The least weasel varies greatly in size over its range. The body is slender and elongated, and the legs and tail are relatively short. The colour varies geographically, as does thepelage type and length of tail. The dorsal surface, flanks, limbs and tail of the animal are usually some shade of brown while the underparts are white. The line delineating the boundary between the two colours is usually straight. At high altitudes and in the northern part of its range, the coat becomes pure white in winter.
Small rodents form the largest part of the least weasel's diet, but it also kills and eats rabbits, other mammals, and occasionally birds, birds' eggs, fish and frogs. Males mark their territories witholfactory signals and have exclusive home ranges which may intersect with or include several female ranges. Least weasels use pre-existing holes to sleep, store food and raise their young. Breeding takes place in the spring and summer, and there is a single litter of about six kits which are reared exclusively by the female. Due to its small size and fierce nature, the least weasel plays an important part in the mythology and legend of various cultures.
The least weasel was given its scientific nameMustela nivalis by Carl Linnaeus in his12th edition of Systema Naturae in 1766; itsepithetnivalis comes from theLatin wordnix meaning "snow" because it grows a white coat during the winter season.[2]: 6 Thetype locality wasVästerbotten in Sweden.[2]: 1 As an animal with a very wide distribution, the morphology of the least weasel varies geographically. The species was reviewed by Reichstein in 1957 and again by van Zyll de Jong in 1992 and Reig in 1997. Youngman (1982) placed it in the subgenusMustela while Abramov (1999) considered it should be included in the subgenusGale. Based on skull characteristics, Reig (1997) proposed that thetaxon should be split into four species,M. subpalmata,M. rixosa,M. vulgaris andM. eskimo. Abrimov and Baryshinikov (2000) disagreed, recognising onlyM. subpalmata (theEgyptian weasel) as a separate species.[3] However, Rodrigueset al. (2016) recognizedM. subpalmata as a distinct population ofnivalis rather than a distinct species.[4]
Within the genusMustela, the least weasel is a relatively unspecialised form, as evidenced by itspedomorphic skull, which occurs even in large subspecies.[5] Its direct ancestor wasMustela praenivalis, which lived in Europe during theMiddle Pleistocene andVillafranchian.M. praenivalis itself was probably preceded byM. pliocaenica of thePliocene. The modern species probably arose during theLate Pleistocene.[6] The least weasel is the product of a process begun 5–7 million years ago, when northern forests were replaced by open grassland, thus prompting an explosive evolution of small, burrowing rodents. The weasel's ancestors were larger than the current form, and underwent a reduction in size to exploit the new food source. The least weasel thrived during theIce Age, as its small size and long body allowed it to easily operate beneath snow, as well as hunt in burrows. It probably crossed to North America through theBering land bridge 200,000 years ago.[7]
The least weasel has a high geographic variation, a fact which has historically led to numerous disagreements among biologists studying its systematics. The least weasel's subspecies are divided into three categories:[8]
Theboccamela group (large least weasels): Very large weasels with large skulls, relatively long tails and lighter coloured pelts. Locally, they either do not turn white or only partially change colour in winter. They inhabitTranscaucasia, from westernKazakhstan toSemirechye and in the flat deserts ofMiddle Asia. They are also found in Morocco, Algeria, and Tunisia.[8]
Thenivalis group (medium-sized least weasels): Medium-sized weasels, with tails of moderate length, representing a transitional form between the former two groups. They inhabit the middle and southern regions of European Russia,Crimea, theCiscaucasus, western Kazakhstan, the southern and middleUrals and the montane parts of Middle Asia, except theKopet Dag.[8]
A medium-sized subspecies with a tail of moderate length, constituting about 20–21% of its body length. In its summer fur, the upper body is a dark brownish or chestnut colour, while its winter fur is pure white. It is probably a transitional form between the smallpygmaea and the largevulgaris.[9]
A very large subspecies, with a long tail constituting about 30% of its body length. In its summer fur, the upper body is light brownish or chestnut with yellowish or reddish tints, with some individuals having a brownish dot on the corners of the mouth and sometimes on the chest and belly. The winter fur is not pure white, being usually dirty white with brown patches.[11]
A very large subspecies with a long tail constituting about 25–30% of its body length. In its summer fur, the upper body is very light sandy brown or pale-yellowish. The fur is short, sparse and coarse, and does not turn white in winter.[13]
A medium-sized subspecies with a tail constituting about 24% of its body length. The colour of the summer fur is light-brownish, while the winter fur is white.[15]
A very small subspecies, with a short tail which constitutes about 13% of its body length. In its summer coat, the dorsal colour is dark brown or reddish, while the winter fur is entirely white.[16]
The smallest subspecies and the smallest livingmammaliancarnivore in the world. In its summer coat, the fur is dark reddish-brown, while the winter fur is pure white.[17]
A somewhat larger subspecies thannivalis with a longer tail, which constitutes about 27% of its body length. In its summer fur, the upper body varies from being light brownish to dark chestnut, while the winter fur is white in its northern range and piebald in its southern range.[18]
Southern European Russia from the latitude of southern Voronezh and Kursk districts,Crimea,Ciscaucasia, and the northern slopes of the main Caucasus, eastward to theVolga. Outside the former Soviet Union, its range includes Europe southward to theAlps and thePyrenees. Introduced toNew Zealand.[19][20]
Skull of a least weaselLeast weasel at theBritish Wildlife CentreSkulls of along-tailed weasel (top), astoat (bottom left) and least weasel (bottom right), as illustrated inMerriam'sSynopsis of the Weasels of North America
The least weasel has a thin, greatly elongated and extremely flexible body with a small, yet elongated, blunt-muzzled head which is no thicker than the neck. The eyes are small in relation to their head size and are bulging and dark colored. The legs and tail are relatively short, the latter constituting less than half the body length. The feet have sharp, dark-coloured claws, and thesoles are heavily haired.[21] The skull, especially that of the smallrixosa group, has an infantile appearance when compared with that of other members of the genusMustela (in particular, thestoat andkolonok). This is expressed in the relatively large size of thecranium and shortened facial region.[22] The skull is, overall, similar to that of the stoat, but smaller, though the skulls of large male weasels tend to overlap in size with those of small female stoats.[23] There are usually four pairs of nipples but these are only visible in females.
Thebaculum is short,[24] 16 to 20 mm (0.63 to 0.79 in), with a thick, straight shaft.Fat is deposited along the spine, kidneys, gut mesentries and around the limbs. The least weasel has muscular anal glands under the tail, which measure 7 by 5 mm (0.28 by 0.20 in), and contain sulphurous volatiles, includingthietanes and dithiacyclopentanes. The smell and chemical composition of these chemicals are distinct from those of the stoat.[23] The least weasel moves by jumping, the distance between the tracks of the fore and hind limbs being 18 to 35 cm (7.1 to 13.8 in).[25]
Skeleton, as illustrated inLydekker'sThe New Natural History
Dimensions vary geographically, to an extent rarely found among other mammals. Least weasels of theboccamela group, for example, may outweigh the smaller races by almost four times. In some large subspecies, the male may be 1.5 times longer than the female. The tail lengths are also variable, constituting 13 to 30 percent of the length of the body. Average body length in males is 130 to 260 mm (5.1 to 10.2 in), while females average 114 to 204 mm (4.5 to 8.0 in). The tail measures 12 to 87 mm (0.47 to 3.43 in) in males and 17 to 60 mm (0.67 to 2.36 in) in females. Males weigh 36 to 250 g (1.3 to 8.8 oz), while females weigh 29 to 117 g (1.0 to 4.1 oz).[26]
The winter coat is conspicuous when there is no snow on the ground.
The winter fur is dense, but short and closely fitting. In northern subspecies, the fur is soft and silky, but coarse in southern forms. The summer fur is very short, sparser and rougher. The upper parts in the summer fur are dark, but vary geographically from dark-tawny or dark-chocolate to light pale tawny or sandy. The lower parts, including thelower jaw and inner sides of the legs, are white. There is often a brown spot at the corner of the mouth. The dividing line between the dark upper and light lower parts is usually straight but sometimes forms an irregular line. The tail is brown, and sometimes the tip is a little darker but it is never black. In the northern part of its range and at high altitudes, the least weasel changes colour in the winter, the coat becoming pure white and exhibiting a few black hairs in rare circumstances.[22][27]
The least weasel mates in April–July and there is a 34- to 37-daygestation period. In theNorthern Hemisphere, the average litter size consists of 6 kits and these reachsexual maturity in 3 to 4 months. Males may mate during their first year of life, though this is usually unsuccessful. They arefecund in February–October, though the early stages ofspermatogenesis do occur throughout the winter months.Anestrus in females lasts from September until February.[30]
The female raises her kits without help from the male. They are 1.5 to 4.5 g (0.053 to 0.159 oz) in weight at birth. Newborn kits are born pink, naked, blind and deaf, but gain a white coat of downy fur at the age of 4 days. At 10 days, the margin between the dark upper parts and light under parts becomes visible. Themilk teeth erupt at 2 to 3 weeks of age, at which point the young start to eat solid food, though lactation can last 12 weeks. The eyes and ears open at 3 to 4 weeks of age, and by 8 weeks, killing behaviour is developed. The family breaks up after 9 to 12 weeks.[30] There is a single litter each year and least weasels can live for 7 or 8 years.[27]
The least weasel has a typical mustelid territorial pattern, consisting of exclusive male ranges encompassing multiple female ranges. The population density of each territory depends greatly on food supply and reproductive success, thus the social structure and population density of any given territory is unstable and flexible.[31] Like the stoat, the male least weasel extends his range during spring or during food shortages. Itsscent marking behaviour is similar to that of the stoat; it usesfaeces,urine and anal and dermal gland secretions, the latter two of which are deposited by anal dragging and body rubbing. The least weasel does not dig its own den, but nests in the abandoned burrow of another species such as amole or rat.[32] The burrow entrance measures about 2.5 cm (0.98 in) across and leads to the nest chamber located up to 15 cm (5.9 in) below ground. The nest chamber (which is used for sleeping, rearing kits and storing food) measures 10 cm (3.9 in) in diameter, and is lined with straw and the skins of the weasel's prey.[33]
The least weasel has four basic vocalisations; a guttural hiss emitted when alarmed, which is interspersed with short screaming barks and shrieks when provoked. When defensive, it emits a shrill wail or squeal. During encounters between males and females or between a mother and kits, the least weasel emits a high-pitched trilling. The least weasel's way of expressing aggression is similar to that of thestoat. Dominant weasels exhibit lunges and shrieks during aggressive encounters, while subdominant weasels will emit submissive squeals.[32]
Taxidermy exhibit showing a least weasel attacking aEuropean hare, in the Natural History Museum of Genoa
The least weasel feeds predominantly onmouse-likerodents, includingmice,hamsters,gerbils and others. It usually does not attack adult hamsters andrats.Frogs,fish, smallbirds and bird eggs are rarely eaten. It can deal with adultpikas and gerbils, but usually cannot overcomebrown rats andsousliks. Exceptional cases are known of least weasels killing prey far larger than themselves, such ascapercaillie,hazel hen andhares.[34] In England, a favoured prey item is thefield vole (Microtus agrestis). These have fluctuations in population size, and in years of abundance may form up to 54% of the weasel's diet. In years of scarcity, birds form a greater proportion of the diet and female least weasels may fail to breed.[35]
Despite its small size, the least weasel is a fierce hunter, capable of killing arabbit five to 10 times its own weight.[36] Although they are commonly taken, the rabbits are usually young specimens, and become an important food source during the spring, when small rodents are scarce and rabbit kits are plentiful. Male least weasels take a higher proportion of rabbits than females, as well as an overall greater variety of prey. This is linked to the fact that being larger, and having vaster territorial ranges than females, males have more opportunities to hunt a greater diversity of prey.[37]
The least weasel forages undercover, to avoid being seen by foxes and birds of prey. It is adapted for pursuing its prey down tunnels, though it may also bolt prey from a burrow and kill it in the open.[37] The least weasel kills small prey, such asvoles, with a bite to theoccipital region of the skull[34] or the neck, dislocating thecervical vertebrae. Large prey typically dies ofblood loss orcirculatory shock.[37] When food is abundant, only a small portion of the prey is eaten, usually thebrain. The average daily food intake is 35 g (1.2 oz), which is equivalent to 30–35% of the animal's body weight.[34]
In areas where the least weasel issympatric with thestoat, the two species compete with each other for rodent prey. The weasel manages to avoid too much competition by living in more upland areas, feeding on smaller prey and being capable of entering smaller holes. It actively avoids encounters with stoats, though female weasels are less likely to stop foraging in the presence of stoats, perhaps because their smaller size allows them to quickly escape into holes.[40]
Ectoparasites known to infest weasels include thelouseTrichodectes mustelae and themitesDemodex andPsoregates mustela. The species may catchfleas from the nests and burrows of its prey. Flea species known to infest weasels includeCtenophthalmus bisoctodentatus andPalaeopsylla m. minor, which they get from moles,P. s. soricis, which they get from shrews,Nosopsyllus fasciatus, which they get from rodents andDasypsyllus gallinulae which they get from birds.[38]
The least weasel is listed asLeast Concern on theIUCN Red List, because of its wide global distribution and large population that is thought to be not in decline.[1]
17th century print of a least weasel confronting abasilisk
TheAncient Macedonians believed that to see a least weasel was a good omen. In some districts ofMacedon, women who suffered from headaches after having washed their heads in water drawn overnight would assume that a weasel had previously used the water as a mirror, but they would refrain from mentioning the animal's name for fear that it would destroy their clothes.[42]
Similarly, a popular superstition in southernGreece had it that the least weasel had previously been abride, who was transformed into a bitter animal which would destroy the wedding dresses of other brides out of jealousy.[42] According toPliny the Elder, the least weasel was the only animal that was capable of killing thebasilisk:
To this dreadful monster the effluvium of the weasel is fatal, a thing that has been tried with success, for kings have often desired to see its body when killed; so true is it that it has pleased Nature that there should be nothing without its antidote. The animal is thrown into the hole of the basilisk, which is easily known from the soil around it being infected. The weasel destroys the basilisk by its odour, but dies itself in this struggle of nature against its own self.[43]
TheOjibwe believed that the least weasel could kill the dreadedwendigo by rushing up itsanus.[44]
InInuit mythology, the least weasel is credited with both great wisdom and courage, and whenever a mythicalInuit hero wished to accomplish a valorous task, he would generally change himself into a least weasel.[45]
^Rodrigues, M.; Bos, A. R.; Hoath, R.; Schembri, P. J.; Lymberakis, P.; Cento, M.; Ghawar, W.; Ozkurt, S. O.; Santos-Reis, M.; Merilä, J.; Fernandes, Ca. (2016). "Taxonomic status and origin of the Egyptian weasel (Mustela subpalmata) inferred from mitochondrial DNA".Genetica.144 (2):191–202.doi:10.1007/s10709-016-9889-y.PMID26961232.S2CID17450300.
^Rhoades, S. M. (1900). "A New Weasel from western Pennsylvania".Proceedings of the Academy of Natural Sciences of Philadelphia.52:751–754.JSTOR4062685.
^Swenk, M. H. (1926). "Notes onMustela campestris Jackson, and on the American forms of Least Weasels".Journal of Mammalogy.7 (4):313–330.doi:10.2307/1373581.JSTOR1373581.
^Tapper, S. (1979). "The effect of fluctuating Vole numbers (Microtus agrestis) on a population of Weasels (Mustela nivalis) on farmland".Animal Ecology.48 (2):603–617.Bibcode:1979JAnEc..48..603T.doi:10.2307/4182.JSTOR4182.
^King, C. M. (1977). "The effects of the nematode parasiteSkrjabingylus nasicola on British weasels (Mustela nivalis)".Journal of Zoology.182 (2):225–249.doi:10.1111/j.1469-7998.1977.tb04157.x.
^abAbbott, G. A. (1903),Macedonian Folklore, pp. 108–109, Cambridge University Press
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