Gila Monster

## Description

The Gila monster (Heloderma suspectum) is a heavy slow-moving venomous lizard. It is the largest extant lizard native to North America north of the Mexican border. The name "Gila" refers to the Gila River Basin in the U.S. states of New Mexico and Arizona, where these lizards were once plentiful. Gila monsters are sluggish in nature, so they are not generally dangerous and very rarely pose a real threat to humans. Yet, their exaggeratedly fearsome reputation has led to them sometimes being killed, in spite of the species being protected by state law in Arizona.

## Appearance

Adult Gila monsters 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. 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 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 the constant shed.

## Distribution

Gila monsters are found in the Southwestern United States and Mexico, a range including Sonora, Arizona, parts of California, Nevada, Utah, and New Mexico (potentially including Baja California). They inhabit scrubland, succulent desert, and oak or pine-oak woodland, seeking shelter in burrows, thickets, and under rocks in locations with ready access to moisture. In fact, Gila monsters seem to like water and can be observed immersing themselves in puddles of water after a summer rain. In Mexico, they can be found in lower mountain slopes and adjacent plains and beaches. They avoid living in open areas such as flats and farmland.

## Behavior

Gila monsters spend 90% of their time underground in burrows or rocky shelters. They are active in the morning during the dry season (spring and early summer); later in the summer, they may be active on warm nights or after a thunderstorm. These lizards are generally solitary creatures but may gather in communal areas and share shelters. Gila monsters have poor eyesight and when they hunt, they use their extremely acute sense of smell to locate prey, especially eggs. Their sense of smell is so keen, they can locate and dig up chicken eggs buried 15 cm (6 in) deep and accurately follow a trail made by a rolling egg. Gila monsters may even climb trees and cacti in search of eggs. During cold winter months, these lizards brumate in their burrows until spring.

## Diet

Gila monsters are carnivores (scavengers). Their diet includes small birds, small mammals, frogs, smaller lizards, insects, bird and reptile eggs and carrion.

## Reproduction

Gila monsters breed in May and June and just before the mating season males have been observed engaging in combats. In this combat, the dominant male lies on top of the subordinate one and pins it with its front and hind limbs. Both lizards arch their bodies, pushing against each other and twisting around in an effort to gain the dominant position. The male usually initiates courtship by flicking his tongue to search for the female's scent. If the female rejects his advances, she will bite him and crawl away. Females lay eggs in July or August, burying them in sand 5 in (13 cm) below the surface. The clutch consists of 2 to 12 eggs: 5 is the average. The incubation lasts 9 months, as the hatchlings emerge during April through June the following year. The hatchlings are about 16 cm (6.3 in) long and can bite and inject venom upon hatching. The juveniles usually attain reproductive maturity at three to five years old. After egg-laying, adult Gila monsters gradually spend less time on the surface to avoid the hottest part of the summer (although they may be active in the evening), eventually starting their hibernation around November.

## Population

### Threats

Illegal collection and habitat destruction due to urbanization and agricultural development have adversely affected Gila monster numbers. In 1952, they became the first venomous animal to be given legal protection.

### Number

The IUCN Red List and other sources don’t provide the number of the Gila monster total population size. Currently, this species is classified as Near Threatened (NT) on the IUCN Red List and its numbers today are decreasing.