Gila Monster Activity Patterns

Gila monster woodcut, 1879
This near hill silhouetted by an early March sunset is the winter retreat of several Gila monsters that gather from the surrounding flats each fall. March brings increased activity as they move around between various shelters on the hill and bask in the spring sun. Soon they will move down to their individual home ranges on the flats. Pinal Co., Arizona

Gila monsters are poorly understood. One reason is the fact that most of their life is spent underground and out of sight. It is difficult to study an animal that spends nearly all of its life hidden.

Although Gilas can be seen throughout the year, even basking at the entrance of their shelters on unseasonably warm winter days, most of their above-ground activity occurs during two distinct periods of time--spring and monsoon season. Their reproduction, feeding, and even metabolic controls are uniquely adapted to these short activity periods.

After a winter of hibernation, Gilas emerge in the spring to feed and mate. After this 90-day peak activity period they rarely come to the surface until the summer rainy season. In fact, even during these activity periods they are active for only brief periods of time. Consequently, more than 99 percent of the Gila monster’s life is spent inactive and underground.

Adult Gilas are predominately diurnal during their spring activity. To avoid the extreme heat of the desert, most of their activity occurs in the morning and the late afternoon. During the summer monsoons, they are predominantly nocturnal.