Gila monster Gila monster The Gila monster ("Heloderma suspectum", ) is a species of venomous lizard native to the southwestern United States and northwestern Mexican state of Sonora. A heavy, typically slow-moving lizard, up to long, the Gila monster is the only venomous lizard native to the United States and one of only two known species of venomous lizards in North America, the other being its close relative, the Mexican beaded lizard ("H. horridum"). Although the Gila monster is venomous, its sluggish nature means it represents little threat to humans. However, it has acquired a fearsome reputation, and is sometimes killed despite
Mexican beaded lizard back to the Cretaceous period. The genus "Heloderma" has existed since the Miocene, when "H. texana" ranged over most of North America. Because the helodermatids have remained relatively unchanged morphologically, they are occasionally regarded as living fossils. Although the beaded lizard appears closely related to the monitor lizards (varanids) of Africa, Asia, and Australia, the wide geographical separation and unique features not found in the varanids indicate the beaded lizard is better placed in a separate family. The species was first described in 1829 by Arend Wiegmann as "Trachyderma horridum", but he renamed it "Heloderma horridum" six months later. Its