaps or contains the ranges of several females. He marks it with droppings, urine and gland secretions, which he spreads by dragging his rear and rubbing his body. Range size depends on prey: where voles are dense, ranges shrink. In spring, or when food runs short, a male wanders far beyond his range.

Older males dominate females and young males. A dominant male threatens and attacks a subordinate male, who squeals and retreats. Females fight back, so they are seldom attacked, but they submit to the top male. A weasel must eat often, so it forages at any hour, day or night. It moves in bounds, and the tracks of the fore and hind feet lie 18 to 35 centimetres apart.

Weasels sometimes perform a series of leaps and twists with an arched back and bristling fur, called the weasel war dance. One idea is that the dance confuses prey, but weasels also dance with no audience. Kits dance most, in play with their siblings. Where the stoat shares its ground, the weasel keeps to higher land, smaller prey and smaller holes, and avoids meeting it.

Communication and senses

Smell is the main sense, and a weasel hunts by nose in dark tunnels. Sight and hearing help in the open, and long whiskers pick up vibrations and guide it in tight spaces. Scent from the anal glands marks the den and the range. The same glands can fire a foul, sulphurous fluid at an enemy.

The weasel has four basic calls. A guttural hiss shows alarm, and short barks and shrieks follow when it is provoked. A shrill wail or squeal means it is cornered. A soft trill passes between a male and a female, or between a mother and her kits. Kits squeak and chirp to their mother and to each other.

Reproduction and life cycle

Mating runs from April to July in most of the range, with some breeding at any time of year. Both sexes take several partners, and males do not fight over females. Courtship is rough, with biting and tumbling until the male grips the female by the neck. Mating can last more than an hour, and the long act triggers ovulation.

Pregnancy lasts 34 to 37 days, and a litter usually holds four to six kits, though 1 to 13 have been recorded. Kits weigh 1.5 to 4.5 grams at birth and are pink, naked, blind and deaf. White down appears at four days, the milk teeth come through at two to three weeks, and the eyes open at three to four weeks. Kits can kill by eight weeks, and the family breaks up after nine to 12 weeks. The mother does all the care, and she brings meat to the nest from about two weeks.

In a lemming peak a female may raise three litters in a year, but one or two is usual. Kits mature at three to four months, so a spring kit can breed in its first summer. Most wild weasels live only 1 to 2 years, and few kits survive to weaning. The wild record is about 4 years, and a captive weasel reached 10.

Predators and threats

Almost every larger predator eats weasels. Remains turn up in the droppings of red foxes, sables, polecats, stoats, eagle owls and buzzards. Barn, barred and great horned owls catch them most often, and hawks and falcons take adults. Snakes such as the black rat snake and the copperhead take kits, and foxes dig out nests. The weasel lacks the black tail tip that draws a hawk's strike away from a stoat's body, so it is more exposed.

Fleas from the nests of moles, shrews and rodents infest the weasel. A nematode, Skrjabingylus nasicola, lives inside the sinuses of the nose and can deform the skull, but it seems to do little harm. Starvation is a constant threat, because the weasel stores little fat and burns energy fast. The species faces no human threat on a large scale.

Population and conservation

The IUCN lists the least weasel as Least Concern. It has a huge range and a large population that is not thought to be in decline. Numbers rise and fall with the rodents: in the Arctic, weasels boom and crash with the lemmings. It is common in Europe and Asia and less so in North America, where it is still not rare.

No large conservation programme appears to exist for the species. In New Zealand the weasel is an introduced pest, and it preys on ground-nesting birds such as the brown kiwi. Trappers catch it by accident in traps set for larger fur bearers. Pelts have little value, though some trim luxury coats and mittens.

Relationship with humans

The weasel does people a service by killing the rodents that eat grain and spread disease. Farmers have long blamed it for taking chickens, but there is little evidence that it preys on livestock. It is seldom seen, because it hunts under cover and moves fast. A cornered weasel probably bites, but it poses no danger to people.

In Britain the weasel is probably known more from stories than from sightings. In English, weasel words means evasive language, a phrase that Theodore Roosevelt made popular. Unlike the ferret, the least weasel has probably never been bred as a working animal. Zoos rarely keep it, and captive animals have lived 5 to 6 years on average.

In culture and myth

In ancient Macedonia, a weasel sighting was a good omen. Macedonian women with a headache after washing in water left out overnight blamed a weasel, which had used the water as a mirror. They would not say its name, in case it shredded their clothes. In southern Greece the weasel was once a bride, turned into a bitter animal that tears the dresses of other brides. In Aesop's fable, Aphrodite changes a weasel into a woman, but at the wedding feast the bride leaps after a mouse. Pliny the Elder wrote that the weasel's smell was the one thing that could kill a basilisk.

Ojibwe stories give the weasel the power to kill a wendigo by entering its body from below. Inuit tradition makes the weasel a sign of wisdom and courage, and a hero takes its shape for a brave deed. In seventeenth-century England the witch hunter Matthew Hopkins listed weasels among the familiars of witches. Women in Greece and Rome tied the weasel to childbirth and to midwives.