The GILA monster is a species of venomous lizard native to the Southwestern United States and parts of Mexico. It is the only venomous lizard native to the United States, and is one of two species of venomous lizards in North America. The GILA monster is a large lizard, growing up to 24 inches in length, and is characterized by its bright orange or yellow coloring and black markings. It is a slow-moving creature, and feeds mainly on small mammals, birds, and eggs.