Mustelidaebadgers, otters, weasels, and relatives


Mustelidae is the largest family within Carnivora and is comprised of 56 species in 22 genera. Members of this family include weasels, stoats, polecats, mink, marten, fishers, wolverines, otters, badgers and others. While many authors have traditionally considered skunks a subfamily within Mustelidae, recent molecular evidence indicates that skunks do not lie within the mustelid group and instead are recognized as a single family, Mephitidae, a systematic understanding which is accepted here (Dragoo and Honeycutt, 1997; Flynn et al., 2005; Marmi et. al., 2004; Sato et. al., 2003; Sato et. al., 2004). (Dragoo and Honeycutt, 1997; Flynn, et al., 2005; Marmi, et al., 2004; Nowak, 1991; Sato, et al., 2003; Sato, et al., 2004; Vaughan, et al., 2000; Whitaker and Hamilton, 1998)

Mustelids inhabit all continents except Australia and Antarctica, and do not occur on Madagascar or oceanic islands. Members of this group can be found in diverse habitats, which include both terrestrial, aquatic and marine environments. Mustelids are mainly carnivorous, with various members of the family exploiting a great diversity of both vertebrate and invertebrate prey. Mustelids are generally proficient hunters; some weasels can take prey larger than themselves. Members of this family often hunt in burrows and crevices, and some species have evolved to become adept at climbing trees (e.g., marten) or swimming (e.g., sea otters, mink) in search of prey. (Nowak, 1991; Sato, et al., 2003; Vaughan, et al., 2000; Whitaker and Hamilton, 1998)

Generally, mustelids have elongate bodies with short legs and a short rostrum, as typified by weasels, ferrets, mink, and otters. Wolverines and badgers have broader bodies. An order of magnitude difference in size exists between the smallest and largest mustelid species. The smallest species is the least weasel (Mustela nivalis), weighing between 35 and 250 grams. Wolverines (Gulo gulo) and sea otters (Enhydra lutris) reach 32 kg and 45 kg, respectively. All mustelids have well developed anal scent glands, which serve various functions, including territorial marking and defense. (Hutchings and White, 2000; Nowak, 1991; Vaughan, et al., 2000)

Geographic Range

Members of the family Mustelidae inhabit all continents except Antarctica and Australia. They do not occur on Madagascar or oceanic islands, but have been introduced to New Zealand. (Dragoo and Honeycutt, 1997; Sato, et al., 2003; Vaughan, et al., 2000)


Mustelidae are distributed from the arctic to the tropics and occupy nearly all terrestrial habitats. Several species are semi- or nearly fully aquatic and inhabit freshwater rivers and streams, as well as coastal marine waters. (Nowak, 1991; Vaughan, et al., 2000)

Physical Description

Adult mustelids range in size from 114 mm and 25 g (least weasel) to over 1 m and 45 kg (sea otters). These animals are generally long-bodied with short legs. Most species have slender bodies, but some, like badgers (Mustelinae, Mustelinae) and wolverines have much broader bodies. The skull is elongate with a relatively short rostrum. Adult males are generally about 25 percent larger than females of the same species. The ears are short, as are the legs, each of which bears five digits. The claws do not retract and, in digging species, are especially robust. Mustelids are digitigrade or plantigrade. The dental formula varies among species: 3/3, 1/1, 2-4/2-4, 1/1-2 = 28-38. The canines are long, and the carnassials are well-developed. The upper molars are often narrow in the middle, giving them an hourglass shape. Mustelids have a powerful bite; in many species, the large postglenoid process locks the lower jaw into the upper, causing the lower jaw to only move in the vertical plane, without any rotary motion. (Nowak, 1991; Vaughan, et al., 2000; Whitaker and Hamilton, 1998)

  • Sexual Dimorphism
  • male larger


Mating systems vary both within and among species. Many species are polygynous and/or promiscuous. Some species are social, while others are solitary. Social organization can vary within species as well. Mustelids require prolonged periods of copulation to induce ovulation of an unfertilzed egg. As a result, copulation may last for several hours before fertilization can be successful. (Amstislavsky and Ternovskaya, 2000; Johnson, et al., 2000; Vaughan, et al., 2000)

Most mustelids breed seasonally, but the length of the reproductive period varies among species. Day length often dictates the onset of the breeding season, which usually lasts 3 to 4 months. Many mustelids undergo delayed implantation, with the fertilized embryo taking up to 10 months (e.g. Meles meles) to implant in the uterus in some species. Environmental conditions such as temperature and day length determine when implantation occurs. Mustelids that live in more seasonal climates are more likely to exhibit delayed implantation. Following implantation, gestation typically lasts 30 to 65 days. Females give birth to a single litter each season, the size of which varies within and among species. For example, sables have an average litter size of 2.2, but can give birth to anywhere from 1 to 7 pups. The mountain weasel averages 8.7 pups per litter, but can have between 3 and 14 young in a single bout of reproduction. Generally, mustelids are altricial, being born small and blind. They reach sexual maturity between 8 months and two years following birth. (Amstislavsky and Ternovskaya, 2000; Nowak, 1991; Thom, et al., 2004; Vaughan, et al., 2000)

Young are generally born in an alricial state, requiring extenisive care and protection from their mother. Young mustelids typically are able to care for themselves when they are about two months old. Females defend territories in order to acquire enough resources to care for their young and most often nurse and protect them in a burrow or den. (Johnson, et al., 2000; Nowak, 1991)

  • Parental Investment
  • altricial
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female


Mustelids typically live between 5 and 20 years in the wild. (Nowak, 1991)


Members of the family Mustelidae are either diurnal or nocturnal. Many of the long, narrow-bodied species are quick and agile, and move in a bounding, scampering fashion. The broader-bodied forms have a more lumbering gait. Some species are adept climbers, while others are excellent swimmers. Many species spend a great deal of time on the ground, searching for food in crevices, burrows, or under cover. Many species shelter in burrows. (Nowak, 1991; Vaughan, et al., 2000)

Social behavior varies both within and among species, and may vary in relation to local environmental conditions such as food availability. For example, European badgers are known to form groups with several males and females that are all reproductively active within the group. Yet in other parts of their range, European badgers may live solitarily or in pairs.Many species are territorial for at least part of the year, with individuals competing over hunting areas or access to mates (e.g., Mustela erminea). (Johnson, et al., 2000)

Communication and Perception

Vision and hearing are important in Mustelidae, but olfaction is particularly well developed. In addition to using scent cues to find food, scent-marking is the main form of communication in this family. Secretions from well-developed scent glands function in territorial interactions, indicate reproductive state, and are used in other social contexts. The degree and function of scent marking varies among species, and according to social and environmental conditions within species. (Hutchings and White, 2000; Nowak, 1991; Vaughan, et al., 2000)

Food Habits

Mustelids are primarily carnivorous, but some species may at times eat plant material. A wide range of animal taxa are preyed upon by various members of this family; many mustelids are opportunistic feeders rather than specialists. However, many mustelids are especially adept at capturing small, mammalian prey. Weasels, for example, are capable of chasing and capturing rodents in their burrows. Otters are well-adapted to chasing and capturing aquatic prey, including fish, crustaceans, and other aquatic invertebrates. Mustelids hunt in a variety of terrestrial, aquatic, and arboreal habitats. Some species regularly prey on animals larger than themselves. Some species have been known to store food (e.g., Mustela, Gulo). (Nowak, 1991; Vaughan, et al., 2000)


Mustelids are generally small carnivores, and are therefore subject to predation by larger carnivores such as canids with which they co-occur. They may also fall prey to large snakes (Serpentes), raptors (Falconiformes), and owls (Strigiformes). Some mustelids secrete noxious chemicals to discourage predators. In some of these species, aposematic color patterns can help ward off predators. (Bright, 2000; Nowak, 1991)

Ecosystem Roles

Mustelids mainly impact their communities through their effects on prey populations. Many species limit rodent and bird populations. In some cases, mustelids limit rodents that are considered pests, in other cases, mustelids threaten rare bird species. Some species, such as sea otters (Enhydra lutra) are keystone predators, enhancing the diversity of their community by keeping highly competitive prey species in check. Honey badgers (or ratels, Mellivora capensis) have developed commensal relationships with both humans and honey guides (Indicator indicator), using both to aid in the location of bee colonies. (Bright, 2000; Macdonald and King, 2000; Nowak, 1991)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Many mustelids help control rodent populations that are considered to be pests. In addition, many are hunted and/or raised for their pelts, which are often considered highly valuable (e.g., the pelts of mink and sable). Some species have been domesticated and are traded as pets (e.g., ferrets). (Bright, 2000; Nowak, 1991)

  • Positive Impacts
  • pet trade
  • body parts are source of valuable material
  • controls pest population

Economic Importance for Humans: Negative

Some mustelids are considered pests, either for harming poultry livestock, for threatening other species in the wild, or for transmitting diseases. European badgers have been implicated in the transmission of bovine tuberculosis. Cattle may become infected from grazing on land where badgers have defecated. Up to 20% of badgers carry the disease in areas where bovine tuberculosis is a problem. Since 1975, badgers have been culled in the United Kingdom, but there is no conlcusive evidence that it has helped control bovine TB. As mammalian carnivores, mustelids can also be infected by, and transmit, rabies. (Bright, 2000; Gough and Rushton, 2000; Nowak, 1991)

Conservation Status

Some mustelid species are considered highly threatened by the IUCN, while other species are so abundant that they are considered pests. Approximately 38% of all species of Mustelidae are considered threatened,which is a much higher proportion than mammals in general (15%). Habitat destruction is a serious risk to species with restricted habitat requirements such as otters and martens. Smaller carnivores that are restricted to small habitat fragments may also be at risk to predation by larger carnivores that can more easily move among fragments. Hunting has been a problem for some species, while others, particularly tropical mustelids, do not seem to be declining as a result. Endangered mustelids include: Colombian weasels (Mustela felipei), European mink (Mustela lutreola), Indonesian mountain weasels (Mustela lutreolina), marine otters (Lontra felina), southern river otters (Lontra provocax), sea otters (Enhydra lutris), and giant Brazilian otters (Pteronura brasiliensis). Sea mink (Neovison macrodon) became extinct in recent times. (Bright, 2000; Gough and Rushton, 2000)

Numerous re-introduction programs for various mustelid species have met with mixed success. Generally, "soft" re-introductions, those that allow the animals to acclimate to their new surroundings while in a temporary enclosure, are more successful than "hard" re-introductions, in which captive-bred animals are released directly into the wild. Black-footed ferrets (Mustela nigripes) are considered extinct in the wild, although several re-introduction programs are underway. (Bright, 2000)

  • IUCN Red List [Link]
    Not Evaluated

Other Comments

The earliest mustelid fossils are from the Old World and have been dated to the Oligocene (33.5 – 23.8 mya) or mid-Miocene (23.8 – 5.3 mya). There is debate regarding which fossils from these epochs represent possible ancestral forms that led to Mustelidae and which fossils represent the first modern mustelids.


Matt Wund (author), Tanya Dewey (editor), Animal Diversity Web.




World Map



World Map



World Map



World Map



World Map


uses sound to communicate


living in landscapes dominated by human agriculture.





bilateral symmetry




brackish water

areas with salty water, usually in coastal marshes and estuaries.


an animal that mainly eats meat

causes or carries domestic animal disease





uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.



delayed implantation


desert or dunes











mainly lives in water that is not salty.


An animal that eats mainly insects or spiders.

intertidal or littoral






keystone species



marshes are wetland areas often dominated by grasses and reeds.


eats mollusks, members of Phylum Mollusca


having the capacity to move from one place to another.




specialized for swimming


active during the night



World Map

pet trade



an animal that mainly eats fish






having more than one female as a mate at one time





saltwater or marine


scent marks


scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season



stores or caches food







uses touch to communicate






Living on the ground.





tropical savanna and grassland




temperate grassland





uses sight to communicate



young precocial

young are relatively well-developed when born



Bright, P. 2000. Lessons from lean beasts: conservation biology of the mustelids. Mammal Review, 30: 217-226.



Gough, M., S. Rushton. 2000. The application of GIS-modelling to mustelid landscape ecology. Mammal Review, 30: 197-216.

Hutchings, M., P. White. 2000. Mustelid scent-marking in managed ecosystems: implications for population management. Mammal Review, 30: 157-169.

Johnson, D., D. MacDonald, A. Dickman. 2000. An analysis and review of models of the sociobiology of the Mustelidae. Mammal Review, 30: 171-196.


Macdonald, R., C. King. 2000. Biology of mustelids: reviews and future directions. Mammal Review, 30/3-4: 145.


Nowak, R. 1991. Carnivora: family Mustelidae. Pp. 1104-1105 in Walker's Mammals of the World, Vol. 2, 5th Edition. Baltimore: Johns Hopkins University Press.



Thom, M., D. Johnson, D. Macdonald. 2004. Evolution and delayed implantation in the Mustelidae (Mammalia: Carnivora). Evolution, 58/1: 175-183.



Wilson, D., D. Reeder. 1993. Mammal Species of the World, A Taxonomic and Geographic Reference. Washington, D.C.: Smithsonian Institution Press. Accessed July 01, 2005 at