Komodo dragons are the largest and heaviest lizards in the world. The largest wild dragons weigh about 155 pounds. They were thought to be one of few lizards like iguanas, Gila monsters and Mexican beaded lizards, that have a venomous bite. Scientists are thinking that number may now actually be as many as 100 species of lizards that use venom. Komodo dragons produce venom from glands in their lower jaw with multiple ducts between their teeth, unlike a single duct that leads to the fangs like that of a cobra. Venomous lizards and snakes are both descended from a common ancestor that lived 200 million years ago.