Related Biomes
Least Weasel
Mustela nivalis
The least weasel is classified as the world's smallest carnivore. As with other weasels, it is typically described as being curious, alert and bold - actively investigating every hole and nook they encounter during their hunting rounds in search of small rodent prey. Currently, the least weasel enjoys a circumboreal distribution throughout the Holarctic, and in North America it is found throughout Alaska and Canada and southward to the U.S. Great Lakes and midwestern states. During the late Pleistocene, their range extended further south into Missouri, Kentucky and Tennessee.
Least Weasel (Mustela nivalis) at the British Wildlife Centre, Surrey, England - photograph taken Sunday 17. August 2008. By Keven Law (originally posted to Flickr as On the lookout...) [CC-BY-SA-2.0 (www.creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons
Length: males 13-26 cm (5.1-10.2 in) body, 1-9 cm (0.4-3.5 in) tail; females 11-20 cm (4.3-7.9 in) body, 2-6 cm (0.8-2.4 in) tail
Weight: males 36-250 g (1.3-8.8 oz); females 30-117 (1.1-4.1 oz)
Physical Description:
The least weasel has the long, slender, flexible body and short limbs of all weasels, and extant individuals are readily distinguished from other North American weasels by the lack of a black tip on the tail. Paleontological remains are more difficult to distinguish, given the size overlap between large male least weasels and small male ermine. In the summer, the least weasel is covered with chocolate brown fur along its back and sides and white fur on the belly, and in winter, its fur changes to completely white.
The least weasel utilizes a wide variety of habitats, including marshes, meadows, cultivated fields, brushy areas and open woods. They avoid dense forests, sandy deserts and open areas without some form of brush cover. To some extent, their habitat preference is guided by the availability of rodent prey.
Least weasels are specialist predators of small mammals, particularly shrews, voles, mice, lemmings, and other small rodents. Their slender build allows them to easily hunt within the tunnels and burrows of their prey, and they kill quickly by biting the back of the skull. When rodents are scarce, they will eat birds' eggs and nestlings, insects, lizards, frogs, young lagomorphs (rabbits and hares), and even occasionally carrion (Sheffield and King 1994; Svendsen 2003).
As with other weasels, the least weasel moves by walking or jumping, and they travel at the relatively slow speed of about 8-10 km/hr (Svendsen 2003). They are extremely alert and curious, and will actively investigate any hole or potential hiding spot encountered during their regular hunting rounds. Young members of this species spend a great deal of time play fighting with each other, but adults tend to be solitary outside of mating. These animals are active both day and night, as well as throughout the year. As with other weasels, individuals communicate with each other through scent markings as well as vocally.
It is thought that the least weasel migrated across the Bering land bridge and into North America during the Wisconsinan glaciation (Kurtén and Anderson 1980). Climatic and ecological conditions during this time enabled the least weasel to inhabit more southernly regions than it currently occupies, and it has been recovered from sites in the U.S. ranging from Nevada to Tennessee.
The least weasel's distribution is determined, in part, by the availability of preferred prey and habitat; therefore it is no surprise that these predators migrated northward as the glaciers retreated, following the migration of northern rodent species, such as the arctic shrew, collared lemmings and boreal red-backed voles. Much of their current range was covered by ice sheets during the late Pleistocene, although the southern portion of this current range overlaps with portions of their late Pleistocene distribution, including the northern Midwest.
Least weasel remains have been recovered from Late Glacial Maximum aged deposits in a number of upland caves throughout the central and southern Midwest. These sites include Crankshaft Cave in eastern Missouri and Meyer Cave, just across the Mississippi in Illinois, Welsh Cave in northern Kentucky, Cheek Bend Cave in central Tennessee and Baker Bluff Cave in northeast Tennessee.
- Unlike other weasels, the fur of a least weasel will fluoresce under ultraviolet light, producing a lavender color (Svendsen 2003).
Kurtén, B, Anderson, E. 1980. Pleistocene Mammals of North America. Columbia University Press, New York.
Sheffield, S., King, C. 1994. Mustela nivali. Mammalian Species 454: 1-10.
Svendsen, G. E. 2003. Weasels and Black-footed Ferret. In Wild Mammals of North America, edited by Feldhamer, G. A., and B. C. Thompson, 650-661. The Johns Hopkins University Press, Baltimore, MD.
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