Least weasels apparently do not always experience delayed implantation. In the southern portion of their geographic range they can produce three litters per year. In Alaska, litters of 3 to 10 young are born from early May through June. Variations in time of breeding and birth depend in part on the latitude. Weasels in northern Alaska breed about two weeks later than those in the south.
Weasels usually nest in small rodent burrows, stumps, rock outcroppings, or under old buildings.
The nest is often lined with mouse fur. The number of young born and the number that survive until weaning depend in large part on the abundance of food in the mother's home range. Young weasels remain in the den for 30 to 45 days, at which time they are about two-thirds grown. After emerging, they stay near the home den for a week or two before beginning to accompany their mother on foraging trips. At this time, they disperse away from their mother's home range.