All weasels are mustelids but not all mustelids are weasels

Most people know at least one species of otter and maybe even a badger or two, but as for ferret-badgers, martens, the tayra, wolverine, etc., are all of these mustelids just weasels? Not exactly. In fact, many of these animals are grouped by genus and considered distinct species in the family Mustelidae. And although this family is often loosely referred to as the so-called “weasel family” fewer than half of the approximately 70 distinct mustelid species are weasels. To say or imply that all mustelids are weasels would be similar to saying all canids are dogs or that all procyonids are raccoons.

Scientifically speaking, true weasels comprises those belonging to the genera Mustela and Neogale (a.k.a. subfamily: Mustelinae).^(3)(4)(5)(6) While seemingly harmless, labelling all mustelids weasels can not only potentially spread behavioural misconceptions about non-weasel species (given the historical stigma associated with the word), such a broad generalisation can also in a sense undermine the family’s evolutionary differences and unique environmental struggles.

Some have misleading common names

With the black-footed ferret (Mustela nigripes) having “ferret” in its name despite not being an actual ferret (Mustela [putorius] furo), the fisher (Pekania pennanti) being called a “fisher cat” when it is neither a cat nor catches fish, the wolverine (Gulo gulo) being nicknamed a “glutton” when they are not gluttonous, and ferret-badgers being called… well, “ferret-badgers”, it is easy to understand why so many people unfamiliar with mustelids are confused over what they are and their nature. While we understand that these are just common names and nicknames, certain misnomers (especially when used in popular culture) have contributed to a giant confusing mess with often little to no clarity for those who seek it.

To be clear, we respect cultures and do not believe in telling others what they should call an animal. However, that does not change the reality that many common names and nicknames for mustelids in English are not only confusing, they can potentially be harmful when they lead to behavioural misconceptions or species misidentification. While scientific names are helpful for clarity, it is unrealistic to expect the average person to pay attention to them or use them in casual conversation, especially since they are not always provided in media or arguably that memorable or pronounceable. This is why regardless of the reason a mustelid was given a particular name, on this website we feel it is important to let people know certain names can be misleading, so they can be better informed and help lesson much of the avoidable confusions.

A tip regarding “American” in mustelid common names

When someone says “American badger”, are they referring to a badger species found in North America or South America? Is it an animal widespread throughout the Americas, or is it only found in the United States?

Whatever the definition or opinion of what it means to be an American, when it comes to mustelid common names in English, it is safe to say the term usually refers to the continent of North America. This is because the often so-called American marten (Martes americana), American mink (Neogale vison), and American stoat (Mustela richardsonii) are native to both the United States and Canada, with species like the American badger (Taxidea taxus) also being native to these countries and Mexico. What can also be confusing is that many native English speakers only associate the term American with the United States, so it can mislead some into thinking these species are exclusively native to or found in said country. The “American marten”, for example, has a significantly larger range in Canada compared to the United States.

Of course there would be more clarity if all these species simply had North added to their common names to undoubtedly refer to the continent (or northern half of the Americas), but this is usually not the case outside of our website. However, for some reason many will make an exception for Lontra canadensis, which is often called the North American river otter.

They possess anal scent glands for communication

With the exception of the sea otter (Enhydra lutris),⁽⁷⁾ all mustelids possess well-developed anal glands that produce a strong-smelling secretion for scent marking.⁽⁸⁾ There is a common conception that the word Mustela is in reference to this musky odour, when it probably derives from the Latin words mus (mouse) and telum (spear),⁽⁹⁾ among other possibilities.

The term mustelid also has nothing to do with scent, as sometimes assumed. In fact, musk is not something that is even unique to mustelids. This would be apparent to anyone who has ever smelled the secretion of a red fox (Vulpes vulpes), lesser anteater (Tamandua tetradactyla), or any other animal that commonly marks territory or use anal glands for communication or defence.

It is also usually not the animal itself that continuously has a pungent odour, as commonly believed, but rather the residue of their glandular oils or the scent of their faeces or urine. Wild mustelids themselves are very clean animals that frequently groom their fur, and are really not that much muskier than many other mammals. As for domestic mustelids like the ferret, they typically only develop a “bad” odour when kept in unsanitary conditions or fed an improper diet (particularly low-quality kibble), which most people opt for due to convenience. Practically any mammal would face similar issues under such circumstances.

They make a range of sounds

Most mustelids are stealthy and rarely make noise to give their location. However, when under threat or socialising, we may hear some of their unique vocalisations. There is a tendency for some to generalise all mustelids as “dookers”, when this is far from the case. Dooking is an onomatopoeia usually in reference to the chuckling vocalisation made by an excited ferret (Mustela [putorius] furo). Other mustelids are known to make similar to considerably different types of sounds when excited such as purring/clucking/barking (martens),⁽¹⁰⁾ zheeping/low trilling/chattering (wild weasels),⁽¹¹⁾ and purring/humming/barking (otters).⁽¹²⁾ It is not clear if these sounds are universal to subfamilies of their type.

If getting information from a documentary or amature media, be aware that filmmakers will sometimes add generic animal sounds to a film for effect. These sounds can sometimes be completely inaccurate to a species. An iconic example would be the bald eagle (Haliaeetus leucocephalus), where the vocalisations many have been conditioned to associate with them are actually that of the red-tailed hawk (Buteo jamaicensis).⁽¹³⁾

There is more on the menu than eggs, poultry, and fish

Similar to the misconception in popular culture that mice mainly or exclusively eat cheese and rabbits carrots, the diet of weasels and weasel-like species is sometimes stereotyped as only consisting of eggs, poultry, or rodents, as well as all otter species exclusively consuming fish. Many mustelids are opportunistic feeders and will eat a variety of foods depending on the season, their location, and perhaps even individual taste. The following are just a few foods certain subfamilies have been reported to consume (view our references for specific species certain foods apply to):

Melinae, Helictinae, Mellivorinae, and Taxidiinae: Amphibians, small reptiles, rodents, gastropods, invertebrates, eggs, fruits, nuts, seeds, roots, insects, mushrooms, and honey.^(14)(15)(16) In the case of the ratel (Mellivora capensis), in some areas they will sometimes prey upon other small or young carnivores.⁽¹⁷⁾

Mustelinae, Ictonychinae, and Guloninae: Amphibians, small reptiles, crustaceans, invertebrates, rodents, birds, fish, moles, shrews, rabbits, hares, eggs, fruits, nuts, seeds, insects, mushrooms, honey, other small to large herbivores, and sometimes other small or young carnivores.^{(18)(19)(20)(21)(22)(23)}

Lutrinae: Amphibians, small reptiles, crustaceans, invertebrates, fish, insects, birds, and small mammals.^(24)(25)

Their environmental struggles are often overlooked

Sometimes the relentless emphasis on the aggression and predation habits of most mustelids in media is not only arguably monotonous (it should come as no surprise that wildlife can be aggressive and that predators kill other animals), it can also lead some people to assume that mustelids have it easy and are practically invincible in the wild. Often not enough attention is given to their daily struggles.

Most mustelids are not just predators, they are also prey

Many mustelids are prey to a number of predators such as dogs, wolves, bobcats, coyotes, foxes, bears, and birds of prey, with humans in particular being the greatest threat to nearly all species when it comes to habitat encroachment and destruction, overhunting, road traffic accidents, trapping, unregulated fur trade, and illegal trafficking. Like most wildlife, mustelids have to be very cautious to survive, and the often regurgitated and glamorised assertion that they are “fearless” inaccurately implies they do not acknowledge danger. There is a reason most are hard to spot even in areas where they are abundant.

Regarding stealth, some scientists believe climate change is affecting the mortality of weasel species that change white for winter, due to camouflage mismatch.^(26)(27) Mustelids such as the North American wolverine (G. g. luscus) are also vulnerable due to disappearing snowpack.⁽²⁸⁾

They all risk injury, illness, and starvation like other mammals

While trying to catch a meal, mustelids can sometimes sustain a paralysing or fatal injury from their prey, or even the surrounding elements. The hunt is not always successful, as often portrayed in media. Several species are also susceptible to morbidity and mortality due to canine distemper, amyloidosis, pulmonary and gastro-intestinal helminths, and bacterial respiratory infections.^(29)(30)

If all the above was not enough, most mustelids live predominantly solitary lives, with the female being solely responsible for rising their young—boldly and diligently risking their lives for the many mouths that depend on them for nourishment and protection. Many species also have both a high basal metabolic rate (BMR) and short gastrointestinal (GI) tract. So while they may be quick and efficient hunters, the trade off is that they are metabolically inefficient and will perish if they do not eat within a few hours throughout the day.⁽³¹⁾ For some species, they are constantly on the brink of starvation in winter.⁽³²⁾

Although mustelids are capable of living for several years in the wild, most typically die before their first year of life. We encourage anyone who genuinely aims to educate the pubic about these animals to avoid parroting the usual talking points, and instead present a comprehensive view of their circumstances.

References

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What Are Mustelids?

Badgers | Ferret-Badgers | Fisher | Grisons | Martens | Otters | Tayra | Weasels | Wolverine