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Mexican beaded lizard

Heloderma horridum

Description: Mexican beaded lizards are closely related to the Gila monsters – the only two known venomous lizards. They are dark-brown to black with orange or yellow spots. The skin is composed of beaded scales called osteoderms that contain bits of bone, thus giving the lizards their ‘armor’. The scales that cover the top of their body are large and hard; soft scales cover the belly portion. They have a cylindrical body; a wide flat head; short strong legs with five clawed toes; and a long, thick tail. Their salivary glands are modified and contain venom. These glands lie under the grooved teeth in the lower jaw. Since the venom is slow moving, the Mexican beaded lizard must hold fast after the initial bite and keep gnawing or chewing in order to get the venom into its victim. Although the poison is extremely painful and recovery may take several weeks, it is not usually lethal. They are immune to the venom of other poisonous lizards and rattlesnakes.

Size: Males reach lengths of 35 inches (90 cm) and females, slightly shorter at about 30 inches (76 cm). In both sexes, the tail makes up about 50% of their length.

Behavior: Mexican beaded lizards are active at night. During the day, they spend most of their time hiding in burrows (called hibernacula) or under rocks. Also, during the winter months they enter a quiet state similar to hibernation, surviving off fat that is stored in their tail. After leaving the hibernacula for the season, the male lizards compete for the chance to mate. The winning male, usually the larger one, will nuzzle the female’s chin, lick her skin and caress her nose. Their walk is an awkward waddle, however they can move quickly when needed.

Diet: They are carnivores, eating birds, frogs, lizards, rodents, snakes and small mammals, swallowing them whole. They will also eat bird and reptile eggs, breaking the eggs open first.

Senses: The tongue is used as a sensory organ to gather scents.

Communication: They warn off would be predators by making a hissing sound.

Reproduction: Females lay a clutch of 3-13 elongated eggs that she buries and then leaves alone. After an incubation period of about six to seven months, the young hatch with sharp teeth and poisonous venom.

Habitat/range: Mexican beaded lizards are found in open forests, washes and woodland areas throughout western Mexico and Guatemala.

Status: Listed as Least Concern on the IUCN Red List and on CITES Appendix II due to habitat destruction.