Gila Monster

NPS photo

Meet the Monster

The Gila (pronounced HEE-lah) Monster (Heloderma suspectum) is one of the best known and most often asked about, but it is one of the rarest to encounter of all the Sonoran Desert reptiles. One of only two venomous lizards in North America, it is the only one found in the United States. (The other venomous species, the closely-related Beaded Lizard, is found from southern Sonora, Mexico, to Guatemala.) Folklore, tall tales and Hollywood movies have endowed the Gila Monster with powers and potency far beyond those possessed by any actual creature. But the facts about this unique lizard are fascinating and require no embellishment.

Identifying Characteristics

The Gila Monster is the largest lizard in the United States. It grows to 22 inches (560 millimeters) long and can weigh over a pound (450 grams). Its upper surface is covered with bead-like scales. It has a long, rounded body, a big head and a round tail. Short, stout legs possess long toes with sharp claws used in digging and climbing. The snout is solid black, and the body has a banded color pattern of black with pink, orange, salmon.

 

Natural History

Gila Monsters are not known to be rare, but they are not commonly seen as they spend the majority of their time underground and out of sight, an adaptation for hot, dry desert conditions. They live in burrows and may be seen sometimes sharing them with other reptiles such as snakes or desert tortoises (although they eat tortoise eggs when they can get them). These burrows are essential for their survival.

Gila Monsters are active above ground, hunting and exploring when the ambient conditions are right. In spring and fall, this is mostly morning and evening; in the summer, they are typically active at night. Sometimes in winter, Gila monsters will emerge to bask in the sun. But most of the time, they’re underground.

When they are not underground, Gila Monsters are easily overlooked. Their colored pattern matches the dappled shade of a desert shrub, and the dark snout is seldom seen in the shadows. They can easily detect nearby activity of a human or other animal and will do their best to remain hidden, often by just backing into rocks or vegetation.

Gila Monsters are carnivores. They use their tongues to pick up faint scents and can hunt for prey and water any time of day. They eat newborn or young rabbits, young packrats, and other rodents still on the nest, as well as eggs, nestling birds, lizards, and occasionally small snakes. During such meals, the lizard may eat up to 35% of its own body weight (over 50% in the case of young Gila Monsters) (get reference), storing the food as fat in its tail and lower abdomen.

 

Distribution and Habitat

The Gila Monster occurs from Nevada to the north to northern Sinaloa, Mexico to the south (Don confirmed this with references). Its habitat is mainly rocky lowlands and desert scrub, desert grassland, and rocky canyons, and in Saguaro National Park they have been found at high as 7,000 feet (2,134 meters) in elevation. They are not usually found in agricultural areas.

 

Reproduction

Gila monsters usually lay 4-5 eggs in underground burrows, in mid-late June just prior to the start of the summer monsoon season. The hatchlings bite their way out of their soft-sided eggs in early winter, but are known to remain in place underground, nourished by their egg yolk, until the following spring. New hatchlings average about 6 1/2 inches long and about 1.2 ounces in weight. This may seem small, but hatchlings are considerably larger than the size of an adult Banded Gecko (Coleonyx variegatus), a little, thin-skinned lizard with which it is sometimes confused.

Predation

Gila Monsters have many potential predators, including coyotes, foxes, bobcats, hawks and owls. Young are more vulnerable to attack, and some predators dig up and eat the eggs. Adult Gila Monsters have little to fear, as their color and pattern warn of their potential danger. People represent the Gila Monster's primary threat through habitat loss by development, illegal poaching, and roadkill.

Venom and Bites

Gila Monsters are venomous. A Gila Monster bite is a serious and painful medical emergency and always calls for a trip to the Emergency Room. The venom can cause shock (rapid drop in blood pressure) among other problems, and their reptile mouths harbor human-unfriendly bacteria.

Gila Monsters do not have fangs and can’t strike, so a bite from one is always the result of an individual putting their body parts near a Gila Monster’s mouth. Gila Monsters produce venom in glands in their lower jaws. This is mixed with saliva and pulled into the wound along grooved teeth by capillary action. Thus, the longer the lizard hangs on, or "chews," the greater the amount of venom introduced. Reasonably cautious people who watch where they put their hands and feet will not be bitten by a Gila Monster.

 

Legal Protection

Gila Monsters are protected by state law in each of the states where they occur: Arizona, California, Nevada, Utah, New Mexico, and Mexico. Arizona the first state to give them legal protection, and the species was the first venomous reptile offered protection in the United States. Also, in Saguaro National Park, all plant and animal life, as well as geological and cultural resources, are strictly protected by Federal law. Federal and State protections mean that it is illegal to possess or relocate (dead or alive), harass, injure, or cause the death of a Gila Monster. If you are lucky enough to see a Gila Monster in its natural habitat, enjoy the sighting, take photos, but do not attempt to touch or otherwise bother it. The best thing you can do for Gila Monsters is to educate yourself, you family and your friends about the desert and its amazing animal life.

 

Gila Monster Photo Community Science Project

Saguaro National Park has a photo database of Saguaro National Park Gila Monsters. Our first photo dates from 2001; most are from 2010 onwards. Our goal is to follow individual lizards over time to learn about their habitat usage, health, range, longevity, and whatever else we can learn from our data.

The park encourages visitors to take pictures of Gila monsters they see while hiking. If it’s possible to get the back, left/and or right side, and the tail, without getting too close to or stressing out the lizard, please send all the photos with the location, as high resolution as reasonably possible, to [e-mail]

 

Gila Monster Project

The park encourages visitors to take pictures of Gila monsters they see while hiking. Park staff uses this data to monitor them over time.

 

Living with Wildlife - Saguaro National Park (U.S. National Park Service)

Gila monsters are well known in the park but are rarely seen. Their distinct beaded pattern is unique to each individual and reflects the texture of tiny, individual nodules of bone found within their skin. As urban development pushes further into their native habitat, Gila monsters face similar issues to horned lizards and desert tortoises. The best way to support conservation efforts of the Gila monster is to educate yourself and keep your distance from them if you encounter one in the wild. If you do see one, enjoy it!

• Keep a respectful distance. Never attempt to touch or handle them.
• If you see one at the park, take a photo and contribute it to our ongoing Gila monster photo identification project.
• Keep your dog on a leash and never take a dog on non-paved trail.