Gila Monster (Heloderma suspectum)

Gila Monster overview

The Gila monster is a heavy, slow-moving venomous lizard of the Sonoran, Mojave and Chihuahuan deserts and the largest lizard native to the United States. Its skin is covered in bead-like scales patterned in black with pink, orange or yellow, a warning to predators. It spends around 90 to 95 percent of its life underground in burrows and rock shelters, emerging mainly in spring to raid nests for eggs and young animals. Fat stored in its thick tail lets it survive on just a few large meals a year. It is named after the Gila River basin of Arizona and New Mexico.

How Long Do Gila Monsters Live?

Gila monsters live about 20 years in the wild and 20–30 years in captivity. Their slow metabolism, underground lifestyle and venomous defense keep adult mortality low. They mature slowly, at around three to five years, so populations recover slowly when adults are removed.

How Much Does a Gila Monster Weigh?

A typical adult Gila monster weighs 350–700 g (12–25 oz). Weight swings considerably through the year because fat is stored in the tail, and large, well-fed individuals can reach about 2 kg. A thin tail is a sign that the animal has gone a long time without food.

How Long Is a Gila Monster?

Gila monsters grow 40–56 cm (16–22 in) long, including the short, thick tail. That makes them the largest native lizard in the United States. The closely related Mexican beaded lizard grows larger still, reaching around 90 cm.

How Long Do Gila Monsters Eggs Take to Hatch?

In the wild, Gila monster eggs take around 10 months to hatch; in incubators they hatch in about 4 months. Females lay 2–12 eggs in an underground nest in July or August, and hatchlings emerge the following spring, which suggests development slows or pauses over winter.

What Do Gila Monsters Eat?

Gila monsters are carnivores that eat mainly eggs and nestlings, including quail and tortoise eggs and baby rabbits and rodents. A Gila monster can eat up to a third of its body weight in one meal, and three or four big meals can supply its energy needs for a whole year.

Diet type: carnivore. Mostly the eggs of birds, tortoises, lizards and snakes, and helpless nestlings such as baby rabbits, rodents and ground-nesting birds, found by scent and dug out of nests and burrows.

Where Do Gila Monsters Live?

Gila monsters live in desert scrub, rocky foothills and canyon bottoms of the southwestern United States and northwestern Mexico, up to about 1,500 m. They favor places with boulders, burrows and some moisture, and avoid open sandy flats and farmland.

Are Gila Monsters Endangered?

The Gila monster is listed as Near Threatened on the IUCN Red List, and its population is decreasing. Urban sprawl, roads and illegal collecting are the main threats. It became the first venomous animal in the United States to receive legal protection when Arizona protected it in 1952.

Near Threatened

Gila Monster fun facts

• A hormone in Gila monster saliva, exendin-4, led to exenatide, a widely used type 2 diabetes drug and a forerunner of modern GLP-1 medications.
• Gila monsters have no fangs for injecting venom; it flows from glands in the lower jaw along grooved teeth while the lizard holds on and chews.
• They spend roughly 90 to 95 percent of their lives hidden underground.
• The Gila monster and its close relatives the beaded lizards were long thought to be the only venomous lizards, until venom was identified in monitors and other groups.
• Their beaded appearance comes from osteoderms, tiny bones embedded under each scale.

Gila Monster FAQ

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