Heloderma horridum

The Mexican beaded lizard (Heloderma horridum) or beaded lizard is a species of venomous lizard in the family Helodermatidae, one of the two species of venomous beaded lizards found principally in Mexico and southern Guatemala. It and the other members of the same genus, including the Gila monster (Heloderma suspectum), are the only lizards known to have evolved an overt venom delivery system. The Mexican beaded lizard is larger than the Gila monster, with duller coloration, black with yellowish bands. As it is a specialized predator that feeds primarily upon eggs, the primary use of its venom is still a source of debate among scientists. This venom has been found to contain several enzymes useful for manufacturing drugs in the treatment of diabetes, and research on the pharmacological use of its venom is ongoing.

Threatened throughout its range by overcollection and habitat loss, it is a CITES protected species. The Guatemalan beaded lizard (H. charlesbogerti) is one of the rarest lizards in the world, with a wild population of fewer than 200.