Frank DiMeo/University Photography

Imported pets like Pogona vitticeps, the bearded dragon lizard of Australia, have no innate fear of poisonous insects in North America.

Just one firefly, with its poisonous lucibufagin chemicals, is enough to kill a lizard, a lesson that American zookeepers and pet owners are learning the hard way.

Some of the most popular lizards in zoos and private collections are from parts of the world without poisonous fireflies -- and without the innate distaste most animals in North America seem to have for the little beetle with the trademark glow. But a summer rash of reptile and amphibian deaths has prompted Cornell University biologists to go public, in advance of their scheduled publication in a scholarly journal, with the warning: Don't let your lizards eat fireflies.

The chemical is a self-defense toxin, and is not the substance that makes fireflies glow.

"We first noticed the effect in birds and spiders more than 20 years ago. Birds that eat just about any other insect will reject fireflies of the genus Photinus and the reason is their highly toxic self-defense compounds that we named lucibufagins," says Thomas Eisner, Cornell's Schurman Professor of Chemical Ecology and one of the authors of a scientific article in the August 1999 Journal of Chemical Ecology.

"In the 20 years since Tom Eisner and Jerry Meinwald (Cornell's Goldwin Smith Professor of Chemistry) discovered lucibufagins, reptiles have become one of the most popular kinds of pets in this country," says Cornell herpetologist Kraig Adler, professor of neurobiology and behavior. "Tropical fish used to outnumber reptiles as pets, 20 to one, and now they're neck and neck. An estimated 20 million Americans keep reptiles and amphibians, and exotic or non-native 'herps' are popular in zoos, as well," says Adler, who is the faculty adviser to the Cornell Herpetology Club and an author of the Journal of Chemical Ecology report.

"Reptiles and amphibians from habitats without the poisonous type of fireflies seem not to know any better," Adler says. "They will eat anything that flies by."

That's what happened recently at the Philadelphia Zoo with two Pogona (bearded dragon) lizards. When zoo keepers moved the colorful reptiles to an outdoor enclosure to feed on the summer crop of insects, lizards that are native to Australia were killed by the common North American Photinus fireflies. The lizards' jaws opened in a wide gape as they tried to regurgitate. Their skin color changed from tan to black. And they died within hours. When the lizards' stomach contents were sent to the Eisner laboratory at Cornell, researchers found Photinus fireflies among the other ingested insects.

Thomas Eisner/Cornell University

Photinus ignitus, a common North American firefly, contains enough lucibufagin toxin to kill a lizard.

The Cornell biologists received similar reports of firefly toxicosis in White's tree frogs, which also are native to Australia and were fed fireflies by their owner in Ohio; in a rock lizard that is native to Central Asia and was fed a single firefly on Long Island, N.Y.; and a chameleon, a native of Africa that was fed five or six fireflies in Illinois. Not all the animals showed the distinctive change in skin color and not all managed to regurgitate their last meal, but each evidently died of lucibufagin toxicosis. The remorseful owner of the tree frogs reported that the insects continued to flash, even after ingestion, and that their bioluminescent light could be seen through one frog's body wall.

"Lucibufagins are not the bioluminescence chemicals that make fireflies glow," according to Andrés González, a Cornell doctoral student of neurobiology and co-author of the firefly toxicosis report. "They are self-defense toxins, in the class of chemicals called steroidal pyrones, with a molecular structure similar to bufodienolides in toads and cardenolides in certain plants."

In experiments at Cornell to test bearded dragons' indiscriminate taste for anything that moves, undergraduate biology student Richard Glor offered a variety of insects — but not fireflies, which already were known to be lethal — to the laboratory reptiles. They ate everything, including a bombardier beetle that was spraying its hot, irritant defense chemical at the time, Glor reported as a co-author of the Chemical Ecology article.

Eisner says that fireflies in Australia probably do not have lucibufagin-like toxins, although their chemistry has not been studied.

"Bearded dragons are beautiful animals," Adler says. "They're one of the most tractable lizards — they love to be held in your hand -- and like most reptiles, they're clean and relatively odor-free so they make good pets. But they do have one problem: They don't know about poisonous insects in this country. Please, don't let your lizards eat fireflies."

Instead, the Cornell herpetologist recommends, bearded dragons should be fed a balanced diet of insects that are known to be safe, such as crickets and mealworms, and plants, such as chopped carrots and lettuce.

Other authors of the article, "Firefly Toxicosis in Lizards," are Michael Knight, a veterinary toxicologist at the ASPCA's National Animal Poison Control Center in Urbana, Ill., and Scott R. Smedley, a former postdoctoral researcherr at Cornell who now teaches biology at Trinity College in Connecticut. The firefly toxicosis study was funded, in part, by a grant from the National Institutes of Health.