There are only two venomous lizards in the world, and both live in the Southwest; the Gila Monster and the Mexican beaded lizard. The shy Gila Monster is one of seven reptiles species protected by Arizona law since 1952. They are the surviving members of an ancient beaded lizard family, distinguished by their colorful beaded skins. Both species live in Sonora, Mexico, but only the Gila Monster can be found in the Sonoran and Mojave Deserts. Seldom seen, these unusual creatures are living fossils, honored by primitive man, and if not carefully guarded doomed by civilized man.
Gila Monsters are large lizards with stout bodies, big heads, powerful jaws, and short, sturdy digging legs. They have big feet with large toes and long, strong claws. Gila Monsters grow to nearly two feet and have a black snout, short sausage-shaped tail and black tongue. Their body colors vary from black to coral pink to black with orange, yellow with cream. Fat for future energy and metabolic water is stored in the tail as well as in the abdominal body. A well-fed Gila Monster does not have to drink water and seldom does. Its prey serves as its sole source of food as well as water.
Unlike snakes, the venom glands of the Gila Monster are in the lower jaw. They do not have control over their venom. It is always injected instantaneously when it bites down with grooved and sharp-edged teeth in both jaws. The Gila's defensive bite does not deliver enough venom to be lethal. However, the venom contains substances that quickly cause excruciating pain. This weapon system is designed for defense rather than gathering food.
Gila Monsters are sedentary reptiles that return year after year to the same cold-season home. Spending most of their time underground, they leave winter dens in the late spring and retire to the cooler, moist underground of lower valleys. The home range of a Gila Monster seldom exceeds more than a mile in any direction. Being daytime creatures, they are strong climbers, posses good daylight vision and excellent hearing and are hard to fool when in familiar ground. Gila Monsters usually move slowly but they are not clumsy creatures and can be deceptively fast.
Gila Monsters are believed to live from 10 to 25 years. Adult Gilas may be preyed upon by coyotes, hawks such as the Harris Hawk, and owls including the great horned owl. Young Gila monsters are probably eaten by other reptiles including the rattlesnake. Humans are their primary enemies and road kills take a large toll in Arizona every year.
Ref: Greater Pinnacle Peak Association