The Gila monster is a species of venomous lizard

Lizard

Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...

 native to the southwestern United States

Southwestern United States

The Southwestern United States is a region defined in different ways by different sources. Broad definitions include nearly a quarter of the United States, including Arizona, California, Colorado, Nevada, New Mexico, Oklahoma, Texas and Utah...

 and northwestern Mexican state of Sonora

Sonora

Sonora officially Estado Libre y Soberano de Sonora is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided into 72 municipalities; the capital city is Hermosillo....

. A heavy, slow-moving lizard, up to 60 cm (2 ft) 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

Beaded lizard

The Beaded lizard is a species of venomous lizard found principally in Mexico and southern Guatemala. Along with its congener, the Gila monster , it is the only lizard to have evolved an overt venom delivery system, and has long been considered the only venomous lizard...

 (H. horridum). Though the Gila monster is venomous, its sluggish nature means that it represents little threat to humans.