Distribution

1. Western and southern Mexico, Guatemala 
2. Southwest USA (far southwest Utah, far southern Nevada and southeast California, Arizona, far southwest New Mexico) and Mexico (Sonora)

Biology

Besides venomous snakes, helodermatids are the only venomous reptiles. In this genus, there are only two species in existence today.

Sturdy lizards with a wide head that is flat on the top and a blunt snout. Limbs short, toes with sharp claws. Tail normally thick. Total length 25–70 cm. Body covered with rounded scales. Basic colouring dark brown to black, usually with variable markings or patches of pink, yellow or orange.

Helodermatids move very slowly and are active in the evening or at night, although in cool weather they are also active during the day. H. suspectum lives in desert regions and mesquite grassland, H. horridum more often in wooded regions.

  Fig. 4.491 Heloderma suspectum.

Venom is produced in modified sublabial glands and is conducted via several excretory ducts to the base of a number of teeth in the lower jaw. The teeth are conical in shape and curve backwards slightly; they have deep grooves on the back and especially on the front. Some of the teeth in the upper jaw also have such grooves, but they are not associated with venom glands. The animals are not capable of delivering large amounts of venom quickly. Thus these lizards do not let go of their victim once they have bitten, but rather use chewing motions to inject venom into the wound. Once these lizards have sunk their teeth into their victim, they are very difficult to remove, even with the use of extreme force.

Risk

Accidents are rare. Bites occur chiefly when the animals are handled. No known fatalities.

Signs and symptoms

Pain, swelling, nausea, vomiting, arterial hypotension.

Treatment

Symptomatic.

Literature (biological)

Campbell and Lamar 1989, Russell 1983, Russell and Bogert 1981, Tinkham 1971, Mebs 1995b