Gila Monster

Appearance

A heavy, slow-moving lizard, up to 60 cm long, the Gila monster is the only venomous lizard native to the United States and one of only two known species of venomous lizards in North America, the other being its close relative, the Mexican beaded lizard. Though the Gila monster is venomous, its sluggish nature means that it represents little threat to humans. However, it has earned a fearsome reputation and is sometimes killed despite being protected by state law in Arizona.

Naming

There are two subspecies of Gila monster: the reticulate Gila monster and the banded Gila monster. The reticulate Gila monster lives in the southern region of the Gila monster's range, while the banded Gila monster is a northern subspecies occurring primarily in the Mojave Desert. The reticulate Gila monster tends to have its lighter markings broken up by dark scales, giving it a reticulated pattern, while the banded Gila monster generally has more unbroken bands of lighter scales.

The Gila monster has one close living relative, the beaded lizard, as well as many extinct relatives in the Helodermatidae whose evolutionary history may be traced back to the Cretaceous period. The genus "Heloderma" has existed since the Miocene, when "H. texana" lived, and fragments of osteoderms from the Gila monster have been found in late Pleistocene deposits near Las Vegas, Nevada. Because the Helodermatids have remained relatively unchanged morphologically, they are occasionally regarded as living fossils. Although the Gila monster appears closely related to the monitor lizards of Africa, Asia and Australia, their wide geographical separation and the unique features not found in the varanids indicate that the Gila monster is better placed in a separate family.

The name "Gila" refers to the Gila River Basin in Arizona, where the Gila monster was once plentiful. "Heloderma" means "studded skin", from the Ancient Greek words "helos", "the head of a nail or stud", and "derma", "skin". "Suspectum" comes from the describer, paleontologist Edward Drinker Cope, who suspected that the lizard might be venomous due to the grooves in the teeth.

Distribution

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.

Status

Urban sprawl and habitat destruction has adversely affected Gila monster numbers. As a result, Gila monsters are protected by Arizona and Nevada state law; it is illegal to "harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect the Gila Monster." In 1952, they became the first venomous animal to be given legal protection. Gila monsters are listed as Near Threatened by the IUCN. In 1963, the San Diego Zoo became the first zoo to successfully breed Gila monsters in captivity.

Habitat

They inhabit scrubland, succulent desert, and 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. They avoid living in open areas such as flats and farmland.Gila monsters spend 90% of their time underground in burrows or rocky shelters.

Food

The Gila monster feeds on small birds, mammals, frogs, lizards, insects, and carrion. The Gila monster feeds primarily on bird and reptile eggs, and eats infrequently, but when it does feed, it may eat up to one-third of its body mass. It uses its extremely acute sense of smell to locate prey, especially eggs. Its sense of smell is so keen that it can locate and dig up chicken eggs buried 15 centimetres deep and accurately follow a trail made by rolling an egg.

Prey may be crushed to death if large or eaten alive if small, swallowed head-first and helped down by muscular contractions and neck flexing. Unusually, after food has been swallowed, the Gila monster immediately resumes tongue flicking and search behavior, probably as a result of a history of finding clumped prey such as eggs and babies in nests. Gila monsters are able to climb trees and cacti in search of eggs.