Window on Nature
By Lowell & Kaye Christie, F47246
When most people think of lizards, they picture a cute little critter with a long tail and a lively disposition. But you’ll need to conjure an entirely different image for this desert reptile — it’s a real monster. Gila monsters (Heloderma suspectum) aren’t cute, nor are they little; and they’re not very lively except when hungry or threatened.
An adult Gila (pronounced hee’-la) monster grows to be 1-1/2 to 2 feet long. It has a stout body and fat tail, and is covered with pebbly scales. Gila monsters are predominately black, with pink, orange, or yellow markings. The color is somewhat subdued, so the animal isn’t easily seen.
Gila monsters are one of only two species of venomous lizards. (The other is the Mexican beaded lizard.) The Gila has a generally sluggish behavior and benign disposition, and typically will flee from rather than attack a human. But if you make a pest of yourself, a Gila monster can bite quickly and hold on tenaciously. Unlike a venomous snake, however, a Gila introduces only a small amount of venom into the victim. Gila monsters don’t inject the poison through hollow fangs like a snake. A Gila monster’s teeth are grooved and allow the venom, which comes from glands in its lower jaw, to ooze through the grooves and into the victim.
Gila monsters don’t look for trouble, but when it comes, they’re ready to defend themselves. Unlike poisonous snakes, Gila monsters typically do not hit and run, but may bite down hard and hold on. An irate Gila monster actually will chew the venom into its adversary. Fortunately, the experience is rarely fatal to humans.
Although a bite isn’t likely to cause death in humans, even minor bites are, at the very least, excruciatingly painful. A friend of ours, who experienced such a bite firsthand, works with poisonous animals as a museum curator. He admits that he was plain careless on one occasion.
Gila monsters use their venom primarily as a defensive weapon and seldom for catching food. The strength of their bite quickly kills their prey, which consists of young rodents, rabbits, and hares. They may augment their diets with small birds, other lizards, insects, and bird and reptile eggs.
Gila monsters can be found from southern Nevada and the southwestern corner of Utah south through the desert areas of Arizona and into Mexico. Extreme southwestern New Mexico and a tiny portion of California are included as well. Gila monsters range to approximately 5,000 feet in elevation, and they seem to prefer the wetter, rockier palo verde-saguaro scrub of the Sonoran Desert to the drier, sandier conditions found in the Mojave and Chihuahuan deserts. Even so, you are far more likely to see this monster in a desert museum than in the wild.
With all our time spent in the desert, we’ve spotted a Gila monster only twice. Lowell glimpsed one while driving through Saguaro National Monument, and we both saw one when it showed up at our campsite. It didn’t stay too long, though, so we didn’t have to figure out how we’d chase it away before we had to take the dog out.
That isn’t to say that there haven’t been any Gila monsters around during our travels. A Gila’s keen vision and hearing will help it avoid being detected. That, coupled with its stay-at-home attitude and protective coloration, makes it hard to notice.
Gila monsters spend most of their lives hidden below the ground. They aren’t lazy; they just don’t need to spend much time making a living. These large lizards store fat in their tail and in their bodies. (A swollen tail indicates that a Gila monster is well fed.) And they can eat massive meals — up to one-third of their body weight. Gila monsters also have low resting metabolic rates. Clearly, they don’t need to search for food very often. One source indicated that Gila monsters can consume enough calories to last them an entire year in just three or four large meals.
Most of their aboveground activity occurs in the spring. Not only is this the mating season, but it’s the time when their main food sources are most abundant.
It was long believed that Gila monsters are predominantly nocturnal in habit and quite rare, because they are so seldom seen. But today, Gila monsters are known to be most active during the day (diurnal), particularly in the mornings and evenings, and more common than formerly believed. Otherwise, this shy and inoffensive creature is a homebody that prefers to stay in its burrow. Rumor has it that, when not foraging, a Gila monster will spend more than 98 percent of its time underground or lounging near the entrance to its den.
To no one’s surprise, Gila monsters become more sociable during the breeding season, which typically begins in May. The males go through a combat ritual to determine who gets first choice of the ladies, but once the pecking order is established, they go back to their solitary lives.
Females don’t beat such a hasty retreat. They have eggs to produce and lay. Unless it has been a particularly bountiful spring, the female will need to take on more food. No matter how much food she eats at this stage, her tail will actually decrease in diameter as she uses up her fat stores for egg production. The number of eggs a female will lay varies from as few as two to as many as a dozen, depending on the size of the female and the availability of food. Once the eggs are laid (in July or August), they incubate in her burrow for approximately a year. The young hatch in early or middle summer of the following year, already capable of fending for themselves. It takes a young Gila monster approximately three years to reach adulthood, and it may live for as many as 25 years.