Sunday 16 July 2023

The Stinky Family: Skunks

Unlike raccoons, there was relatively little confusion on the part of early zoologists as to what general sort of animal the skunks were. Since the animals are not native to Europe, the first Europeans knew of them was when they reached the Americas. The closest analogy they could think of among familiar animals was a polecat, and in some parts of America, they are still referred to as such today. However, an indigenous name for the animal (probably Algonquian) won out in English, and "skunks" they became.

Skunks did make it on to the first recognised list of scientific animal names in 1758, as Viverra putorius - the latter half of which, again, means "polecat". The first half indicates that Linnaeus, probably having only a minimal description to go on at the time, considered them to belong with the civets and mongooses, as a sort of generic small, bitey, mammal. That did not last; in 1795, an encyclopedia jointly published by  Cuvier and Geoffroy gave them their own genus. The name for this, Mephitis, comes from a goddess of noxious underground gases worshipped in pre-Roman and Roman Italy - the sort of thing that only tribes living near a volcano are likely to come up with. 

At least some European languages, such as Spanish, still use a variant of Mephitis as their name for the animal, although most have stuck with "skunk", and some of the Germanic ones have the local form of "stink-beast" as an acceptable alternative. Which, in fairness, is to the point.

In the early 19th century, once the idea of animal "families" as we know them today had caught on, skunks were moved away from the mongooses and placed, together with the polecats, in the weasel family, Mustelidae. As it became recognised that there was at least some distinction between them and the true polecats, French-Italian naturalist Charles Bonaparte (a nephew of Napoleon) raised them to the level of subfamily in 1845, apparently as an afterthought in a text on a different subject. There they remained, for well over a century, the similarity to other mustelids being obvious.

Obvious but, as it turns out, wrong. This was suspected as early as 1989, and over the following couple of decades, evidence mounted up that the true mustelids were, in fact, more closely related to raccoons than they were to skunks. Thus, the only way to keep skunks in the weasel family would have been to group the raccoons in with them too. That was considered unhelpful, at best, and so the skunks as a whole were elevated to become a family in their own right: the Mephitidae.

This is not, it has to be said, an especially large family; it exists because the skunks don't belong anywhere else rather than because there are a great many species. Neither is it particularly distinctive, as one might surmise given its long placement with the mustelids. Most of the generalisations we could make about skunks would be equally true of other animals.

Skunks are smallish animals, with most species being about the size of a cat. They walk on the soles of their feet and have many of the features we would associate with a small carnivorous mammal, such as sharp claws and a keen sense of smell. The general pattern of the teeth is essentially the same as that of mustelids; each side of the jaw has three peg-like incisors and an enlarged canine tooth, followed by a variable number of cheek teeth. The latter are adapted for slicing meat in most species, although not to the extent seen in cats, reflecting a diet that, while heavy in animal content, tends towards the omnivorous.

There are, perhaps, two common features of skunks that immediately come to mind. It is, however worth noting that neither is unique, since both are shared by the zorilla and its relatives, animals that look astonishingly skunk-like but really are mustelids as skunks were once thought to be. First of these features is the fact that all living species of skunk have a black-and-white coat pattern, which is often striking. This is thought to be a warning which, of course, relates to the second feature.

Skunks stink.

Well, they don't actually stink themselves, or at least no more than any other animal does. But they do have enlarged glands on either side of their anus that produce an extremely noxious fluid that they can spray on anything that disturbs them. These glands are also found in mustelids, and evolved from the sort of regular anal scent glands that many carnivorous mammals use to mark their territory and signal to one another. In some mustelids, that's all they're used for, but many species can use them in defence (and not just the zorilla). Which goes some way to explaining why it wasn't obvious that skunks were distinct from their weasely kin.

The compounds responsible for the noxious smell of skunk spray are sulphurous organic chemicals, of which the most prominent are thiols - essentially alcohols where the oxygen atom is replaced by sulphur. These are accompanied by sulphurous acetates, which are not quite so intense as the thiols, but linger on whatever they are sprayed on and are difficult to remove. Similar compounds are found in human sweat, but these are less potent, and, in any event, are present at much lower concentrations. This gives a hint to their evolution; they were originally sweat glands, before becoming specialised as scent-marking organs, and eventually developing into their full defensive form.

The stink glands are essentially small sacs, with a sheath of muscle around them that the skunk can contract at will, and with a small papilla - essentially a fleshy nozzle- to direct the spray outwards. The skunk can choose to release the spray as a fine cloud that covers a wide area, or as a directed jet, which is more focussed, but has greater intensity, depending on how close the intended target is. Skunks seem to be able to spray almost from the point that they are born, and the glands contain far more liquid than the skunk could possibly use in a single go, thus ensuring that, to all intents and purposes, they will never "run out" - they have been recorded spraying up to a dozen times in short succession when sufficiently provoked. (Realistically, if an attacker isn't deterred by the first couple of sprays, the skunk will likely be dead before it gets many more in).

As noted above, there are not a great many species in the skunk family compared with some others. They are not, for example, as diverse as the raccoons. Even so, as with most mammal families, there are more than most people are likely aware of and over the next four months, I intend to cover them all in detail.

[Photo by Wallace Keck, in the public domain.]

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