We’re the ones with language, so we have the power to call one of our fellow vertebrates a monster. As lizards go, the Gila monster is unusually clunky, chunky, and large—not a lissome tropical creature like a gecko or chameleon. It’s not pretty, and it is venomous, a trait that inevitably complicates any relationship. Still, loathing the creature is irrational; being careful around it is not.
North America’s largest lizard gets the first part of its name from the Gila River, which runs through Arizona and New Mexico. Its habitat is the desert scrub and dry foothills of the Sonoran, Chihuahuan, and Mojave deserts. The creature is the subject of dozens of dread-inducing bits of folklore that are, at best, unverifiable. (Unlucky male camper in the desert wakes up to find a Gila monster chewing on some tender body part. Lizard spits venom in someone’s eye. Lizard springs several feet in the air to attack. Parachutist lands on lizard. Lizard’s foul breath can kill you.)
The creature’s lumbering form and sinister look play a part in popular culture. In The Treasure of Sierra Madre, for example, a Gila monster is part of a suspenseful ordeal for the character played by Humphrey Bogart. In Meet Me at the Morgue, a 1953 mystery by Ross MacDonald (a writer as good as Raymond Chandler), a sullen blonde says of her suitor, “Big offers he makes. Mink coat, a new car, a trip to Honolulu. I told him I’d sooner go with a Gila monster.” As part of the 1950s trend for enlarging animals to make them scarier, the creature is the subject of a 1959 B movie, The Giant Gila Monster. First victims? Necking teenagers.
Herpetologists, bless them, find the 2-foot-long, lumbering lizard fascinating and beautiful. Its body has bands of black alternating with the colors of an Arizona sunset –pink, buff, or orange. They hope that more knowledge will lead to less detestation, perhaps grudging respect. (One unexpected Gila monster fact is that a research scientist at a Bronx Veterans Affairs hospital found in the 1990s that something in Gila monster venom lowers plasma glucose to normal range in people with Type 2 diabetes. A synthesized version is now an ingredient in the widely used diabetes drug Byetta.)
Though the Gila monster is shy, and you should consider yourself lucky if you see one in the desert, there is certainly reason to be careful in its presence. Its bite is extremely painful, though very rarely fatal. Of the 5,000 or so known lizard species, the Gila monster (Heloderma suspectum) is among the few that are venomous. Another is its neighbor to the south, the Mexican beaded lizard (Heloderma horridum). (Note: “Beaded lizard” is a much better, less prejudicial choice for a name than “monster.” In both The Treasure of the Sierra Madre and The Giant Gila Monster, the lizard shown in the films is called a Gila monster but is actually a Mexican beaded lizard.) A few years ago, Australian researchers proposed that Indonesia’s infamous Komodo dragon could also deliver venom. (It was previously believed the dragon’s mouth was so full of muck that the victim died of a bacterial infection.)
The lizard’s species name comes from the Greek helos for stud, as in the head of a nail, derma for skin. The suspectum because the man who named it—paleontologist E.D. Cope, in 1869—at first only suspected that the lizard was venomous. It took another half-century to confirm it. With their studs they’re well armored, but a determined coyote can still rip one apart, and free-ranging cats often kill immature Gila monsters. A Gila monster can live up to 28 years; the most common cause of death, as more of the desert is paved, is being run over by a car. With a nonautomotive predator, the lizard’s first line of defense is to retreat. If cornered, it exhibits a repertoire of warning signals, including hissing and opening its mouth wide.
The nail-head look comes from osteoderms, bony beads embedded in the skin. Jan Johnson, an Arizona-Sonora Desert Museum curator who cares for 20 Gila monsters, says their hide feels like an exaggerated basketball. An X-ray shows, in addition to the usual spine and leg bones, an array of polka dots.
Careless handling, which Johnson does not engage in, is the usual cause of bites. The vast majority of verifiable recorded bites (about 150 in the past 60 years) are on the finger or hand, delivered by a pet whose apparent passivity lulled its owner into handling the creature, or by a wild Gila monster avoiding capture. (Collecting Gila monsters in the wild is against the law.) Some of the bites occurred during a demonstration in a classroom or lecture, which has to have been deeply embarrassing as well as painful. Inebriation is often involved. There’s a verified story of a man in a bar bitten while playing a kind of Russian roulette by reptile, repeatedly sticking a finger into the animal’s mouth.
The last recorded fatality was in Casa Grande, Ariz., in 1930. As reported in the Arizona Republic, “Tom Reap, 62 years old, proprietor of the Moore pool hall, died at 12:20 o’clock this noon in the Casa Grande hospital, two hours after he had been bitten by a Gila monster.” The story continues with useful information about what not to do with a venomous lizard. “Mr. Reap was playing with the animal in the pool hall when he was bitten. The animal had been brought into the hall by one of the patrons and several were standing around looking it over and discussing it when Mr. Reap appeared. He began tapping it on the nose, witnesses said, and upon being cautioned replied: `Oh, it wouldn’t hurt you even if it did bite.’ ”
Reportedly it took a helpful pool hall patron five minutes, using a pair of pliers, to detach the lizard from Mr. Reap.
Which brings us to the Gila monster’s venom delivery mode. The creature is loath to use its ultimate weapon, but once deployed the system is absolutely terrifying. The Gila monster is the pit bull of reptiles. Its short, sturdy skull with blunt, black snout is adapted to a long bite. (The shape works; it hasn’t changed much in the past 23 million years.) Venomous snakes by contrast have fragile skulls, built to conform to the shape of whatever they’re eating, often something bigger than they are. Snake venom is injected, hypodermic-style, through fangs in the front of the mouth, and it acts quickly. The point is to subdue prey before its thrashing injures the snake.
If you are so astoundingly foolish or unfortunate as to be bitten by a Gila monster, it will get a good grip and then chew; it can hold on for as long as 15 minutes. The grinding releases venom from glands into grooves in its sharply tipped teeth. (All venom, incidentally, is modified saliva.) Oddly and inefficiently, the two glands are located near the bottom teeth, and the poison must travel upward, presumably by capillary action.
The longer the bite, the more venom enters the victim’s body, via lacerations made by the teeth. One emergency medicine handbook provides “tips and tricks” for removing the animal. These include the following: Don’t pull or pry it off; that increases the possibility of leaving teeth in the wound. A flame under the jaw or immersion in water may work.
In addition, there’s this rather considerate advice: “Put the animal’s feet on the ground so it doesn’t fear falling.” And a particularly ominous note: “Always take special care to prevent reattachment of the animal to the victim or subsequent attachment to the person removing the animal.” Doctors are advised when cleaning the wound to make sure all the teeth are removed.
The effect of the venom, potent but not as damaging as a rattlesnake’s, is excruciating pain that has been described as a steady burning, like a spine embedded in the flesh, lasting up to 24 hours. There’s no commercially available antivenin; doctors treat pain and swelling and the most dangerous possible effect, a drastic lowering of blood pressure.
Gila monsters use their venom sparingly and primarily as defense against predators rather than to subdue prey. (Their fellows in using venom primarily for defense are the platypus and the stonefish.) Daniel D. Beck, author of Biology of Gila Monsters and Beaded Lizards, says he has often seen Gila monsters “delicately swallow” young cottontails without the chewing or pumping that’s displayed when they envenomate an enemy. The lizards’ favored foods are bird and reptile eggs, newborn small mammals, and bird nestlings—food sources that do not put up much of a fight. Eggs seem to be their favorite; the lizard splits the egg and, kittenlike, laps up the yolk. A Gila monster can eat one-third of its body mass at one sitting and survive on three good meals a year.
Because they don’t go out foraging often and they stay in a cool place in the summer, you’d be fortunate to see a Gila monster in the wild, Beck says. “You’d have to be a fool to be bitten,” says Beck, who has not suffered a bite. A Gila monster spends 95 percent of its time in a burrow, out of the sun, venturing out mostly in spring to find food and a mate.
Like everything that lives, Gila monsters are driven by hunger, fear, and the need to reproduce. What looks sinister and snakelike—the forked tongue flicking out every few seconds—is the lizard’s way of experiencing the world. The Gila monster is essentially tasting the air, picking up clues as to where there might be some quail eggs to eat, a likely mate, or a coyote to avoid. When the lizard’s tongue pulls back in, the two tips are inserted into little holes in the roof of the mouth. This delivers the captured odor particles to the Jacobson’s organ, named for 19th-century Danish anatomist Ludvig Levin Jacobson. Some of the chemical compounds bind to receptor molecules, sending messages to the lizard’s brain. Other reptiles have the Jacobson’s organ, as do some amphibians and mammals.
The Gila monster evolved such a keen sense of smell because food in an arid environment is widely distributed. The creature rarely runs, but it can trudge for miles. Most people’s impression of Gila monsters, from seeing overfed specimens in a zoo, is that they’re obese and lethargic. Smaller lizard species, in contrast, are in danger of being eaten and adapted by being well camouflaged or very fast. (And there’s their amazing ability to drop the tail when threatened. The severed tail continues to twitch, keeping a predator’s attention.)
The Gila monster does not give up its tail, which is as useful a camel’s hump for fat and water storage. In times of scarcity, the tail shrinks down to something like a ballpoint pen rather than the usual kielbasa sausage.
Low metabolism and frugal energy use are advantages in food-scarce regions. But recently it has been found that though they have a low metabolic rate, Gila monsters possess high aerobic capacity and surprising endurance.
Beck demonstrated this by putting a Gila monster on a rubber treadmill with a Dixie cup over its head. A tube from the cup sends the lizard’s exhalations to a gas analyzer and calculates the rate of oxygen consumption. How does a Gila monster respond to this gymlike activity? Some object, Beck says, but most keep on tramping “in a kind of trance. Into the Zen of being a lizard.”
In the wild, Beck tracks the lizards’ long routes by radio transmitters implanted surgically (with difficulty because of the studded skin). He and other scientists have found, by using radio telemetry, that a lizard is loyal to a couple of particular shelters. Sensibly, they find a south-facing haven in winter, one that’s cooler and moister in the summer.
Beck loves them, but when asked what a Gila monster’s life is like he has to say “dull.” They do spend most of their time doing nothing. However, from April to June, there is drama, ritual combat that’s a challenging endurance test. Two males meet in what is essentially a wrestling match, arching and flexing sumo-fashion. The contest, which can go on for hours, ends when one has forced his opponent to the ground and remains on top. Though equipped with venom and sharp claws, the males, sensibly, do not kill or wound each other. The loser walks away unscathed; the winner, having proved his fitness to reproduce, gets breeding territory or, better, a shelter with a female inside.
When a female has been won, the victorious male lies beside her and rubs his chin on her back and neck. If she accepts him, she raises her tail and the male moves his tail under hers, bringing their vents into contact. Copulation lasts from half an hour to an hour. Which brings us to the hemipenis. Like snakes and other lizards, a male Gila monster has a retractable penis that pops out like the finger of an inflatable glove, an advantage on rocky soil. Actually, he has two; they pop out together but only one at a time is used. The hemipenises are elongated tubular structures stored in the tail, decorated with tubercles in a fashion Beck calls “flounced ornamentation.”
In July or August, the female lays one to 12 eggs in an underground hole. Incubation may last nearly 10 months, and the 4-inch-long young may not emerge until a year after insemination.
For millions of years, human beings figured very little in Gila monsters’ quiet lizard lives. Then we began building deep into the desert. One of Beck’s formerly prime locations for studying Gila monsters is St. George, Utah, now the site of a fast-growing retirement community. (Someone in one of those newly built units probably has a bottle of Byetta in the medicine cabinet.) Desert houses, surrounded by irrigated land, provide attractively moist, shady environments for the bolder lizards, which is beginning to create a problem. Every year dozens of Gila monsters (and thousands of rattlesnakes) are removed from properties in Phoenix and Tucson. From the homeowner’s point of view, the lizard is large and scary—and protected by state law; killing it is not a legal option. From the herpetologists’ point of view, there are too many Gila monsters run over by cars and too little unpaved, unspoiled desert habitat left for them.
Beck, who grew up exploring deserts in his native Utah, allows that the Gila monster doesn’t seem beautiful to most people, “But they’re an indication that we live in a beautiful place. Lose them and the beauty is diminished.”
Read more from this series on revolting creatures: the eel, the centipede, the skunk, the snapping turtle, the vulture, the tick, the jellyfish, the hyena, the slug, the mosquito, and the tarantula.
