The genus Mustela, as treated by Larivère and Jennings (2009), includes 17 species, as follows:
1. Amazon Weasel (Mustela africana). The very poorly known Amazon Weasel (Mustela africana) received its scientific name based on a specimen believed to have originated in Africa (Hall 1951), but in fact this species is known only from the Amazon basin in Bolivia, Brazil, Ecuador, Colombia, and Peru. These weasels have been reported from primary forest and humid riparian habitats and are reported to be good swimmers and climbers. (Larivère and Jennings 2009 and references therein) The Amazon Weasel and Colombian Weasel are the only known Mustela species that occur exclusively in South America.
2. Altai Mountain Weasel (Mustela altaica). This weasel, found in parts of central and northeastern Asia, occurs in alpine meadows, steppes, and forests from 1500 to 4000 m. It feeds on a variety of small animals, as well as berries. Although mainly terrestrial, it climbs and swims well. (Larivère and Jennings 2009 and references therein)
3. Ermine (Mustela erminea). The Ermine (Mustela erminea) is also often known as Stoat or Short-tailed Weasel. It is distributed broadly across much of North America and Eurasia, from tundra and alpine meadows to temperate woodlands, marshes and riparian habitats, and farmland, occurring from sea level up to 3000 m. The diet consists mainly of small mammals (rodents and lagomorphs), but also includes other small animals, bird eggs, and fruit. The species was introduced to New Zealand to control rabbit populations and is now considered a pest because of its impact on native bird populations. Ermine are trapped for their fur in North America and Russia. With the exception of some populations in the southern part of the range, the coat changes in the fall from brown above and whitish below to all white (except for the black tail tip) and this white winter fur has long been used in trimming coats and making stoles. (Larivère and Jennings 2009 and references therein)
4. Steppe Polecat (Mustela eversmanii). The Steppe Polecat (Mustela eversmanii) is found from southeastern Europe through central and northeastern Asia in steppe, open grasslands, and semi-desert. The diet includes small mammals and other small animals. These weasels may spend much of their time exploring the burrows of small mammals in search of prey. Although this species is not very well known, it is not believed to be threatened over most of its range. (Larivère and Jennings 2009 and references therein)
5. Colombian Weasel (Mustela felipei). The Colombian Weasel (Mustela felipei), which is known only from a handful of specimens from northern Ecuador and western Colombia, was first described in 1978 (Izor and de la Torre 1978). Very little is known about this weasel, which may be South America's rarest carnivore, known only from a region of around 10,000 km2 where deforestation is ongoing. Most specimens have been collected near riparian areas at elevations between 1700 m and 2700 m. (Larivère and Jennings 2009 and references therein)
6. Long-tailed Weasel (Mustela frenata). The Long-tailed Weasel (Mustela frenata) is found across southern Canada and most of the United States south through Mexico, Central America, and western South America to Bolivia. Long-tailed Weasels are found in a wide range of habitats, from forested areas to agricultural fields, but are especially associated with open brushy or grassy areas near water. In Canada and the northern United States, the summer coat, which is brown above and whitish below, becomes all white (except for the black tail tip) in winter; Long-tailed Weasels in the southern United States, Mexico, and Central America (which do not molt into a white summer coat) have distinctive white or yellow facial markings. The diet consists mainly of rodents and other small mammals. Although mainly terrestrial, Long-tailed Weasels can climb and swim well. Long-tailed Weasels, which are relatively common over most of their range, are trapped in North America for their white winter fur. (Larivère and Jennings 2009 and references therein)
7. Japanese Weasel (Mustela itatsi). The Japanese Weasel (Mustela itatsi) was previously considered to be a subspecies of the Siberian Weasel. This weasel is native to Japan but has been introduced to Hokkaido (Japan's second largest island) and Russia (South Sakhalin); it was introduced to Zamami Island (in Okinawa, Japan) in 1957 and 1958. Japanese Weasels are often found near water and sometimes near human dwellings. The diet is reported to consist of insects, reptiles, small mammals, fish, arthropods (including crustaceans), and fruit. This nocturnal weasel is considered common throughout its range. It has been introduced in some areas for the purpose of controlling rats and snakes. (Larivère and Jennings 2009 and references therein)
8. Yellow-bellied Weasel (Mustela kathiah). The Yellow-bellied Weasel (Mustela kathiah) is found from northeastern India and Nepal to southern and eastern China and south through Laos and Vietnam. It occurs in pine forests up to 4000 m, above the timber line. In western Himalaya it is found from 3000-5200 m in the cold deserts, but in Hong Kong it occurs at much lower altitudes, from near sea level to over 200 m. These weasels are reported to feed on rodents, birds, eggs, lizards, frogs, insects, and fruit. Although populations are not known to be threatened, little is known about this species. (Larivère and Jennings 2009 and references therein)
9. European Mink (Mustela lutreola). The European Mink is found along rivers, streams and lakes, rarely more than 100 m from freshwater. Areas with densely vegetated banks are preferred. Although the American Mink (Neovison vison) and European Mink are morphologically and ecologically similar, molecular phylogenetic analyses indicate that they are not actually closely related within the subfamily Mustelinae (Harding and Smith 2009 and references therein). The European Mink is very patchily distributed and has been extirpated from much of its original range in Europe, with populations now found in Belarus, Estonia, France, Latvia, Romania, Russia (west of the Urals), and northern Spain (recently colonized). It is extinct in Austria, Bulgaria, Czech Republic, Germany, Hungary, Montenegro, Poland, Serbia, and Slovakia and populations have declined elsewhere in Europe. Habitat loss and degradation has resulted from hydroelectric development, river channelization, and water pollution. Although its fur is less valuable than that of the American Mink, the European Mink was nevertheless widely trapped commercially. Now legally protected, accidental trapping still occurs. In some areas, automobiles are a source of mortality. Competition with alien invasive American Mink has been suggested as a possible threat, as has hybridization with European Polecats in Spain and France. The diet includes small mammals, birds, amphibians, fish, molluscs, crabs, and insects. Water Voles (Arvicola amphibius) are often a major component in the diet. Conservation efforts are ongoing. (Larivère and Jennings 2009 and references therein)
10. Indonesian Mountain Weasel (Mustela lutreolina). The Indonesian Mountain Weasel (Mustela lutreolina) is found only in Indonesia, in the highlands of Java and South Sumatra. Specimens have been collected at elevations from 1000-2200 m. Virtually nothing is known about this species. (Larivère and Jennings 2009 and references therein)
11. Black-footed Ferret (Mustela nigripes). The Black-footed Ferret (Mustela nigripes) is known only from North American from the Great Plains west to the Rocky Mountains. Long thought to be extinct, a specimen was taken by a ranch dog in Wyoming in 1981, triggering the discovery of a small surviving population and a major recovery and reintroduction effort that is ongoing. Black-footed Ferrets are found on short- and mid-grass prairies and semi-arid grasslands, where they are closely associated with Cynomys prairie dogs, which constitute most of their diet. Their conservation status remains very precarious.
12. Least Weasel (Mustela nivalis). The Least Weasel (Mustela nivalis) is distributed across Europe, much of Asia, North Africa, and northern North America. The species has been introduced to New Zealand; Malta and Crete in the Mediterranean; and the Azores Islands and, apparently, Sao Tome Island in the eastern Atlantic Ocean; introduced populations have had serious detrimental impacts on some native fauna. Least Weasels occur in a wide range of habitats with good cover and abundant prey, including agricultural fields, grasslands, forests, prairies, riparian woodlands, hedgerows, mountains (up to 4000 m), alpine meadows, steppes, semi-deserts, and coastal dunes, as well as around human habitations. They feed mainly on small rodents, but other small prey are taken as well. This species is believed to be relatively common in Eurasia, but rarer in North America. (Larivère and Jennings 2009 and references therein)
13. Malay Weasel (Mustela nudipes). The Malay Weasel (Mustela nudipes) is found in Borneo, peninsular Malaysia, Sumatra, and southern Thailand. It is found in rainforests, with records from 400 to 1700 m, often near water. The diet includes small mammals, birds, amphibians, and reptiles. Although this species is poorly known, it is not believed to be threatened. It is eaten in parts of Sarawak (in Malaysian Borneo) and there is some evidence of traditional medicinal use. (Larivère and Jennings 2009 and references therein)
14. European Polecat (Mustela putorius). The European Polecat (Mustela putorius), which is the possible ancestor of the domestic Ferret, is found across most of Europe west of the Urals and in Morocco. It occurs in forests, meadows, abandoned fields, and agricultural areas, often near water. European Polecats may be found near humans, but avoid dense urban areas. The diet includes amphibians, small mammals, birds, fish, and invertebrates. At one time European Polecats in western Europe were widely hunted for sport and fur and persecuted as pests, but these threats are now much reduced. Accidental mortality occurs from cars and secondary rodenticide poisoning. In Russia and Morocco this species is commonly hunted. Other possible threats include hybridization with Ferrets in the United Kingdom and competition with the introduced American Mink. (Larivère and Jennings 2009 and references therein)
15. Siberian Weasel (Mustela sibirica). The Siberian Weasel (Mustela sibirica) is broadly distributed across northern and southeastern Asia. It has been introduced to several Japanese islands. Siberian Weasels are found in forest, forest steppe, and mountains from 1500 to 5000 m. They are often found in river valleys, near swamps, and in areas with dense ground vegetation, around villages, and in cultivated areas. These weasels are mainly terrestrial, but can climb and swim well. Siberian Weasel populations are believed to be generally secure and the species is important in the fur trade. (Larivère and Jennings 2009 and references therein)
16. Back-striped Weasel (Mustela strigidorsa). The Back-striped Weasel (Mustela strigidorsa) is found in western China and parts of adjacent southern and southeastern Asia. It is found mainly in evergreen forests in hills and mountains, but has also been recorded from plains forest, dense scrub, secondary forest, grassland, and farmland from 90-2500 m. The diet is said to include small rodents. This is a poorly known species, but it has been seen both on the ground and in trees. Populations may be declining. Back-striped Weasels are sold for use in traditional medicine in Laos. Several thousand pelts were sold annually in China in the 1970s; outside China, this species is sold occasionally in Laos and Vietnam. Although these weasels are not known to have high economic value, accidental trapping may be having a serious impact on populations. (Larivère and Jennings 2009 and references therein)
17. Egyptian Weasel (Mustela subpalmata). The Egyptian Weasel (Mustela subpalmata), known only from Egypt, has often been considered conspecific with the Least Weasel (i,e., belonging to the same species), but is now recognized as a distinct species. It is found in fields and along irrigation canals, as well as in towns and villages. The diet is said to include small rodents and insects. Virtually nothing is known about this species, but it is not known to be at risk. (Larivère and Jennings 2009 and references therein)
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