The Four Sub-Species of
Heloderma horridum

A full grown Heloderma Horridum Exasperatum (Beaded Lizard)

The Mexican Beaded Lizard is one of only two venomous lizards in the world, the other being the Gila Monster (Heloderma suspectum). It’s latin name consists of the two words Heloderma horridum. Heloderma, meaning studed skin, and horridum, meaning horrible (horrible studded lizard). This seems quite a fitting name for this unique animal, although I don't think they're horrible at all. Heloderm lizard's skin consists of several tiny beads called ostioderms. Each bead contains a tiny piece of bone that gives them almost an armor plated skin.

The lifespan of these lizards is said to be around thirty years, although in my opinion it’s more like fifty. For females, average adult size is 30in and three and a half to five pounds. For males, average adult size is 36in and five to six pounds. Exceptionally large males can reach 40in and close to ten pounds.

Most Beaded Lizards reach sexual maturity at two and a half to three years old. Once oviposition occurs, the incubation period is around 165 to 215 days. At about that time the hatchlings will pip their head out of the egg. It usually takes two or three days for them to come all the way out, absorbing their yolk sack and ingesting the liquid content of their egg. Newly hatched neonates are usually five to six inches and weigh around 40 grams. Until the animals are substantial in size, sexing is nearly impossible. Males generally have much broader heads and longer necks, with females having narrower heads and shorter necks, although there’s always exeptions to every rule.

A picture of a Heloderma horridum alvarezi. Photograph credit: Dennis Sheridan

Types of Beaded Lizards

Class: Reptilia Order: Squamata Family: Helodermatidae
• Heloderma horridum horridum
• Heloderma horridum charlesbogerti
• Heloderma horridum alvarezi
• Heloderma horridum exasperatum
Only the horrdium and exasperatum types are bred in the United States by private individuals. The charlesbogerti type has been bred by the San Diego Zoo.


From top to bottom: An adult, a two year and a yearling	Size Comparison: Male on the left, Female on the right

The animals originate in the Pacific Drainages from Southern Sonora, Mexico to Southwestern Guatemala and two Atlantic drainages, from Central Chiapas, Mexico to Southeastern Guatemala. Habitat is primarily tropicial deciduous forest and thorn scrub forest, also found in pine-oak forest, with elevations from sea level to 1500 meters. In the wild, the animals are only active from April to mid-November. They spend only about an hour per day above the ground, and their natural diet is consistent of reptile and bird eggs and occasionally small mammals. The lizard uses its venom primarily as a defensive weapon. (Johnson, J. P. and C. Ivanyi, 2001. North American Regional Beaded Lizard Studbook. 3rd Edition. Arizona-Sonora Desert Museum.)


H.h. exasperatum habitat - Southern Sonora, Mexico Photography by C.M. Gienger	A Rio Fuerte beaded lizard in climbing a tree. Photography by C.M. Gienger

The venom glands are located in the lower jaw. At the base of each tooth is a grooved pit for venom delivery. The venom is delivered by the lizard by a chewing motion, a rather crude delivering device. The bite from an animal is extremely painful and can be potentially fatal, but this is only in extremely rare cases. See Bob Applegate's website for an actual bite account.


A pair of Heloderma horridum exasperatums mating.	Heloderma horridum Eggs with hatchlings starting to pip.

The jaw of a Gila Monster, very similar to Beaded Lizards

To the left: A tooth of a Heloderma horridum, notice the pit in the tooth.
To the right: The Jaw of a Gila Monster (Similar to a Beaded Lizard)
Both drawings come from Bogart and Del Campo's The Gila Monster and Its Allies and were drawn by S.B. McDowell ©1956

The Four Sub-Species of Heloderma horridum

Types of Beaded Lizards

The Four Sub-Species of
Heloderma horridum