Gila monsters are most active at night. They shelter from the heat of the day in rocky crevices or burrows abandoned by mammals. However, in northern parts of their range, the lizards are completely inactive for several months during the winter. Inactive individuals rely on fat stored in their tails to keep them alive when they cannot feed.
Gila monsters mate in springtime, and their copulation can last for over an hour. The eggs develop inside the females for about ten weeks. They then bury the eggs in areas that are often bathed in sunlight. The eggs incubate for up to ten months.