Ed Yong in Not Exactly Rocket Science:
In 1969, an American biologist named Walter Auffenberg moved to the Indonesia island of Komodo to study its most famous resident—the Komodo dragon. This huge lizard—the largest in the world—grows to lengths of 3 metres, and can take down large prey like deer and water buffalo. Auffenberg watched the dragons for a year and eventually published a book on their behaviour in 1981. It won him an award. It also enshrined a myth that took almost three decades to refute, and is still prevalent today.
Auffenberg noticed that when large animals like water buffalo were injured by the dragons, they would soon develop fatal infections. Based on this observation, and no actual evidence, he suggested that the dragons use bacteria as a form of venom. When they bite prey, they flood the wounds with the microbes in their mouths, which debilitate and kill the victim.
This explanation is found in textbooks, wildlife documentaries, zoo placards, and more. It’s also wrong. “It’s an enchanting fairy tale, which has been taken as gospel,” says Bryan Fry from the University of Queensland.
In 2009, Fry discovered the true culprit behind the dragon’s lethal bite, by putting one of them in a medical scanner. The dragon has venom glands, which are loaded with toxins that lower blood pressure, cause massive bleeding, prevent clotting and induce shock. Rather than using bacteria as venom, the dragons use, well, venom as venom.