It’s not their dirty mouths

Komodo dragons kill prey with venom, not oral bacteria, study suggests

Add shock-inducing venom to the list of reasons to avoid Komodo dragons. The fierce lizard may kill its prey in a way similar to some snakes, researchers report online May 18 in Proceedings of the National Academy of Sciences. The finding contradicts the widely held notion that Komodo lizards rely on nasty bacteria and resulting infection to kill prey.

DIRECT HIT A new study shows Komodo dragons probably use venom, not toxic bacteria, to kill prey. IMAGE: Chris Kegelman

Scientists recently discovered Komodo dragons possess six venom glands on each side of the lower jaw. Bryan Fry, et al.

The world’s largest living lizards, Komodo dragons are fervent predators found only in Indonesia. The dragons are quick, strong and large (the largest reported was more than 10 feet long and weighed in at 366 pounds), and they can take down prey as large as deer. “These things are incredible killing machines,” says Bryan Fry of the University of Melbourne in Australia, who coauthored the new study. 

Just how these deadly lizards kill has been controversial. Conventional wisdom held that after inflicting a bacteria-laden bite, the dragons would track wounded prey and wait days for sepsis to set in before dining.

“In the minds of many biologists, that just didn’t make sense,” comments Christopher Shaw, a biological chemist at Queen’s University Belfast in Northern Ireland. “If you’ve evolved to be the size of a Komodo dragon, it seems to be a waste of time.”

What’s more, rare sightings of the lizards hunting didn’t fit with this method. Victims typically died quickly and quietly after going into shock, the authors say. “No one’s actually seen a Komodo dragon track a prey for three days until it dies of septicemia,” Fry says. “It’s an absolute fairy tale.”

And though the lizards wouldn’t win any gold stars at the dentist, Komodos may have a bad rap for oral hygiene. The Komodo dragon’s mouth is no nastier than those of other predators, Fry says. “A lion has a larger bacterial load.”

MRI scans of a Komodo dragon head turned up six venom glands on each side of the lower jaw. All together, these glands can hold 1.2 milliliters of venom per animal. “It’s astounding,” Fry says. “I didn’t expect it to be that intricate of a structure. It was just jaw dropping when we got the first MRI results.”

A technique called mass spectrometry turned up in Komodo venom many proteins known to be in snake venom. In particular, compounds known to widen blood vessels and thin the blood — which induces shock — were present.

Fry and his colleagues injected the venom into rats and confirmed that their blood pressure and aortic tension decreased. After the injection, the rats also became still, an outward sign of shock.

This new paper puts to bed once and for all the issue of how the Komodo dragon kills, Shaw says. The authors “produce some pretty convincing evidence that these are venomous lizards.”

Laura Sanders

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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