Gila monsters spend most of their lives hidden below the ground. This is responsible for the limited information we have about them. 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 to about 22 inches 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 can consume their entire yearly energy budget in three or four large meals.

Most of their above ground activity occurs in 3 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 mainly diurnal (active during the day) with activity occurring mainly in the morning.

Gila monsters have a home range of about one square mile. They are usually solitary animals, but do gather in communal areas in the spring for mating.