The least weasel is a mouse-sized animal with the typical weasel body shape: a long, slender body with short legs; a small, flattened head only slightly wider than the long neck; short, round ears; prominent whiskers; and small, beady eyes. The tail is very short, being less than 1/5 as long as the head and body. In summer, adults are brown above and white below, with white on the chin and toes. The tail is brown, and although there may be a few black hairs at the very tip, it lacks the prominent black tip of the long-tailed weasel. In winter, color can vary from completely brown to almost completely white. In Missouri, in the southern extent of the range, winter coats are usually brown.
Similar species: The long-tailed weasel is larger, with total length 11½–17½ inches, tail length 3–6¼ inches, and weight 2½–9½ ounces. It has a black tail tip. Although it occurs statewide, it is most common in the south-central and southwestern portions of Missouri (whereas the least weasel is limited to northern Missouri).
Total length: 5¾–9¾ inches; tail length: ¾–1½ inches; weight: 1¼–2 ounces. Adult males are slightly larger than adult females.
Probably present in all northern counties of Missouri. We are at the southern extent of its overall North American range.
Habitat and Conservation
The least weasel lives in low, sparse ground cover such as pastures, stubble fields, and marshy areas, sometimes even mouse-infested barns. They usually go where the mice are. They make their homes in mole runs or pocket gopher burrows they have taken over. They can enter holes in the ground less than an inch in diameter.
Our smallest carnivore, this species is state-ranked as vulnerable and is a species of conservation concern.
Food
Least weasels eat more than half their body weight each day — equaling about 1 to 1½ mice a day. Mice and other small rodents are the major foods, but insects and small birds are probably taken, too. Excess food is often stored in a cache or in their burrows for future use. In killing live, adult mice — often the same size as themselves — least weasels grab the prey by the back of the head, then bite through the skull several times in succession. It takes them about 30 seconds to kill a mouse.
Status
A Missouri species of conservation concern. Vulnerable to extirpation from Missouri. Generally rare, with a sporadic distribution. Abundance varies locally and seasonally, probably in relation to fluctuations in rodent populations, their main food supply.
Life Cycle
Breeding occurs throughout the year, but least often in winter. There are 2 or more litters annually, with 1–6 young per litter. Gestation lasts for about 35 days (with no delay before implantation, unlike the long-tailed weasel). The young are born hairless, toothless, and helpless; they are weaned by about 6 weeks of age, when they make their first kills. Males can breed at 8 months of age; females are sexually mature at 4 months and can have 2 litters their first year.
Human Connections
Although much too small to be a furbearer, least weasels provide important services to humans by helping control rodent populations. As our smallest carnivore, they are fascinating and unique. They are apparently poisoned secondarily from exposure to poisons set out to kill rodents.
Ecosystem Connections
Although they are fierce predators, helping to control rodent populations, least weasels are also victims of predators, including the long-tailed weasel. Hawks, owls, foxes, coyotes, housecats, and snakes also eat them. Internal and external parasites also feed on them — albeit on a smaller scale.
