Species Fact Profile: Mexican Beaded Lizard (Heloderma horridum)

                                                      Mexican Beaded Lizard

                                           Heloderma horridum (Wiegmann, 1829)

Range:  Central and Western Mexico, Northern Central America 

Habitat: Semi-Arid Grasslands, Desert, Scrub Forest, Sea Level to 1500 Meters

Diet:  Small Mammals, Birds, Lizards, Frogs, Insects, and (especially) Eggs

Social Grouping: Solitary

Reproduction:  Reach sexual maturity at two and a half to three years old.  Breeding season is February through March.  Copulation lasts 30-60 minutes.  Female lays 3-13 elongated eggs about two months later, buried in a hole 10-15 centimeters deep, then left on their own.  Eggs hatch at about 6 months.  Young are about 20 centimeters and weigh about 40 grams at time of hatching.  Young are seldom seen, believed to stay mostly underground until they are larger, at about 2-3 years

Lifespan: Up to 50 years

      Conservation Status:  IUCN Least Concern.  CITES Appendix II

• Body length 90-76 centimeters (about half of which is tail).  Males are slightly longer and much heavier than females, weighed up to 4 kilograms compared to the 1.4-2 kilograms for a female
• Body is cylindrical with a thick tail.  Head is wide and flat, legs and short and strong.  Upper part of the body is covered with large, hard scales (each consisting of a small bead of bone, or an osteoderm), while those on the belly are smaller and softer.  Males generally (but not always) have broader heads and longer necks than females
• Scales are predominately black or dark brown, with some yellow spotting scattered on the tail and neck.  Younger lizards tend to have more yellow in blotches and bands, darkening with age.  Chiapan subspecies tend to be all black
• Late name translates to “Horrible Nail-Skin”, referring to the studded appearance of the scales
• Along with Heloderma suspectum (Gila monster) and the Guatemala beaded lizard, this is the only truly venomous lizard.  Venom flows from the glands through grooved teeth on the lower jawbone.  As the lizard gnaws on its prey, venom is drawn in through capillary action
• Bites are not considered fatal to humans, but are extremely painful and will require medical treatment.  Almost all bites occur when victim is attempting to handle the animal.  Bitten humans first become agitated, then very drowsy, arterial pressure drops, and respiratory failure.  In humans, causes swelling, weakness, sweating, and drop of blood pressure.  The lizards are immune to their own venom
• The venom is being studied for its pharmacological use, especially for the treatment of diabetes, as well as Alzheimer’s, HIV, and breast and lung cancer
•    Few natural predators – coyotes and raptorial birds.  Venom is used for defense – lizard will threaten enemies by gaping and hissing before attempting to bite
• Primarily nocturnal.  Spends the day in burrows, either dug itself or by other animals.  Slow and sluggish when it first emerges, become more active and aggressive as the night wears on.  Most terrestrial, but will climb low trees and shrubs as well
• Most prey is swallowed whole, except eggs, which are broken first.   Eggs are the favorite food – confiscated animals rescued from collectors can often be induced to eat other food sources by pouring egg on a mouse or other prey item.  Prey is primarily found by scent – pink forked tongue is used in association with Jacobson’s organ, similar to a snake or varanid. 
• Fat is stored in the tail, giving it a swollen appearance when well fed.  Lizard can survive off of fat stored here for when food is scarce.  Tail cannot grow back if lost
•  Once listed as four subspecies across its range – H. h. alvarezi (Chiapan beaded lizard), H. charlesbogerti (Guatemalan beaded lizard), H. exasperatum (Rio Fuerte beaded lizard), and H. horridum (Mexican beaded lizard). Guatemalan beaded lizard is now usually now listed as a full species; sometimes so are the others.  
• Population believed to be in decline, size not known  The Guatemalan subspecies/species is the most endangered of the beaded lizards (possibly the most endangered lizard in the world) with a wild population of less than 200 individuals
• Primary threats are loss of habitat (including forest fires and mortality associated with road construction) and collection for the pet trade.  Also killed opportunistically by local people who are afraid of being bitten
• Local superstitions surround this species include the beliefs that it can cause lightning strikes with its tail or cause a pregnant woman to miscarry just by looking at her.  Also believed to be far more venomous than it actually is (feared more than rattlesnakes)