The tail of the least weasel contains only a few black hairs. Long slender skulls and sinuous bodies equip the weasel for its niche in life. If the head can fit into a burrow, then the remainder of the body can easily fit as well. Weasels are powerful animals for their size. In both species the males are about 25 percent larger than females.
Weasels are primarily solitary animals except during the mating and whelping seasons.
Reproductive pairing is usually temporary. Females may be bred by more than one male. Mating typically occurs in mid- to late summer. Fertilization of the ova is followed by a period during which the eggs do not implant in the uterus. No development occurs during this period.