The beaded lizard or Mexican beaded lizard (Heloderma horridum) is found in Guatemala and Mexico. Along with its close cousin, the Gila monster (Heloderma suspectum), they are known as one of the two venomous lizards in the world. Their venom is similar to that of some snakes (e.g., the western diamondback rattler). There are a number of subspecies, including H. h. exasperatum, H. h. alvarezi, and H. h. horridum. Adult Mexican beaded lizards range from 30 to 36 inches (76 to 91 cm) in length. They are substantially larger than their relative the gila monster, which only reaches lengths of 12 to 16 inches. Sometimes the two species are confused, but the size of the beaded lizard is an easy way to determine the difference.
This species is found in at low to moderate elevations in the Pacific foothills of Mexico from southern Sonora to Chiapas, and along the Pacific drainages in southeastern Guatemala (Departamento de Santa Rosa). It has an elevational range of around 400 to 1,000 m asl.
This lizard is most regularly encountered in tropical deciduous forest, but can also be found in thorn forest, tropical scrubland, and low elevation oak forest. It does not seem to be present in disturbed areas.
This species is protected by Mexican law under the category A (Threatened), and it has been recorded from several protected areas. In Guatemala it is protected by national legislation, with part of the species range within protected areas. It is listed on Appendix II of CITES. Additional research is needed into the taxonomic status, distribution and threats to this species.