Gila Monster

The Gila Monster is the largest lizard in the United States!

The Gila monster is not just the largest lizard in the United States, it’s one of four North American lizards that are venomous. The others are species of Mexican beaded lizards that are found in Guatemala and Mexico. Despite its venom, the Gila monster is a rather lethargic animal and is not dangerous to humans. Found in the Mexican Sonora and the southwestern United States, its conservation status is near threatened.

5 Incredible Gila Monster Facts!

• A group of Gila monsters is called a lounge.
• They go into a state called “brumation,” which is hibernation for cold-blooded animals.
• They store fat in their tails. This allows them to fast for months.
• The Gila monster has high “aerobic scope values.” This means they take in and use oxygen very quickly from a resting state to a state of maximum exertion. This allows the normally sluggish lizard to enjoy periods of intense activity.
• The Gila monster has grooves in its teeth through which it injects venom.

Gila Monster Scientific name

The Gila Monster is classified in the kingdom Animalia, class Reptilia, and family Helodermatidae. The species name is Heloderma suspectum.

There are no subspecies of these animals, though the four Mexican beaded lizards were once thought of as subspecies. They are the Chiapan beaded lizard, whose scientific name is Heloderma. alvarezi; the Guatemalan beaded lizard, H. charlesbogerti; the Rio Fuerte beaded lizard, H. exasperatum, and the Mexican beaded lizard, H. horridum.

The Gila monster gets its common name because it was once plentiful in the Gila River Basin of New Mexico and Arizona. As for its scientific name, Heloderma, or “studded skin,” comes from two ancient Greek words. “Helos” refers to a nail head. “Derma” is the Greek word for skin. Edward Drinker Cope, the American paleontologist, provided the word Suspectum, for at first the lizard was believed to be a subspecies of the Mexican beaded lizard. As for “monster,” this rather large lizard probably appeared rather monstrous to the people who first came upon it. There was even a myth in the Old West that the giant lizard had poisonous breath, a belief shared by the Apache. In fact, the Gila monster’s venom does have a smell, but the smell itself isn’t toxic.

Gila Monster Appearance & Behavior

Though there seem to be no records kept of the largest giant Gila monster, the animal can grow to 22 inches long and weigh 4 pounds. Though this makes it a hefty reptile, it’s still smaller in size than its cousins, the beaded lizards. The size of these animals can be as much as 36 inches long, and they can weigh close to 9 pounds. However, the Gila monster is more colorful. Its patterned hide is thought to be a type of camouflage that hides the animal from both predators and prey.

Though it’s hard to tell male and female monsters apart, the heads of males tend to be more massive and have more of a triangular shape.

The Gila Monster is notable for its skin. Like other reptiles, its body is covered in scales, but the scales bear tiny, round bones called osteoderms. These osteoderms are found everywhere on the animal but its belly and the skin forms patterns of yellow or pink against black. The legs, feet, neck, head, and chin of the animal are also black, as are its eyes and tongue.

The patterns on the lizard’s hide grow more complex as it ages, though Gila monsters in the northern part of the range tend to hold on to the pattern they had as juveniles. Like fingerprints, no two of these animals have identical scale patterns.

Like other lizards, the animal sheds its skin as it grows. Females are notable because they shed their skin in one large piece in the fortnight before they lay eggs. The males shed their skin piecemeal, and younger Gila monsters seem to shed all the time.

These lizards are usually solitary and spend much of their time secreted in burrows. They will come out to hunt and warm themselves in the sun. Males have been known to fight for mating rights during the breeding period. Like Sumo wrestlers, the one who pins his rival to the ground wins. Otherwise, the reptile is considered docile.

Gila Monster Habitat

The lizard’s habitat is found in the deserts and dry places of southern Nevada and California’s San Bernardino County. It’s also found in southwestern Utah, southern and western Arizona, the southwest part of New Mexico, and down into Sonora and Sinaloa in Mexico. Elevations range from sea level to 4921 feet. Though it is a creature of the desert, the lizard needs to live near a steady supply of water.

During the dry season, the lizard emerges from its shelter in the morning. During the summer it may emerge at night when the air is warm but after the dangerously hot sun has set, for it needs to maintain a body temperature of about 86 degrees Fahrenheit. If it gets too hot, the lizard can lower its temperature by expressing water through its cloaca, a ventral opening through which they both excrete and reproduce.

The lizard doesn’t migrate but moves from one shelter to another every few days. Besides underground burrows, these shelters can be crevices and thickets.

Gila Monster Diet

The animal isn’t fussy when it comes to diet. They can go months without eating and only needs a few meals a year to stay healthy.

What Does the Gila Monster Eat?

The lizard’s diet includes the young of mammals such as rabbits, ground squirrels, and mice. It also takes other lizards, insects, eggs, snakes, frogs, and birds that are small enough for it to handle. The lizard is not above eating carrion.

More interesting facts about their diet: young Gila monsters are capable of ingesting prey that is half their body weight at one sitting. Adults can ingest prey that’s about a third of their body weight.

The animal finds prey through an exquisite sense of smell and like a snake has a forked tongue that can pick up molecules of a particular scent. The tongue sends the molecules to the Jacobson organ, whose opening is in the top of the lizard’s mouth. The lizard can then tell what kind of prey it is pursuing. The Gila monster has no problem climbing trees, cacti, or walls in search of a meal.

Like a snake, the Gila monster can swallow its prey whole, sometimes while it’s still alive. It will crush the prey to death if it’s too large to swallow. Right after it eats, the Gila monster will search for more prey.

What Foods are Bad for the Gila Monster?

A Gila monster that’s kept in captivity shouldn’t be given raw, store-bought eggs because of the risk of salmonella poisoning. They should be given water to drink, but it should not come in so large a container that it tempts the lizard to bathe in it. The animal might be so enamored of a soak that it won’t want to do anything else!

Gila Monster Predators & Threats

What Eats the Gila Monster?

Like so many other animals, Gila monsters are most at risk for being prey themselves when they’re young. Gila monster hatchlings seem to be the favorites of snakes, especially the King snake. Older lizards are taken by coyotes, larger birds of prey, and badgers. Since the lizard doesn’t move very quickly, it is easy for predators to simply pounce upon one once it’s out in the open and can be subdued before it can defend itself. A badger might go so far as to dig a Gila monster out of its burrow.

Unfortunately, the greatest threat to the Gila monster is humans. Because of human encroachment and habitat destruction, the population of the lizards is declining. Some people collect wild Gila monsters for pets, even though it is illegal to do so in some states.

Drought, probably exacerbated by climate change, is another reason that Gila monster populations are declining.

Gila monsters were often relocated to other areas when the land they were on was needed for housing or agriculture. They often returned, even if they were relocated miles away. More and more, humans are being encouraged to simply live with the Gila monsters they might find in their neighborhood, as the giant lizards really aren’t dangerous.

Reproduction, Babies, and Lifespan

The Gila monster is sexually mature when it’s about 4 to 5 years old. Its mating season starts in April or May when food is abundant. The male searches for a receptive female, flicking his tongue to catch her scent. When he finds a female he’ll caress her back and neck with his chin as he clasps her with his hind legs. If she doesn’t want him, she’ll bite him and crawl from under him. If she’s receptive, she’ll raise her tail, and he’ll position his tail under hers to make sure their cloacae come into contact. They’ll stay that way for half an hour to an hour, though some matings have been seen to last for as little as 15 minutes and others as long as 2.5 hours. Males mate with several females if the females are willing.

After she’s mated, the female Gila monster will be gravid for about two to three months then finally lay her eggs in an underground burrow in late summer. She may repurpose the burrow of a ground squirrel, but she does not incubate or guard the eggs. Eggs hatch in October, but baby Gila monsters or hatchlings go into brumation immediately and don’t surface until the next May.

Gila monster hatchlings are ready to fend for themselves when they are born, which means they can bite and inject venom. They are a little over 6 inches in size and live off their internal yolk sac until they can emerge and find food. Their parents do not provide care.

The reproductive strategy is similar to that of the Mexican beaded lizard, but the Mexican beaded lizard becomes sexually mature at a later age and mates in late summer and fall. The female also lays many more eggs than the Gila monster female. A beaded lizard can lay as many as 30 eggs.

The Gila monster lives about 8 years in captivity, though at least one lizard lived for 20 years. They have been known to live for 40 years in the wild.

Population

There are several thousand wild Gila monsters, with between 450 and 800 animals in Utah alone. The animal is so secretive it’s hard to arrive at a definitive number. Still, the numbers are declining, and the Gila monster is considered near threatened. This means that though the animal isn’t critically endangered, endangered, or vulnerable, it’s feared that it will achieve one of those statuses soon. Nevada, Utah, and Arizona protect the Gila monster.

Gila Monster In the Zoo

There are many zoos in the United States that have Gila monsters, though they are notoriously hard to breed in captivity. They include the:

• North Carolina Zoo
• Smithsonian’s National Zoo
• San Diego Zoo
• Stone Zoo – Zoo New England
• Louisville Zoo