Gila monsters have remained essentially unchanged since dinosaurs roamed the world.The Gila monster and its cousin, the Mexican beaded lizard, are the world’s only two dangerously venomous lizards. Unlike venomous snakes, who use venom primarily for dispatching prey, Gila monsters’ venom is for self-defense. There are two subspecies, the reticulate Gila monster and the banded Gila monster, which differ mainly in the regions they occupy.

Living Fossils

The genus name Heloderma comes from Greek and means “studded skin.” The Gila monster’s beaded skin is unusual among modern reptiles, but it was common among dinosaurs millions of years ago. The ancestors of Gila monsters have been traced back to the Cretaceous Period. Despite some evolutionary modifications, not much has changed between those lizards and the Gila monsters surviving today. For this reason, Gila monsters are often seen as living fossils, giving scientists an up close and personal look at life in the time of the dinosaurs. Gila monsters, along with their relatives, Mexican beaded lizards, are the world’s only two dangerously venomous lizards.


According to the International Union for Conservation of Nature (IUCN), the Gila monster is listed as Near Threatened. They are sometimes killed out of fear of their poisonous bite; however, the most likely reason for their decline in population comes from habit loss due to overdevelopment. There is also a small, illegal pet trade for Gila monsters, although they are protected by state laws.


Gila monsters are found in the southwestern United States and northwestern Mexico. They live in arid regions, although they prefer to stay near moisture. They are found in succulent desert areas as well as canyons and arroyos. Gila monsters spend a lot of time in underground burrows as well. During the winter they hibernate to escape the cold desert conditions, and during the summer they spend midday underground to avoid the harsh desert sun.


The primary food source of the Gila monster is eggs of birds, lizards, snakes, turtles, and tortoises. They will also occasionally dine on small mammals, birds and lizards. A Gila monster will smell out its prey by flicking its tongue, which provides it with an excellent sense of smell. Gila monsters tend to go long periods without consuming any food, so they will often fill up when they choose to eat. After eating such large quantities of food, they can store a considerable amount of fat in their tails. This fat will provide them with energy in the future.


A Gila monster is distinguished by its yellow, pink, and black beaded scales. Its broad head and neck are generally black, along with its legs and clawed feet. The black and pink or yellow will form stripes or spots along the body, usually followed by a striped tail. Its body is very large and stout, accompanied by a short, fat tail. Adult Gila monsters will grow to be about 20 inches long. This stocky body does not allow it to sprint very fast, which is part of the reason they are not considered very threatening to people. However, Gila monsters do have great endurance, particularly the males. This may be in part because the males have been known to wrestle with each other for hours, competing for dominance and a better chance at reproductive success.