Gila monster

Common Name:
Gila monster
Scientific Name:
Heloderma suspectum
Type:
Reptiles
Diet:
Carnivore
Group Name:
Lounge
Average Life Span In Captivity:
Up to 40 years
Size:
20 inches
Weight:
4 pounds
IUCN Red List Status:
Near threatened
Current Population Trend:
Decreasing

What is a Gila monster?

The Gila monster (pronounced HEE-luh) is a small, striking lizard with black scales and an array of orange stripes and spots. Along with their close cousins, the beaded lizards, Gila monsters belong to one of the only families of venomous lizards on Earth.

Gila monsters appear pebbly in appearance due to a living coat of armor. Osteoderms, or tiny chips of bone embedded within the skin, give the lizards a degree of protection against predators, such as coyotes and hawks.

Gila monsters spend more than 90 percent of their lives below ground, which makes them difficult for scientists to research. However, some radiotracking work has revealed that the animals will, on occasion, travel more than a mile at a time in search of food or possibly mates.

While the species is often described as strictly nocturnal, above-ground sightings during the day do also occur.

Habitat and diet

Gila monsters are native to the American Southwest and Northwestern Mexico. They inhabit dry areas, such as the Mojave, Sonoran, and Chihuahuan deserts.

With most of their lives spent below ground, Gila monsters use their long claws to dig burrows. However, they will also make use of burrows already on the landscape. Jason Jones, state herpetologist for the Nevada Department of Wildlife, says that some lizards will use the same burrows year after year, and that during the mating season, multiple Gila monsters may share a burrow.

Lack of suitable burrows may actually limit how many Gila monsters are in a given area, says Jones.

Favorite Gila monster foods include bird, tortoise, and snake eggs, as well as newborn bunnies and ground squirrels. Sometimes, the lizards will even climb tall cacti in search of bird nests and the tasty treats they contain.

In between feedings, which can be extremely infrequent, Gila monsters survive on fat stored inside their tails.

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In fact, when evaluating Gila monster fitness, scientists actually dunk the lizard’s tail in a cylinder of water to see how much liquid is displaced. The more water, the bigger the tail, and the healthier the Gila monster!

Gila monster venom

Unlike most snakes and spiders, which inject their venom using long fangs that function like hypodermic needles, Gila monster venom is wicked up from glands on the lower jaw by tiny grooves on each tooth. This means that to really envenomate their victims, the Gila monster actually has to clamp down and then chew.

Interestingly, Gila monsters appear to use their venom almost exclusively for defensive purposes. This is because their favorite foods—bird, tortoise, and snake eggs—can’t fight back.

(What's the difference between venom and poison?)

While people rarely encounter Gila monsters in the wild, bites do sometimes occur. Symptoms include swelling, intense burning pain, vomiting, dizziness, weakness, rapid heart rate, and/or low blood pressure.

One study of calls made to U.S. poison control centers revealed that 105 Gila-on-human bites occurred between the years 2000 and 2011. Fortunately, most bites were not serious: less than half required a visit to a health care facility and no deaths occurred.

If you should ever find yourself in the unlikely situation of having a Gila monster attached to your person, experts recommend positioning the lizard so that all four of its feet are firmly planted on the ground. If it still does not release you, then attempt to pry the animal’s jaw open with a strong stick. Rinse the wound with water and seek medical attention immediately.

Gila monster venom can also be helpful, however. In the last two decades, scientists have used its chemical composition to inspire novel medicines for diabetes and obesity. One such drug, known as semaglutide and marketed under the brand names Ozempic, Wegovy, and Rybelsus, has become so popular as a weight-loss treatment that it has led to shortages in the United States.

(How harnessing the powers of venom is leading to new medicines.)

Reproduction

Between April and June, male Gila monsters compete in wrestling matches that can go on for hours. After the loser skulks away, the winner mates with the female. In late July, she finds a good nest where she lays four to eight eggs, leaves, and never looks back.

At least, that’s what scientists currently believe. The truth is, reproduction is one of the areas of the Gila monster’s life history that remains shrouded in mystery, says Jones.

Another is how the young lizards survive once they do hatch. Juveniles are almost never spotted in the wild.

Conservation

The Gila monster is currently considered near threatened by the International Union for Conservation of Nature. Several range states have put restrictions in place meant to protect the species. For instance, in Utah it is illegal to handle Gila monsters without a permit, and Arizona forbids anyone from collecting, killing, or selling Gila monsters.  

Gila monsters remain a popular species in the legal pet trade, however ownership is banned in some states.

Editor's note: This story was updated on March 29, 2023.

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