In the Sonoran Desert, lizards are particularly conspicuous to the casual observer because so many are diurnally active.
Most species are carnivorous and the majority are important consumers of insects.
In both species, the young are well-known to eat insects while the adults are chiefly or exclusively herbivorous. It is a predatory scavenger specializing in the eggs and helpless young of reptiles, birds, and small mammals. Its brief surface sojourns from subterranean retreats occur mainly in April and May, the best seasonal window for activity requiring moderate daytime temperatures and reaping an energy bonanza from the spring bounty of eggs and nestlings. The Gila monster beats a dignified retreat when approached, but halting if pressed, and hissing loudly with mouth agape. The evolutionary origin and subsequent radiation of the Gila monster is unclear.