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.
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).
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.