Heloderma

HELODERMA, beaded lizard, the only venomous lizard (family Helodermatidae, suborder Lacertae, class Reptiles); has two species—H. suspectum Cope and H. horridum Wgm. (see figure 1); up to 1 foot in length; lives in Arizona (U.S.A.) and Mexico.

Figure 1.

Nocturnal animal. Under the lower jaw it has on each side a large five-lobed venom gland with five excretory ducts that pour the venom into the grooved teeth of the lower jaw (see figure 2). When biting, not only venom but also the mucous secretion of other glands in the oral cavity enters the wound. The venom of the beaded lizard causes respiratory arrest due to its effect on the respiratory centers. Large doses of the venom cause tetanic contractions of the respiratory muscles. The heart is also affected by the venom. First, blood pressure falls due to centrally originating vasodilation. Then it somewhat equalizes due to the compensatory work of the heart, and finally falls completely due to weakening of the heart. The effect of H. venom on humans is described differently. Some authors admit the possibility of death from a bite by H., while others consider the venom to be weaker. Sensitivity of different animal species to H. venom is not the same. For example, cats and hedgehogs are more resistant to it. By repeated injections of increasing doses of H. venom, animals can be immunized against this venom.