Gila Monster and Mexican Beaded Lizard: Helodermatidae

The two species in this family, the Gila monster and the Mexican beaded lizard, are both large, heavy-bodied lizards coated with small, rounded bumps that look like the beadwork on clothing. The bumps, which are actually pebblelike scales, cover the tops of the arms, legs, head, and tail, as well as the back and sides of the body. These lizards have rather short, but strong arms and legs and long, thin claws. The tail may be thin or thick, depending on how well-fed the individual is. This is because these lizards store fat in their tails. Beaded lizards have slightly longer tails than the Gila monsters. An average beaded tail is at least two-thirds the length of the entire body, but the typical Gila tail is about half the total body length. Unlike many other lizards, these two species also have thick, forked tongues. Members of the same species can look very different from one another. Some adults are brightly patterned, while others are faded and dull. The patterns may be made up of spots, blotches, circles, bands, or squiggles on a background of pink, orange, yellow, dark gray, or black. Juveniles are usually banded.

Gila monsters and Mexican beaded lizards are the only two venomous (VEH-nuh-mus) lizards in the world. Unlike venomous snakes that deliver venom from the upper jaw and through grooves in just the two fangs, these lizards store their venom in the lower jaw and deliver it through grooves in numerous teeth.

Adult Gila monsters and beaded lizards range from 12 to 18 inches (30 to 45 centimeters) from the snout to the vent, which is a difficult-to-see opening on the underside of the lizard at the beginning of the tail, or 14 to 39 inches (35 to 100 centimeters) from the snout to the tip of the tail. They weigh 1.0 to 4.4 pounds (450 grams to 2 kilograms). The beaded lizard can grow larger than the Gila monster.