Stoat

Name and taxonomy

Carl Linnaeus named the stoat Mustela erminea in 1758, with Sweden as the type locality. The word stoat probably comes from Dutch stout, meaning bold, or from a Gothic word that means to push. Ermine may come from the name Armenia, where early writers thought the animal originated, or from an old Germanic root. North Americans call the animal the short-tailed weasel. A male is a dog, hob or jack, and a female is a jill. A group is a gang or a pack, though stoats seldom gather.

For a long time the stoat was treated as a single species with a range around the whole northern hemisphere. A study in 2021 split it into three species. Mustela erminea in the strict sense covers Eurasia and Alaska. The American ermine, M. richardsonii, takes most of North America, and the Haida ermine, M. haidarum, lives on islands off the Pacific coast. Within the narrower species, 21 subspecies are recognised.

Evolution and relatives

The species descends from Mustela palerminea, a carnivore that was common in central and eastern Europe in the Middle Pleistocene. The line began to take shape 5 to 7 million years ago, when open grassland replaced northern forest. Grassland brought a boom in small burrowing rodents, and the stoat's forebears shrank to follow them underground. The stoat appeared in Eurasia soon after its North American counterpart, the long-tailed weasel, appeared about 2 million years ago.

Ice ages suited the stoat. A small, long body let it hunt under snow and inside burrows when larger predators struggled. Its ancestors crossed into North America over the Bering land bridge about 500,000 years ago. Genetic work places the American ermine and the Haida ermine as its closest relatives.

Appearance

The stoat has the classic weasel build: a long, almost cylindrical body, a long neck, short legs and a small triangular head. The head sits far in front of the shoulders. The eyes are round, black and slightly bulging, and the ears are short, rounded and pressed to the skull. The whiskers are very long. Each foot has five toes with large claws that do not retract.

Males are about 25% longer than females and 1.5 to 2 times their weight. Head and body run 18.7 to 32.5 centimetres in a male and 17 to 27 cm in a female. The tail measures 6.5 to 12 cm and always exceeds a third of the body length. Males average 258 grams, and females weigh under 180 g. Oddly for a carnivore, stoats get smaller further north, the reverse of the usual rule.

In summer the back and head are sandy brown and the belly is white, with a straight line between the two. Twice a year the coat moults, slowly in spring and quickly in autumn, in response to day length. In the north the winter coat is entirely white apart from the black tail tip. Further south the winter coat stays brown but grows denser and sometimes paler. The black tail tip never changes, and it is the surest way to tell a stoat from a least weasel.

Habitat and range

The stoat lives right around the northern hemisphere. In Europe it reaches south to about 41 degrees north in Portugal. It lives on most European islands except Iceland, Svalbard and those of the Mediterranean. In Asia it runs from the Caucasus and the western Himalaya across Siberia to Mongolia, northern China and Japan. In North America the strict species holds Alaska, western Yukon and Arctic Canada east to Greenland. It lives from sea level to 3,000 metres. GBIF holds records from 56 countries.

The stoat is not fussy about habitat. It uses tundra, alpine meadow, woodland, marsh, riverbank, farmland and hedgerow, wherever there is cover and prey. In British Columbia it turned up in every forest type surveyed, from dry pine to wet cedar and from fresh clear-cuts to old growth. In Finland, females settled where voles were most abundant, and dominant males took the next best ground.

Two islands show what the stoat does when it arrives somewhere new. Settlers brought stoats from Britain to New Zealand in the 1880s to control rabbits, over the objections of scientists. Bird numbers fell within six years. Stoats reached Orkney, north of Scotland, in 2010 and began to eat Orkney voles and ground-nesting birds. By 2024 an eradication project had trapped more than 6,300 stoats there at a cost of £7.9 million.

Diet and hunting

Mouse-like rodents are the core of the diet everywhere. The stoat also takes rabbits, hares, water voles, hamsters, pikas and lemmings, animals that often outweigh it. Birds, eggs, fish, shrews, frogs, lizards and insects fill in when mammals are scarce. In Britain, rabbits are a major food, and males eat more of them than females do. In Denmark, where there are no rabbits, rodents make up 84% of the diet. In New Zealand the stoat eats mostly birds, including kiwi, kaka and parakeets.

A stoat eats about 50 grams a day, a quarter of its own weight. It hunts in a fast zigzag, checking every hole and crevice, and often rises on its hind legs to look around. Small prey dies at once when the stoat bites the neck from behind. A rabbit is too big for the stoat's short canines to reach the spine, and it usually dies of shock. The stoat wraps its body around larger prey and bites repeatedly at the base of the skull.

Females hunt further into tunnels than males, because they are smaller. Stoats climb trees to raid nests, and they are frequent thieves at nest boxes. When food is plentiful, a stoat kills more than it can eat and stores the extra in a side chamber of its den. The famous stoat dance in front of rabbits may confuse the prey, or it may be a symptom of a parasite in the nasal passages.

Behaviour and social life

Stoats live alone. A male holds a territory that takes in one or more smaller female territories, and he defends it against other males. Home ranges are typically 10 to 40 hectares but can reach 200. Old dominant males may hold ranges 50 times larger than those of young low-ranking males. Density rises and falls with prey and runs at about 2 to 6 stoats per square kilometre.

Territory means something different in each season. In autumn and winter males keep to their own ground. In spring and summer many males give up their territories and roam widely in search of females. Females stay put through the breeding season. Both sexes mark boundaries with urine, droppings and scent, and neighbours avoid one another.

The stoat digs no burrow of its own. It takes over the tunnels of the rodents it kills and lines the nest with their fur. It also dens under tree roots, in hollow logs, rock piles, haystacks, stone walls and even old magpie nests. Each stoat keeps several dens across its range. It is mainly nocturnal but may be active at any hour, in bursts of three to five hours. A stoat may travel about 1 kilometre in a night, and up to 15 km when prey is thin.

Communication and senses

The stoat has sharp senses of smell, sight, hearing and touch. It tracks rabbits and rodents mainly by scent, finds insects by sound and fish by sight. The long whiskers probably help it feel its way through dark tunnels.

Scent does most of the talking. Large anal glands produce a strong musky smell from several sulphur compounds, released when the stoat is attacked or aggressive. Glands on the cheeks, belly and flanks leave a different, less volatile scent when the animal rubs against objects. An anal drag says that a territory is occupied, and body rubbing goes with fights. Chemical cues are probably how a female tells males that she is ready to mate.

The stoat is usually silent. Kits chirp finely, and adults trill with excitement before mating. A nervous stoat hisses and mixes in sharp barks. An aggressive one shrieks and screeches for long periods.

Reproduction and life cycle

The stoat has one of the strangest breeding cycles of any mammal. Mating takes place between April and July, and a single copulation can last an hour. The fertilised embryos then stop developing and float free in the womb for nine to ten months. Active growth resumes with the longer days of March, and the young are born the following April or May. Total gestation is therefore about 300 days, though the embryo grows for little more than a month. An adult female spends almost her whole life either pregnant or in heat.

Stoats are not monogamous, and a litter often has more than one father. A female can reabsorb her embryos, and in a hard winter she may lose the whole litter this way. Litters range from 3 to 18 kits and usually hold four to nine. At birth the kits are blind, deaf and toothless, with a coat of fine white down. Milk teeth appear at three weeks, solid food at four weeks, and the eyes open at five to six weeks. Kits huddle for warmth until about five to seven weeks, because they cannot yet control their body heat.

The female raises the litter alone, and the kits hunt with her by eight weeks. Females are fertile at only two to three weeks old, while still blind and hairless, and adult males often mate with them before weaning. Males mature at 10 to 11 months. Life is short. A wild stoat typically lives one to 2 years, and the wild record is 7 years. The captive record is 12.5 years, from an animal that was wild born.

Predators and threats

Red foxes and sables kill stoats, and so does a long list of birds. Hawk-owls, short-eared owls, buzzards, kites, goshawks, eagle-owls and golden eagles all take them. In North America, martens, fishers, badgers and domestic cats join the list. The stoat's escape is its speed and its ability to run over snow or vanish down a burrow.

Disease and parasites kill many. The nematode Skrjabingylus nasicola invades the nasal sinuses, erodes the bone and lowers fertility, and it can kill by pressing on the brain. Shrews are thought to carry the worm to stoats. Tuberculosis has been recorded in stoats in New Zealand and the former Soviet Union, and captive animals suffer from distemper. In continental Europe 26 flea species live on stoats, along with ticks, lice and mites picked up from prey and borrowed nests.

People trap stoats for fur, and in places that pressure has been heavy. Russia once supplied half the world's catch. On the Iberian Peninsula the stoat depends on two water vole species that are themselves declining. In New Zealand and Orkney the stoat is the threat, and people trap it to save birds.

Population and conservation

The IUCN lists the stoat as Least Concern because of its enormous range around the northern hemisphere. It is considered common across most of that range. No global count exists, and local numbers swing with the rodent supply. Densities of 2 to 6 animals per square kilometre are typical in good habitat.

The stoat has little formal protection and little need of it in most countries. CITES lists one Indian subspecies on Appendix III. Fur trapping continues in Russia and North America, though demand for pelts has fallen.

In New Zealand the conservation story runs the other way. The stoat is among the world's 100 worst invasive species, and it kills kiwi, takahē and other flightless birds. A heavy beech seed fall in 2005 and 2006 fed a rodent boom, then a stoat boom. Over half the takahē died where no traps were set. The wild takahē population fell by a third between 2006 and 2007. Trapping programmes now protect many reserves, and Orkney has run a full eradication since 2018.

Relationship with humans

For most of history the stoat mattered to people as ermine. White winter pelts were sewn together, black tail tips hanging, to line the coronation cloaks of kings and the robes of peers. Catholic prelates wore ermine in the 15th century, and the robes of the United Kingdom House of Lords still carry it. Oxford and Cambridge trim academic hoods with it, though rabbit fur or fake fur now often stands in. The Tlingit and other peoples of the Pacific Northwest fixed ermine skins to regalia and cedar hats as marks of status.

Russia ran the biggest trade. Trappers there caught stoats in box traps and jaw traps or used dogs near villages, and they avoided guns to spare the pelt. The species was a fundamental item of the Russian fur trade until the 20th century. Today thousands are still trapped each season, but the market is small.

On a farm the stoat is both a pest and a helper. It can take poultry when it gets into a henhouse, though it rarely does. It is an excellent mouser and kills the rats and mice that eat stored grain. It does not attack people, and a bite happens only when someone handles one. The stoat inspired Tina and Milo, the mascots of the Milano Cortina winter Olympic and Paralympic games of 2026.

In culture and myth

In Irish mythology the stoat was almost a person. Stoats were said to live in families and to hold rituals for their dead. They were also thieves, and their saliva was said to poison a grown man. To meet a stoat at the start of a journey was bad luck, unless you greeted it as a neighbour. Some Irish tales held that a stoat carried the soul of an unbaptised infant.

Among the Komi people of the Urals, the stoat stands for a beautiful and desired young woman. A European legend claims that a white stoat would rather die than dirty its coat. Chased by hunters, it would turn and give itself up rather than run through mud. That story made the ermine a symbol of purity, and it is the emblem of Brittany and its earliest flag. In heraldry, ermine is a white field scattered with black marks that stand for the tail tips.

Henry Peacham's Emblem 75 shows an ermine chased by a hunter and two hounds under the motto Purity Bought with His Own Death. Leonardo da Vinci painted Cecilia Gallerani holding an ermine in Lady with an Ermine. Medieval writers also tied the ermine to the Virgin Mary, and one tale said it conceived through its ear. In parts of Britain the animal was linked with witches and read as an omen of death.