Body length: up to 2 feet (60 centimeters)
Weight: 1.5 to 3 pounds (0.7 to 1.4 kilograms)
Life span: up to20 years in the wild, over 30 years in zoos
Incubation: 50 days
Number of eggs laid: 3 to 13 eggs
Length at hatch: almost 6 inches (15 centimeters)
Age of maturity: 3 to 5 years
Conservation status: vulnerable
The Gila monster and its close cousin, the beaded lizard Heloderma horridum, are the only two venomous lizards in the world.
In 2005, the Food and Drug Administration of the United States approved a drug for the management of type 2 diabetes based on a protein from the Gila monster’s saliva. The drug is sometimes referred to as “lizard spit.”
The Gila monster is named for the Gila River in Arizona.
It has been reported that the Gila monster may flip over while its jaws are still clamped onto prey. This move may help its venom flow into the wound.
The Gila monster is the largest lizard native to the United States.
In 1963, the San Diego Zoo hatched its first Gila monsters, a first for any zoo in the world. We earned the prestigious Edward H. Bean Award from the Association of Zoos and Aquariums for propagation of the species.
Reptiles: Gila Monster
Range: northwestern Mexico and southwestern United States
What’s in a name?
As the name might suggest, the Gila (pronounced HEE-la) monster has one of the worst reputations in the reptile world. This lizard is often feared and has been described as frightful and repulsive, especially in local folklore. It has been accused of many things, such as spitting venom, leaping several feet in the air to attack, stinging with its tongue, and killing people with gusts of poisonous breath. We’re glad you’re reading this fact sheet to learn the truth about these interesting lizards!
Gila monsters are heavy-bodied lizards covered with beadlike scales of black and yellow or pink. They are solitary and live in desert and semidesert areas with just enough moisture to support a few shrubs. The lizards prefer rocky foothills and avoid open areas. They are inactive much of the time, hiding in burrows or under rocks. During cold winter months, Gila monsters stay in their burrows and have fat stores in their tails to keep them alive. When springtime comes, they begin to hunt again. During the summer, the lizards only come out in the evening.
The Gila monster is venomous and the venom is made by a row of glands in the lizard’s lower jaw. When the lizard bites, small grooves in the teeth help the venom flow into the victim. The bite of a Gila monster is very strong and the lizard may not loosen its grip for several seconds. It may even chew so that the venom goes deeper into the wound. A Gila monster bite is painful to humans but rarely causes death. The biggest problem you might have if a Gila monster bit you is trying to get the lizard to release its grip! But you really shouldn't worry, as Gila monsters tend to avoid humans and other large animals. To warn off potential predators, they will open their mouth very wide and hiss.
A meaty meal
As carnivores, Gila monsters do not have very good eyesight; when they hunt, they use their senses of taste and smell. To track prey, the Gila monster flicks its forked tongue out to pick up scent particles in the air. These lizards are not very fast, so they need to sneak up on animals and bite them before they get away. Their prey includes birds’ eggs and nestlings, rodents, frogs, lizards, insects, centipedes, and worms; they may also eat carrion. Gila monsters don’t chew their food, they just swallow it whole; however, they do break open eggs. The venomous saliva of the Gila monster may be more useful as a defense against predators than for hunting, because most of the lizard’s prey is small enough to be subdued by the strength of the bite.
Breeding season for Gila monsters is usually in early summer. The female digs a hole, lays a clutch of large, leathery, oval-shaped eggs in the hole, and covers them. The eggs are not buried very deep, so the heat of the sun incubates them. About four months later, the baby Gila monsters break out of their eggs and crawl to the surface. They are only a few inches long, but look like miniature adults with more vivid coloring. The hatchlings are ready to begin life on their own, no training required!
Help for Gila monsters
Much of the scrubland of the Gila monster's habitat has been cleared for agriculture and other human activities. Domestic cats and dogs often kill the lizards and some are illegally collected for the pet trade. In 1952, the Gila monster became the first venomous animal in North America to be given legal protection.