You’ve heard of bomb dogs? Avalanche rescue dogs? Arson dogs? Now man’s best friend is the latest weapon in war on everything from mold and termites to invasive weeds and bladder cancer.

“Cocaine or peanut butter, it doesn’t matter. If something has a unique odor, you can train a dog to detect it,” says Bill Whitstine, owner of Florida Canine Academy, in Safety Harbor, Florida (www.mold-dog.com). A canine training pioneer, Whitstine trained America’s first mold dog, a pound-rescued Jack Russell terrier named Petey. The mold-sniffing Tahoe is another Whitstine grad, as are hundreds of other pups with the skills to track a wide range of odors.

The idea of teaching canines to detect household pests and toxins came to Whitstine, a former arson investigator and trainer of dogs who sniff out fire accelerants, when an exterminator inspected Whitstine’s home for termites and pronounced it clear. Thirty days later an undetected swarm appeared in the walls. Figuring that if a dog could detect accelerant then surely termites could be added to the repertoire, Whitstine taught a Humane Society–rescued beagle named Tracker to nose out the bugs. Then he asked the pest controller back for a demonstration.

“Don’t laugh,” he warned.

“Laugh, my foot. How much?” replied the amazed inspector.

That a pooch proboscis can home in on smuggled currency or underground pipeline leaks surprises few in the canine world. “A dog’s nose is about 1 million times more sensitive than a human’s,” says veterinarian Aine McCarthy. Humans have about 5 million olfactory receptors that track odors. In contrast, dogs boast anywhere from 125 million to 200 million densely packed receptors. And dogs have 13 times as much nasal membrane covered with olfactory receptors as humans do. With more room for membrane and receptors, the best scent dogs are those with longer muzzles; “smush-nose” varieties (like pugs or bulldogs) don’t do as well in scent detection.

During his first field season, Finney, a black Lab trained to track grizzly and black bear scat used for ursine research, took off running in a dense Washington state forest, with trainer Megan Parker in hot pursuit. After going just a short distance, the pup sat down looking very pleased with himself. “All I could think was, ‘Oh, Finney, you’re such a goof. Let’s get back to work,’” recalls Parker, who is co-founder of Working Dogs for Conservation in Missoula, Montana (www.workingdogsforconservation.org). “There was nothing there.” Dropping down on all fours, though, Parker came across some berries in a barely recognizable, desiccated sample of years-old bear droppings. “It was that ‘wow’ moment when you realize how great these noses are,” she says now.

“Super sniffers” rarely boast fancy pedigrees. In fact, Parker asserts, many pooches that make lousy pets are ideal working dogs: “We look for dogs that would drive the average owner crazy—the ones that can’t take their eyes off the stick or the Frisbee, and would choose chasing it over food or even breathing. Finney is so high-energy he would chase his ball into an active lava flow,” she laughs. Whitstine, who regularly finds his trainees at the Humane Society of Pinellas in Clearwater, Florida, says that what most would call bad behavior is really higher intelligence. “It’s like the kid who acts out in school. He’s just bored and needs an accelerated class.”

Qualities like rowdiness and toy drive are exactly what attracted Whit-stine to Pharaoh, a 2-year-old Lab/shepherd mix being trained to track the threatened indigo snake for U.S. Fish & Wildlife. After hundreds of hours and $30,000 in training, Pharaoh started field trials in August. For Whitstine, the trick is to teach the dog to concentrate—even in wilderness environments—so that it recognizes the specific type of snake and ignores squirrels, tortoises, corn snakes and other distractions.

Florida Canine Academy seems like a regular 3,000-square-foot home. Only this “home” boasts false floors, hinged baseboards and secret compartments inside cabinets and behind toilets and walls—the better to hide target scent. Dogs train in 15-minute rotating stints—work, play, rest, observation of another working dog, then repeat. All receive the same basic training (about 200 hours’ worth), then over the course of another 200 to 400 hours learn to home in on a specific scent. Compare it to going to medical school and then taking up a specialty.

One of the fastest-growing niches is dogs that help with natural conservation. Whether trained to find invasive, noxious weeds or scat from an endangered species, these animals are prized for their ability to cover a lot of ground in a short time. Working Dogs for Conservation has trained canines to scout out brown tree snakes (while avoiding poisonous toads) in Guam, find Colorado’s elusive black-footed ferret and, in Kenya, locate cheetah scat.

When Nightmare, a rambunctious shepherd, pauses to dig at a young knapweed plant, her GPS system registers the location so that her handler can retrace their steps to the weed and eradicate it. Scientists envision a day when such highly trained dogs and their handlers will locate numerous invasive plants at their earliest stage of growth, preventing them from destroying valuable ecosystems.

Dogs taught to track the threatened Mojave desert tortoise are much like bomb dogs. In essence they treat the tortoise like an explosive—meaning they don’t flip it over or paw it, explains Dr. Mary Cablk of the Desert Research Institute in Reno, Nevada. “With only one or two of the elusive, salad-plate-sized tortoises found per square mile, dogs have a distinct advantage over people,” she says.

What really has scientists excited these days is the news that dogs may be able to detect disease. In 1989, the medical community noted patient reports claiming that their dogs detected malignant tumors just by smell. Recently, research is backing up those stories. Lawrence Myers, an associate

Though Tahoe may not have a nose for cancer cells, he has easily proved his worth. Working room by room, he quickly sniffs walls, floors and cabinet interiors. At the first whiff of mold, he sits, then “alerts”—points with his nose—toward the target scent. Olsen follows, and at each alert places a marker. After Tahoe does his job, Olsen performs a visual inspection and takes samples. “He’s a wonderful tool,” she says. “Not only does he save a building owner time and money, but he’s right about 99 percent of the time. So if he doesn’t alert, you can rest assured that there’s no mold and no need for expensive air-sample tests.”

New and varied roles for scent-detection dogs means many animals that would previously have gone unwanted are now taking on important work: saving lives, property and the environment. Canines may never replace blood tests or high-tech air-quality samplers, but they are proving to be useful tools for the scientific community. As Whitstine points out, “The last thing that sniffs Air Force One is not a machine, but a dog.”