Lizard, Mexican Beaded

Heloderma horridum horridum  

One of only two types of poisonous lizards, beaded lizards have a dark body with yellow bands on the tail. There are small bumps (beads) covering the entire body. There are venom glands in the lower jaw. Size of average adult is a length of 36 inches and a weight of 5 pounds. The Mexican Beaded Lizard ranges from 76.2-91.44cm in length and weighs approximately 2.27 grams. The tail is the longest portion of the lizard making up approximately 50% of the body. The beaded lizards have a cylindrical body with a long, thick tail. The head is widespread and flat, and the legs are short and strong. Large, hard scales cover the top of the lizards’ body, while the belly side is coated with soft scales. The scales are bead-like and are predominately dark black or brown on the top and bottom of the lizard. Yellow spots are scattered along the tail and the neck. Younger individuals have thicker bands and larger blotches of yellow on their bodies when compared with the adults. Helodermatidae refers to the beaded or venomous lizards, the only known poisonous lizards. The grooved fangs of Helodermatidae are similar to serpents of the division Opisthoglypha. The grooved teeth are on the lower jaw bones, along with the poison glands, which are arranged at the rear edge. The venom passes from these glands through a channel to the roots of the grooved teeth. The venom is drawn into the wound by capillary action as the lizard chews its prey. 








Mexico, mostly along Pacific coast; The Heloderma horridum is found throughout central and western Mexico from latitude 25, southward to northern Central America.


Subhumid tropics to arid areas; Heloderma horridum is found in semi-arid rocky regions. The areas are sparsely vegetated canyon bottoms, open forest, and washes. These lizards are often found on rock ledges.

Life Expectancy

Sexual Maturity


In the wild: small mammals, birds, lizards and eggs In the Zoo: Mice In the adult stage, the Mexican Beaded Lizard is carnivorous. Its diet consists of small mammals, birds, lizards, frogs, insects, and eggs of birds and reptiles. All their prey is swallowed whole, except for eggs, which are broken first. When food is scarce, the Mexican Beaded Lizard lives off fat reserves in the tail. Fat is stored in the tail of the lizard making it appear swollen. After the fat reserves are used up the tail appears thin again.


IUCN - Least Concern, CITES - Appendix II


These lizards hunt for food year around. They are primarily nocturnal (active at night) and they can climb, burrow and swim. The Heloderma horridum dwells in self-dug or pre-existing burrows during the day and becomes active at night. When the lizard first leaves its burrow it moves slowly and clumsily but as the night progresses it becomes more aggressive. In this more active state, the Mexican Beaded Lizard can “turn and snap with the agility of an angry dog”. When the Mexican Beaded Lizard inflicts a vigorous bite, the victim goes through many stages. The first stage is the inability to sit or stand. The animal becomes drowsy and then experiences paralysis. Respiration becomes slow and labored until the heart exerts an increase of activity. The arterial pressure begins to take a great fall due to vascular dilation and the prey dies. Although the venom may have these effects on its small prey, bites are rarely fatal to humans in good health. The breeding season is in February and March and copulation lasts 30-60 minutes. About 2 months later, females lay 3-13 elongated eggs and bury them at a depth of about 12.5cm. The female then abandons the eggs. Incubation takes about 6 months. Each hatchling may be up to 20 cm long. The Mexican Beaded Lizard has very few enemies besides humans, coyotes, and some raptorial birds. Having few natural enemies gives the hatchlings a greater chance for survival.


The Mexican Beaded Lizard uses its venom not only to kill its prey, but also to subdue potential predators such as humans, coyotes, and raptors. The lizard also gapes and hisses to fend off its enemies. These behaviors are effective in keeping the number of predators at a minimum.

Special Interests

Humans are gaining economically by using the lizards in a worldwide pet trade. A Mexican Beaded Lizard can be sold at a price of $1,500.00. Even though a bite from Heloderma horridum is not usually life threatening to humans, the wound must still be medically treated. This can be considered a negative impact upon health care costs for treatment and anti-venomous serum.



Challenges: -habitat destruction: slash and burn agriculture -suffocation in burrows: slash and burn agriculture -over collection Humans are not only a threat to the Mexican Beaded Lizard because they kill them for fear of their venom, but are also destroying the habitat upon which these lizards depend. Therefore Heloderma horridum is protected under the Convention on International Trade in Endangered Species of Wild Flora and Fauna II (CITES II) and the International Union for the Conservation of Nature and Natural Resources V (IUCN V).

Jacksonville Zoo History


Range of the Jaguar