Least weasel

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]

• The pygmaea–rixosa group (small least weasels): Tiny weasels with short tails, 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.[8]
• 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 Semirechye and in the flat deserts of Middle Asia. They are also found in Morocco, Algeria, and Tunisia.[8]
• 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 Köpet Dag.[8]

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. Anestrus in females lasts from September until February.[29]

The female raises its kits without help from the male. They are 1.5 to 4.5 g (0.05 to 0.16 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. 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.[29] There is a single litter each year and least weasels can live for 7 or 8 years.[28]

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.[30] Like the stoat, the male least weasel extends its 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.[31] 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.[32]

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.[31]

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 rodents, including mice, hamsters, gerbils and others. It usually does not attack adult hamsters and rats. Frogs, fish, small birds and bird eggs are rarely eaten. It can deal with adult pikas and gerbils, but usually cannot overcome brown rats and sousliks. Exceptional cases are known of least weasels killing prey far larger than themselves, such as capercaillie, hazel hen and hares.[33] 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.[34]

Despite its small size, the least weasel is a fierce hunter, capable of killing a rabbit five to 10 times its own weight.[35] 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.[36]

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.[36] The least weasel kills small prey, such as voles, with a bite to the occipital region of the skull[33] or the neck, dislocating the cervical vertebrae. Large prey typically dies of blood loss or circulatory shock.[36] When food is abundant, only a small portion of the prey is eaten, usually the brain. The average daily food intake is 35 g (1 oz), which is equivalent to 30–35% of the animal's body weight.[33]

Least weasels driven from a mountain hare carcass by a stoat, as illustrated in Barrett-Hamilton's A History of British Mammals

The least weasel is small enough to be preyed upon by a range of other predators.[37] Least weasel remains have been found in the excrement of red foxes, sables, steppe and forest polecat, stoats, eagle owls and buzzards.[38] The owls most efficient at capturing least weasels are barn, barred, and great horned owls. Other birds of prey threatening to the least weasel include broad-winged and rough-legged buzzards. Some snake species may prey on the least weasel, including the black rat snake and copperhead.[32] 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.[37]

In areas where the least weasel is 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.[39]

Ectoparasites known to infest weasels include the louse Trichodectes mustelae and the mites Demodex and Psoregates mustela. The species may catch fleas 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.[37]

Helminths known to infest weasels include the trematode Alaria, the nematodes Capillaria, Filaroides and Trichinella and the cestode Taenia.[37] 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.[40]

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.

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.[42] According to Pliny the Elder, the least weasel was the only animal that was capable of killing the basilisk:

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]

The Ojibwe believed that the least weasel could kill the dreaded wendigo by rushing up its anus.[44]

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.[45]

• Harris, Stephen; Yalden, Derek (2008). Mammals of the British Isles (4th Revised ed.). Mammal Society. ISBN 978-0-906282-65-6.
• Kurtén, Björn (1968). Pleistocene mammals of Europe. Weidenfeld and Nicolson.
• Heptner, V. G.; Sludskii, A. A. (2002). Mammals of the Soviet Union. Vol. II, part 1b, Carnivores (Mustelidae and Procyonidae). Washington, D.C. : Smithsonian Institution Libraries and National Science Foundation. ISBN 90-04-08876-8.
• Macdonald, David (1992). The Velvet Claw: A Natural History of the Carnivores. New York: Parkwest. ISBN 0-563-20844-9.
• Merriam, Clinton Hart (1896). Synopsis of the weasels of North America. Washington : Govt. Print. Off.
• Merritt, Joseph F.; Matinko, Ruth Anne (1987). Guide to the mammals of Pennsylvania. University of Pittsburgh Press. ISBN 0-8229-5393-5.