Wolverine

Name and taxonomy

Linnaeus described the wolverine in 1758, and it now stands alone in the genus Gulo. Gulo is the Latin word for glutton, and the animal carries that label in many languages. The French call it glouton, the Italians ghiottone and the Germans Vielfrass. Wikipedia traces the German name to a Norwegian word, fjellfross, that meant mountain cat, so the gluttony may rest on a mistranslation. The English name probably means a little wolf, and the Finnish ahma also means glutton.

In French-speaking Canada the animal is the carcajou, a word borrowed from the Innu language. Quickhatch, another Canadian name, comes from East Cree. Its strong smell earned it the nicknames skunk bear and nasty cat. Two subspecies are usually accepted: G. g. gulo in Eurasia and G. g. luscus in North America. Some authors treat the whole species as one population that circles the pole.

Evolution and relatives

The wolverine belongs to the family Mustelidae, with the weasels, otters, badgers and martens. Genetic work places its closest relatives among the martens and the tayra of Central and South America. All of them descend from a common ancestor that lived in Eurasia. Only the sea otter, the giant otter and the African clawless otter grow larger among living mustelids. A European badger can match a wolverine's weight in autumn, when it is fat for winter.

Most North American wolverines seem to descend from one founding group. That group probably spread out from Beringia, the land bridge region, after the last ice age. The conclusion is uncertain, because samples from the depleted southern range are hard to collect. Like other mustelids, the wolverine keeps a low, long body plan that suits a life of digging, climbing and squeezing into dens.

Appearance

A wolverine is built low and long, with a broad round head, small eyes and short rounded ears. It stands 36 to 45 centimetres at the shoulder, about the height of a medium dog. A male usually weighs 11 to 18 kilograms, and a female 8 to 12 kg. Soviet writers mentioned males of 32 kg, but the standard reference on Soviet mammals doubted those figures. Males run about 10 to 15% longer than females and can be 30 to 40% heavier.

The fur is thick, dark and oily, and it sheds water so well that frost does not settle on it. A pale buff or gold stripe runs from each shoulder along the flank to the rump, where the two stripes meet above the tail. Some animals wear a silvery mask on the face, and some have white patches on the throat or chest. Each paw has five toes and long curved claws, and the animal walks on the flat of its foot. Those wide feet spread its weight over snow, so it can travel where hooved prey sinks and stalls.

The jaws are unusually strong for the size of the skull. A study of bone strength at the jaw joint gave the wolverine the highest value of any carnivore tested, 940.8 newtons, ahead of the cheetah. One upper molar is turned sideways, and this tooth lets the animal shear meat off a carcass that has frozen hard.

Habitat and range

The wolverine lives in the boreal forest, the alpine zone and the tundra all around the northern hemisphere. The largest numbers are in northern Canada, Alaska, the Nordic countries and across Russia into Siberia. It also occurs in the Baltic states, the Russian Far East, northeast China and Mongolia. In Europe and Russia it reaches south to about 50 degrees north. GBIF holds records from 23 countries, but many of those are zoo animals or single wanderers.

It prefers open forest near the tree line, high grassland and rocky slopes with few people. Cold matters more than the type of vegetation, because cold keeps a cached carcass fresh for weeks. Females dig their birth dens into deep snow in February and use them until the kits are weaned in May. So breeding is limited to places where the snowpack survives into late spring. A warming climate is expected to shrink that zone.

Wolverines once lived south into Colorado, Indiana, Pennsylvania and New England. Trapping and forest clearance pushed them out of those areas in the 19th and early 20th centuries. Small numbers persist in the North Cascades of Washington and the northern Rocky Mountains of Idaho, Montana and Wyoming. Single animals have reached California, Colorado and Utah, but none of those states has a breeding population. In 2020 a female with two kits was seen on Mount Rainier, the first there in over a century.

Diet and hunting

The wolverine is first of all a scavenger. In winter and early spring almost all of its food is carrion. It follows the trails of wolves and lynx and cleans up what those hunters leave. It will also steal a fresh kill, and hunters have watched it chase bears, cougars and even wolf packs off a carcass. Its fast, messy feeding gave it the glutton name, but that habit probably reflects a hard climate where a meal is rare.

It is a capable hunter too. Most prey is small or medium sized: voles, lemmings, hares, marmots, ground squirrels, beavers and porcupines. In deep snow it can bring down caribou, roe deer, wild sheep, red deer and even moose. The hooved animal sinks, and the wolverine does not. It kills a large animal with a bite to the neck that cuts the tendons or crushes the windpipe. On the attack it can run at up to 48 kilometres per hour for a short distance. It also takes eggs, geese, insect larvae, roots and berries when it finds them.

A wolverine in Denali National Park was recorded eating golden eagle nestlings, and one in Sweden killed an adult eagle on its nest. When food is plentiful the animal buries the surplus and sprays the cache with scent. A nursing female in late winter depends on those stores. Wolverines in Scandinavia hunt more than those in North America, perhaps because there are fewer wolves to leave kills behind.

Behaviour and social life

The wolverine lives alone, and adults meet only to mate. Each adult defends a range against others of its own sex and marks it with urine and gland scent. A male's range can pass 620 square kilometres and takes in the smaller ranges of several females. ADW gives male ranges of 600 to 1000 square kilometres and female ranges of 50 to 350, and a winter range can reach 2,000. Radio collars show an animal can cover hundreds of kilometres in a few months.

It is active in the dark and in daylight, and it does not slow down in winter. Where the sun does not set or rise for weeks, it may alternate bouts of three to four hours of activity and sleep. It moves at a loping gallop that it can hold for 10 to 15 kilometres without a rest, at perhaps 15 km per hour. A day's travel can total 45 km. It climbs trees quickly and swims well, but most of its life is spent on the ground.

For all its reputation, a wolverine avoids wolves and bears when it can, because a fight with them can kill it. Play has been seen between mates, between siblings and between a mother and her kits. Captive animals also play with objects.

Communication and senses

Scent is the main language of the wolverine. Like most mustelids, it has a pair of anal glands. Their secretion marks the borders of a range, a food cache and a female in season. Chemists found 123 different compounds in that secretion across six animals, with only six shared by all. Urine carries a second set of signals, including pine-scented terpenes that come from the conifer needles the animal swallows. That urine keeps black-tailed deer and snowshoe hares away from a marked spot.

A scavenger must find carcasses at long range, so the sense of smell is excellent. Hearing is good, and eyesight is thought to be poor. The wolverine is quiet, and it only grunts or growls when it is annoyed.

Reproduction and life cycle

Mating takes place from May to August, and the female chooses the moment. Copulation triggers ovulation, as in many mustelids. The fertilised egg then waits for about six months and implants in early winter. Once it implants, the embryo grows for only 30 to 50 days, so the whole pregnancy can last from 120 to 272 days. A female that cannot find enough food does not carry the litter to term.

She gives birth in a snow den between January and April, usually to two or three kits, and at most five. A newborn weighs about 85 grams and is covered in white fur. The kits are weaned at about three months and begin to forage for themselves at five to seven months. They reach adult size within their first year and become mature at two to three years. A female breeds only every second year.

The father visits the den until weaning, and some kits travel with him for a while at about six months. A successful male keeps a lasting bond with two or three females, while other males never breed. Wild wolverines typically live 5 to 7 years, and the oldest wild animal on record reached 13. One captive wolverine lived to 19.5 years.

Predators and threats

The gray wolf is the most important natural predator, with many recorded deaths in both North America and Eurasia. A pack may kill a wolverine to defend a kill or a den of pups. Cougars, black bears and brown bears kill adults now and then, and a golden eagle can take a young animal. A wolverine that can reach a tree usually escapes, so wolves succeed mostly in open country. When wolves move into an area, the resident wolverine is thought to leave.

People are the greater threat. Trappers shoot wolverines that raid fur traps, and herders shoot them for taking reindeer. Roads, mines and resorts break up the huge ranges the animal needs. Starvation and trapping are the main causes of death in the wild. The animal also hosts many parasites, from tapeworms and roundworms to ticks and ear mites.

Population and conservation

Nobody knows how many wolverines exist. The species lives at very low density, and in Scandinavia the estimate is one animal per 200 to 500 square kilometres. The IUCN lists it as Least Concern. It covers a vast area, holds large populations and is not falling fast enough to qualify as Near Threatened. The European populations are at greater risk than the global picture suggests.

In the United States it has gone from almost all of its old range, and hunting is legal only in Alaska and Montana. In November 2023 the US Fish and Wildlife Service listed the animals of the lower 48 states as threatened. Colorado passed a reintroduction law in 2024 and plans to release 15 wolverines a year for three years. That will be the first attempt to return the species to a region it had lost.

Russia manages the wolverine as a game animal, and heavy hunting there has cut numbers. Sweden pays farmers and herders who find and report a den. Other Nordic countries control numbers in reindeer country through licensed hunting. About 100 wolverines live in zoos, and captive breeding works only with difficulty and high losses of kits.

Relationship with humans

Wolverine fur does not frost up, so trappers and Arctic peoples used it to line parka hoods. The trade is small today. The animal is a famous nuisance to trappers, because it eats animals caught in traps and can spring a trap with a stick. It breaks into cabins and food stores, eats what it can and sprays the rest. It has even bitten open tinned food.

Wolverines live far from people and are rarely seen even where they are common. No source records an unprovoked attack on a person, and the animal is thought to slip away long before a hiker notices it. In 2009 a collared young male, M-56, walked about 800 kilometres from Wyoming into Colorado. A ranch hand shot it in North Dakota in 2016, the first wolverine confirmed there in 150 years.

In culture and myth

In Innu tradition the wolverine is Kuekuatsheu, a trickster who made the world. After a great flood he built a boat for the animals, then sent a mink to bring up mud and shaped an island from it. Many of his stories are rude and funny. The Mi'kmaq and Passamaquoddy know the wolverine as Lox, a thief and trickster who often travels with the wolf. The Dene of northwestern Canada tell of it as a trickster and shaper of the world, much as the Navajo tell of the coyote.

Alaskan Athabaskan people respect its strength, and some hang a wolverine tooth on a baby's basket as a charm. In parts of northern California the wolverine was a lucky animal and a clever gambler in stories. A few spirit-animal websites call it the totem of the Norse god Tyr, but no early source appears to support that.

Michigan calls itself the Wolverine State, and the University of Michigan uses the animal as its mascot. The link may come from an 18th century fur trade at Sault Ste. Marie, or from an insult aimed at early settlers. Wild wolverines are almost unknown in the state, and the one seen in 2004 was the first in 200 years. Marvel's Wolverine, the clawed mutant Logan, took his name from the animal's ferocity and short stature.