BLACKSBURG - Rattlesnakes have been using their unmistakable noisemakers to warn off humans ever since the two species first stumbled upon each other in the North American forests.

Now, two Virginia Tech researchers believe the venomous snakes' rattles may hold warnings of another danger: toxic chemicals hidden in the environment. By trimming a few rattles off of wild rattlers, the pair hope to develop a non-intrusive and painless method of detecting the presence of harmful chemicals in the small-animal food chain. And they are turning to the local community for help in getting close to these frequently unwelcome neighbors.

"If people will give me a call if they know they have rattlesnakes on their property ... I would just stop by and capture the rattle," Steven Holladay, a professor of anatomy and toxicology at Virginia Tech's veterinary college, said as nonchalantly as if he were talking about collecting water samples. "I'm not interested in removing the snakes, though."

Holladay, who previously researched how pesticides affect local turtle populations, became interested in snake skins while monitoring mice on a U.S. Army base for exposure to toxins from exploded bombs and other chemical sources. If the mice accumulated toxins in their system - and these mice did - Holladay reasoned their predators would show signs of contamination as well.

Scientists have known for decades that many chemicals - such as those found in pesticides - collect in the fatty tissues of fish, birds and even humans, often remaining there for years. Perhaps the best-known example of toxic accumulation is the bald eagle, which was nearly driven to extinction in the United States from eating fish and animals tainted with the now-banned pesticide DDT.

What makes Holladay's research unique is his testing technique.

During earlier experiments, Holladay fed corn snakes low levels of organochlorides, a group of chemical compounds frequently found in older pesticides. After the snakes shed their skin, Holladay ground the skins, combined them with a liquid solution and extracted the chemical residue. He then asked a toxicology lab to identify the chemicals in the residue.

Turns out, snakes use their skin as a sort of toxic disposal system.

"We don't even need to see the snakes," he said. "We just need the skins and we'll tell you what type of pollution we've got."

Holladay and his research partner, associate professor Robert Gogal, are trying to duplicate those results on rattlesnakes, which live throughout the rocky forests of Southwest Virginia and neighboring states. But instead of using skin sheddings, the pair are collecting several "buttons" off the rattle, which is essentially a hard extension of the snake's skin.

A rattlesnake gains another button on its rattle each time it sheds, often adding four a year. The rattling sound occurs when the snake, feeling threatened, vibrates its muscular tail, causing the loosely interlocking buttons to rub against one another.

"It's like clipping your toenails," Holladay said of trimming the rattles for his research. "The snake doesn't care. There's no pain."

Of course, that doesn't mean the snakes are happy participants.

On Thursday, a small windowless lab in the basement of the Virginia-Maryland Regional College of Veterinary Medicine was filled with the unmistakable sound of nervous rattlesnakes as Holladay and Gogal demonstrated the clipping process on one of six captive-born diamondback rattlers.

Holladay, who has been capturing venomous and non-venomous snakes since his childhood in North Carolina, does all of the snake handling. Afterlifting a 3- to 4-foot Eastern diamondback out of its tank with a long pole, Holladay carefully lowered the snake to the floor. Although slightly sedated, the snake quickly pulled itself into a defensive coiled position, ready to strike.

Holladay then carefully pinned the snake with a long tool before grasping it just behind the head and lifting it onto the operating table. Gogal demonstrated how he would trim a few buttons off the tail, leaving enough for the snake to still make its presence well known to interlopers.

In the wild, Holladay said he would likely attempt to lead the snake into a special clear plastic tube that prevents the animal from turning around and striking. Once inside the tube, Gogal would trim some of the rattle.

"He'll catch 'em and I'll clip 'em," added Gogal, an associate professor of immunology at both the vet school and the Virginia College of Osteopathic Medicine in Blacksburg.

Holladay said he wants to hear from residents throughout the New River and Roanoke valleys who know the location of rattlesnakes. If interested, Holladay will visit the property to collect the samples. He cautioned residents against trying to capture the potentially deadly snakes on their own.

"I would recommend to anybody who encounters one of these to leave it alone," Holladay said while glancing at his clearly agitated snakes. "They are much more powerful an animal than people think, and they are much quicker than people think."