Ontario has three species of small weasels: the short-tailed weasel, or ermine (Mustela erminea), the long-tailed weasel (Mustela frenata) and the least weasel (Mustela rixosa). The first two species have more economic importance than the third. The least weasel, the smallest carnivore in the world, is quite rare. The Indians of Alaska believed that a man who caught such a weasel was destined for wealth and power, probably because this creature was so seldom found. The pelt of the weasel has long been associated with luxury and royalty. However, the weasel has played a minor role in the fur trade.

The short-tailed weasel, or ermine, is found throughout North America. The long-tailed weasel is found in southern Canada. The least weasel, although rare, is distributed throughout Canada north of the Great Lakes.

All three species have sharp, moderately large teeth, small eyes and small rounded, fully haired ears. Sight, smell and hearing are well developed in all weasels. Because the least weasel is so seldom harvested, attention here is focused on the more common species.

~ Short-tailed Weasel (Ermine)
Ermine males are 26.9 to 28.5 cm (10.6 to 11.2 in) long and weigh 74.7 to 171.1 g (2.4 to 5.5 oz). Females are 22.1 to 26.2 cm (8.7 to 10.3 in) in length and weigh 43.5 to 71.5 g (1.4 to 2.3 oz). The ermine pelt consists of short, soft underfur and long, coarse, glossy guard hairs. The sexes are alike in colouration, which changes with the seasons to provide camouflage. In summer, the upper parts of the ermine’s coat are dark brown and the head and legs are darker still. The chin, throat, and insides of the legs range from a white shade to pale yellow. The last third of the tail is black year-round. Between October and December, the pelt changes to white with a yellow tinge on the back and underparts. Between March and April, the white winter coat gives way to the brown of summer.

~ Long-tailed Weasel
The long-tailed weasel is larger than the ermine, and about the size of the grey squirrel. Males measure 34.5 to 44.5 cm (13.6 to 17.5 in) and weigh 93.3 to 248.8 g (3 to 8 oz). Females are 27.9 to 33 cm (11 to 13.4 in) long and weigh 80.9 to 121.3 g (2.6 to 3.9 oz). The fur is short and moderately fine. The sexes are alike in colouration and change from brown to white where winters are cold. The colouration and moults are similar to those of the ermine, but the spring moult begins on the back. It proceeds down the body and causes facial markings to become brindled.

Life History
The females of these weasel species mature earlier than the males, at about three or four months of age. Males may not be capable of mating until they are one year old or more. Gestation takes about nine months and litters are born in spring, around April or May. The young, born in litters of six or eight, are blind, flesh-coloured, and naked except for short, fine, white hairs on the neck. Weaning occurs within just over a month, at which time the male parent begins to bring food to the underground nest. At seven or eight weeks, the young are old enough to hunt. They remain with the family unit until late summer. Although weasels may live to be five or six years old, most die of natural causes before their first birthdays.

Weasels prefer woodlands, open countryside with hedgerows, holes in stone piles or walls, thickets, and fencerows. They are usually found near water, and can sometimes be seen around buildings, woodpiles, brush heaps, haystacks and logs. Dens are loose structures with three or four tunnels connecting them to the world outside. They are about 15 cm (6 in) below ground and are lined with the fur of rats or mice, or with fine grass or leaf fragments.

Food and Feeding Behaviour
The weasel preys on mice, rats, voles, rabbits, chipmunks, shrews, frogs, lizards, small snakes, birds, bats, insects and earthworms. It also eats birds’ eggs and will attack poultry. The weasel stalks its prey persistently, tracing its scent and pouncing from a few feet away. The attack is quick, and a bite through the back of the skull made as the weasel hugs the prey to its long body causes instant death. After the kill, it always drinks water. The head and brain are eaten first. Since the weasel can eat the equivalent of one-third of its own weight within 24 hours, it often kills more than it needs, and caches the leftovers in burrows. The short-tailed (ermine) and least weasels are particularly dependent on mice.

Weasels are active throughout the year, seldom remaining long in the den. Mainly nocturnal, they also hunt during the day. They are usually solitary, but sometimes pairs are spotted even outside of the mating season. Good swimmers, weasels are also very alert, curious and bold. Ermine, in particular, are likely to stamp their feet when annoyed. All species emit the characteristic musk odour when alarmed. The ermine may put signposts along its trails by leaving long, spiral-shaped, black or brown droppings here and there. Home ranges of weasels can vary between 12 and 162 ha (about 30 and 400 ac).

Population Changes
Shortages of mice can affect both the ermine and the least weasel populations. All three species are susceptible to numerous predators, including humans, large hawks, owls, foxes, domestic cats, large snakes, coyotes and dogs. Internal parasites include the guinea worm and kidney worm. The latter is contracted from infected earthworms.

Weasels are of limited economic value to trappers, but are important for their role in controlling the rodent populations in farming country. There is no closed season on weasels, but they should not be taken in early fall when their white coats are sprinkled with dark brown hairs. These “greybacks”, as they are called, produce pelts of low quality. Pelts are prime around December. It is important that the white fur be kept free of stains. There is no quota on the weasel in Ontario.