Genus/species: Heloderma suspectum
The Gila monster is one of only two species of venomous lizards (its cousin, the Mexican beaded lizard, is the other). It can bite quickly and hold on tenaciously. Rather than injecting venom through hollow fangs like venomous snakes do, Gilas have enlarged, grooved teeth in their lower jaw. When they bite, their powerful jaws chew the venom in through capillary action along the grooves in these teeth. Gila monster venom is about as toxic as that of a western diamondback rattlesnake. However, a relatively small amount of venom is introduced in a Gila bite.
The dorsal coloration of the Gila monster is black with pink or orange. In the southern subspecies, the reticulated Gila monster, the light markings, or bands, are broken up to form a reticulated pattern. In the northern subspecies, the banded Gila monster, the light markings generally form an unbroken band across the back.
Gila monsters spend most of their lives hidden below the ground. There are three things that make them particularly well suited for the harsh environment in which they live. First, they are large lizards (the largest in the U.S.) measuring up to about 22 inches (56 cm) in total length, and are able to store more energy than smaller lizards. They store fat in their tail and in their bodies. Second, they are capable of eating relatively large meals. They have been observed in the wild eating meals up to one third of their body weight. Third, Gilas have low resting metabolic rates. Their low metabolic rates, and the ability to eat large meals, combined with their large capacity to store fat, make frequent searching for food unnecessary. Therefore, they are rarely seen above ground. It has been suggested that Gilas may consume their entire yearly energy budget in three or four large meals.
Most of their above-ground activity occurs in three months in the spring. Not only is this when mating occurs, but it is when their main source of food (vertebrate nests) is most abundant. They are diurnal but most activity occurs in the morning. Gila monsters have a home range of about one square mile (1.6 km2). They are usually solitary animals, but do gather in communal areas in the spring for mating.
Distribution and Habitat
The range of the Gila monster is primarily in Arizona and Mexico, the extreme southeastern corner of California, the southern tip of Nevada, and the southwestern corners of Utah and New Mexico. It is named for the Gila River in whose drainage it is a common resident.
Gila monsters are desert dwellers, living near washes and arroyos and in semiarid rocky regions of desert scrub or grasslands. Gila monsters also seem to prefer rocky foothills and avoid open flats and agricultural areas. They can live in elevations up to 5,000 feet (1,500 m).
Diet in the Wild
Gila monsters most often prey on small birds and mammals, eggs, lizards, frogs, insects, and carrion.
In late April to early June, courtship and male-to-male combat take place. Females lay two to 12 leathery eggs that overwinter below ground and hatch ten months later in the next spring. Hatchlings are about six inches (15 cm) long and are miniature replicas of their parents.
They may live 20 or more years in zoos, possibly longer in the wild.
Listed as threatened under the United States Endangered Species Act and listed on CITES Appendix II. They are threatened by habitat destruction: overgrazing, truck farming, and the planting of cotton. They are also protected under Arizona law.
With very few natural predators, they may spend up to 98 percent of their lives in or at the mouth of a burrow. Gila monsters enjoy a mixed reputation with Native Americans. While the Tohono O'Odham and the Pima believed that the lizard possessed a spiritual power capable of causing sickness and the Apache believed that its very breath could bring death, the Seri and Yaquai believed in the healing powers of the lizard's hide.
A component of Gila monster venom called exendin-4 was recently investigated for its in treating type-2 diabetes. This peptide stimulates the secretion of insulin in the presence of elevated blood glucose levels. It also has the effect of slowing gastric emptying. Phase I clinical studies have recently begun with this exciting experimental drug.