Male black-footed ferrets are about 10% larger than females, and can reach up to 58 cm (23 in.) long, including the tail.

Last noted in Saskatchewan in 1937, this weasel is now considered to be extirpated in Canada. Occasional sightings in Canada have been made since then, but no colonies have become re-established. It has fared little better in the United States.

An animal of North America's arid, shortgrass prairies, it lived primarily with, and on, prairie dogs. The Black-footed ferret is one of the few predators that has become so specialized towards a single type of prey that it can't switch to another type when its primary prey becomes scarce. Wide-scale poisoning programs to eradicate prairie dogs and the destruction of grassland habitat killed off the black-footed ferret. It now survives in a few places in the western United States where ranchers are compensated for not disturbing prairie dog towns, and where management programmes for the prairie dog and the black-footed ferret are being developed.