First it was suntan lotion and insect repellent. Someday it may be a repellent for alligators and crocodiles.
That could be good news to wary fishermen, swimmers, divers - even golfers - in alligator territory such as Florida and Louisiana.In some parts of the world, a repellent could save lives. The Nile River in Africa, for example, is home to a human-eating species of crocodile.
Paul Weldon of Texas A&M University, a biologist who has done research on crocodilians at the St. Augustine Alligator Farm, says development of an alligator repellent is "a distinct possibility."
The secret lies in secretions of body chemicals called pheromones, the mysterious aromas used for communication throughout the animal world. Alligators and crocodiles are no exception, Weldon has learned. They rely on their sense of smell to communicate.
In the past four years, Weldon has collected chemical secretions from hundreds of crocodiles and alligators in zoos, farms and wildlife refuges all over the country.
From an immobilized crocodile here he carefully extracts secretions from two button-shaped glands near its tail and under its jaw.
"We think the scents emitted by the glands near the tail are used to attract mates. Those in the throat probably mark territories," says Weldon, whose work has been supported by the National Geographic Society.
He holds up a small tube containing musky-smelling secretions from the tail glands. "We've suspended cotton balls scented with the stuff over seemingly empty waterways, and alligators invariably appear," he says. "I do a lot of work in Louisiana, and this smell wafts through many swampy areas during the alligator mating season down there."
The alligator's sense of smell also plays a part in its search for prey. Cheesecloth bags filled with nutria remains - the swamp-dwelling rodent is one of the alligator's favorite meals - invariably draw the hungry predators.
"The bags are suspended over the water on a kind of clothesline contraption," Weldon explains. "Even on the darkest nights, the gators find the bags and lunge out of the water to get them, so we know they're using airborne scents to zero in on the nutria."
Bags filled with non-food items also draw alligators, but the crocodilians soon lose interest. "They grab the bag, hold on for a second and release it," says Weldon. "I'm almost certain the scent attracts them, but then taste organs detect chemical cues when something isn't edible."
Alligator expert Kent Vliet, a biologist at the University of Florida, hails Weldon's work as "truly groundbreaking. For the first time, we're getting a detailed analysis of these secretions. It's already clear that crocodilians have a much better sense of smell than they've been given credit for."
But Vliet thinks the big reptile's reputation as a fearsome killer is much overblown, thanks to "fanciful fiction, Tarzan movies and the like."
Alligators live in the southeastern United States and eastern China. Their more lethal cousins, crocodiles, are common throughout the world's sluggish tropical waters and swamps.
Some large, aggressive species of the swift-moving crocodile, such as those in the Nile and the saltwater crocodile of Australia and Southeast Asia, regard humans as food. They claim hundreds of human lives every year, Vliet says.
But the heavier-bodied, more sluggish American alligator is far less menacing. Florida has a million or more of them, and Louisiana has about 500,000, Vliet estimates.
In the past 40 to 45 years, he says, Florida has recorded only eight alligator-caused human deaths; Louisiana has had none. Five to eight alligator bites of humans are reported annually in Florida, he says.
Crocodilians can be especially dangerous, Vliet says, during mating season or when they think their young are threatened.
Pets, particularly dogs, are at risk all the time. "That's because alligators probably seek out similar-sized mammals - such as rabbits, raccoons and skunks - as prey in the wild," he says.
Wary of humans, gators usually keep their distance, but they get an altogether different perspective when they see a swimmer. "They view a head and perhaps a bit of shoulder or arm, and see that as fair game," Vliet explains.