Hiker's Notebook: Skunk

Photo from Smithsonian Institution Megatransect of Appalachian Trail 2008

Common Name: Striped Skunk, Polecat, Zorrillo (Spanish), Wood pussy - In the Algonquian dialect of the Abnaki Indian Tribe, the "animal that sprayed" was called segankw, an appellation that was derived from the combination of 'sek' meaning to urinate and 'a'kw' meaning fox. The Indian word first appeared in print as squuncke in 1634 - over time, this was colloquialized to the now common name skunk.

Scientific Name: Mephitis mephitis - Both the genus and species name come from the Latin word which means 'a noxious exhalation from the earth' or 'malaria.' The Latin word became a part of English lexicon without modification. Mephitis is a bad stench or odor (perhaps emanating from the earth) and mephitic is its adjectival form.

There are eleven species of skunk in the Americas that share a common trait in their expulsion of mephitic liquid when threatened from two glands located on either side of the anal opening. The most common is the striped skunk (M. mephitis) followed by the spotted skunk (Spilogale putorius - which literally means 'spotted weasel that stinks' in Latin). They are officially assigned to the Weasel Family (Mustelidae) along with badgers, otters, weasels and ferrets since they are small, ground-dwelling, furry carnivores. However, a phylogenic study using mitochondrial DNA sequencing completed in 1997 determined that the skunks were a monophyletic (deriving from a single common parent form) clade (a group that contains homologous features) within the polyphyletic mustelids. Based on this analysis, the taxonomy of skunks is distinct enough to warrant assignment to a separate family. The family name Mephitidae has been suggested. The odiferous defensive strategy employed by the skunks, their homologous feature, certainly warrants special attention if not special categorization.

The chemistry of skunk spray or skunk musk, as it is often called, has lagged other research owing in large part to a natural aversion to its formidable aroma. The first record of its investigation was in 1862, when two German chemists (Swarts and W�hler) obtained skunk musk from a colleague in the United States. They concluded on distillation of the substance that it contained nitrogen and sulfur. In 1879, the German chemist Dr. O. L�w confirmed the findings of his predecessors, but was unable to proceed any further due to collegial problems with the scent. On his return to New York from an expedition to Texas in 1872 to collect the secretion, L�w writes in a letter that "I started a few chemical tests � when the whole college rose in revolt, shouting 'A skunk, a skunk is here.' I had to abandon the investigation." The first full analysis of skunk musk was conducted by Thomas Aldrich working at the Laboratory for Physical Chemistry at Johns Hopkins University in 1897. He described his samples, which he obtained from Maine as "limpid fluid, of golden-yellow or light-amber color, of a characteristic, penetrating, and most powerful odor." In spite of this, he was apparently able to conduct his experiments without raising a hue and cry on the Baltimore campus.

The fundamental compounds associated with skunk spray that impart their olfactory malevolence are organosulfur compounds called thiols. Thiol is a generic name for molecules that contain a sulfur-hydrogen (SH) bond, just as alcohol is a generic name for an organic molecule with an oxygen-hydrogen (OH) bond. The prefix 'thi' is a combination form that derives from the Greek 'thei' which means sulfur or brimstone (from the Middle English combination of burn and stone). The simplest thiol is methanethiol (CH₃SH) which has a smell of rotting vegetable matter and is released by decaying matter in general. It is one of the sulfur compounds responsible for halitosis and flatulence. Thiols are added to natural gas in order to impart a recognizable smell to the otherwise odorless and highly flammable methane. This practice was instituted by congressional legislation in the United States as a result of a natural gas explosion that killed almost three hundred students and teachers at the New London School in New London, Texas in 1937. Since vultures are attracted by the thiol smell of decaying flesh, gas pipeline leaks can be located by looking for a kettle of vultures immediately above. Thiols are often referred to as mercaptans in the literature. This term, from the Latin mercurium captans, which literally meaning 'seizing mercury,' is due to the propensity of thiols to combine chemically with mercury.

Aldrich's 19^th Century research consisted of boiling the skunk oil to obtain its volatile fractions which occurred in two ranges from 100˚C to 130˚C and 130˚C to 150˚C. Based on the previous work by the German chemists that identified sulfur as one of the primary elements, he began to look for appropriate thiol compounds that would fall with in these ranges. Ruling out the low molecular weight thiols such a methanethiol based on the observed boiling point, he concluded that the primary constituent of skunk spray was likely to be butanethiol (C₄H₉SH) then known as butyl mercaptan, which is one of four compounds that have slightly different bonding arrangements between the constituent atoms. It wasn't until well into the 20^th Century that more advanced techniques for the analysis of the molecular configuration of compounds, such as gas chromatography - mass spectroscopy (GC-MS), that a the full complexity of skunk spray was revealed (and that Aldrich was not quite correct). It is now known that the chemistry created by the striped skunk for its primary defensive weapon is comprised of three different thiols, primarily (E)-2-buten-1-thiol (C₄H₈SH) which is 40 percent of total effluent, three thioacetates, and one alkaloid.

The chemistry of skunk spray, though of academic interest, is of no consequence without some consideration of its provenance. Jared Diamond offers the view of the evolutionary biologist in 'The Third Chimpanzee' that "natural selection made skunks evolve to secrete bad-smelling chemicals; those skunks with the worst smells survived to produce the most baby skunks." That is to say that the chemistry is incidental to the function of keeping predators away. Consequently, spotted skunks have a slightly different spray chemistry from their striped brethren that includes the thiols but is absent the thioacetates and the alkaloid, which they evolved just as specifically as their other traits that distinguish them as a species. What all skunks share is starkly contrasted striping of the fur, usually the black and white pattern of M. mephitis. This aposematic coloration is complementary to their defensive spray mechanism; aposematic refers to the use of structures or colors by an animal to provide a facile visual identification as a means of defense. As a further accentuation of the implied hazard that their fur color conveys, a skunk will go through an elaborate ritual of dancing, hissing and stamping to call attention to itself when threatened. They use the spray only as a last resort, saving what meager supply that they have (about 15 cubic centimeters or cc's) by using only about 3 cc's for each encounter. It takes a skunk more than a week to make a fresh batch, a period during which they are subject to predation.

Skunk spray can be directed with great accuracy at more than 15 feet and is hence highly effective in warding off almost all predators, up to and including bears and humans. In addition to the obvious olfactory distress, it can also cause nausea, lacrimation (tearing) skin irritation and, according to Aldrich writing in 1896, it is toxic in high concentrations and can be fatal. This latter assertion is based on a report written in 1881 by Dr. Conway of the Virginia Agricultural and Mechanical College in Blacksburg, Virginia (now Virginia Tech) based on his experience in a case involving a small group of students at the college. According to the report, several boys obtained a vial of skunk spray and administered it by forced inhalation to one of their school mates as a prank. When the victim succumbed and could not be revived, the doctor was called. He arrived to find the victim to have symptoms that included "total unconsciousness, relaxation of the muscular system, extremities cool, pupils natural, breathing normal, pulse 65, temperature 94;which condition he remained for one hour." The remedial treatment consisted of the administration of "small quantities of whiskey at short intervals, per orem, with some difficulty getting him to swallow." When the victim revived, he had a slight headache but was otherwise unaffected. There was no clear determination by the doctor as to the magnitude of the dosage nor was their any account as to the extent of the smell the victim may have retained. Based on this anecdote, Aldrich concluded that a high enough dose could result in death due to the anesthetic effects apparent in the symptoms - consistent with an overdose of any anesthetic.

The increase in the human population density in the Americas since the colonial era and its ultimate incursion into the native habitats of the skunk has led to more frequent encounters between them. As humans and their attendant pet animals are perceived as and can in fact be a danger to a skunk, the targeting of the former by the latter with the concomitant skunk spray shower is a leitmotif of American frontier folklore. The odious result has engendered myriad folk remedies for deodorizing that range from vinegar to tomato juice. The net result of dousing the fur of a pet animal with one of the noted liquid cures is to simply cover one aroma with that of another. The perceived effect of neutralization of the original stench is due to the combination of what is known as olfactory fatigue - the nose gets used to it - with the substitution of a different and pungent smell. However, since the smell is due to the chemistry of the spray, the true antidote uses a chemical reaction to alter the chemistry. Thiol oxidizes to sulfonic acid as the hydrogen sulfur bond is broken and replaced with three oxygen sulfur bonds (C₄H₈SH becomes C₄H₈SO₃H); sulfonic acid is essentially odorless. The tried and true recipe for a pet-friendly deskunking oxidizer is to mix 1 quart of hydrogen peroxide (H₂O₂) with � cup of sodium bicarbonate (NaHCO₃) or baking soda and apply it to fur for a five minute soak, rinsing and repeating as necessary. There is a second, more subtle effect of skunk spray that occurs long after the thiol scent is chemically neutralized. Thioacetates hydrolyze to thiol but they do not oxidize and are therefore not converted in the deskunking process. Consequently, when a pet is subject to a high humidity condition, even if this is quite some time from the initial encounter, the perception of skunk spray will become manifest due to this hydrolytic reaction.

Aside from being mephitic, the habits of Mephitis mephitis are fairly standard for a furry forest denizen. They are crepuscular, solitary omnivores, changing their diets to suit the changes in the environment and the season. Among other things, they eat fungi, insects and their larvae, berries, small rodents, birds and human garbage. They are noted for their consumption of honeybees, effected by puncturing the nest and feeding on the bees drawn to the breech. The alternative name 'polecat' is thought to derive from the French word for hen, poule, due to their association with barnyard predation. The Spanish word for skunk is zorrillo, which means 'little fox,' another well known henhouse raider. Skunks operate primarily using the senses of sight and smell (they do not spray each other), as they have very limited vision that can only detect the shape of an object beyond a few meters. Due to the pungency of their effluent spray and the aposematic coloration of their fur that advertises this capability, skunks are seldom preyed on by other animals. The exception is their nemesis, the great horned owl, with a negligible olfactory capability. Sexually, skunks are polygynous in that the male will mate with more than one female, though the female raises the litter of kits alone without any participation of the male. This was not likely to have been considered in the creation of the amorous P�p� Le Pew.