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Vernacular Name GILA MONSTER

GEOGRAPHIC RANGE Southwestern U.S. and northwestern Mexico.

HABITAT Succulent desert and dry sub-tropical scrubland, hillsides, rocky slopes, arroyos and canyon bottoms (mainly those with streams).

CONSERVATION STATUS  IUCN: Near Threatened (2016).  Population Trend: Decreasing.  Threats: - illegal exploitation by commercial and private collectors. - habitat destruction due to urbanization and agricultural development.

COOL FACTS  Their common name “Gila” refers to the Gila River Basin in the southwest U.S.  Their skin consists of many round, bony scales, a feature that was common among dinosaurs, but is unusual in today's reptiles.  The Gila monster and the Mexican beaded lizard are the only lizards known to be venomous. Both live in North America.  Gila monsters are the largest lizards native to the U.S.  Gila monsters may bite and not let go, continuing to chew and, thereby, inject more venom into their victims. Venom is released from the venom glands (modified salivary glands) into the lower jaws and travels up grooves on the outside of the teeth and into the victims as the Gila monsters bite. The lizards lack the musculature to forcibly inject the venom; instead the venom is propelled from the gland to the tooth by chewing. Capillary action brings the venom out of the tooth and into the victim. Gila monsters have been observed to flip over while biting the victim, presumably to aid the flow of the venom into the wound.  Bites are painful, but rarely fatal to humans in good health. While the bites can overpower predators and prey, they are rarely fatal to humans in good health although humans may suffer pain, edema, bleeding, nausea and vomiting.  Their food requirements are reduced by a low metabolic rate, as well as the relatively cool body temperatures they maintain for most of the year. Gila monsters are able to survive for months without food as they store fat in their particularly large tails. Gila Monster 2/6

More than a dozen peptides and proteins have been isolated from Gila monsters’ venom. One of these, helodermin, has been shown to inhibit the growth of lung cancer.  In 2005 the U.S. Food and Drug Administration approved the drug exenatide (marketed as Byetta) for the management of type 2 diabetes. It is a synthetic version of a protein, exendin- 4 derived from the Gila monster’s saliva.  No other egg-laying lizard in North America over-winters their eggs and hatches them the following year like the Gila monster.  Among Native American tribes, Gila monsters had a mixed standing. The Apache believed that their breath could kill a man. Tonono O’Odham and the Pima believed that they possess a spiritual power that could cause sickness. In contrast, the Seri and the Yaqui believed that Gila monsters’ hides had healing properties.  Gila monsters have even starred as monsters in a B movie, The Giant Gila Monster .

DIET  In wild: small newborn mammals, lizards and birds, ground-nesting birds and lizards as well as eggs (of birds, lizards, snakes, turtles, tortoises) and carrion.  In zoo: dead mice and eggs.

MEDIAN LIFE EXPECTANCY  Male: unknown.  Female: unknown.

ENEMIES - DEFENSE  Enemies: feral or domesticated cats and dogs; humans.  Defense: - cryptic coloration; their black snout makes them difficult to see as they look out of their burrows. - if threatened, these lizards will back away hissing with their mouth wide open, and, if provoked, they will attack and bite surprisingly quickly. - their bites are mildly poisonous, secreting nerve-attacking venom into their mouths from large glands under their chins. Large, grooved lower teeth carry poison into bite wounds. Rarely fatal to healthy humans. Because their teeth are not directly connected with poison glands in their lower jaws, the lizards hang on when biting and chewing to allow venom to enter the wounds.

MATING - CARE OF THE YOUNG  Courting: during breeding season, males perform a series of ritualized wrestling matches, whereby combatants straddle each other and then perform a body twist in an effort to gain a superior position.  Mating: occurs usually in May, but may range during the late spring-summer months (Apr.- Jun.).  Copulation: the male tongue-flicks to seek a female’s scent while rubbing his cloaca on the ground. When a male locates a female, he lies by her and rubs his chin on her back and neck while holding her with his hindlegs. If a female objects to the male, she will try to bite him while crawling out from underneath. If receptive, she raises her tail. The male then moves his tail under hers, bringing their vents into contact. Copulation lasts from 30 minutes to an hour. Gila Monster 3/6

 Clutch: usually 5, range 1-12, eggs are laid in sandy soils, burrows or under rocks, normally from late-Jun. to mid-Aug. and unusually remain incubating underground throughout the winter  Incubation: an average of 10 months.  Hatchlings: emerge usually in May (range Apr-Jun.). Independent, they are able bite and inject venom upon hatching.  Sexual Maturity: 3-5 years.  Birthing Interval: every other year.

SOCIAL INTERACTION  Gila monsters are relatively social creatures. Studies have shown that they recognize and interact with many individuals throughout their home range and have been seen in shelters together in separate years.  In late April through late May, 6 or more individuals may occupy burrows at a time.

LIFE STYLE  Activity Period: diurnal.  Feeding: - they eat meals infrequently and can consume a meal of 33% of their body weight. - they often uses their tongues as feelers and to taste or lap up food. - they use their extremely acute sense of smell to locate prey, especially eggs. Their sense of smell is so keen that they can locate and dig up chicken eggs buried 5.9” deep and accurately follow a trail made by rolling an egg, - they use their powerful claws to dig out animals’ nests. - prey may be crushed to death if large or eaten alive. If small, prey may be swallowed head-first and helped down by muscular contractions and neck flexing. Prey are rarely envenomated. - unusually, after food has been swallowed, they immediately resume tongue flicking and search behavior, probably as result of a history of finding clumped prey, such as eggs and babies, in nests,  Locomotion: when they are active on the surface, they tromp with an awkward, lumbering gait.  They prefer staying under rocks in locations with ready access to moisture, in burrows of other animals and in holes they dig themselves. They avoid living in open areas such as flats and farmland.  Although Gila monsters have a low metabolism and one of the lowest and slowest lizard sprint speeds, they have one of the highest aerobic scope values (the increase in oxygen consumption from rest to maximum metabolic exertion) among lizards, which allows them to engage in intense aerobic activity for a sustained period of time. Observations indicate that males have a higher aerobic scope than females, presumably because of sexual selection for a trait advantageous in prolonged combat.  Gila monsters are mainly active during the 3-month period (Mar.-May) after they emerge from their late Nov.-Feb. hibernation.  They are active in the morning during the dry season (spring and early summer). Later in the summer they may be active on warm nights or after a thunderstorm. Gila Monster 4/6

 As an adaptation to their harsh desert environment, Gila monsters spend 95% of their time hidden underground within shelters (rocky crevices, burrows, trees) or mammal burrows hibernating during the winter and sheltering from the midday sun in the summer. Also, since water evaporates from their skin easily compared to other lizards, staying underground reduces rates of evaporation.  Generally the animals occupy 2 burrows over the course of a year, one from autumn through early spring and another during the warmer spring and summer months.  When active on the surface, they maintain a body temperature of about 86 degrees F and can travel long distances (more than 0.6 miles) in search of food and mates.  Gila monsters seem to like water and can be observed immersing themselves in puddles of water after a summer rain.

PHYSICAL  General Description: heavily built, cylindrical. Large and stout with a short, fat tail and broad head.  Size: head/body length, 10"-18" with maximum of 2’; tail, 50%-55% of body length.  Color: typically brown or black, often mottled with salmon. Black, orange, pink or yellow broken blotches, bars and spots, with bands extending onto its blunt tail. Head, chin, tail, neck, legs and feet: black.  Head: large with bead-like scales.  Scales: small, rounded, bead-like scales cover the body, tail and legs and gradually change to plates beneath.  Skin: their skin consists of several tiny beads, called osteoderms. Each bead contains a tiny piece of bone that gives them almost an armor-plated skin. They shed their skin in patches periodically.  Eyes: small, black.  Ears: opening is a narrow oblique or ovoid slit.  Nose: extremely acute sense of smell.  Tongue: broad, flat, slightly forked.  Teeth: most have 2 grooves that conduct the venom, a nerve toxin, from glands in the lower jaw. The toxin is not injected like that from a snake, but flows into the wound as the lizard chews on its victim. The teeth are loosely anchored, which allows them to be broken off and replaced throughout life.  Tail: short, fat. The tail stores fat. When food is scarce, they absorbs the fat in their tails as nourishment.  Legs: strong and stout forelegs.  Feet: 5 heavily clawed toes on each foot suitable for digging.

TAXONOMY Phylum / Subphylum Chordata / Vertebrata Class Reptilia Order Squamata Family Helodermatidae Genus / species Heloderma suspectum

 Its genus name, Heloderma , derives from the scales on its back. " Helos " means nail or stud. "derma" means skin. Gila Monster 5/6

 Its species name “ suspectum ” comes from its describer, paleontologist Edward Drinker Cope, who suspected that the lizard might be venomous due to the grooves in the teeth.

REFERENCES - Halliday, Tim and Kraig Adler. 1986 The Encyclopedia of Reptiles and Amphibians . New York: Facts on File. - Hammerson, G.A., Frost, D.R. & Gadsden, H. 2007. Heloderma suspectum. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.1. www.iucnredlist.org. Downloaded on 16 August 2012. - Murphy, James B. and Neil Schlager (eds). 2004 Grzimek’s Animal Life Encyclopedia . Vol. 7: Reptiles; Turtles & Tortoises to Lizards & Snakes. Farmington Hills, MI: The Gale Group. - Arizona-Sonora Desert Museum: www.desertmuseum.org/books/gila.html - Gila Monster: en.wikipedia.org/wiki/Gila_monster - Gila Monster: www.arkive.org › Reptiles - Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2008. The Animal Diversity Web (online). http://animaldiversity.org. - Stewart Stewart, M. 2003. "Heloderma suspectum" (On-line), Animal Diversity Web. http://animaldiversity.ummz.umich.edu/site/accounts/information/Heloderma_suspectum.htm l. - The IUCN Red List of Threatened Species. Version 2016.1. www.iucnredlist.org. Downloaded on 5 July 2016 .

Prepared by: Lourene Nevels and Judy Ehrman, docents Date: 05-16-10 Photo by: John Bernard, docent Map by: Dave Schaffer – Bob Sloane, docents Approved by PZ: Date: Reformatted by: Dave Schaffer, docent Date: 08-16-12 Gila Monster 6/6

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