Modern Science Takes a Look at an Ancient Monster
Gildart, Bert, National Wildlife
Look at an Ancient Monster
From the depths of his winter burrow in New Mexico's Chihuahuan Desert, a Gila monster claws to the surface and peers at the rocky landscape with his reptilian eyes. The male flicks his forked tongue and "tastes" the spring air. It is mating season and "flavored" molecules urge the suitor toward a distant female. Not only is he following her signals, this particular Gila monster is also one of a select few that emit high-tech information to herpetologist Dan Beck of Central Washington University--by means of miniature, temperature-sensing radio transmitters.
"We've learned these lizards have an incredible sense of direction," says Beck, who has spent much of the past 15 years studying the creature and its travels--and is known among colleagues as Dr. Gila Monster. "Gila monsters," he says, "function in a complex world of chemicals and use an assortment of metabolic tricks we've only now begun to understand."
His study subject has been around since the age of the dinosaurs. At 24 inches and one-and-a-half pounds, the Gila (pronounced Hee-la) monster is the nation's largest lizard. It is also the country's only poisonous lizard. The creature produces venom when it bites down. Biting compresses poison glands in the reptile's lower jaw. The glands then release toxin that travels up along grooves in the teeth to its victim. Acting on nerves, the venom creates intense pain--as one of Beck's colleagues will never forget.
"It felt like a wave of fire," says University of Arizona scientist Cecil Schwalbe, recalling a 1989 demonstration at a state wildlife booth where he erred in his handling of a Gila monster and as a result was hospitalized with severe shock. "It was the worst pain I've ever experienced in my life," he says. "The creature locked onto my finger and then started shaking. Pain shot up my arm. It was weeks before I returned to normal."
Jude McNally, assistant director at the Arizona Poison Control Center, confirms that Gila monsters can indeed be painfully poisonous. However, he notes, there are no medical records substantiating a single human fatality from such bites.
In recent years, scientists have learned more facts about how Gila monsters use their venom. On two separate occasions, Beck watched the creatures invade rabbit burrows and swallow baby rabbits whole. Both times, a single meal consisted of four rabbits. Because the lizards consumed their prey without the characteristic chomping required to activate venom, Beck gleaned a piece of anecdotal evidence. Added to other field observations, it convinced him that the venom is used for defense against coyotes, hawks, and owls--not for predation.
The rabbits represented a gluttonous intake, and herpetologists know that such a meal can provide a Gila monster with nearly half its yearly nutritional requirements. Unused energy is stored in the large, sausage-shaped tail and drawn on as needed. A fat tail indicates a well-nourished Gila monster.
Because Gila monsters can exist on so few meals, Beck has been fascinated by the lizards' metabolic abilities. From the lab, he learned that the reptiles have an unusually low metabolism rate, but he wanted to know more. Since 1983, the scientist has implanted radio transmitters in the abdominal cavities of wild Gila monsters. From the signals--as well as laboratory measurements--he has learned that the animals' metabolic rate lowers at decreased body temperatures, thereby reducing food needs. "It means," he says, "that Gila monsters can spend up to 95 percent of their lives underground and not have to spend a lot of time foraging. …