Why Skunks Evolved Their Smelly Spray

Skunk spray is so potent that it can knock you out or even kill you—and now we know why the North American mammals evolved the noxious stuff.

Skunks are nocturnal, and their predators rely heavily on scent to navigate in the dark. But skunks evolved a counterattack: Their foul and damaging spray foils would-be attackers, according to Ted Stankowich, co-author of a new study on the subject in the International Journal of Organic Evolution.

a picture of a man holding a skunk
Shawn Geary holds a skunk during Skunkfest, held annually in North Ridgeville, Ohio. Photograph by Vincent J. Musi

“Mammals use scent a lot in their daily lives, so being able to spray a predator with something that’s truly awful would knock them out,” said Stankowich, an animal behaviorist at the University of California, Long Beach. “When dogs get sprayed, they might get chemical burns.”

For the study, Stankowich and colleagues did an extensive study of 181 species in the order Carnivora, of which the skunk is a member, and compared them to see how predation and other variables influenced the evolution of “noxious weaponry” like spraying.

This form of defense is a type of chemical weapon found often in nature. In skunks, the oily spray is stored in a skunk’s anal sacs and can shoot out of their butts up to ten feet (three meters) away. (Also see “Why Skunks Have Stripes: To Point to Fierce Anal Glands?)

All carnivores have these anal glands, but not all of them stink, said the University of New Mexico’s Jerry Dragoo, a biologist who was not affiliated with the study. For example, beaver secretions smell like vanilla and are used to mark territory.

But skunk spray includes chemicals called thiols, sulfur-containing compounds that help give the liquid its awful stench. Thiols are also used in anesthetics and antispasmodics, which is why they have such a profound physical effect on potential predators.

One Tough Mammal

Dragoo noted that skunk musk is a highly effective means of avoiding physical confrontation and buying extra time to get away from hungry predators.

“If a big animal is coming after you, and you can spray a noxious chemical at it, they usually stop chasing you,” Dragoo said. “The skunk can defend itself.” (Watch a skunk video.)

But skunks—to their credit—generally use spraying as a last resort, flashing their black-and-white colors, doing a little dance, and thumping the ground as a first warning.

They’re also scrappy, with teeth and claws they’re not afraid to use.

And it seems to work: Stankowich noted that skunks rarely die from being killed by predators.

Rosy Skunks? 

High concentrations of skunk spray are toxic and potentially fatal to humans, according to a 1999 study in Chemical EducatorThe powerful stuff has been likened to tear gas because it can cause temporary blindness, coughing, and gagging. 

But not for Dragoo, one of the few scientists willing to study the Pepe Le Pews of the animal kingdom. When Dragoo first started surveying the woodland creatures, he was surprised to find that he wasn’t affected by their odoriferous excretions—turns out, he’s one of the few that cannot smell skunk musk.

“The first skunk that sprayed me, I wasn’t sure what happened,” he said. “I looked at the animal, and he looked back at me, and there were yellow spots all over me. I couldn’t understand why people were making such a fuss.”

After three days in the field, Dragoo returned to work unknowingly smelling to high heaven, and “they wouldn’t let me back in the building.”

“People complain that their eyes are burning; they’re gagging and wheezing,” he said. “They have to leave.”

“Skunk spray all smells like rose petals to me!”

Follow Mollie Bloudoff-Indelicato on Twitter.

Mollie Bloudoff-Indelicato is a science journalist who loves em dashes, ’80s music and parasites. She has a master’s degree from the Columbia University Graduate School of Journalism with concentrations in science journalism, photography, and radio reporting. Contact her at news@mbloudoff.com, and follow her on Twitter at @mbloudoff.

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