Most dangerous lizard

The Gila monster (Heloderma suspectum) is a large, up to 60 centimetres (24 inches), heavy built, brightly coloured lizard that lives in the arid parts of Mexico and south-western USA. They have eight well-developed venom glands in their lower jaws and carry enough venom to kill two adult humans. The venom is not injected but seeps into the wound caused when the Gila monster bites its victim with its sharp fragile teeth. Because of this, a lizard may continue to hang on after it has bitten and actively chew for several minutes. The lizard's teeth may even become embedded in the victim's wound after it has let go. In one study of 34 people bitten by these animals (most of them in captivity), there were eight fatalities. The lizard only attacks when provoked and under normal circumstances is relatively harmless.

The Gila monster is also the most venomous lizard, with LD50 (lethal dose) values for its venom as low as 0.4 mg/kg recorded when administered intravenously in mice. The term LD50 represents the dose of venom that proves lethal to 50% of a test population.

The closely related Mexican beaded lizard (Heloderma horridum), from western coastal Mexico, is slightly larger and darker than the Gila monster. It too has a venomous bite although fatalities from either species are rare.