Least Weasel

The least weasel, *Mustela nivalis*, is the world's smallest carnivore, with adults typically 16–22 cm long and weighing only 25–70 g — small enough to pass through a 20 mm (3/4 in.) opening. It is distinguished from the long-tailed weasel and stoat by its very short tail (under 25% of body length) that lacks a black tip. Summer coat is dark brown above with an irregular white throat and belly line; northern animals turn entirely white in winter. Unlike most mustelids the least weasel has no delayed implantation, so females can raise 2–3 litters of 3–7 young per year with gestation of about 35 days, allowing populations to track vole cycles closely. Their metabolism is so high they must eat 40–60% of body weight daily and can starve within 24 hours without food.

Least weasels hunt almost exclusively small rodents — voles, deer mice, and shrews — following prey directly into their burrow systems, a niche no other predator of that size occupies. They are active in short bouts of 10–30 minutes around the clock, alternating hunting with rest in cached nests. Populations rise and crash with vole abundance, and in vole-poor years dispersing animals push into farmyards, barns, and outbuildings looking for mice. They are generally beneficial around agricultural properties, removing large numbers of rodents, and rarely take poultry larger than chicks or quail. When cornered they hiss, chatter, and release a strong musk; they seldom bite humans unless handled.