The GILA monster is a venomous lizard native to the southwestern United States and northwestern Mexico. It is the only venomous lizard native to the United States, and one of only 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 coloration and black markings. Its venom is delivered through grooved teeth in its lower jaw, and can cause intense pain and swelling.