Least weasels breed and reproduce year-round, with the possible exception of winter. Delayed implantation does not occur, and two or more litters may be produced each year. A female's estrus lasts four days. Young are blind and naked, but develop rapidly. Immatures reach adult length after about eight weeks, and adult weight when 12-15 weeks old.
Females mature sexually in four months, males in eight.
Least weasels inhabit meadows, fields, brushy land, or woods. Least weasels rarely travel more than 100 yards from their home burrows, and the average individual range is estimated at two acres. This tiny weasel occupies a lower position in the food chain than ermines and long-tailed weasels. It is preyed on by the larger weasels, snakes, owls and cats. Longevity in the wild is not known.