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World’s smallest carnivore!

The Least Weasel (Mustela nivalis) is the smallest of all mustelids and has a wide distribution in the Northern Hemisphere (Europe, Asia, North America and Northern Africa), and is an introduced species in Chile, Argentina, the Falkland Islands, New Zealand, Australia, the Canary Islands, Crete, Malta, Madeira Island, Sao Tome, Bermuda, and Azores. With such a large distribution, there is a corresponding range of variation in size, color and tail length. There are currently 18 recognized subspecies.


Least Weasels have slender, elongated bodies and relatively short limbs and tails, compared with other members of the Mustela genus. The subspecies of the Least Weasel is grouped into three types:

  • Pygmaea-rixosa group, which are the smallest weasels. These are the northern-most weasels, and their coats turn from brown to white in the winter.
  • Nivalis group, which are the average-sized weasels. They can be found in the middle and southern parts of its European and Asian range.
  • Boccamela group, which are the largest weasels. Their coat color tend to be lighter than the summer pelts of the other two groups, and do not change fully or at all in winter. They are found in the southernmost parts of its natural Northern Hemisphere.

There is some pronounced sexual dimorphism in the Least Weasel, with males generally growing to longer body lengths than females. The average body length for males is 5 to 10 inches (13 to 26 cm), while females range from 4.5 to 8 inches (11.4 to 20.4 cm). Males weigh 1.3 to 8.8 ounces (36 to 250 grams) and females weigh 1 to 4.1 ounces (29 to 117 grams).


The bulk of the Least Weasel’s diet consists of very small rodents like mice, gerbils, voles, young rats, pika and hamsters. It does not often go for prey that is significantly larger than itself, but it can. Least Weasels have been known to successfully hunt and kill rabbits, hens and grouse. The body size of the Least Weasel allows it to pursue prey down narrow tunnels of burrows, and it must forage cautiously and stay out of sight of foxes and birds of prey. Least Weasels most often kill their prey by biting the skull of smaller prey, or administering a bit to the back of the neck, dislocating the cervical vertebrae. Large prey typically dies of shock or blood loss.


Least Weasels establish autonomous territories, and only tolerate members of the opposite sex during the breeding season, which lasts from April to July. After a 34 to 37-day gestation period, females will give birth to a litter of up to 6 kits. She will nurse them for up to 12 weeks, but the kits learn hunting behavior by 8 weeks. The young go off to establish their own territories after about three or four months. Least Weasels employ a wide range of vocalizations and scent marking to communicate with each other.


Least Weasels are considered to be a species of least concern by the IUCN, due to their wide distribution and presumed healthy populations. It has been shown that the use of rodenticides have negative effects on the Least Weasel, because they eat small rodents which have been exposed to the poison. Least Weasels have played a part in the mythology of several peoples throughout its range. Pliny the Elder wrote that the Least Weasel was the only animal capable of killing a basilisk (although the weasel dies along with it). Inuit people believed the Least Weasel to possess both courage and wisdom, and mythical heroes would often transform into Least Weasels to accomplish great deeds. During the 1600s in England, Least Weasels were believed to be the familiars of witches.

Source for all images used in this post.

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