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Gila Monster and Mexican Beaded Lizard: Helodermatidae

Gila Monster (heloderma Suspectum): Species Account

Physical characteristics: The Gila monster is a slow-moving, heavy-bodied lizard with rather short, clawed arms and legs and upper skin that looks beaded. The beads are actually rounded scales that appear on the top of the head, back, tail, and limbs and down the sides of the body. The color of the skin and scales differs from individual to individual, but most have at least some pattern, which can be quite bright and beautiful, of squiggles, spots, blotches, circles, and bands. Colors range from pink, orange, and yellow to black and dark gray. Well-fed Gila monsters have thick tails, which store fat. This species and the Mexican beaded lizard are the only two venomous lizards in the world. Adult Gila monsters commonly grow to about 20 inches (50 centimeters) in length from head to tail tip.

Geographic range: The Gila monster makes its home in the southwestern United States and in Sonora, Mexico.

Gila monsters need to eat only three large meals a year to survive. (Joe McDonald/Bruce Coleman, Inc. Reproduced by permission.)

Habitat: Gila monsters live in warm habitats, including deserts, grasslands, and shrubby forests, sometimes on flat ground and sometimes on hillsides. They spend most of their time in underground burrows, inside large cracks in rocks, or in other hiding places, only coming above ground for about one hour a day.

Diet: Gila monsters need to eat only three large meals a year to survive. They store fat in the tail and then use it up between meals, which can be several months apart. Their favorite foods include lizard, snake, and bird eggs, as well as young cottontail rabbits and rodents.

Behavior and reproduction: They remain in burrows or other hiding places for all but about one hour a day when they venture out to look for food or mates. If they feel threatened, they will hiss and sometimes snap at or bite the attacker. Once they bite, they have a very strong grip and may hold it for five minutes or longer. Males and females court and mate from late April to early June, and in July and August the females lay eggs in a damp sand nest. Babies are about 6.5 inches long from snout to tail tip when they hatch.

Gila monsters and people: A Gila monster bite can be painful, but it is almost never fatal to humans. The last reported death from a bite occurred in 1930. Bites rarely happen, however, and usually result from a person's carelessness in picking up the lizard.

Conservation status: The World Conservation Union (IUCN) considers the species to be Vulnerable, which means that it faces a high risk of extinction in the wild. Habitat loss and illegal collection are the main problems the lizards face. ∎



Badger, D. Lizards: A Natural History of Some Uncommon Creatures— Extraordinary Chameleons, Iguanas, Geckos, and More. Stillwater, MN: Voyageur Press, 2002.

Brown, David E., and Neil B. Carmony. Gila Monster: Facts and Folklore of America's Aztec Lizard. Salt Lake City, UT: University of Utah Press, 1999.

Campbell, Jonathan A., and William W. Lamar. The Venomous Reptiles of Latin America. Ithaca, NY: Comstock Publishing Associates, 1989.

Lowe, Charles H., Cecil R. Schwalbe, and Terry B. Johnson. The Venomous Reptiles of Arizona. Phoenix: Arizona Game and Fish Department, 1986.

Martin, James, and Joe McDonald. Poisonous Lizards: Gila Monsters and Mexican Beaded Lizards. Minneapolis, MN: Capstone Press, 1999.

Mattison, Chris. Lizards of the World. New York, NY: Facts on File, 1989.

Web sites

"Gila Monster." Animal Planet: Corwin's Carnival of Creatures. http://animal.discovery.com/fansites/jeffcorwin/carnival/lizard/gilamonster.html (accessed on October 16, 2004).

"Gila Monster." Enchanted Learning. http://www.enchantedlearning.com/subjects/reptiles/lizard/Gilamonster.shtml (accessed on October 16, 2004).

"Gila Monster." WhoZoo. http://www.whozoo.org/anlife2000/jamiebritt/gilaindexrev.html (accessed on November 3, 2004).

"Mexican Beaded Lizard." Lincoln Park Zoo. http://www.lpzoo.com/tour/factsheets/herps/beaded_lizard.html (accessed on October 16, 2004).

Additional topics

Animal Life ResourceDinosaurs, Snakes, and Other ReptilesGila Monster and Mexican Beaded Lizard: Helodermatidae - Physical Characteristics, Diet, Behavior And Reproduction, Gila Monsters, Mexican Beaded Lizards, And People - GEOGRAPHIC RANGE, HABITAT, CONSERVATION STATUS