Gila monster

• 1. Introduction

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  The Gila monster, a stocky desert lizard of the American Southwest, once drew a crowd in Tombstone, Arizona, with nothing more than a newspaper notice. The Tombstone Epitaph wrote about a specimen that a local man had caught on the 14th of May 1881 on the road to Grand Central Mill. The paper declared it "no baby at that" and guessed it was probably the largest ever captured in Arizona. At 27 inches long, it went on show at Kelley's Wine House on Allen Street, near the Grand Hotel. Readers from the East were told to inspect "his Aztecship" now, in case they stumbled across one later and got badly frightened. That fright has followed the animal ever since. It is a heavy, slow-moving reptile, and it is the only venomous lizard native to the United States. Its name still makes people flinch. So how dangerous is it really? What does a creature that rarely hurries actually do with its days? And how did a venom once feared across the frontier end up helping people manage a modern disease?

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• 2. Studded Skin

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  The scientific name Heloderma is Ancient Greek for studded skin. It joins helos, the head of a nail or stud, with derma, meaning skin. The common name points to the Gila River Basin in Arizona and New Mexico, where the lizard was once plentiful. The species name suspectum comes from its describer, the paleontologist Edward Drinker Cope. Cope first treated the new specimen as a northern variant of the beaded lizard already known from Mexico. Then he noticed grooves in its teeth and suspected it might be venomous.

  A typical adult measures 26 to 36 cm from snout to vent. Its tail adds roughly 20% to the body size, and the largest animals reach 51 to 56 cm in total length. Most weigh between 550 and 800 g. That makes it the largest living lizard native to North America north of the Mexican border. It has a stout snout, a massive head and small-looking eyes that a nictitating membrane can shield.

  The scales of the head, back and tail hide little pearl-shaped bones called osteoderms. The belly scales have none. Adults show yellow to pink markings on black, though lizards living among darker rocks can look darker overall. Hatchlings begin with a plain, uniform pattern, and it changes sharply within their first 6 months. Females shed in one go for about 2 weeks before laying eggs, often in one large piece. Adult males usually shed in smaller segments during August. Telling the sexes apart takes experience, although males often have larger, more triangular heads.

  Four living relatives share the family, and all are beaded lizards. Three live in Mexico: Heloderma exasperatum, Heloderma horridum and Heloderma alvarezi. A fourth, Heloderma charlesbogerti, lives in Guatemala. The family line reaches back to the Cretaceous, when Gobiderma pulchrum and Estesia mongolensis lived. The genus Heloderma itself dates to the Miocene, represented by H. texana. Because these lizards have changed so little in form, they are sometimes called living fossils. They look like cousins of the monitor lizards of Africa, Asia and Australia. Yet the wide gap in geography and their distinct features put them in a family of their own. The most recent trace of the Gila monster's own ancestors turned up near Las Vegas, Nevada, where osteoderm fragments sat in deposits 10,000 to 8,000 years old.

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• 3. Life Underground

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  Roughly 90% of a Gila monster's life passes in burrows or rocky shelters. The lizard lives in scrubland, succulent desert and oak woodland, and it avoids open flats and grasslands. Many of its shelters sit in Navajo Sandstone or basaltic lava flows. Water matters to it, and animals have been seen standing in puddles after a summer rain. No records exist from Baja California.

  A study of a population in southwestern Utah showed how little time the animals spend above ground. Activity peaked from late April to mid June. Across an active season of about 90 days, a lizard was out and about on only ten of them. A typical outing covered 210 m, though a few animals travelled more than 1 km. Until early summer the lizards move to a different shelter every 4 to 5 days, which helps them find a suitable microclimate. They come out in the morning during the dry spring and early summer. Later in the year they may roam on warm nights or after a thunderstorm. Their surface body temperature sits near 30 C. Close to 37 C, limited evaporation through the cloaca can cool them by up to 2 °C.

  The desert has shaped their body in quieter ways too. A slow metabolism lets a Gila monster use less than half the energy expected for a lizard its size. It stores water in its urinary bladder and reabsorbs it through the bladder wall. Fat accumulates in the tail. That reserve explains the feeding pattern, since three to four large meals in spring are claimed to power a whole season. Young animals can swallow up to half their body weight in one sitting, and adults up to a third.

  The menu runs from young rabbits, hares, mice and ground squirrels to small birds, snakes, lizards, frogs and insects. Carrion and the eggs of birds, lizards, snakes and tortoises are also on it. A very acute sense of smell does the searching. The forked, black-blue tongue gathers scent molecules and carries them to the Jacobson organ in the roof of the mouth. Large prey may be crushed to death, while other prey is eaten alive, usually head first, with muscle contractions and neck flexing pushing it down. Afterward the lizard may flick its tongue again at once, looking for eggs or young in the same nest. It can also climb trees, cacti and even fairly straight, rough walls.

  Speed is not its strength. It is one of the slowest lizard sprinters, yet its endurance and maximal aerobic capacity are high compared with other lizards. That stamina matters when predators such as coyotes, badgers and raptors are around. Hatchlings face snakes, including kingsnakes, and a battle of stamina of another kind awaits adult males in the breeding season.

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• 4. Venom Machinery

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  Snakes make venom in glands behind the eyes, but the Gila monster makes it in modified salivary glands at the tips of its lower jaws. It has no strong muscle around the gland to squeeze the venom out. Instead, a tube leads the venom to the base of the lower teeth. Capillary action then draws it into two grooves along each tooth, and chewing works it into the victim. The teeth are firmly anchored to the jaw. When one breaks or wears out, the tooth behind it moves forward, and the lizard replaces teeth throughout its life.

  Bright colors may warn predators away from an animal that can inflict great pain. The diet backs up that idea. Because the lizard mostly eats eggs and small, helpless animals, researchers think the venom evolved for defense rather than for hunting.

  More than a dozen peptides and other substances have been isolated from the venom. They include hyaluronidase, serotonin, phospholipase A2 and several kallikrein-like glycoproteins. The glycoproteins account for the pain and swelling of a bite, and they do so without causing compartment syndrome. Four potentially lethal toxins have also been found, and they cause bleeding in internal organs and bulging of the eyes. A further toxin, helothermine, causes lethargy, partial paralysis of the limbs and a drop in body temperature in rats.

  In February 2024, a Colorado man died after a pet Gila monster held on to him for 4 minutes. An autopsy attributed the death to the bite and its venom. The source counts it as the only confirmed fatality since 1930. Earlier deaths were rare, and they involved adults who had been drinking heavily or whose treatment had been mismanaged. For a healthy adult the venom is normally not fatal, but the experience is brutal. Symptoms include excruciating pain, swelling and weakness as blood pressure drops quickly.

  The lizard bites fast and may not let go without help. A victim may submerge it in water or pry its jaws open with a knife or stick. Yanking it free is risky, because its sharp teeth can cause severe lacerations. The YouTuber Coyote Peterson described the bite as "like hot lava coursing through your veins". He called it "the worst pain he had ever experienced". It is generally regarded as the most painful venom made by any vertebrate.

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• 5. Frontier Fears

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  On the 8th of May 1890, southeast of Tucson in Arizona Territory, Walter Vail, owner of the Empire Ranch, caught what he thought was a dead Gila monster. He tied it to his saddle. It bit the middle finger of his right hand and would not let go. A ranch hand pried its mouth open with a pocket knife, cut the finger to make it bleed, and tied saddle strings around finger and wrist. They summoned Dr. John C. Handy of Tucson, who took Vail back to town. Vail's throat glands stayed swollen and bleeding for some time afterward.

  Dr. George Goodfellow of Tombstone, a friend of Handy, became one of the first to study the real effects of the venom. Pioneers on the frontier believed the lizard's breath was foul and toxic and its bite fatal. Scientific American printed a report in 1890 saying the breath was fetid and could overcome insects and small animals. Goodfellow offered local residents $5.00 for each specimen, bought several and collected more himself. In 1891 he deliberately provoked a captive lizard into biting his finger. The bite made him ill and he spent five days in bed, yet he recovered completely. When the magazine ran another report claiming the lizard could kill people, he wrote back with his own experience. He knew several people who had been bitten and had not died.

  Other tall tales outlived him. People said the lizard could spit venom like a spitting cobra, or leap several feet through the air to attack. Another story held that it had no anus and expelled waste through its mouth. That tale may trace to the venom's intense, specific smell.

  Native American peoples held varied views. The Apache believed its breath could kill a man. The Tohono O'Odham and the Pima thought it carried a spiritual power that could cause sickness. The Seri and the Yaqui, by contrast, credited its hide with healing properties. The Navajo, or Dine, believe the Gila monster was the first medicine man.

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• 6. Medicine from Venom

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  In 2005, the U.S. Food and Drug Administration approved a drug called exenatide, sold as Byetta, for managing type 2 diabetes. Exenatide is a synthetic modification of exendin-4, a protein first isolated from Gila monster venom. Exendin-4 is specific to Heloderma suspectum. It is one of several bioactive peptides in the venom that have drawn the most attention, along with helodermin, helospectin and exendin-3.

  The lizard protein works because it is 53% identical to a human hormone called GLP-1, which the digestive tract releases. GLP-1 helps regulate insulin and glucagon. It also raises insulin secretion and boosts the growth and survival of beta cells. The lizard version lasts much longer in the body than the human hormone. With a sustained-release injection formula, a single dose helps diabetics hold their blood glucose steady for a week. A 3-year study of people with type 2 diabetes found healthy, sustained glucose levels on exenatide. The drug also slows the emptying of the stomach and lowers appetite, which contributes to weight loss.

  Exendin-4 became the basis for a whole class of medicines, the GLP-1 receptor agonists. They are used for type 2 diabetes and for obesity and metabolic syndrome.

  Some other venom peptides act like vasoactive intestinal peptide, or VIP. VIP relaxes smooth muscle and regulates water and electrolyte secretion between the small and large intestines. These peptides can bind to VIP receptors in many human tissues. One of them, helodermin, has been shown to inhibit the growth of lung cancer cells in vitro.

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• 7. The Hatching Mystery

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  On the 28th of October 2016, a backhoe was digging beside the outer walls of a house in a suburb of northern Tucson. It scooped up a Gila monster nest holding five eggs that were in the middle of hatching. That accident ended decades of speculation. One theory had held that young hatch in the fall and stay underground. A second proposed that a nearly developed embryo waits inside the egg through winter and hatches in spring. Hatchlings had been seen on the surface from the end of April to early June, weighing about 35 g. The backhoe find showed they hatch near the end of October. They go straight into hibernation and reappear in May and June, when prey should be plentiful.

  The cycle starts in early March, when adults emerge from brumation. They mature sexually at 4 to 5 years old and mate in April and May. A male begins courtship by flicking his tongue to find the female's scent. If she is not interested, she bites him and chases him off. In captivity, successful mating has lasted from 15 minutes to two and a half hours. Only a single attempt outside a shelter has ever been recorded. The female lays eggs from the end of May into June. A clutch can reach eight eggs, though more than six is rare. Incubation in captivity takes about 5 months, depending on temperature. The newborns are about 16 cm long and can bite and inject venom from the moment they hatch.

  Males also wrestle during the mating season. The dominant male lies on top of the other and pins him with his front and hind limbs. Both arch their bodies, push and twist, each trying to win the top position. A bout ends when the pressure gives out, and it may start again. Males with more strength and endurance are thought to father more young. That fits the animal's high aerobic scope, the rise in oxygen use from rest to full effort, which is among the highest of any lizard. It allows sustained, intense exertion despite a low metabolism.

  Summer brings less time on the surface, as the lizards avoid the hottest weeks. Females that have laid eggs are exhausted and thin, and they must work hard to rebuild their reserves. Brumation begins again in October. In captivity, a Gila monster can live up to 40 years.

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• 8. Neighbors and Mascots

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  In 1952, the Gila monster became the first venomous animal in the world to receive legal protection. Today it is protected in every state of its range, and international trade falls under Appendix II of CITES. The IUCN lists it as near threatened, while NatureServe calls it Apparently Secure. Even so, in Arizona it is sometimes killed despite state law.

  Habitat loss from construction and farmland is considered perhaps the greatest threat to the whole family. Moving a lizard out of the way can seem kind, but it often backfires. Animals relocated up to 1.2 km tend to return to where they were found within 2 months. The trek costs up to five times their normal energy use and leaves them more exposed to predators. Animals moved much farther may become disoriented, and their survival is doubtful. A better approach, according to the source, is teaching residents about the lizard's limited toxicity and lifestyle, so people tolerate it or even take pride in such a unique roommate.

  Captivity has been a separate challenge. In 1963, the San Diego Zoo became the first zoo to breed Gila monsters successfully. In the last two decades, experienced breeders have passed on their knowledge to other herpetologists struggling with Heloderma reproduction.

  In fiction, the lizard has played the villain. The film The Giant Gila Monster starred a monster that was actually portrayed by a Mexican beaded lizard. The animal had a minor role in The Treasure of the Sierra Madre. Brock Brower's 1971 novel The Late Great Creature gives its fictional horror star, Simon Moro, fame for playing the reptilian Gila Man. In the 2011 animated film Rango, Ray Winstone voices a Gila monster outlaw named Bad Bill.

  The lizard has also become a mascot and a symbol. Eastern Arizona College in Thatcher has Gila Hank, a gun-toting Gila monster in a cowboy hat. In 2017, the Vegas Golden Knights chose a Gila monster named Chance as their mascot. Utah named it the official state reptile in 2019. In 2023, the Australian band King Gizzard and the Lizard Wizard released a single called "Gila Monster" from the album PetroDragonic Apocalypse. The album's cover features the lizard, and it runs through the album's concept narrative.

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