HOW COME? Skunks have natural 'keep away' signs

What makes skunk spray smell so awful? asks a reader.

It's hard to miss a skunk ambling across the yard. Rabbits, groundhogs and field mice are usually brown or gray, blending into grass and twigs. But skunks are like mammalian penguins, garbed in fashion-forward black and white, right down to their bold, bushy tails.

See a skunk, and it's natural to recoil. Under those fluffy tails, skunks store a yellow, oily liquid in grape-sized "musk" glands. Each holds about a tablespoon of oil, and each spray releases up to a teaspoon of the smelly stuff. A skunk can shoot a stream of noxious liquid 10 to 15 feet.

But skunks are thrifty with their spray, saving it for when they feel genuinely threatened. Before the first spray, skunks usually give fair warning: A skunk may growl, hiss like a cat, chatter his teeth, stamp his feet. Just before he sprays, he'll raise his tail -- and sometimes do a handstand.

If a clueless creature (say, a dog) doesn't retreat, the skunk may aim straight for his face. Skunk spray is like tear gas, leaving eyes burning, stinging and watering.

But even after the stinging tears stop, the noxious fumes linger. Skunk spray has a lot in common with rotten eggs, or natural gas with added sulfur scent. The culprit: odorous compounds called thiols. The thiols' sulfur and hydrogen atoms attach to nose receptors that detect hydrogen sulfide, that rotten egg / swamp gas smell.

Skunk spray also contains thioacetates, compounds that break down into thiols. So even as the original odorants dissipate, new ones replace them, making for a lingering aroma on clothing or fur.

With such a potent defense, why would skunks evolve with coloring that screams for attention? Scientists think the strong color scheme warns off other animals. A 2011 study found that meat-eating mammals with bold colors are likely to burrow, be nocturnal, and to live in open habitats. Many of them, like black-and-white honey badgers, are ferocious biters.

But another study found that it's not just bold coloring and patterns that telegraph that "keep-away" message. Researchers at the University of California, Davis dyed some stuffed skunks gray, and some small stuffed foxes black and white. Using night-vision cameras, they watched other animals react to the stuffed intruders.

In areas where living skunks roamed freely, animals reacted warily to the black-and-white stuffed skunks and foxes. But they also steered clear of the gray skunks. A skunky body shape, it seems, is as intimidating as black-and-white fur to those who've experienced real skunks in action.