Editing Least weasel

{{Short description|Species of mammal}}
{{Good article}}
{{Use dmy dates|date=September 2020}}
{{Speciesbox
| name = Least weasel
| fossil_range = Late [[Pleistocene]] – Recent
| image = Mustela nivalis -British Wildlife Centre-4.jpg
| image_caption = Least weasel at the [[British Wildlife Centre]], [[Surrey]], [[England]]
| status = LC
| status_system = IUCN3.1
| status_ref = <ref name=iucn>{{cite iucn |title=''Mustela nivalis'' |amends=2016 |author1=McDonald, R.A. |author2=Abramov, A.V. |author3=Stubbe, M. |author4=Herrero, J. |author5=Maran, T. |author6=Tikhonov, A. |author7=Cavallini, P. |author8=Kranz, A. |author9=Giannatos, G. |author10=Kryštufek, B.  |author11=Reid, F. |year=2019 |page=e.T70207409A147993366 |doi=10.2305/IUCN.UK.2016-1.RLTS.T70207409A147993366.en |access-date=18 February 2022}}</ref>
| genus = Mustela
| species = nivalis
| authority = [[Carl Linnaeus|Linnaeus]], 1766
| range_map = Least Weasel area.png
| range_map_caption = Global range of the least weasel
}}

The '''least weasel''' ('''''Mustela nivalis'''''), '''little weasel''', '''common weasel''', or simply '''weasel''' is the smallest member of the [[genus]] ''[[Mustela]],'' [[Family (biology)|family]] [[Mustelidae]] and [[Order (biology)|order]] [[Carnivora]]. It is native to [[Eurasia]], [[North America]] and [[North Africa]], and has been introduced to [[New Zealand]], [[Malta]], [[Crete]], the [[Azores]], and [[São Tomé Island|São Tomé]]. It is classified as [[least concern]] by the [[IUCN]], due to its wide distribution and large population throughout the [[Northern Hemisphere]].<ref name=iucn/>

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 the [[pelage]] 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. Eighteen subspecies are recognised.

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 with [[Territory (animal)#Scent marking|olfactory 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.

==Taxonomy and evolution==
The least weasel was given its scientific name ''Mustela nivalis'' by Carl Linnaeus in his [[12th edition of Systema Naturae]] in 1766; its [[specific name|epithet]] ''nivalis'' comes from the [[Latin]] word ''nix'' meaning "snow" because it grows a white coat during the winter season.<ref name=MS>{{cite journal |last1=Sheffield |first1=S. R. |last2=King |first2=C. M. |date=1994 |title=''Mustela nivalis'' |url=https://academic.oup.com/mspecies/article/doi/10.2307/3504183/2600691 |journal=Mammalian Species |issue=454 |pages=1–10 |doi=10.2307/3504183 |jstor=3504183}}</ref>{{rp|6}} The [[Type locality (biology)|type locality]] was [[Västerbotten]] in Sweden.<ref name=MS/>{{rp|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 subgenus ''Mustela'' while Abramov (1999) considered it should be included in the subgenus ''Gale''. Based on skull characteristics, Reig (1997) proposed that the [[taxon]] should be split into four species, ''M. subpalmata'', ''M. rixosa'', ''M. vulgaris'' and ''M. eskimo''. Abrimov and Baryshinikov (2000) disagreed, recognising only ''M. subpalmata'' (the [[Egyptian weasel]]) as a separate species.<ref>{{cite book |title=Mammal Species of the World: A Taxonomic and Geographic Reference, Volume 12 |editor-last=Wilson |editor-first=Don E. |editor-last2=Reeder |editor-first2=DeeAnn M. |year=2005 |publisher=JHU Press |isbn=978-0-8018-8221-0 |pages=616–617 |url=https://books.google.com/books?id=JgAMbNSt8ikC&pg=PA1601}}</ref> However, Rodrigues ''et al''. (2016) recognized ''M. subpalmata'' as a distinct population of ''nivalis'' rather than a distinct species.<ref>{{Cite journal |last1=Rodrigues |first1=M. |last2=Bos |first2=A. R. |last3=Hoath |first3=R. |last4=Schembri |first4=P. J. |last5=Lymberakis |first5=P. |last6=Cento |first6=M. |last7=Ghawar |first7=W. |last8=Ozkurt |first8=S. O. |last9=Santos-Reis |first9=M. |last10=Merilä |first10=J. |last11=Fernandes|first11=Ca. |date=2016 |title=Taxonomic status and origin of the Egyptian weasel (''Mustela subpalmata'') inferred from mitochondrial DNA  |journal=Genetica  |volume=144 |issue=2 |pages=191–202 |doi=10.1007/s10709-016-9889-y |pmid=26961232 |s2cid=17450300}}</ref>

Within the genus ''Mustela'', the least weasel is a relatively unspecialised form, as evidenced by its [[pedomorphism|pedomorphic]] skull, which occurs even in large subspecies.<ref name=s972>{{Harvnb|Heptner|Sludskii|2002|p=972}}</ref> Its direct ancestor was ''Mustela praenivalis'', which lived in Europe during the [[Middle Pleistocene]] and [[Villafranchian]]. ''M. praenivalis'' itself was probably preceded by ''M. pliocaenica'' of the [[Pliocene]]. The modern species probably arose during the [[Late Pleistocene]].<ref name=k102>{{Harvnb|Kurtén|1968|pp=102–103}}</ref> The least weasel is the product of a process begun 5–7&nbsp;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 the [[Last Glacial Period|Ice 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 the [[Bering land bridge]] 200,000 years ago.<ref name=mac205>{{Harvnb|Macdonald|1992|p=205}}</ref>

===Subspecies===
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:<ref name=s975>{{Harvnb|Heptner|Sludskii|2002|pp=975–978}}</ref>

* The ''pygmaea–rixosa'' group (small least weasels): Tiny weasels with short tails, [[Neoteny|pedomorphic]] skulls, and pelts that turn pure white in winter. They inhabit northern [[European Russia]], [[Siberia]], the [[Russian Far East]], [[Finland]], the northern [[Scandinavian Peninsula]], [[Mongolia]], northeastern [[China]], [[Japan]] and [[North America]].<ref name=s975/>
* The ''boccamela'' 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 inhabit [[Transcaucasia]], from western [[Kazakhstan]] to [[Jetisu|Semirechye]] and in the flat deserts of [[Middle Asia]]. They are also found in Morocco, Algeria, and Tunisia.<ref name=s975/>
* The ''nivalis'' 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]], the [[Ciscaucasus]], western Kazakhstan, the southern and middle [[Urals]] and the montane parts of Middle Asia, except the [[Kopet Dag]].<ref name=s975/>

{| class="wikitable" width=80% font=90%
|- bgcolor="#115a6c"
!Subspecies
!Trinomial authority
!Description
!Range
!Synonyms
|----
|Common least weasel<br />''M. n. nivalis''
([[Nominate subspecies]])
[[File:Mustelanivalisnivalis.png|150 px]]
|Linnaeus, 1766
|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 small ''pygmaea'' and the large ''vulgaris''.<ref name=s982>{{Harvnb|Heptner|Sludskii|2002|p=982}}</ref>
|The middle regions of [[European Russia]], from the [[Baltic states]] to the middle and southern [[Urals]], northward approximately to the latitude of [[Saint Petersburg]] and [[Perm, Russia|Perm]], and south to the [[Kursk Oblast|Kursk]] and [[Voronezh Oblast]]s. Outside the [[former Soviet Union]], its range includes [[Northern Europe]] (except for [[Ireland]], [[Iceland]], [[Finland]] and parts of the [[Scandinavian Peninsula]]) and [[Hokkaidō]].
|<small>''caraftensis'' (Kishida, 1936)</small><br />
<small>''kerulenica'' (Bannikov, 1952)</small><br />
<small>''punctata'' (Domaniewski, 1926)</small><br />
<small>''yesoidsuna'' (Kishida, 1936)</small>
|----
|Allegheny least weasel<br />''M. n. allegheniensis''
|Rhoads, 1901
|Similar to ''M. n. rixosa'', but is larger, has a broad skull and darker coat, and is more adapted to live in [[deciduous]] forests<ref>{{cite journal |author=Rhoades, S. M. |year=1900 |title=A New Weasel from western Pennsylvania |journal=Proceedings of the Academy of Natural Sciences of Philadelphia |volume=52 |pages=751–754 |jstor=4062685}}</ref>
|The northeastern United States ([[Michigan]], [[Pennsylvania]], [[New York (state)|New York]], [[Virginia]], [[North Carolina]], [[Ohio]], [[Illinois]], [[Wisconsin]], [[West Virginia]], and [[Indiana]])
|
|----
|Transcaucasian least weasel<br />''M. n. boccamela''
[[File:Mustela-nivalis.jpg|150 px]]
|Bechstein, 1800
|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.<ref name=s980>{{Harvnb|Heptner|Sludskii|2002|p=980}}</ref>
|[[Transcaucasia]], [[southern Europe]], [[Asia Minor]] and probably western [[Iran]]
|<small>''italicus'' (Barrett-Hamilton, 1900)</small>
|----
|Plains least weasel<br />''M. n. campestris''
|Jackson, 1913
|
|The [[Great Plains]] of the United States ([[South Dakota]], [[Iowa]], [[Nebraska]], and [[Kansas]])
|
|----
|Caucasian least weasel<br />''M. n. caucasica''
|Barrett-Hamilton, 1900
|
|
|<small>''dinniki'' (Satunin, 1907)</small>
|----
|Alaskan least weasel<br />''M. n. eskimo''
|Stone, 1900
|A small subspecies. Resembles ''M. n. rixosa'', but has a duller colour, a larger skull and a shorter tail.<ref>{{cite journal |author=Swenk, M. H. |year=1926 |title=Notes on ''Mustela campestris'' Jackson, and on the American forms of Least Weasels |journal=Journal of Mammalogy |volume=7 |issue=4 |pages=313–330 |doi=10.2307/1373581 |jstor=1373581}}</ref>
|[[Alaska]], the [[Yukon]], and the [[Northwest Territories]]
|
|----
|Turkmenian least weasel<br />''M. n. heptneri''
|Morozova-Turova, 1953
|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.<ref name=s981>{{Harvnb|Heptner|Sludskii|2002|p=981}}</ref>
|The deserts and semi-deserts of southern [[Kazakhstan]] and [[Middle Asia]] from the [[Caspian Sea]] to [[Jetisu|Semirechye]], southern [[Tajikistan]], [[Koppet Dag]], [[Afghanistan]] and northeastern [[Iran]]
|
|----
|Japanese least weasel<br />''M. n. namiyei''
|Kuroda, 1921
|Smaller than ''M. n. rixosa'' and paler than ''M. n. eskimo''. Resembles ''M. n. pygmaea'', but the head and body are longer and the tail considerably longer.<ref>{{cite journal |author=Kuroda, N. |year=1921 |title=On three new mammals from Japan |journal=Journal of Mammalogy |volume=2 |issue=4 |pages=208–211 |doi=10.2307/1373554 |jstor=1373554 |url=https://www.biodiversitylibrary.org/part/90605}}</ref>
| Northern [[Honshū]] ([[Aomori Prefecture|Aomori]], [[Akita Prefecture|Akita]] and [[Iwate Prefecture|Iwate]] Prefectures)
|
|----
|Mediterranean least weasel<br />''M. n. numidica''
[[File:Mustelanivalisiberica.png|150 px]]
|Pucheran, 1855
|The largest subspecies
|[[Morocco]], [[Algeria]], [[Egypt]] (formerly thought to be a distinct species, the [[Egyptian weasel]]), [[Malta]], the [[Azores Islands]] and [[Corsica]]
|<small>''albipes'' (Mina Palumbo, 1868)</small><br />
<small>''algiricus'' (Thomas, 1895)</small><br />
<small>''atlas'' (Barrett-Hamilton, 1904)</small><br />
<small>''corsicanus'' (Cavazza, 1908)</small><br />
<small>''fulva'' (Mina Palumbo, 1908)</small><br />
<small>''galanthias'' (Bate, 1905)</small><br />
<small>''ibericus'' (Barrett-Hamilton, 1900)</small><br />
<small>''meridionalis'' (Costa, 1869)</small><br />
<small>''siculus'' (Barrett-Hamilton, 1900)</small>
<small>''subpalmata'' Hemprich & Ehrenberg, 1833</small>
|----
|Montane Turkestan least weasel<br />''M. n. pallida''
|Barrett-Hamilton, 1900
|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.<ref name="s984">{{Harvnb|Heptner|Sludskii|2002|p=984}}</ref>
|The montane parts of [[Turkmenistan]], [[Uzbekistan]], [[Tajikistan]], [[Kazakhstan]] and [[Kirgizia]], as well as the Chinese parts of the same mountain systems and perhaps in the extreme eastern parts of [[Hindukush]]
|
|----
|Siberian least weasel<br />''M. n. pygmaea''
|J. A. Allen, 1903
|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.<ref name="s978">{{Harvnb|Heptner|Sludskii|2002|p=978}}</ref>
|All of [[Siberia]] (except for southern and southeastern [[Transbaikalia]]); the northern and middle [[Urals]], northern Kazakhstan and the [[Russian Far East]], including [[Sakhalin]], the [[Kuril Islands]] and the [[Korean Peninsula]]; all of [[Mongolia]] (except for the eastern part), and probably northeastern [[China]]
|<small>''kamtschatica'' (Dybowksi, 1922)</small>
|----
|Bangs' least weasel<br />''M. n. rixosa''
[[image:Mustela nivalis (two, fighting).jpg|200 px]]
|Bangs, 1896
|The smallest subspecies and the smallest living [[mammal]]ian [[carnivore]] in the world. In its summer coat, the fur is dark reddish-brown, while the winter fur is pure white.<ref name=m14>{{Harvnb|Merriam|1896|pp=14–15}}</ref>
|[[Nunavut]], [[Labrador]], [[Quebec]], [[Minnesota]], [[North Dakota]], [[Montana]], [[Saskatchewan]], [[Alberta]], and [[British Columbia]]
|
|----
|Middle European least weasel<br />''M. n. vulgaris''
|Erxleben, 1777
|A somewhat larger subspecies than ''nivalis'' 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.<ref name=s983>{{Harvnb|Heptner|Sludskii|2002|p=983}}</ref>
|Southern European Russia from the latitude of southern Voronezh and Kursk districts, [[Crimea]], [[Ciscaucasia]], and the northern slopes of the main Caucasus, eastward to the [[Volga]]. Outside the former Soviet Union, its range includes Europe southward to the [[Alps]] and the [[Pyrenees]]. Introduced to [[New Zealand]].<ref name=long>Long, J. L. (2003). ''Introduced Mammals of the World: Their History, Distribution and Influence''. Cabi Publishing. pp. 271–272. {{ISBN|9780643099166}}</ref><ref>{{cite book |title=The Handbook of New Zealand Mammals |last=King |first=C. |year=2005 |publisher=Oxford University Press |isbn=0-19-558477-5 |page=287}}</ref>
|<small>''dumbrowskii'' (Matschie, 1901)</small><br />
<small>''hungarica'' (Vásárhelyi, 1942)</small><br />
<small>''minutus'' (Pomel, 1853)</small><br />
<small>''monticola'' (Cavazza, 1908)</small><br />
<small>''nikolskii'' (Semenov, 1899)</small><br />
<small>''occidentalis'' (Kratochvil, 1977)</small><br />
<small>''trettaui'' (Kleinschmidt, 1937)</small><br />
<small>''vasarhelyi'' (Kretzoi, 1942)</small>
|----
|}

==Description==
[[File:Mustela nivalis 03 MWNH 768.jpg|thumb|Skull of a least weasel]]
[[File:Weasel GIF.GIF|thumb|Least weasel at the [[British Wildlife Centre]]]]
[[File:Frenataermineanivalis.png|thumb|Skulls of a [[long-tailed weasel]] (top), a [[stoat]] (bottom left) and least weasel (bottom right), as illustrated in [[Clinton Hart Merriam|Merriam]]'s ''Synopsis 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 the [[sole (foot)|sole]]s are heavily haired.<ref name=s967>{{Harvnb|Heptner|Sludskii|2002|pp=967–969}}</ref> The skull, especially that of the small ''rixosa'' group, has an infantile appearance when compared with that of other members of the genus ''Mustela'' (in particular, the [[stoat]] and [[Siberian weasel|kolonok]]). This is expressed in the relatively large size of the [[cranium]] and shortened facial region.<ref name=s969>{{Harvnb|Heptner|Sludskii|2002|p=969}}</ref> 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.<ref name=h468/> There are usually four pairs of nipples but these are only visible in females.

The [[baculum]] is short,<ref>{{Cite book |last=King |first=C. M. |url=https://books.google.com/books?id=In48DwAAQBAJ&dq=baculum&pg=PA199 |title=The Natural History of Weasels and Stoats: Ecology, Behavior, and Management |date=2007 |publisher=Oxford University Press, USA |isbn=978-0-19-530056-7}}</ref> {{cvt|16|to|20|mm}}, 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 {{cvt|7|by|5|mm}}, and contain sulphurous volatiles, including [[thietane]]s and dithiacyclopentanes. The smell and chemical composition of these chemicals are distinct from those of the stoat.<ref name=h468>{{Harvnb|Harris|Yalden|2008|p=468}}</ref> The least weasel moves by jumping, the distance between the tracks of the fore and hind limbs being {{cvt|18|to|35|cm}}.<ref name=s991>{{Harvnb|Heptner|Sludskii|2002|p=991}}</ref>

[[File:Weaselskeleton.jpg|thumb|Skeleton, as illustrated in [[Richard Lydekker|Lydekker]]'s ''The New Natural History'']]
Dimensions vary geographically, to an extent rarely found among other mammals. Least weasels of the ''boccamela'' 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 {{cvt|130|to|260|mm}}, while females average {{cvt|114|to|204|mm}}. The tail measures {{cvt|12|to|87|mm}} in males and {{cvt|17|to|60|mm}} in females. Males weigh {{cvt|36|to|250|g}}, while females weigh {{cvt|29|to|117|g}}.<ref name=s970>{{Harvnb|Heptner|Sludskii|2002|pp=970–972}}</ref>

[[File:Mustela winter.jpg|thumb|right|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 the [[Mandible#Other vertebrates|lower 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.<ref name=s969/><ref name=Collins>{{cite book |title=Mammals |last=Konig |first=C. |year=1973 |publisher=Collins & Co. |isbn=978-0-00-212080-7 |page=167}}</ref>

==Distribution and habitat==
[[File:Alaska Weasel.jpg|thumb|right|Alaskan least weasel (''M. n. eskimo'')]]
[[File:Walid soukkou 99.jpg|thumb|right|Least weasel in northern Algeria]]
The least weasel has a [[circumboreal]], [[Holarctic]] distribution, encompassing much of [[Europe]] and [[North Africa]], [[Asia]] and parts of northern [[North America]]. It has been introduced to [[New Zealand]],<ref name=long/> [[Malta]], [[Crete]], the [[Azore Islands]] and also [[São Tomé Island|São Tomé]] off West Africa. It occurs throughout Europe, except [[Ireland]], and on all major [[Mediterranean]] islands.<ref>{{cite journal |author1=Rodrigues, M. |author2=Bos, A.R. |author3=Schembri, P.J. |author4=De Lima, R.F. |author5=Lymberakis, P. |author6=Parpal, L. |author7=Cento, M. |author8=Ruette, S. |author9=Ozkurt, S.O. |author10=Santos-Reis, M. |author11=Merilä, J. |s2cid=20057808 |year=2016 |title=Origin and introduction history of the Least Weasels (''Mustela nivalis'') on Mediterranean and Atlantic islands inferred from genetic data |journal=Biological Invasions |volume=19 |pages=399–421 |doi=10.1007/s10530-016-1287-y |url=https://www.researchgate.net/publication/308991117}}</ref> It also occurs on [[Honshu]] and [[Hokkaido]] Islands in [[Japan]] and on [[Kunashir]], [[Iturup]], and [[Sakhalin]] Islands in [[Russia]].<ref name=iucn/>

The least weasel inhabits fields, open woodland, bushy and rocky areas, parks and gardens at elevations of up to about {{cvt|3000|m}}.<ref name=Collins/>

Fossilised remains of the least weasel are known from [[Denisova Cave]].<ref>{{Cite journal |last1=Puzachenko |first1=A. Yu. |last2=Titov |first2=V. V. |last3=Kosintsev |first3=P. A. |date=2021 |title=Evolution of the European regional large mammals assemblages in the end of the Middle Pleistocene – The first half of the Late Pleistocene (MIS 6–MIS 4) |journal=[[Quaternary International]] |volume=605–606 |pages=155–191 |doi=10.1016/j.quaint.2020.08.038 |bibcode=2021QuInt.605..155P}}</ref>

== Behaviour and ecology ==
===Reproduction and development===
The least weasel mates in April–July and there is a 34- to 37-day [[gestation period]]. In the [[Northern Hemisphere]], the average litter size consists of 6 kits and these reach [[sexual maturity]] in 3 to 4 months. Males may mate during their first year of life, though this is usually unsuccessful. They are [[fecund]] in February–October, though the early stages of [[spermatogenesis]] do occur throughout the winter months. [[Estrous cycle#Anestrus|Anestrus]] in females lasts from September until February.<ref name=h474>{{Harvnb|Harris|Yalden|2008|p=474}}</ref>

The female raises her kits without help from the male. They are {{cvt|1.5|to|4.5|g}} 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. The [[milk 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.<ref name=h474/> There is a single litter each year and least weasels can live for 7 or 8 years.<ref name=Collins/>

===Territorial and social behaviours===
[[File:Mustela nivalis (two, fighting).jpg|thumb|left|Two least weasels fighting]]
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.<ref>{{cite journal |author=Erlinge, S. |year=1974 |title=Distribution, territoriality and numbers of the Weasel ''Mustela nivalis'' in relation to prey abundance |journal=Oikos |volume=25 |issue=3 |pages=308–314 |jstor=3543948 |doi=10.2307/3543948 |bibcode=1974Oikos..25..308E}}</ref> Like the stoat, the male least weasel extends his range during spring or during food shortages. Its [[scent marking]] behaviour is similar to that of the stoat; it uses [[faeces]], [[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 a mole or rat.<ref name=h471>{{Harvnb|Harris|Yalden|2008|pp=471–472}}</ref> The burrow entrance measures about {{cvt|2.5|cm}} across and leads to the nest chamber located up to {{cvt|15|cm}} below ground. The nest chamber (which is used for sleeping, rearing kits and storing food) measures {{cvt|10|cm}} in diameter, and is lined with straw and the skins of the weasel's prey.<ref name=m277>{{Harvnb|Merritt|Matinko|1987|p=277}}</ref>

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 the [[stoat]]. Dominant weasels exhibit lunges and shrieks during aggressive encounters, while subdominant weasels will emit submissive squeals.<ref name=h471/>

===Diet===
[[File:Donnola vs lepre.JPG|thumb|right|Taxidermy exhibit showing a least weasel attacking a [[European hare]], in the Natural History Museum of Genoa]]

The least weasel feeds predominantly on [[mouse]]-like [[rodent]]s, including [[mice]], [[hamster]]s, [[Gerbillinae|gerbil]]s and others. It usually does not attack adult hamsters and [[rat]]s. [[Frog]]s, [[fish]], small [[bird]]s and bird eggs are rarely eaten. It can deal with adult [[pika]]s and gerbils, but usually cannot overcome [[brown rat]]s and [[souslik]]s. Exceptional cases are known of least weasels killing prey far larger than themselves, such as [[capercaillie]], [[Hazel grouse|hazel hen]] and [[hare]]s.<ref name=s987>{{Harvnb|Heptner|Sludskii|2002|pp=987–988}}</ref> In England, a favoured prey item is the [[field 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.<ref>{{cite journal |author=Tapper, S. |year=1979 |title=The effect of fluctuating Vole numbers (''Microtus agrestis'') on a population of Weasels (''Mustela nivalis'') on farmland |journal=Animal Ecology |volume=48 |issue=2 |pages=603–617 |jstor=4182 |doi=10.2307/4182 |bibcode=1979JAnEc..48..603T}}</ref>

Despite its small size, the least weasel is a fierce hunter, capable of killing a [[rabbit]] five to 10 times its own weight.<ref name=mac208>{{Harvnb|Macdonald|1992|p=208}}</ref> 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.<ref name=h472>{{Harvnb|Harris|Yalden|2008|pp=472–473}}</ref>

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.<ref name=h472/> The least weasel kills small prey, such as [[vole]]s, with a bite to the [[occiput|occipital]] region of the skull<ref name=s987/> or the neck, dislocating the [[cervical vertebrae]]. Large prey typically dies of [[blood loss]] or [[Shock (circulatory)|circulatory shock]].<ref name=h472/> When food is abundant, only a small portion of the prey is eaten, usually the [[brain]]. The average daily food intake is {{cvt|35|g}}, which is equivalent to 30–35% of the animal's body weight.<ref name=s987/>

===Predators and competitors===
[[File:Weaselsvsstoat.png|thumb|Least weasels driven from a [[mountain hare]] carcass by a [[stoat]], as illustrated in [[Gerald Edwin Hamilton Barrett-Hamilton|Barrett-Hamilton]]'s ''A History of British Mammals'']]
The least weasel is small enough to be preyed upon by a range of other predators.<ref name=h475>{{Harvnb|Harris|Yalden|2008|p=475}}</ref> Least weasel remains have been found in the excrement of [[red fox]]es, [[sable]]s, [[steppe polecat|steppe]] and [[European polecat|forest polecat]], [[stoat]]s, [[eagle owl]]s and [[buzzard]]s.<ref name=s992>{{Harvnb|Heptner|Sludskii|2002|p=992}}</ref> The [[owls]] most efficient at capturing least weasels are [[barn-owl|barn]], [[barred owl|barred]], and [[great horned owl]]s. Other birds of prey threatening to the least weasel include [[Broad-winged hawk|broad-winged]] and [[rough-legged buzzard]]s. Some [[snake]] species may prey on the least weasel, including the [[black rat snake]] and [[Agkistrodon contortrix|copperhead]].<ref name=m277/> Aside from its smaller size, the least weasel is more vulnerable to predation than the stoat because it lacks a black predator deflection mark on the tail.<ref name=h475/>

In areas where the least weasel is [[Sympatry|sympatric]] with the [[stoat]], 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.<ref name=h469>{{Harvnb|Harris|Yalden|2008|p=469}}</ref>

=== Diseases and parasites ===
[[Ectoparasite]]s known to infest weasels include the [[louse]] ''Trichodectes mustelae'' and the [[mite]]s ''[[Demodex]]'' and ''Psoregates mustela''. The species may catch [[flea]]s from the nests and burrows of its prey. Flea species known to infest weasels include ''Ctenophthalmus bisoctodentatus'' and ''Palaeopsylla m. minor'', which they get from moles, ''P. s. soricis'', which they get from shrews, ''Nosopsyllus fasciatus'', which they get from rodents and ''Dasypsyllus gallinulae'' which they get from birds.<ref name=h475/>

[[Helminth]]s known to infest weasels include the [[trematode]] ''[[Alaria (flatworm)|Alaria]]'', the [[nematode]]s ''[[Capillaria (nematode)|Capillaria]]'', ''Filaroides'' and ''[[Trichinella]]'' and the [[cestode]] ''[[Taenia (flatworm)|Taenia]]''.<ref name=h475/> Least weasels are commonly infected with the [[nematode]] ''[[Skrjabingylus nasicola]]'', adults of which are found in the nasal sinuses and can damage the skull. There is no evidence that this has serious detrimental effects on even heavily infested animals.<ref>{{cite journal |author=King, C. M. |year=1977 |title=The effects of the nematode parasite ''Skrjabingylus nasicola'' on British weasels (''Mustela nivalis'') |journal=Journal of Zoology |volume=182 |issue=2 |pages=225–249 |doi=10.1111/j.1469-7998.1977.tb04157.x}}</ref>

==Conservation==
The least weasel is listed as [[Least Concern]] on the [[IUCN Red List]], because of its wide global distribution and large population that is  thought to be not in decline.<ref name=iucn/>

== In folklore and mythology ==
=== Macedonian and Greek culture ===
[[File:Wenceslas Hollar - The basilisk and the weasel.jpg|thumb|17th century print of a least weasel confronting a [[basilisk]]]]
The [[Ancient Macedonians]] believed that to see a least weasel was a good omen. In some districts of [[Macedon]], 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.<ref name="Abbott">Abbott, G. A. (1903), [https://archive.org/details/macedonianfolklo00abborich ''Macedonian Folklore''], pp. 108–109, Cambridge University Press</ref>

Similarly, a popular superstition in southern [[Greece]] had it that the least weasel had previously been a [[bride]], who was transformed into a bitter animal which would destroy the wedding dresses of other brides out of jealousy.<ref name="Abbott"></ref> According to [[Pliny the Elder]], the least weasel was the only animal that was capable of killing the [[basilisk]]:

<blockquote>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.<ref>{{cite web|title=The Natural History|author=Pliny the Elder|editor=John Bostock|editor2=Henry Thomas Riley|editor-link=John Bostock (physician)|editor2-link=Henry Thomas Riley|year=1855|url=http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.02.0137:book=8:chapter=33|access-date=23 August 2022}}</ref></blockquote>

=== Ojibwe and Inuit culture ===
The [[Ojibwe]] believed that the least weasel could kill the dreaded [[wendigo]] by rushing up its [[anus]].<ref>Barnouw, Victor (1979). ''Wisconsin Chippewa Myths & Tales: And Their Relation to Chippewa Life'', p. 53, University of Wisconsin Press, {{ISBN|0-299-07314-9}}</ref>

In [[Inuit mythology]], the least weasel is credited with both great wisdom and courage, and whenever a mythical [[Inuit]] hero wished to accomplish a valorous task, he would generally change himself into a least weasel.<ref>Dufresne, Frank (2005), ''Alaska's Animals and Fishes'', p. 109, Kessinger Publishing, {{ISBN|1-4179-8416-3}}</ref>

==See also==
* [[Smallest organisms]]

==References==
=== Citations ===
{{Reflist}}

=== General and cited references ===
* {{Cite book|last1=Harris|first1=Stephen|last2=Yalden|first2=Derek|title=Mammals of the British Isles|publisher=Mammal Society|edition=4th Revised|year=2008|isbn=978-0-906282-65-6}}
*{{Cite book|last=Kurtén|first=Björn|title=Pleistocene mammals of Europe|publisher=Weidenfeld and Nicolson|year=1968}}
* {{Cite book|last1=Heptner|first1=V. G.|last2=Sludskii|first2=A. A.|url=https://archive.org/details/mammalsofsov212001gept|title=Mammals of the Soviet Union. Vol. II, part 1b, Carnivores (Mustelidae and Procyonidae)|publisher=Washington, D.C. : Smithsonian Institution Libraries and National Science Foundation|year=2002|isbn=90-04-08876-8}}
* {{Cite book|last=Macdonald|first=David|title=The Velvet Claw: A Natural History of the Carnivores|publisher=New York: Parkwest|year=1992|isbn=0-563-20844-9|url-access=registration|url=https://archive.org/details/velvetclawnatura00macd}}
* {{cite book |last=Merriam|first=Clinton Hart|url=https://archive.org/details/synopsisofweasel00merriala|title=Synopsis of the weasels of North America |location=Washington, D.C. |publisher=Govt. Print. Off.|year=1896}}
* {{Cite book|last1=Merritt|first1=Joseph F.|last2=Matinko|first2=Ruth Anne|title=Guide to the mammals of Pennsylvania|publisher=University of Pittsburgh Press|year=1987|isbn=0-8229-5393-5}}

==Further reading==
* {{Cite book|last=Coues|first=Elliott|url=https://archive.org/details/furbearinganima00couegoog|title=Fur-bearing Animals: A Monograph of North American Mustelidae|publisher=Government Printing Office|year=1877}}
* {{Cite book|last=Johnston|first=Harry Hamilton|url=https://archive.org/details/britishmammalsat00john|title=British mammals; an attempt to describe and illustrate the mammalian fauna of the British islands from the commencement of the Pleistocene period down to the present day|publisher=London, Hutchinson|year=1903}}
* {{Cite book|last=Kurtén|first=Björn|title=Pleistocene mammals of North America|publisher=Columbia University Press|year=1980|isbn=0-231-03733-3}}

==External links==
{{Wiktionary}}
{{Commons|Mustela nivalis|''Mustela nivalis''}}
{{Wikispecies|Mustela nivalis|''Mustela nivalis''}}
* [http://www.mnh.si.edu/mna/image_info.cfm?species_id=187 Smithsonian Institution – North American Mammals: ''Mustela nivalis'']

{{Weasels}}
{{Carnivora|M.}}
{{Taxonbar|from=Q25311}}
{{Authority control}}

[[Category:Arctic land animals|Weasel, least]]
[[Category:Carnivorans of Asia|Weasel, least]]
[[Category:Carnivorans of Europe|Weasel, least]]
[[Category:Carnivorans of North America|Weasel, least]]
[[Category:Fur trade]]
[[Category:Fauna of the Holarctic realm]]
[[Category:Least concern biota of Asia]]
[[Category:Least concern biota of Europe]]
[[Category:Least concern biota of North America]]
[[Category:Mammals described in 1766]]
[[Category:Mammals of the Arctic|Weasel, least]]
[[Category:Taxa named by Carl Linnaeus]]
[[Category:Weasels]]