The Least weasel lives deep in the Northeast Asian deciduous forest. It hunts day and night, aided by its sharp nails and long slender body. It is the world’s smallest carnivore. According to Blackfoot legend, this species is the bravest of all animals, a hunter that is bold out of proportion to its size. Modern scientists agree with this view, as every single feature of these graceful, lightning-fast little animals appears to be designed so that they are the perfect predator.
This weasel has a Holarctic circumboreal distribution, including much of North Africa and Europe, Asia and regions of northern North America. Round in a variety of habitats, this animal favors plentiful prey and good cover, including woodland, grassland, mountains, sand dunes, urban areas, moors and marshes.
Except for the breeding season, Least weasels are solitary. They are territorial animals and form gender-based dominance hierarchies, with older males being dominant over juvenile males and females. Least weasels need to eat very regularly so that they do not starve to death, and often they are found foraging at any time, day or night. They commonly use food caching, as they often kill prey bigger than themselves, but only consume a few grams of meat for each meal. Caches are hidden around the den entrance, and latrine sites are as well. An individual scent-marks around a den site with secretions from its anal glands. When startled or cornered, these glands release a bad-smelling fluid that will deter an antagonist. Least weasels also sometimes perform a “weasel war dance”, consisting of a series of twists and leaps, often accompanied by noises like barks, an arched back, stiff limbs, and erection of their caudal and dorsal hairs. Weasels of any age perform the dance, though it is more common in the younger ones, especially kits when playing with their siblings.
This species is polygynandrous (promiscuous), with males and females mating numerous times with many partners. Males defend territories, usually against other males, but in the breeding season they leave their territories to search of females. The breeding season is from March to June (though breeding can occur year-round). Following gestation of 34 - 37 days, a litter of 4 - 6 kits is born. Young are weaned at 4 weeks old and at 8 weeks old they are able to hunt, often going with their mother and hunting in 'gangs’. They are independent when they are 9 - 12 weeks of age and reach sexual maturity when they are 3 - 4 months old.
Threats to this species include simplification and habitat loss. Agricultural changes in many areas have led to the reduction or loss of rough grasslands, prime habitat for Field voles, which is a primary source of food for this species. They are rarely seen and so are considered relatively rare. Population numbers vary with the abundance of prey, and they themselves are vulnerable to a range of predators, such as domestic dogs, cats, and foxes.
The Least weasel has wide distribution and presumed large population, but no estimate of population size is available for this species. Currently the Least weasel is classified as Least Concern (LC) and their numbers today remain stable.
Least weasels, being highly-skilled predators of rodents, play an vital role in initiating or maintaining cycles in rodent populations, an important part of the tundra ecosystem, where specialized predators, like Least weasels, play a role to keep lemming populations in check. In New Zealand, on the contrary, where Least weasels have been introduced, bird species are negatively affected by predation by this species, especially Brown kiwis, which live on the ground.