Are Komodo Dragons Venomous? Venom vs the Bacteria Myth

What the 2009 venom study found

The key evidence came from a team led by Australian biochemist Bryan Fry, published in the journal PNAS in 2009. Using magnetic resonance imaging (MRI) on the preserved head of a Komodo dragon, the researchers found two large glands running along the lower jaw, each divided into several compartments that open between the teeth.

They then removed a gland from a terminally ill dragon at Singapore Zoo and analyzed what it produced. The secretion contained several kinds of toxic proteins, many of them related to the venom proteins of snakes. Their known effects in other animals include blocking blood clotting, widening blood vessels so that blood pressure falls, and causing pain and muscle weakness.

The same study used computer models of the skull to test the bite. Komodo dragons turned out to have a relatively weak bite force for their size compared with a crocodile, but their skulls are built to withstand strong pulling forces. Instead of crushing, a dragon bites and then pulls back with its powerful neck, so the curved, serrated teeth slice through flesh like a saw.

How the venom affects prey

Komodo dragon venom does not paralyze prey in the way cobra venom does. Its main effect is on blood. Anticoagulant proteins keep the wounds bleeding, and other proteins dilate the blood vessels. A large animal such as a deer or wild pig loses blood fast while its blood pressure drops, and it soon becomes too weak to fight back or run.

This explains a pattern hunters and park rangers had noticed for years: bitten animals often look dazed, collapse and bleed heavily from wounds that seem too small to cause so much damage. Researchers think the venom makes the dragon’s hunting style much more efficient, because the prey stops struggling sooner and the dragon risks fewer injuries from hooves, horns and tusks.

Not all scientists agree on how important the venom is. Some argue that the bite alone, with its deep cuts and massive blood loss, would be enough to bring down prey, and that it is not yet clear how much of the effect comes from the toxins. Others point out that a duct system delivering venom into the wound, like the grooves in snake fangs, has not been clearly identified in monitor lizard teeth. The existence of the glands and their toxic proteins is well established; the exact size of their role is still being studied.

The bacteria myth

For much of the 20th century, books and documentaries explained the Komodo dragon’s killing power with bacteria. The idea, built on early field work and a 2002 study that cultured many bacterial species from dragon saliva, was that a dragon’s mouth was full of rotting meat and dangerous germs. A bitten animal would escape, the wound would become infected, and the dragon would follow it for days until it died of blood poisoning.

Later research largely overturned this story. A 2013 study by Ellie Goldstein and colleagues sampled the mouths of 16 captive dragons in three US zoos and found the ordinary range of bacteria seen in many carnivores, with no special set of deadly microbes. Dragons also keep their mouths fairly clean, licking their lips and rubbing their heads on leaves and soil after a meal.

The idea of prey dying slowly from infection probably came from one particular case: water buffalo. Buffalo were brought to the islands by people, and when bitten they often escape into warm, muddy waterholes contaminated with dung. Wounds soaked in that water easily become infected, so a buffalo that got away from a failed attack could sicken days later. That is a result of the buffalo’s habits, not proof of a toxic mouth.

How Komodo dragons actually kill

Field studies show that Komodo dragons are ambush predators that try to kill on the spot. A dragon waits beside a trail, charges in a short burst and bites the legs, belly or throat. Wild pigs and deer are often killed within minutes, and successful hunts of larger prey usually end within half an hour. Several dragons may then gather to feed, drawn by smell.

Venom, sharp teeth, a strong pull and sheer weight all play a part. Learn more about the prey they take in what do Komodo dragons eat.

Other venomous lizards

The Komodo dragon is not alone. The Gila monster of the southwestern United States and the Mexican beaded lizard have been known to be venomous for more than a century. Their venom glands also sit in the lower jaw, and they chew venom into a bite through grooved teeth.

Since 2005, research has shown that many monitor lizards and some iguanian lizards have glands producing toxin-like proteins. Together with snakes, these lizards are placed in a group that some scientists call Toxicofera. For most of these species the venom is mild to people, causing pain and swelling at most. A large Komodo dragon is different simply because of its size, and serious bites need emergency medical help immediately. For a wider view of animal venoms, see the most venomous animals.