12 Biting Facts About Gila Monsters


Its gnawing, long-lasting bites are incredibly painful, it's the largest native lizard in the United States, and its venom inspired a popular diabetes 2 medicine. Meet the Gila monster.


Our world is home to more than 4600 lizard species. Up until fairly recently, scientists believed that only two of these—the Gila monster and its close relative, the Mexican beaded lizard—produced venom. But it turns out that this talent is fairly widespread. During the mid-2000s, biochemist Bryan Fry identified venom-secreting glands within the mouths of various iguanas, alligator lizards, and monitor lizards. He discovered a terrifying fact: Apparently, the gigantic Komodo dragon (an extra-large monitor) is venomous as well.


Should you see one of these lizards in the wild, admire it all you like, but give the animal plenty of space. A frightened Gila monster will open its purple-gummed maw and hiss in a theatrical display that clearly says, “Back off!” But some people don’t get the message. When an aggressor fails to retreat, Gila monsters deploy their secret weapon—and the delivery method can be almost as painful as the toxin itself. In general, getting bitten by a venomous snake is a fairly quick process. A few serpents—like rattlers—have hollow fangs that act like syringes, pumping venom into the victim’s bloodstream. Others possess grooves on the sides of their teeth along which droplets of venom flow with surprising efficiency. Both methods allow most venomous snakes to inject their dangerous cocktails in a matter of seconds.

By comparison, a Gila monster’s technique is tortuously long. With its powerful jaws, the lizard will clamp down on the victim and keep its grip for up to 15 minutes at a time. All the while, it gnaws, which draws venom from storage glands situated in the lower jaw. Slowly, this substance moves along tooth grooves and enters the open wound. If you ever get bitten by a Gila monster, the worst thing you could do is lift it up off of the ground—this will only inspire the critter to hang on. Try dunking its head under some water instead.

Although bites are almost never fatal to human beings, they’re intensely painful. Furthermore, according to the Arizona Poison and Drug Information Center, “Victims may … experience localized swelling, nausea, vomiting, high blood pressure, weakness, faintness, excessive perspiration, chills, and fever. Some people have experienced severe reactions resulting in breathing difficulties.” Given the lizards’ passive disposition around people, though, they aren’t likely to lash out unless provoked. Tellingly, most reported bites occur on people’s hands, suggesting that the monster in question was being handled or prodded when it struck.


A Gila monster can’t lose and re-grow its tail (as many other lizards do), but the appendage is still very useful. Well-fed individuals maintain fat reserves inside their tails, which—in conjunction with a low resting metabolic rate—enables the venomous critters to survive on as few as three or four large meals per year.


Adult Gila monsters can measure a respectable 2 feet long and weigh 5 pounds or more. Not too shabby. Such proportions render this species larger than any other indigenous lizard within the U.S. However, Gila monsters would look puny next to invasive green iguanas and Nile monitors. Both animals now inhabit Florida and may grow to be more than 5 feet long.

If you’d like to observe one in its natural habitat, go west. Above the Mexican border, Gilas are most commonly encountered in southern, central, and western Arizona. The reptile most likely takes its name from the Gila River basin, which encompasses much of the Grand Canyon State. You might also find specimens in neighboring regions of California, Utah, Nevada, or New Mexico. In Mexico, meanwhile, Gilas frequent Sonora and western Chihuahua.


One might think that Gila monster venom makes for a useful hunting tool. But according to many herpetologists, it’s mostly reserved for self-defense purposes—the critters seldom envenomate their prey. That doesn't keep Gilas from catching and consuming small mammals, birds, and lizards. Another menu option is raw eggs, which the creatures really seem to relish. Smaller eggs are typically swallowed whole. On the other hand, really large ones—like those of desert tortoises—are a bit more challenging to devour. Usually, Gilas crack these eggs open and then lap up the contents with their forked tongues. In pursuit of eggs or hatchlings, the lizards may resort to climbing trees, ascending as high as eight feet off the ground in order to raid a vulnerable nest. Consider yourselves warned, desert birds.


Not all Gila monsters look alike. Newborns have a flashy color scheme that consists of alternating bands, half of which are black while the others range anywhere from pink to yellow to orange. Some individuals more or less keep this same pattern as adults. However, over time, other specimens start to adopt a more marbled appearance, with blotches of black haphazardly scattered across a vibrant orange background. The differences might be more than skin-deep: A few herpetologists believe that the two major varieties constitute separate subspecies, which are referred to as banded and reticulated Gila monsters, respectively.


The mating season for this species spans from April to July. It’s a time when the southwest plays host to grueling displays of strength known as Gila monster wrestling matches. Such contests are intense affairs, to say the least. When two adult males cross paths in late spring or early summer, there’s a good chance that the rivals will entwine their bodies and try to pin each other to the ground. After one of them succeeds, the contestants separate, but this doesn’t mean the fight is over. Daniel D. Beck—the world’s leading authority on Gila monsters—once observed a duel that went on for 13 individual rounds over a period of almost three hours. Such contests rage on until a participating lizard finally backs down.

To the victor go the spoils—namely, a desirable breeding territory. If the winner is especially lucky, his hard-won turf will encompass a fertile female’s shelter. However, she might not accept his advances. The male begins his breeding ritual by lying down alongside his prospective partner. Assuming she doesn’t try to ward off this Casanova by biting at him, the couple proceeds to wrap their tails together. Gila monster sex can last for more than an hour. Pregnant females usually lay one to 12 eggs in late July or August. Their broods hatch around 10 months later.


Out of sight, out of mind. Many people who live in Gila monster country never see one because the lizards rarely exit their shelters. According to Beck’s research, typical Gilas remain underground for more than 95 percent of their lives. Ideal abodes include abandoned mammal burrows, pack rat nests, and crevices beneath large rocks. Every year, they usually spend the equivalent of just three to four weeks on the surface. Such excursions tend to take place at night and occur most frequently in April and May.


In 1890, a Scientific American article wrongly claimed that Gilas have killer halitosis. “The breath is very fetid, and its odor can be detected at some little distance from the lizard,” read the piece. “It is supposed that this is one way in which the monster catches the insects and small animals which form a part of its food supply—the foul gas overcoming them.” Back in those days, Gila monsters were said to possess such atrocious breath because they allegedly lacked anuses. Therefore, it was reasoned, regurgitation must be the lizards’ only means of expelling waste, hence the odor. (For the record, that theory, too was mistaken: Gilas do in fact have anuses.) Such myths were commonplace during this period. Another popular yarn, to cite but one example, maintained that when a Gila monster bit someone, it wouldn’t let go until either sundown arrived or a thunderstorm rolled in.


The desert can be harsh. To cope with their arid environment, Gila monsters have evolved urine bladders that serve as reservoirs, storing up water for later use. During droughts, Gilas empty these organs, allowing the water kept therein to recirculate throughout the body. So far as we know, no other lizard species uses such a mechanism, although it has been found in certain turtles and amphibians. Because of this redistribution system, Gila monsters can go 81 days without drinking. But there is a trade-off: Full bladders often weigh the reptiles down, making them more vulnerable to predators.


Nearly 25 million Americans suffer from type 2 diabetes. Many of them can now say that their lives are a lot more manageable thanks, surprisingly enough, to Gila monster venom. In 1992, endocrinologist John Eng found that this dangerous substance contains a peptide he dubbed exendin-4. When introduced to the human bloodstream, the compound increases the production of insulin. Although our bodies release a similar hormone, enzymes in the blood usually degrade it in less than 2 minutes. On the other hand, exendin-4 can remain functional for hours on end.

Recognizing the peptide’s potential, Eng spearheaded an effort to synthesize exendin-4. Once this was achieved, the compound became the key ingredient in a drug known as Byetta. Approved by the FDA in 2005, Byetta is now a hugely popular medication for those with type 2 diabetes. As you might expect, Eng is now a passionate Gila monster fan. “It really is a beautiful lizard,” he once said. “Like many other animal species, it is under pressure from development and other environmental concerns. The question is, what other animal has something to teach us that can be of future value? And plants, too? We will never know their value if they are gone.”


Fans of Mystery Science Theater 3000 may be familiar with a 1959 drive-in classic titled The Giant Gila Monster. The picture stars a 70-foot Gila monster who roams the countryside gobbling up hitchhikers, truck drivers, and amorous teenagers. Like many giant creature films of yore, The Giant Gila Monster features a real animal—in this case, a lizard—plodding through miniature houses and streets. (Weren’t those the days, huh?) Ironically, the effects team used a Mexican beaded lizard for these scenes instead of an actual Gila. But maybe we should cut the filmmakers a little slack. In their defense, the Mexican beaded lizard is a very close relative of the Gila; both species belong to the same genus, and they have overlapping ranges. 

Andreas Trepte via Wikimedia Commons // CC BY-SA 2.5
Climate Change Has Forced Mussels to Toughen Up
Andreas Trepte via Wikimedia Commons // CC BY-SA 2.5
Andreas Trepte via Wikimedia Commons // CC BY-SA 2.5

Researchers writing in the journal Science Advances say blue mussels are rapidly evolving stronger shells to protect themselves against rising acid levels in sea water.

Bivalves like mussels, clams, and oysters aren’t good swimmers, and they don’t have teeth. Their hard shells are often the only things standing between themselves and a sea of dangers.

But even those shells have been threatened lately, as pollution and climate change push the ocean's carbon dioxide to dangerous levels. Too much carbon dioxide interferes with a bivalve’s ability to calcify (or harden) its shell, leaving it completely vulnerable.

A team of German scientists wondered what, if anything, the bivalves were doing to cope. They studied two populations of blue mussels (Mytilus edulis): one in the Baltic Sea, and another in the brackish waters of the North Sea.

The researchers collected water samples and monitored the mussel colonies for three years. They analyzed the chemical content of the water and the mussels’ life cycles—tracking their growth, survival, and death.

The red line across this mussel larva shows the limits of its shell growth. Image credit: Thomsen et al. Sci. Adv. 2017

Analysis of all that data showed that the two groups were living very different lives. The Baltic was rapidly acidifying—but rather than rolling over and dying, Baltic mussels were armoring up. Over several generations, their shells grew harder.

Their cousins living in the relatively stable waters of the North Sea enjoyed a cushier existence. Their shells stayed pretty much the same. That may be the case for now, the researchers say, but it definitely leaves them vulnerable to higher carbon dioxide levels in the future.

Inspiring as the Baltic mussels’ defiance might be, the researchers note that it’s not a short-term solution. Tougher shells didn’t increase the mussels’ survival rate in acidified waters—at least, not yet.

"Future experiments need to be performed over multiple generations," the authors write, "to obtain a detailed understanding of the rate of adaptation and the underlying mechanisms to predict whether adaptation will enable marine organisms to overcome the constraints of ocean acidification."

University of Adelaide
Scientists Find Potential Diabetes Drug in Platypus Venom
University of Adelaide
University of Adelaide

The future of diabetes medicine may be duck-billed and web-footed. Australian researchers have found a compound in platypus venom (yes, venom) that balances blood sugar. The team published their results in the journal Scientific Reports.

So, about that venom. The platypus (Ornithorhynchus anatinus) may look placid and, frankly, kind of goofy, but come mating season, the weaponry comes out. Male platypuses competing for female attention wrestle their opponents to the ground and kick-stab them with the venom-tipped, talon-like spurs on their back legs. It’s not a pretty sight. But it is an interesting one, especially to researchers.

Animal venoms are incredible compounds with remarkable properties—and many of them make excellent medicine. Many people with diabetes are already familiar with one of them; the drug exenatide was originally found in the spit of the venomous gila monster. Exenatide works by mimicking the behavior of an insulin-producing natural compound called Glucagon-like peptide 1 (GLP-1). The fact that the lizard has both venom and insulin-making genes is not a coincidence; many animal venoms, including the gila monster’s, induce low blood sugar in their prey in order to immobilize them.

It’s a good strategy with one flaw: GLP-1 and compounds like it break down and stop working very quickly, and people who have trouble making insulin really need their drug to keep working.

With this issue in mind, Australian researchers turned their attention to our duck-billed friends. They knew that platypuses, like people, made GLP-1 in their guts, and that platypuses, like gila monsters, make venom. The real question was how these two compounds interacted within a platypus’s body.

The researchers used chemical and genetic analysis to identify the chemical compounds in the guts and spurs of platypuses and in the guts of their cousins, the echidnas.

They found something entirely new: a tougher, more resilient GLP-1, one that breaks down differently—and more slowly—than the compounds in gila monster spit. The authors say this uber-compound is the result of a "tug of war" between GLP-1’s two uses in the gut and in venom.

"This is an amazing example of how millions of years of evolution can shape molecules and optimise their function," co-lead author Frank Gutzner of the University of Adelaide said in a statement.

"These findings have the potential to inform diabetes treatment, one of our greatest health challenges, although exactly how we can convert this finding into a treatment will need to be the subject of future research."


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