What Are Mustelids?

Global geographic range of mustelids

For starters, not all are weasels

Most of us know what otters are, but as for badgers, martens, the American mink, wolverine, etc., are all of these mustelids just weasels? Not exactly. In fact, many of these animals form their own genus and are 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. Technically, the true weasel family comprises those belonging to the genera Mustela(1) and Neogale(2) (a.k.a. subfamily: Mustelinae). For this reason, broad labels that imply all mustelids are weasels are not only misnomers, they also undermine the family’s evolutionary differences.

A brief history

Mustelidae (pronounced “muh·steh·luh·dai) is the largest family within the order Carnivora, and also one of the most successful—with distribution on all continents save for Antarctica and Australia, as well as Madagascar and oceanic islands.(3) They are also among the most primitive, having been around for some 15 million years and undergone few anatomical changes from the first carnivorans that appeared about 40 million years ago. This does not by any means indicate they underdeveloped—on the contrary, through adapting to niches in a vast variety of environments, the mustelids have taken on an equally wide range of forms, while still having kept parts of the original design. Studying mustelids and how they function offers a rare glimpse into ancient times and evolution in effect.

The family Mustelidae comprises eight subfamilies(4)

► Guloninae

Martens, the fisher, tayra, and wolverine.

► Helictinae

Ferret-badgers

► Ictonychinae

Grisons, striped, Saharan striped, and marbled polecats, as well as the Patagonian and African striped weasels.

► Lutrinae

Otters

► Melinae

True badgers

► Mellivorinae

Honey badger

► Mustelinae

True weasels and the American mink.

► Taxidiinae

American badger

Mustelids have an identity crisis

With the black-footed ferret (Mustela nigripes) having “ferret” in its name (despite not being a true ferret), the fisher (Pekania pennanti) being called a “fisher cat” (despite not being a cat), martens being called “tree weasels” and otters “water weasels” or ”river dogs” (the latter two neither true weasels nor dogs), 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. While we understand that most of these are just English common names and nicknames, they certainly make describing the family a lot more challenging!

To be clear, we respect cultures and do not believe in forcing others to change their way of speaking. However, that does not change the fact that many common names and nicknames are not only misleading, they can potentially be harmful when they contribute to misinformation. The average person does not pay attention to scientific names for clarity. That said, people should still be informed about the issue so they can recognise the differences in other ways, and help lesson much of the confusion.

A tip regarding “American” in mustelid common names

Regardless of the argument 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 American marten (Martes americana), American mink (Neogale vison), and American stoat (Mustela richardsonii) are native to both the United States and Canada, with some species like the American badger (Taxidea taxus) also being native to these countries and Mexico. Of course, there would be more clarity if these species simply had “North” added to their common names, but this usually is not the case. However, for some reason an exception was made for the North American river otter (Lontra canadensis).

They possess anal scent glands for communication

With the exception of the sea otter (Enhydra lutris),(5) all mustelids possess well-developed anal scent glands that produce a strong-smelling secretion for sexual signaling, identification, defense, and marking territory.(6) There is a common conception that the word “Mustela” is in reference to this musky odour, when it probably more likely derives from the Latin words mus (mouse) and telum (spear).(7)

They make a range of sounds

Most mustelids are very stealth animals 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 to stereotype all mustelids (particularly those that are weasel-like) as “dookers”, when this is far from the case. “Dooking” refers to the chucking vocalisation made by an excited ferret (Mustela furo). Other mustelids are known to make similar to considerably different types of sounds when excited, such as purring/barking (martens), zheeping/low trilling (weasels), and purring/squealing (otters).

More than just predators

We often hear mustelids being described as super predators, but where is the attention to them also being super mothers? These animals will go above and beyond to provide for their young—boldly and tirelessly risking their lives for the many mouths that depend on them for nourishment. Not only that, but they also must pass down their experience to their young, so they too will have the skills needed to survive.

Sometimes the constant focus on their predation habits is not only arguably monotonous, it can also lead people to assume mustelids have it easy and are practically invincible in the wild. Truth is many of the smaller species are prey to a number of larger predators such as wolves, bobcats, coyotes, foxes, 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, unregulated fur trade, and illegal trafficking. Several species are also susceptible to the canine distemper virus (CDV), which is often fatal.(8) If all this was not enough, many of the smaller weasel species 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.(9)

References
  1. Koepfli, Klaus-Peter, et al. “Multigene phylogeny of the Mustelidae: resolving relationships, tempo and biogeographic history of a mammalian adaptive radiation”. BMC biology 6.1 (2008): 10.
  2. Patterson, Bruce D., et al. “On the nomenclature of the American clade of weasels (Carnivora: Mustelidae)”. Journal of Animal Diversity 3.2 (2021): 1-8.
  3. Wund, M. 2005. Mustelidae“. (On-line), Animal Diversity Web. Accessed December 30, 2020.
  4. Law, Chris J., Graham J. Slater, and Rita S. Mehta. Lineage diversity and size disparity in Musteloidea: testing patterns of adaptive radiation using molecular and fossil-based methods“. Systematic Biology 67.1 (2018): 127-144. p. 133.
  5. Kenyon, Karl W. (1969). “The Sea Otter in the Eastern Pacific Ocean”. Washington, D.C.: U.S. Bureau of Sport Fisheries and Wildlife. p. 4.
  6. Hutchings, Michael R., and Piran CL White. Mustelid scent‐marking in managed ecosystems: implications for population management“. Mammal Review 30.3‐4 (2000): 157-169.
  7. King, Carolyn M., and Roger A. Powell. The Natural History of Weasels and Stoats: Ecology, Behavior, and Management. Oxford University Press, 2006. p. 3.
  8. Van Moll, P., et al. Distemper in wild carnivores: an epidemiological, histological and immunocytochemical study“. Veterinary microbiology 44.2-4 (1995): 193-199.
  9. King, Carolyn M. The Advantages and Disadvantages of Small Size to Weasels, Mustela Species”. Carnivore behavior, ecology, and evolution. Springer, Boston, MA, 1989. 302-334.

What Are Mustelids?

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