information:classification, structural:scholar_edition, linguistic:voice_change, structural:summarization, stylistic:tone
Life cycle

The Gila monster emerges from brumation in early March. Gila monsters sexually mature at 4–5 years old. It mates in April and May. The male initiates courtship by flicking his tongue to search for the female's scent. If the female rejects his advances, she will bite him and chase him away. When successful, copulation has been observed in captivity to last from 15 minutes to two and a half hours. There is only a single record of attempted mating outside of a shelter. The female lays eggs at the end of May into June. A clutch may consist of up to eight (rarely more than six) eggs. The incubation in captivity lasts about 5 months, depending on the incubation temperature. The hatchlings are about 16 cm (6.3 in) long and can bite and inject venom as soon as they are hatched.

The egg development and hatching time of young in the wild has been a subject of ongoing speculation. The first model stated that youngsters hatch in fall and stay underground. The second theory postulated a nearly developed embryo remains inside the egg over winter and hatches in spring. Hatchlings (weight about 35 g (1.2 oz)) are observed at the end of April to early June.

Discussions of the exact egg development and hatching cycle of the Gila monster came to an abrupt and unexpected end on October 28, 2016, when a backhoe was digging at the outer walls of a house in a suburb of northern Tucson. The backhoe extracted a nest of a female Gila monster with five eggs in the process of hatching. The Gila monster is now known to hatch near the end of October and immediately proceed into hibernation without surfacing. They then appear on the surface from May through June the following year when prey should be abundant.

In summer, Gila monsters gradually spend less time on the surface to avoid the hottest part of the season; occasionally, they may be active at night. Females that have laid eggs are exhausted and thin, fighting for survival, and have to spend extra effort to "reconstitute". The brumation of Gila monsters begins in October. Gila monsters can live up to 40 years in captivity, though rarely.

Little is known about the social behavior of Gila monster, but it has been observed engaging in male to male combat, in which the dominant male lies on top of the subordinate one and pins it with its front and hind limbs. While fighting, both lizards arch their bodies, pushing against each other and twisting around in an effort to gain the dominant position. A “wrestling match” ends when the pressure exerts their forces, although bouts may be repeated. These bouts are typically observed in the mating season. Males with greater strength and endurance are thought to enjoy greater reproductive success. Although the Gila monster has a low metabolism and one of the lowest lizard sprint speeds, it has one of the highest aerobic scope values (the increase in oxygen consumption from rest to maximum metabolic exertion) among lizards, allowing it to engage in intense aerobic activity for a sustained period of time.