This artical appeared in The New York Times - SCIENCE - July 27, 1999
|To call the bearded dragon lizard a voracious
eater would be an understatement. It happily consumes most any insect,
no matter what the defense mechanism of the prey. It will gobble a cockroach
that sprays irritating chemicals, or a moth laden with foul-tasting alkaloids.
It has even been known to lunch on a bombardier beetle after being sprayed in the face with a hot, nasty liquid that is enough to deter lesser lizards. Like a glutton suffering only temporary distraction, the bearded dragon simply wipes the stuff off its chin and chomps away.
But the lizard, an increasingly popular pet among reptile lovers in the United States, can go an insect too far, according to scientists at Cornell University. And the meal that can do it in is the common firefly.
In a paper to be published in The Journal of Chemical Ecology, the Cornell scientists and others relate firsthand accounts from lizard owners who, running short on the customary fare, crickets, fed fireflies to their pets. Within minutes after eating even one of the flashing insects, a bearded dragon starts shaking its head violently, gapes with open mouth as if trying to vomit and develops severe breathing trouble. Shortly after, it keels over, dead.
Fireflies have long been known to be toxic, said Thomas Eisner, a professor of chemical ecology at Cornell and an author of the paper. Twenty years ago, after spending a summer feeding over 100 different insect species to a thrush and having fireflies be one of the few that the bird rejected, Dr. Eisner determined that fireflies contain a type of steroid, which he called lucibufagin. It is similar to plant steroids like digitalis, which is famous as a stimulant for the heart.
Fireflies use the chemical as a defense against predation, Dr. Eisner said, and have one of the highest concentrations of steroids found in nature. The lizards, he said, "are overdosing on a heart drug."
While birds and other predators, including other types of lizards, know to stay away from fireflies, bearded dragons, which are native to Australia, do not.
"Obviously, they come from an area of the world where they don't have to deal with a lot of defensive insects," Dr. Eisner said. "It's amazing how fearless they are of prey."
North American lizards have probably evolved a genetic predisposition to avoid fireflies, said Kraig Adler, a Cornell biology professor and another of the paper's authors.
|"Those foolish enough to eat them are no longer with
us," Dr. Adler said. Bearded dragons, being new to this country, are
unfortunate innocents. The popularity of bearded dragons has risen in recent
years as the popularity of keeping lizards of any kind as pets has increased.
By some estimates, 20 million American households now keep at least one
reptile or amphibian.
Bob Mailloux, who breeds bearded dragons in Bonsall, Calif., estimated that about 50,000 of the reptiles are hatched every year in the United states. He breeds 3,000 to 4,000 a year, selling them for up to $300 each. They can live for six years or longer (if they stay away from fireflies).
Lizards, Dr. Adler said, "are the convenient pets of the 90's." Unlike birds or small mammals, lizards have very slow metabolisms, and thus don't eat much. "As long as a lizard has some water, a bust person can go away for a weekend and not worry about it," he said.
Iguanas are the most popular as pets, but they have one major flaw: they can grow to be six feet long. "Ultimately, that's not so convenient," Dr. Adler said.
The bearded dragon )which gets its name from the skin on its neck, which expands to resemble a full beard when the animal is threatened) only grow to about 20 inches as adults. They can also be flamboyantly beautiful; the ones Mr. Mailloux sells often have red-orange skin on the head. And unlike most lizards, which are skittish around humans, bearded dragons will sit on a shoulder of lap and can be fed from the hand.
Mr. Mailloux, who has been breeding the lizards for 18 years, said that he had occasionally heard accounts of death-by-firefly from customers. "A lot of people call us up to ask us things," he said. "Sometimes they'll say 'my dragon just up and died. I fed it a firefly and wondered if that had anything to do with it.'"
The Cornell researchers in the past few months have learned of similar deaths among African chameleons and another type of lizard, one that is native to Eastern Europe. "The implication is that susceptibility to toxicity is a fairly widespread phenomenon." Dr. Adler said.
Their paper is being published next month, but the scientists said that with the firefly season in full swing, and with a lot of bearded dragons around, it was good to get the word out sooner.
"We thought, 'One can actually save some lizards,'" Dr. Eisner said. "Or some fireflies, depending upon which side you're on."