Description: The Gila monster is the largest extant lizard species native to North America north of the Mexican border. Its snout-to-vent length ranges from 10 to 14 inches. The tail is about 20% of the body size, and the largest specimens may reach 20 to 22 inches in total length. Body mass is typically in the range of 1.21 to 1.76 lbs. They appear strong in their body structure with a stout snout, massive head, and "little"-appearing eyes, which can be protected by a nictitating membrane.

The scales of the head, back, and tail contain little pearl-shaped bones (osteoderms) similar to those found in the beaded lizards from further south. The scales of the belly are free from osteoderms. Female Gila monsters go through a total shed lasting about 2 weeks before depositing their eggs. The dorsal part is often shed in one large piece. Adult males normally shed in smaller segments in August. The young seem to be in constant shed. Adults have more or less yellow to pink colors on a black surface. Hatchlings have a uniform, simple, and less colorful pattern. This drastically changes within the first 6 months of their lives.[12] Hatchlings from the northern area of the species' distribution have a tendency to retain most of their juvenile pattern.

The heads of males are very often larger and more triangular-shaped than in females. The length of the tail of the two sexes is statistically very similar, so it does not help in differentiation of the sexes.[13] Individuals with stout tail ends occur in both nature and under human breeding.

Habitat: They inhabit scrubland, succulent desert, and oak woodland, seeking shelter in burrows, thickets, and under rocks in locations with a favorable microclimate and adequate humidity. Gila monsters depend on water resources and can be observed in puddles of water after a summer rain. They avoid living in open areas, such as flats and open grasslands.

Range: The Gila monster is found in the Southwestern United States and Mexico, a range including Sonora, Arizona, parts of California, Nevada, Utah, and New Mexico. No records have been given from Baja California.

Found in these States: AZ | CA | NM | NV | UT

Venom: The venom of a Gila monster is normally not fatal to healthy adult humans. No reports of fatalities have been confirmed after 1930, and the rare fatalities recorded before that time occurred in adults who were intoxicated by alcohol or had mismanaged the treatment of the bite. The Gila monster can bite quickly, and may not release the victim without intervention. If bitten, the victim may attempt to fully submerge the lizard in water, pry the jaws open with a knife or stick, or physically yank the lizard free. While pulling the lizard directly increases risk of severe lacerations from the lizard's sharp teeth, it may also mitigate envenomation. Symptoms of the bite include excruciating pain, edema, and weakness associated with a rapid drop in blood pressure.

Diet: The Gila monster's diet consists of a variety of food items – small mammals (such as young rabbits, hares, mice, ground squirrels, and other rodents), small birds, snakes, lizards, frogs, insects, other invertebrates, carrion, and the eggs of birds, lizards, snakes, and tortoises. Three to four extensive meals in spring are claimed to give them enough energy for a whole season. Nevertheless, they feed whenever they come across suitable prey. Young Gila monsters can swallow up to 50% of their body weight in a single meal. Adults may eat up to one third of their body weight in one meal.

The Gila monster uses its extremely acute sense of smell to locate prey. The strong, two-ended tipped tongue, which is pigmented in black-blue colors, picks up scent molecules to be transferred to the opening of the Jacobson organ around the middle of the upper mouth cavern.

Prey may be crushed to death if large, or eaten alive, most of the time head first, and helped down by muscular contractions and neck flexing. After food has been swallowed, the Gila monster may immediately resume tongue flicking and search behavior for identifying more prey such as eggs or young in nests. Gila monsters are able to climb trees, cacti, and even fairly straight, rough-surfaced walls.

Reproduction: The Gila monster emerges from brumation in early March. Gila monsters sexually matures 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 six (rarely up to eight) eggs. The incubation in captivity lasts about 5 months, depending on the incubation temperature. The hatchlings are about 6.3 inches long and can bite and inject venom as soon as they are hatched.

Status: Listed as Near Threatened because this species is probably in significant decline (but probably at a rate of less than 30% over three generations), especially because of habitat loss throughout much of its range, thus making the species close to qualifying for Vulnerable under criteria A2, A3 and A4.

In 1952, the Gila monster became the first venomous animal to be given legal protection. They are now protected in all states of their distribution. International trade in the species is regulated under Appendix II of CITES.

Subspecies: Two, both found in the United States:
   Banded Gila Monster - Heloderma suspectum cinctum
   Reticulate Gila Monster - Heloderma suspectum suspectum

Taxonomy: