The Gila monster (Heloderma suspectum) is a large, strikingly-colored venomous lizard. The gila monster and the Mexican beaded lizard (Heloderma horridum) are the only members of the beaded lizard family, Helodermatidae. The Gila monster occurs in rocky, semi-arid habitats from the Colorado River basin in the southwestern United States to the western regions of Mexico and Guatemala.
The Gila monster reaches a length of 18 in (46 cm), and is typically black or dark brown, with bright yellow markings. The body is heavy and cylindrical, ending with a thick, rounded tail, where energy reserves are stored against lean times. The head is relatively large, massive, and flattened, with numerous, slightly recurved teeth.
The Gila monster is a terrestrial lizard, and is most active at dawn and dusk. Since the body temperature of Gila monsters depends on environmental temperature, these lizards are less active during the winter in northern parts of their range. Gila monsters can live for 20 years in captivity.
The Gila monster has venom glands on the front part of the lower jaws, and (together with the Mexican beaded lizard) are the world's only venomous lizards.
The venom glands synthesize and store a potent toxin that can cause paralysis of the cardiac and respiratory systems of vertebrate animals. The Gila monster bites and chews a wound in its victim, into which the venom flows by capillary action along deep grooves on the lizard's teeth. The Gila monster is a tenacious biter, using its venomous bite to immobilize prey, and to defend itself against predators. The bite of a Gila monster is painful, but rarely fatal to a human.
The Gila monster eats a wide range of small animals, bird eggs and nestlings, earthworms, and carrion. Food is swallowed whole, except for eggs, which are broken before eating. Like most lizards, the Gila monster uses its forked tongue and an associated sensory organ (Jacobson's organ) on the roof of the mouth for chemosensation, an important aid to finding its food.
Gila monsters lay as many as 13 eggs in a clutch. The eggs are buried, and incubate for as long as 130 days until hatching.
Because it is a potentially dangerous and unusual looking animal, the Gila monster is often kept as a pet. Populations of gila monsters in some areas have been depleted because some people fear and kill these animals, and because they are hunted for their skins and the commercial pet trade.
See also Reptiles.