Skunk - Anal Scent Glands

Anal Scent Glands

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The most notorious feature of skunks is their anal scent glands, which they can use as a defensive weapon. They are similar to, though much more developed than, the glands found in species of the Mustelidae family. Skunks have two glands, one on each side of the anus. These glands produce a mixture of sulfur-containing chemicals such as thiols, traditionally called mercaptans, which have a highly offensive smell that can be described as a combination of the odors of rotten eggs, garlic, and burnt rubber. The odor of the fluid is strong enough to ward off bears and other potential attackers, and can be difficult to remove from clothing. Muscles located next to the scent glands allow them to spray with a high degree of accuracy, as far as 3 m (10 ft). The smell aside, the spray can cause irritation and even temporary blindness, and is sufficiently powerful to be detected by a human nose up to a mile down wind. Their chemical defense, though unusual, is effective, as illustrated by this extract from Charles Darwin's Voyage of the Beagle:

We saw also a couple of Zorrillos, or skunks—odious animals, which are far from uncommon. In general appearance, the Zorrillo resembles a polecat, but it is rather larger and much thicker in proportion. Conscious of its power, it roams by day about the open plain, and fears neither dog nor man. If a dog is urged to the attack, its courage is instantly checked by a few drops of the fetid oil, which brings on violent sickness and running at the nose. Whatever is once polluted by it, is for ever useless. Azara says the smell can be perceived at a league distant; more than once, when entering the harbour of Monte Video, the wind being off shore, we have perceived the odour on board the Beagle. Certain it is, that every animal most willingly makes room for the Zorrillo.

Skunks are reluctant to use this weapon, as they carry just enough of the chemical for five or six uses – about 15 cc – and require some ten days to produce another supply. Their bold black and white coloring, however, serves to make the skunk's appearance memorable. Where practical, it is to a skunk's advantage simply to warn a threatening creature off without expending scent: black and white warning color aside, threatened skunks will go through an elaborate routine of hisses, foot-stamping, and tail-high threat postures before resorting to the spray. Interestingly, skunks usually do not spray other skunks, with the exception of males in the mating season. Though they may fight over den space in autumn, they do so with teeth and claws.

The singular musk-spraying ability of the skunk has not escaped the attention of biologists. The names of the family and the most common genus (Mephitidae, Mephitis) mean "stench", and Spilogale putorius means "stinking spotted weasel". The word skunk is borrowed from the Abenaki name for them, segôgw.

Most predatory animals of the Americas, such as wolves, foxes and badgers, seldom attack skunks, presumably out of fear of being sprayed. The exceptions are dogs, reckless predators whose attacks fail once they are sprayed, and the great horned owl, the animal's only serious predator, which has a poor-to-nonexistent sense of smell.

Skunks are common in suburban areas. Frequent encounters with dogs and other domestic animals, and the release of the odor when a skunk is run over, have led to many myths about the removal of the skunk odor. Due to the chemical composition of the skunk spray, most of these household remedies are ineffective, with the exception of a peroxide formula or other remedies that break down the thiols.

As initially shown by Kenneth K. Andersen and coworkers and more recently, and in more detail, by Wood and coworkers, skunk spray is composed mainly of three low-molecular-weight thiol compounds, (E)-2-butene-1-thiol, 3-methyl-1-butanethiol, and 2-quinolinemethanethiol, as well as acetate thioesters of these. These compounds are detectable by the human nose at concentrations of only 10 parts per billion.