Arizona State Reptile
Reticulate Gila Monster (common name)
Heloderma suspectum suspectum (scientific name)
The reticulate Gila monster is a venomous lizard—the only species of lizard with a poisonous bite in the U.S. and one of only two poisonous lizard species in the world—that lives mostly in the Chihuahuan and Sonoran deserts, the latter of which comprises a large part of Arizona. Though these lizards are the source of both very old Native American legends and modern fears, they are rarely a threat to people. They are very slow, making a bite easy to evade, and though their bites require medical attention, they are not fatal to healthy adults. In addition to one modern relative, the beaded lizard, Gila monsters have many extinct relations and their evolutionary history is known to go back to the Cretaceous period.
The Gila monster is heavy-bodied and tends to move very slowly, an average of about four meters per minute, though it can move or lunge quickly for a very short time if it feels threatened. The reticulate Gila monster usually has a mixture of light yellow or pinkish and much darker bead-like scales called osteoderms, which form a netted pattern on its upper body. The scales on the underside of its body are not round but rectangular.
Young Gila monsters are brightly colored, but they fade with age. The lizard’s tail is thick because it stores fat for the Gila monster to live on while it’s fasting, which these lizards do for months at a time. It also has strong claws, big front feet, and is well adapted for digging. It can see well in bright light and has excellent hearing. A Gila monster smells using its thick, black, forked tongue and a Jacobson's organ, a sensor on the roof of its mouth. The lizard’s venom gland is near the front of its lower jaw under its skin.
Up to 30 years; average of 20 years in the wild
Desert and semiarid areas with rocky, gravelly, or sandy soils and shrubs, especially desert washes and scrublands.
Range: Southwestern U.S. and Mexico, including Arizona, parts of California, Nevada, Utah, New Mexico, and Mexican Sonora and Sinaloa.
Conservation Status: Near Threatened (NT). Protective legislation dates from 1952. These were the first venomous creatures to receive legal protection, which they have in both Arizona and Nevada. Loss of habitat and capturing Gila monsters for pets has reduced the numbers of Gila monsters in the wild.
Gila monsters spend most of their time, perhaps up to 95 percent, in underground burrows or hiding in rocky shelters. They come out in the morning during dry season, from spring to early summer. Later in the year they are more mobile at night if it is warm or has recently rained. Though they are not strong swimmers, Gila monsters seek out water and soak in puddles or swim when they can. The lizards hibernate in winter. Mating occurs when they wake up in springtime. During mating season, adult males mark their territories using scent and wrestle any other males they meet. Females lay an average of five eggs about 45 days after they mate. Young Gila monsters hatch fully developed, with venom glands and teeth.
Gila monsters do not eat often, perhaps five to ten times a year in the wild. They use their sense of smell to find eggs or prey, and can eat up to one third of their of their body weight in a single meal. They swallow eggs whole unless they are too large, and also swallow their prey, mostly young, small animals, whole. Though they prefer to stay on the ground, Gila monsters can climb trees or cacti to get food. They can also sense another animal’s approach through vibrations in the ground. When they bite, venom comes out through the indentations in their teeth.
Top land speed recorded: 15 mph (24 kph)
Bird and reptile eggs, very young or small birds, mammals, frogs, lizards, insects, and carrion.
Breeding interval: Annual
Birthing period: May–June
Average nest size: 5 eggs
Size at birth: Unknown
Click to enlarge an image
Raw Data Source: U.S. Fish and Wildlife Service
Author: World Trade Press