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Planet Earth

The Venomous Gila Monster Isn’t As Scary As You Might Think

Despite their fearsome-sounding name and venomous bite, these desert-dwelling lizards – the largest in the United States – have evolved in unique ways to thrive in an arid climate.

By Lily CareyMay 14, 2024 1:00 PM
Close-up shot of a gila monster under the cactus
(Credit: kwiktor/Getty Images)

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Native to the Sonoran Desert of the American southwest and Mexico, the Gila monster (Heloderma suspectum) might look and sound threatening. But to many, it’s known for its status as the largest lizard — and the only venomous lizard —native to the United States.  

The Gila monster, distinguished by its black-and-pink patterned scales, spends the majority of its life beating the Arizona heat underground. Because of this, though, its habits have long been a mystery to scientists. Growing up to two feet long, the Gila monster’s size sets it apart from many other smaller, more agile Sonoran Desert lizards

“They did not read the book on how to be a desert lizard,” says Dale DeNardo, an environmental physiologist at Arizona State University.  

Yet what some consider to be its weaknesses are actually among the Gila monster’s greatest strengths. Unlike most of the world’s lizards, the Gila monster’s venom allows it to fend off predators despite its lack of agility. They’ve lived in the Sonoran Desert for millions of years, adapting over time to an increasingly arid environment and evolving to store water for survival in the hot, dry Arizona summers. 

While many see them as a threat due to their venom, DeNardo and others say these “iconic” lizards could be facing even greater threats from ever-drier conditions due to climate change. 

Are Gila Monsters Dangerous to Humans? 

Most venomous creatures use their venom to capture their prey. However, because Gila monsters are very large and slow-moving, they primarily eat mouse or rabbit eggs out of nests, meaning they don’t need to envenomate their prey to eat them. 

The Gila monster’s venomous bite evolved solely for self-defense purposes, allowing them to defend themselves against predators like coyotes, owls, and hawks. Because of this, DeNardo says, they don’t attack humans unprovoked. 

“They use it whenever they feel threatened, but they never lunge at people,” he says.  

Indeed, Gila monster attacks on humans are extremely rare. A 2014 analysis found that 105 people contacted a U.S. Poison Control Center about a Gila monster bite from 2000 to 2011. And while most of these cases required a trip to the emergency room, none of them were fatal.  

“It's a bite that's extremely painful,” DeNardo says of the Gila monster’s defense mechanism. “At the time of the bite, it’s much more painful than like a rattlesnake bite. But it's not designed to kill.” 


Read More: Reptiles are Highly Emotional, Contrary to Their Cold Reputation


Breaking Down the Gila Monster's Bite

(Credit: Vaclav Sebek/Shutterstock)

Unlike most other venomous animals, the Gila monster doesn’t inject venom through hollow fangs. Instead, it produces its venom in venom glands in the lower jaw. It has large, grooved teeth that latch onto its prey and inject the venom. Because it often must attach itself firmly to its victims, some have reported that Gila monsters sometimes must be “forcibly disengaged” from bite victims. 

A Gila monster bite can cause excruciating pain for about 45 minutes following the incident, after which the pain typically begins to subside. However, its venom can also cause symptoms such as an elevated heart rate, making it extremely dangerous for people with underlying heart conditions.

In March 2024, a Colorado man died after being bitten by his pet Gila monster. Before that, DeNardo says, there had been no fatalities from a Gila bite for several decades. If you do encounter a Gila monster, your best bet is to keep your distance and not approach it. 


Read More: 8 Facts You Didn't Know About Venom and Toxic Animals


Using Gila Monster Venom for Diabetes Treatment

For some however, the Gila monster’s venom has proven life-saving rather than life-threatening. Its venom contains a key hormone called exendin-4, which coincidentally mirrors a type of glucose receptor found in humans.

Research on this parallel led to the development of semaglutide, a chemical compound used today in popular diabetes and weight-loss drugs like Ozempic and Wegovy.  

These groundbreaking discoveries don’t mean the Gila monster is at risk of being hunted for its venom, though. In 1952, they became the first animal to ever receive legal protection in the United States. Today, most states have laws against not just hunting them, but also handling them and keeping them as pets.  


Read More: Deadly Animal Venom Could Lead To Pharmaceutical Breakthroughs


How Gila Monsters Uniquely Adapt to Their Habitat

One of the main challenges of surviving in the Sonoran Desert is finding enough water to survive. As a forager, the Gila monster faces high rates of evaporative water loss. DeNardo, who studies how Gila monsters and other animals adapt to environmental change in the desert, says most desert-dwellers have evolved to survive on extremely limited amounts of water.   

But instead, the Gila monster stores water in its bladder, allowing it to remain hydrated through the arid summer months. During the rainy season in the desert, the Gila monster tracks down pooled rainwater to replenish its water supply for the coming weeks.  

DeNardo and his colleagues have been researching the Gila monster’s water reserves since the early 2000s, exploring how it uses its bladder to regulate dehydration through the summer.  


Read More: Evolutionary Insight: Inside the Brains of Reptiles and Amphibians


Gila Monsters Find Water in the Desert

(Credit: Vaclav Sebek/Shutterstock)

The lizard even has the ability to sense where water supplies are located, DeNardo says. In a study of dehydrated Gila monsters, DeNardo says his team found that they were able to detect chemical compounds in the air that could lead them to water. 

“There has to be some chemical in the water that is volatile and goes into the air, and the Gila monster can sense this,” he says. 

This unique trait, among many others, has led the Gila monster down a slightly different evolutionary path than other desert lizards. Yet with its large bladder for water storage and venomous bite, these lizards have the ability to both survive extremely dry weather and defend against predators. 

“We're looking at how dehydration influences performance,” DeNardo says. “They can tolerate dehydration, and they look fine, they're doing fine. But we've noticed there are physiological differences in their immune function, there's physiological differences in how warm they heat themselves up after they eat a meal.” 


Read More: These Rare Adaptations Help Animals Survive in the Desert


Are Gila Monsters Endangered?

Today, Gila monsters are still relatively common in the Sonoran Desert, although they’re officially classified as near threatened by the International Union for the Conservation of Nature. However, DeNardo suspects that their numbers could decline in the coming years due to climate change. 

“Our summers are going to get hotter. But more importantly, they're going to get longer before the monsoons start,” he says. “And so these animals are going to get more dehydrated.”  

Under dryer and dryer conditions, DeNardo predicts that animals that have evolved to survive on little water could fare better and adapt more quickly. But because the Gila monster relies on storing larger amounts of water, it could struggle to endure longer periods of dry weather. 

These qualities have evolved over millions of years, allowing the Gila monster’s genome to adapt slowly in response to gradual aridification. Yet with climate change causing rapid changes in weather, DeNardo says it’s crucial to track how these lizards adapt, and to increase conservation efforts to ensure their survival. 

“When it gets hot, they go underground," he says. "But is that going to be sufficient enough to get them through these drier times and not interfere with things such as food searching?"

“When you’re underground, you're not finding food or finding water, so it's okay to be underground escaping the heat," adds DeNardo. "But, at some point, you’ve gotta get out there.”  


Read More: What Is So Interesting About the Komodo Dragon?


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