Resource: Gila Monster

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The Gila (pronounced Hee-la) monster, scientific name Heloderma suspectum, is the largest lizard native to the United States and the only venomous lizard in the U.S. The adult Gila monster has a stout body with a thick tail, short legs, and strong claws. It has a large, blunt head and thick, forked tongue. Adults may be 18–24 inches long from nose to tail and may weigh three to five pounds. Black and pink, yellow, or orange rounded, bead-like scales cover the lizard's back; larger, plate-like scales cover the underside. The color pattern over the back, which varies with individuals, is banded in the northern subspecies but is more mottled and changes with age in the southern subspecies. It is thought that the distinctive color pattern may serve as camouflage or as a warning to potential predators.

The Gila monster's skin doesn't effectively retain moisture even though it lives in the desert. Gila monsters avoid dehydration by living in areas of moderate to high humidity. This reptile gets its name from one of its habitats, the Gila River Valley in southwestern New Mexico and southern Arizona. Its range, including most of the southwestern United States and northern Mexico, features semiarid desert environments with rocky foothills, sandy soil, loose gravel, and low shrubs. It avoids open flats and agricultural areas.

The Gila monster is only active during the spring months when its preferred food, eggs of land-dwelling birds, is available. It spends the other nine months and most springtime days and nights underground in moist, humid shelters such as burrows, or under rocks. It hibernates underground when temperatures drop in the late fall.

In addition to eggs, the Gila monster also eats frogs, insects, baby rabbits or birds, and small rodents. Gila monsters eat huge meals, and can survive months without food because they move slowly, have a slow metabolism, and store surplus food as fat in their tails.

It is thought that the Gila monster is venomous in order to subdue its prey, or perhaps for defensive reasons. When a Gila monster bites, it is very tenacious, chewing and biting as it delivers the neurotoxin venom from glands in its lower jaw through its teeth and into its prey to subdue it. The Gila monster is not aggressive to humans and only bites when it is cornered. There have been no reliable accounts of a human dying from a Gila monster bite, although it is very painful.

Human threats to the Gila monster include collectors, who capture them for breeding and captivity, and habitat destruction, including increased land development, farming, and ranching. The lizards are protected by state law in Utah, Arizona, and Nevada.

To learn more about how desert creatures are adapted to survive in an extreme environment, check out Desert Biome.

Print Questions for Discussion

• How is the Gila monster's skin different from other lizards' skin?
• What are some adaptive characteristics and behaviors of the Gila monster?
• How does a Gila monster survive when it only eats in the spring?
• What are some other animals that you think might share the Gila monster's habitat? Explain your reasoning.