Stoat

• 1. Introduction

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  The stoat, known to science as Mustela erminea, is a small meat-eating member of the mustelid family. By 2024, the Orkney Native Wildlife Project had spent £7.9m trapping more than 6,300 of them. Stoats have lived on that archipelago north of Scotland only since 2010. There they prey on the Orkney vole and on native birds, and an eradication plan began across the islands in 2018.

  Yet the same species is listed as Least Concern on the IUCN Red List, because its range circles the far north of Eurasia and North America. Its white winter coat even has a name of its own, ermine. How does one slender animal become both a costly pest and a symbol that kings cared about? What lets it follow prey into burrows, and why does it carry its young for most of a year? The answers start with a name that nobody can fully agree on.

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• 2. Names and Ancestry

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  The English word stoat probably comes from the Dutch stout, meaning bold, or from the Gothic stautan, meaning to push. The name ermine has a more tangled trail. John Guillim, in his Display of Heraldrie, suggested it derives from Armenia, the country where people thought the species began. Other authors traced it through Norman French to the Teutonic harmin, with its Anglo-Saxon form hearma, which may in turn come from the Lithuanian šarmu. In North America the animal is called a short-tailed weasel. A male is a dog, hob, or jack, a female is a jill, and a group of stoats is a gang or a pack.

  Mustela palerminea, a common carnivore of central and eastern Europe in the Middle Pleistocene, was the stoat's direct ancestor. It reached North America during the late Blancan or early Irvingtonian. The process that produced the modern animal began 5-7 million years ago, when northern forests gave way to open grassland. Small burrowing rodents then evolved explosively, and the stoat's larger ancestors shrank as they exploited this new food supply. The stoat arose in Eurasia soon after the long-tailed weasel appeared in North America 2 million years ago, as its mirror image. That weasel belongs to a different genus, Neogale. During the Ice Age the stoat thrived, because its small size and long body let it work beneath snow and inside burrows. The two animals stayed apart until about 500,000 years ago, when falling sea levels exposed the Bering land bridge. Fossil stoat remains have been recovered from Denisova Cave.

  In 2021, a study split M. erminea into three species. M. erminea in the strict sense covers Eurasia and Alaska, M. richardsonii covers most of North America, and M. haidarum lives on several islands off the Pacific Northwest coast. The stoat's closest living relatives are the American ermine, M. richardsonii, and the Haida ermine, M. haidarum. The Haida ermine partly descends from M. erminea. Among the 21 recognized subspecies, the Irish stoat of Ireland and the Isle of Man and the Fergana stoat of the Tien Shan and Pamir-Alay mountains do not turn white in winter. The Swiss stoat is recorded only from Switzerland, and the Kodiak stoat only from Kodiak Island. Others are named for the Hebrides, Greenland and the Caucasus.

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• 3. Body and Coat

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  A male stoat averages 258 g, while a female weighs less than 180 g. Males run roughly 25% larger than females and weigh 1.5-2.0 times as much. Body length is 187-325 mm in males, against 170-270 mm in females. Tails measure 75-120 mm in males and 65-106 mm in females. Unusually for a carnivore, stoat size tends to shrink with latitude, which contradicts Bergmann's rule. The tail always exceeds a third of the body length, which is longer than a least weasel's proportion but shorter than that of the long-tailed weasel.

  An elongated neck sets the stoat's head exceptionally far in front of its shoulders. The nearly cylindrical trunk does not bulge at the abdomen. The round black eyes protrude slightly, the whiskers are long and brown or white, and the short rounded ears lie almost flat against the skull. Each foot has five toes with large claws that cannot be retracted. Females have four pairs of nipples, which show only in them.

  Large anal scent glands, measuring 8.5 x 5 mm in males, give the stoat a chemical weapon. They are smaller in females. Further scent glands sit on the cheeks, belly and flanks. Secretions left during body rubbing differ chemically from the anal glands' products, which carry more volatile compounds. When attacked or aggressive, the stoat releases the contents of its anal glands. The result is a strong musky odour from several sulphuric compounds, distinct from the smell of the least weasel.

  Twice a year the stoat moults, and the two moults run in opposite directions. In spring the change is slow and moves from the forehead across the back toward the belly. In autumn it is quicker and runs the other way. Day length starts each moult, so it begins earlier in autumn and later in spring at higher latitudes. In the northern range the winter coat turns completely white except for the black tail-tip. Southern forms show less contrast between seasons, and there the coat stays brown, though denser and sometimes paler than in summer. Summer fur is rougher, shorter and sparse, sandy-brown on the back and head and white below. The winter coat is dense and silky, and it is the part of the animal that people have prized most.

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• 4. Delayed Births

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  A fertilized stoat egg can lie dormant for nine to ten months before the embryo implants in the uterus. This pause is called embryonic diapause, and it makes gestation variable, though typically about 300 days. A female that mates in summer therefore gives birth the following spring. Adult females spend almost all their lives either pregnant or in heat. They can reabsorb embryos, and in a severe winter they may reabsorb an entire litter.

  In the Northern Hemisphere, mating happens from April to July. Males are fertile from May to August, and their testes enlarge in spring. Females are in heat only briefly, triggered by changes in day length. Copulation can last as long as 1 hour. Stoats are not monogamous, and litters are often of mixed paternity.

  At birth, kits are blind, deaf and toothless, covered in fine white or pinkish down. Their milk teeth erupt after three weeks, and they eat solid food after four. The eyes open at five to six weeks, and the black tail-tip appears a week later. Lactation ends at 12 weeks. Until five to seven weeks of age the kits regulate their body heat poorly, so they huddle together when the mother is away. Males mature sexually at 10-11 months. Females can be sexually mature at only 2-3 weeks, still blind, deaf and hairless, and adult males usually mate with them before weaning. Males take no part in rearing the young, but the ground they defend shapes how every female lives.

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• 5. Life in the Tunnels

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  About 50 g of food a day, a quarter of its live weight, keeps a stoat going. Mouse-like rodents dominate the diet, but the stoat regularly takes larger rodents and lagomorphs, including animals far bigger than itself. In Russia its prey includes European water voles, common hamsters and pikas, which it overpowers in their burrows. Small birds, fish and shrews matter less, and amphibians, lizards and insects are taken more rarely. It also preys on lemmings.

  In Great Britain, European rabbits are an important food source. The frequency of stoats preying on them rose between the 1960s and the mid-1990s, after the myxomatosis epidemic ended. Males take rabbits more often than females, which depend more on smaller rodents. British stoats rarely kill shrews, rats, squirrels or water voles, though rats may matter locally. In Ireland, shrews and rats are eaten frequently. In mainland Europe, water voles make up a large share of the diet. Hares are sometimes taken, usually young ones, and stoats are known to kill young muskrats.

  The stoat is an opportunistic predator that moves rapidly and checks every burrow or crevice for food. Males are larger and less successful than females at pursuing rodents deep into tunnels. Stoats regularly climb trees to reach birds' nests, and they often raid nest boxes, particularly those of large species. Against big prey such as rabbits, the stoat aims a bite at the spine at the back of the neck. Small prey die instantly. Rabbits typically die of shock, because the stoat's canine teeth are too short to reach the spinal column or major arteries. When the chance arises it may kill more than it needs, and the excess is usually cached and eaten later. The stoat reputedly mesmerises rabbits with a dance, sometimes called the weasel war dance, though this may be linked to infection by the nematode Skrjabingylus.

  Each stoat keeps several dens within its range, and none of them is dug by the stoat itself. It uses the burrows and nest chambers of the rodents it kills, and lines the chamber with their skins and underfur. Dens turn up in surprising places, among them logs piled against the walls of houses, rotting stumps, haystacks, bog hummocks, vacant mud buildings, rock clefts and even magpie nests. A single den has several galleries, mainly within 30 cm of the surface.

  Dominant older males hold territories 50 times larger than those of younger, socially inferior males. Male territories enclose the smaller territories of females, and the males defend them from other males. Range size shifts with the season, following the supply of food and mates. During the breeding season female ranges stay the same, while males become roamers, strayers or transients. Both sexes mark ground with urine and feces. Anal drags announce that a territory is occupied, and body rubbing is associated with agonistic encounters.

  Kits produce a fine chirping, but adult stoats are usually silent. They trill excitedly before mating, and signal submission with quiet trilling, whining and squealing. A nervous stoat hisses, mixing in sharp barks or shrieks, and an aggressive one screeches at length. A forward thrust with a sharp shriek is typical of a stoat defending a nest or retreat site. In kleptoparasitism, a dominant stoat takes the kill of a weaker one, usually after a fight. Submissive animals avoid higher-ranking ones or flee from them.

  Red foxes and sables prey on stoats, and so do birds ranging from small northern hawk-owls and short-eared owls to goshawks, buzzards, kites, golden eagles and Eurasian eagle-owls. Grey herons, though not birds of prey, are known to take them too. In continental Europe, 26 flea species are recorded on stoats. Stoats are largely resistant to tularemia, and tuberculosis has been recorded in those of the former Soviet Union. The nematode Skrjabingylus nasicola erodes the bones of the nasal sinuses and lowers fertility, which makes it one of the most threatening parasites the animal faces.

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• 6. Island Invader

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  In the 1880s, stoats began arriving in New Zealand from Britain, brought in to control rabbits and hares. The animals belonged to the British stoat, M. e. stabilis. Scientists in New Zealand and Britain opposed the plan, among them the New Zealand ornithologist Walter Buller. The warnings were ignored. Within six years, bird populations showed a noticeable decline.

  Ground-nesting and hole-nesting birds are especially exposed, since they have very few ways to escape. In New Zealand the stoat feeds principally on birds. Its victims include the rare kiwi, the kaka, the mohua, the yellow-crowned parakeet and the New Zealand dotterel.

  Seasonal gluts of southern beechmast, the nuts of the beech tree, set off the worst losses. The glut lets rodents multiply, and since stoats also eat rodents, stoat numbers climb in turn. The endangered South Island takahē shows the cost. A stoat plague triggered by the 2005-06 mast wiped out more than half of the takahē in untrapped areas. The wild population dropped by a third between 2006 and 2007. The stoat has since been nominated as one of the world's top 100 "worst invaders".

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• 7. Ermine and Status

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  In the 15th century, Catholic monarchs wore ermine, sometimes in the form of the mozzetta cape. The ceremonial robes of members of the United Kingdom House of Lords have long been trimmed with it, and so have the academic hoods of Oxford and Cambridge. Capes on images such as the Infant Jesus of Prague also used the fur. Prelates of the Catholic Church still wear ecclesiastical garments featuring ermine, a sign of status equal to that of the nobility. Rabbit or fake fur is now often used instead, because of expense or animal rights concerns.

  In heraldry, ermine is a tincture: a white background patterned with black shapes that stand for the stoat's winter coat. Medieval coronation cloaks were lined with many ermine furs sewn together, producing a luxurious white fur hung with black-tipped tails. Because of that link to cloaks, crowns and peerage caps, the tincture was usually reserved for similar uses, such as the linings of crowns and chapeaux and the royal canopy. For the Duchy of Brittany, ermine is an ancient symbol, and it formed the duchy's earliest flag. A design also called ermine is painted onto other furs, such as rabbit, to imitate the winter coat.

  Across Europe the fur marked royalty and high status, and Leonardo da Vinci's portrait Lady with an Ermine shows Cecilia Gallerani holding one.

  The Tlingit and other indigenous peoples of the Pacific Northwest Coast valued the ermine of both M. erminea and M. richardsonii. They attached the skins to traditional regalia and cedar bark hats as status symbols, and also made them into shirts.

  Russia kept the stoat at the centre of its fur trade until the 20th century. At times no less than half the global catch came from within the borders of the former Soviet Union, which supplied the highest grades of pelt. Stoat skins are prized especially in winter coat, and are used to trim coats and stoles. Harvesting never became a specialty in any part of Russia. Most stoats were taken in box-traps or jaw-traps, or with dogs. Guns were rarely used, because they could damage the pelt.

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• 8. Legends and Mascots

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  In Irish mythology, stoats were seen almost as people, animals with families that held rituals for their dead. They were also thought of as noxious thieves, and their saliva was said to be able to poison a grown man. Meeting one when setting out on a journey was bad luck, but greeting the stoat as a neighbour averted it. Stoats were also supposed to hold the souls of infants who died before baptism.

  In the folklore of the Komi people of the Urals, stoats symbolize beautiful and coveted young women. One popular European legend held that a white stoat would die before letting its pure coat be besmirched. Chased by hunters, it would supposedly turn and give itself up rather than risk soiling itself. Henry Peacham's Emblem 75 shows an ermine pursued by a hunter and two hounds, under the title Cui candor morte redemptus, or "Purity Bought with His Own Death". Peacham urged men and women to keep their minds and consciences as pure as the ermine keeps its fur.

  The stoat inspired "Tina and Milo", the mascots of the Milano Cortina Olympic and Paralympic winter games of 2026. Their names come from the host cities, Milan and Cortina d'Ampezzo, and they are portrayed as sister and brother. Tina, the Olympic mascot, symbolizes art, music and the transformative force of beauty. Milo, the Paralympic mascot, is portrayed as born without a leg and learning to use his tail as one, standing for ingenuity, willpower and creativity.

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