This Komodo dragon doesn't kill with pure force like a crocodile, but with a lethal duo of toxins and razor-sharp teeth.
SYDNEY: Rather than using a nasty cocktail of bacteria, as previously believed, Komodo dragons use shock-inducing toxins to kill their prey – a finding that may revolutionise medical treatment for bites.
Komodo dragons (Varanus komodoensis) have delicate skulls compared to other carnivorous lizards such as crocodiles, and it has been something of a mystery how they are capable of tackling large prey, sometimes exceeding 100 kg. The findings, published today in the Proceedings of the National Academy of Sciences, now provide a definitive answer.
"[The bite is like a] serrated dagger dipped in poison," explained Bryan Fry, a biologist from the University of Melbourne, Australia and lead researcher behind the study. And he's in a good position to describe it: Fry once had to have emergency surgery to repair a severed artery from just such a bite.
Antibiotics won't fight venom
The three-metre-long Komodo dragon is the world's largest lizard, found on the Indonesian islands of Komodo, Rinca, Gili, Motang and Flores. They feed on a variety of animals, ranging from frogs to adult deer.
Computer modelling has shown that their lightweight skull and jawbones would snap, however, if brute force was the only tactic they used to catch large prey, said Fry.
Since the 1980's scientists have believed Komodo dragons kill their victims by infecting them with highly virulent bacteria. Treatments for dragon bites currently involve a heavy dose of antibiotics.
To Fry, however, this explanation seemed unlikely – Komodo dragons are extremely clean animals that don't harbour masses of killer bacteria, he said. Fry hopes his work on toxins will now change the way human dragon bites are treated.
Venom induces shock
Fry's team analysed a preserved Komodo dragon head using Magnetic Resonance Imaging (MRI). MRI employs strong magnetic fields to construct a picture of the internal structure of the body. Fry's team saw venom glands inside the head – the most complex reptile venom glands ever described, in fact.
To find out how poisonous the venom was, the researchers removed the glands from a captive and terminally ill Komodo dragon. They then determined the venom's 'protein fingerprint' – the protein make-up, which determines its properties.
They discovered it was similar to other well-studied venoms, such as some snake venom. While not lethal, venoms with similar 'fingerprints' are known to induce shock, lower blood pressure and stop blood from clotting – exactly the symptoms seen in bite victims.
Fry believes it's the lethal duo of shock-inducing toxins and razor-sharp teeth that allows Komodo dragons to slay large animals. They attack with a series of quick bites, slashing the flesh and releasing venom into the wounds, he said. Unable to clot, the wounds bleed profusely. Weakening with each bite, the animal is soon a struggle-free dinner.
"[This study has] convincingly demonstrated that the utilisation of septicaemic bacteria is a pure myth," said evolutionary biologist Nicolas Vidal, from the French National Museum of Natural History, in Paris.
"Although the production of venom by the Komodo dragon is not surprising... the complexity of its glands is amazing," added Vidal, who noted that local people who deal with Komodo dragons in Indonesia already thought the species to be venomous.
