A Blog by Ed Yong

The Myth of the Komodo Dragon’s Dirty Mouth

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. (The full set of experiments is breathtaking in their scope—read about them here.)

Based on a thorough analysis of the dragon’s skull, Fry thinks that they kill with a grip, rip and drip tactic. They bite down with serrated teeth and pull back with powerful neck muscles. The result: huge gaping wounds. The venom then quickens the loss of blood and sends the prey into shock.

That doesn’t discount the possibility that the dragons might also rely on oral microbes. To study these microbes, Fry contacted Ellie Goldstein from the UCLA School of Medicine—an expert on microbes an animal bites. Goldstein has advised people around the world on treating unusual bite wounds, including at least one from a Komodo dragon. “The bacteria-as-venom model seemed to be based on faulty and dated studies,” he says. “There was no really good data on the topic.”

Goldstein tried calling several zoos with captive dragons. “Many would not respond and sometimes actively tried to deter our research for reasons unclear to me,” he says. “The detractors [said] this study had already been done and no new info would result,” adds Kerin Tyrrell, who is part of Goldstein’s team. Fortunately, three zoos in Los Angeles, Honolulu and Houston were more cooperative, and the team managed to swab the mouths of 10 adults and 6 hatchlings.

They found… nothing special. All the microbes they found were common in the skin and guts of their recent meals. There were no virulent species at all, and certainly nothing capable of causing a quick, fatal infection. And the species that were there weren’t particularly abundant. “The levels of bacteria in the mouth are lower than you’d get for a captive mammalian carnivore, such as a lion or Tasmanian devil,” says Fry. “Komodos are actually remarkably clean animals. This is another nail in the coffin to the idea of them using bacteria as a weapon.”

The Komodo dragon: surprisingly clean. Photo by Bryan Fry
The Komodo dragon: surprisingly clean. Photo by Bryan Fry

Of course, you might argue that wild dragons might harbour deadlier bacteria. But the captive animals aren’t living in a sterile environment nor eating sterile food. If wild dragons are truly using bacteria as weapons, the captive ones should at the very least have some way of encouraging bacteria to grow in their mouths. “If they were facilitating the growth of bacteria in their mouths in the wild, they should be doing it in captivity,” says Fry. “They don’t. Their mouths were not dramatically different from the mouth of any other captive carnivore.”

Aside from Auffenberg’s book, the only other support for the bacteria-as-venom hypothesis comes from a team at the Universtiy of Texas at Arlington. In 2002, they found a wide range of bacteria in the saliva of 26 wild dragons and 13 captive ones, including 54 disease-causing pathogens. When they injected the saliva into mice, many of them died and their blood was rich in one particular microbe—Pasteurella multocida.

But Fry thinks the study is laughable. Sure, they studied wild dragons, but the microbes in Fry’s captive animals were actually closer to those from the wild ones in the Texan study. The so-called pathogens they discovered are just normal non-virulent members of an animal’s microbial entourage. And despite making a big deal of Pasteurella, they only found it in 2 of their 39 dragons. Goldstein never saw it in his captive ones.

And worst of all, no single species of microbe has ever been consistently identified in all dragons. How could these lizards rely on a strategy that’s so variable? “It’s evolutionary implausible,” says Fry.

The only remaining lifeline for the bacteria-as-venom hypothesis, says Tyrrell, is that the team only identified the bacteria that they could grow in laboratory cultures. Some species can’t be identified in this way, so one of these might contribute to the dragon’s killing bite.

Fry thinks that bacteria do help to kill the largest of the dragon’s victims, but not in the way that Auffenberg suggested. When the dragons tackle natural prey—medium-sized mammals like deer or pigs—the victims die very quickly from blood loss. The venom helps, but it’s the wounds that are important. But water buffalos are a different story.

These creatures were introduced to Komodo by humans. They’re too big to kill outright and always escape the initial attack. In their natural environment, they’d disappear into wide marshlands, but there’s nothing like that in Komodo. Instead, the buffalos seek refuge in rank water holes, stagnant and contaminated with their own faeces. In this microbial wonderland, their wounds soon become infected. “It’s the same as if you dumped a whole bunch of cow dung in your pool during the peak heat of summer, shaved your legs with a very old razor, and then went and stood in the water for a day,” says Fry. “You’d end up with some very tasty infections!”

Reference: Golstein, Tyrrell, Citron, Cox, Recchio, Okimoto, Bryja & Fry. 2013. ANAEROBIC AND AEROBIC BACTERIOLOGY OF THE SALIVA AND GINGIVA FROM 16 CAPTIVE KOMODO DRAGONS (VARANUS KOMODOENSIS): NEW IMPLICATIONS FOR THE ‘‘BACTERIA AS VENOM’’ MODEL. Journal of Zoo and Wildlife Medicine http://dx.doi.org/10.1638/2012-0022R.1

PS – It’s amazing how many enshrined “facts” about natural history are based on very little evidence. The cheetah’s status as the world’s fastest land animal as based on a single measurement taken in the 1960s. This month, scientists published the first proper measurements of running speed in wild cheetahs… and showed that they really are that fast. Another longstanding fact—that the honeyguide bird leads honey badgers to beehives—turns out to be a lie perpetuated by deceitful documentary-makers.

29 thoughts on “The Myth of the Komodo Dragon’s Dirty Mouth

  1. Another favorite myth is the “sacrificial leaf” on mangrove trees. The myth goes that each plant pumps all its excess salt into one leaf, which turns yellow, dies, and falls off. I have heard this many, many times. Well, one day (around 2010), someone (Joe Grey et al) asked “well, if that’s true, there should be more salt in the yellow leaves than in the green ones, right?” Apparently nobody else, at least nobody else with access to mangroves and a way of measuring the salt content of leaves, had asked that. Punchline, no more salt in the yellow leaves than in the green ones. http://www.glomis.com/ej/pdf/EJ_8-4.pdf

  2. Another such myth is that lemmings commit mass suicides. It was actually documentary film makers for Disney who upon learning that lemmings are actually quite boring decided that they would be much more interesting if they were run off a cliff (and if you notice in the film, the lemmings proceed to swim after falling into the water).

  3. Then there are the lemmings leaping into the sea, but actually pushed off a cliff for a Disney studios documentary.

  4. You had to mention Honey Badger… Well. What about the notion put forth by Randall that “Honeybadger don’t care, honeybadger don’t give a sh**”? I think that one has stood the test of time.

  5. “The detractors [said] this study had already been done and no new info would result”

    Ah, the settled science argument. Now where have we heard that before?

  6. I had terrible problems with standardized tests because I knew too many exceptions to the rules, Science is not nearly as immutable as people like to think. Since everything is influenced by the observer, black is sometimes grey and white is sometimes cream. The smartest people realize this and view science as being dynamic rather than static. Yesterday’s fact is often today’s fiction. A good scientist knows this and acts accordingly.

  7. I wouldn’t call the description of the way dragons “bite prey, (and) flood the wounds with the microbes in their mouths, which debilitate and kill the victim,” an enchanting fairy tale. Just sayin’.

  8. It would be nice if people did science the way Fair Witnesses in Robert Heinlein’s Stranger in a Strange Land did witnessing in trials. Only describe what you are seeing. I think the biggest problem is with the “drawing a conclusion” stage of scientific experimentation. Maybe scientists should stop doing that, and start leaving conclusions up to the people reading their data. Especially when I have run into *so many* studies where the researchers drew a conclusion that I would not have, and which turned out to be incorrect upon further statistical examination. (See also the China Study. Campbell did not pay attention to his own data.)

  9. The next step in our research is to culture the watering holes. We will be sampling widely, not only on Rinca and Komodo islands but also in the native range of the water buffalo as well as in northern Australia where they have also been introduced. The below images illustrate just how putrid the water is and the sort of non-lethal wounds that the water buffalo are getting, that facilitates the entry of the bacteria from the disgusting water,

  10. Mr. Fry, thank you for your research. Its fascinating.
    I wonder if in the future there will be a medical use for dragon venom.
    But in the meantime, how did Mathrew Broderick walk around with one of these things under his arm in that movie with Marlo Brando. And did you see the CG dragon in the last James Bond movie? It just dragged its victim into a hole. Way cool.

  11. Vicattardo in the movie The Freshman (which is highly entertaining BTW), the lizards used were Varanus salvator (Asian water monitor). Same genus as the komodo dragon (Varanus komodoensis) but different species.

  12. Wow! Thanks for this post and thanks to Dr. Fry for the links! So many of my students still tell me about how these lizards kill with a septic bite…someday the truth will overcome the myth. This is a great case study in how science is done.

  13. Let’s not be so quick to disparage the work of our predecessors. I I recall Prof. Auffenburg’s book correctly, the oral bacteria proposal was offered as a testable hypothesis, not as established fact. It is not his fault that no one followed up until recently. Such hypotheses have proved useful, if not always essential, in stimulating further research. The previous assumption had been that it was the extensive wounding that led to death. Auffenburg’s hypothesis was only challenged as it became known that virtually all lizards and snakes have venom components in their saliva.

  14. Steven, you are correct indeed that it was a major science-fail. As the saying goes ‘extraordinary claims require extraordinary evidence’ and bacteria-as-a-weapon would be an unprecedented form of predation strategy. Yet, despite this, it was not previously examined critically. It was instantly accepted because it was enchanting… just like most fairy tales.

  15. Very Informative, for past couple of days I am reading many post which changed my idea about VENOM. How different animals use it and how it works, Simple and yet very effective. Evolution’s remarkable way to adapt the ever changing environment.

  16. It is interesting that this was posted. The documentary “National Geographic-Worlds Creepiest Killers” which was plublished on May 26th 2012 restates that the Komodo Dragon kills due to saliva riddled with bacteria contradicting this very article.

  17. Thank you mr.fry for debunking this myth,not undermining Prof. Auffenburg’s work,but this is how science progresses,till now i believed that only the gila monster and the mexican beaded lizard possesed venom,now even common monitor lizards have shown this feat,now my question is does the venom of the komodo dragon or monitor lizards differ in potency comapred to that of the above mentioned lizards?

  18. WOW, this was so an upgrade in my knowledge. My grade1 daughter is doing a project on the Komodo dragon and this new info has blow her teacher’s mind. Thank you

  19. I’m rather disappointed that no mention is made of the microbial biology and immunology chapter pgs.118-126, by D.Gillespe et al., in Komodo Dragons Biology and Conservation 2002. This does demonstrate that the bacterial profile of wild Komodos and compared to zoo Komodos varies considerably. Pseudomonas sp., Clostridium sp., Ecoli sp., and Serratia sp., seem to be medically significant bacterial if I were to be bitten by a wild Komodo. Furthermore, I have seen inside of a few Komodo mouths, and there is no differentiation of teeth at all, unlike in the Heloderms. I also see no evidence of mandibular swellings to demonstrate the presence of a venom gland. If Komodos who are often sit and wait predators, you would think their native prey the Timor Deer would require a significant amount of venom to succumb to a bite. If not, then why do Gila monsters and Beaded lizards have such prominent venom glands and modified teeth to conduct venom into bites? A considerable amount of knowledge has been gained about Komodo Dragons in the wild since Auffenberg’s time, before so-called myths are dispelled, I would like to see less reliance on dogma.

  20. Auffenberg is right. The form of bacteria that kills an animal when the Komodo dragon bites is also found in the mouths of other carnivores, but the strain inside the Komodo dragon is especially lethal. Scientists have done experiments, and found that the toxins that are also administered during a bite is insufficient to kill. It is the bacteria that kill. It is not a myth. Dr. Fry is perpetrating a falsehood. Komodo dragon do not kill with venom. Komodo dragon has toxic saliva, but humans also have toxic saliva. We are not any more venomous than the Komodo Dragon.

  21. Very interesting. I always thought there had to be more to the subject of the komodo dragons, but wrote it off being only 12 years experienced in comparison to the experts

  22. I respect Dr Fry’s expertise, but Mr Yong’s second paragraph greatly distorts Dr Auffenberg’s published work and appears to be based on popular press sensationalism rather than Auffenberg’s short section, “Transmission of Incapacitating Infections,” in his book “The Behavioral Ecology of the Komodo Monitor.” Auffenberg was a careful well-respected herpetologist who never characterized Komodo monitor saliva as an injected venom. He reviewed reports of “venomous” or “poisonous” saliva in other varanids and the lynx but cautions that initially he was skeptical of them. He offered the following evidence for toxic saliva in komodoensis:
    1. Two human deaths, possibly from septicemia following bites.
    2. Recognition of septic bites on domestic horses and water buffalo in Flores as a significant veterinary problem.
    3. The presence of badly infected wounds on pig and deer (admittedly rarely seen).
    4. Pathogenic bacteria cultured from several specimens in 1972.
    Auffenberg points out that the toxic saliva probably plays a significant, if any, part only in predating the introduced water buffalo, so its predation-enhancing value is probably accidental, not evolved. The infections presumably make a second attack on a weakened prey feasible or directly kill the prey which is then consumed later as carrion. The bacterial flora in wild komodoensis may also depend on carrion feeding which means any captive studies would not apply to natural populations. Auffenberg points all this out in a couple of pages.
    Little attention has been directed to the fact that the environmental conditions of relatively undeveloped tropical countries are conducive to wound infection. Dr Fry points out that there are other potential sources of bacteria such as the waterholes, but waterborne bacteria typically cause gastrointestinal problems, not wound infection.
    Many obstacles to a typical oral venom explanation in komodoensis exist. No enlarged salivary glands or fangs are present in any monitors. However, we now know that many salivary enzymes, particularly anticoagulants, in snakes and lizards could qualify as at least weak venoms, depending on your definition of venom. These factors seem to occur in carnivorous species which makes sense since a salivary anticoagulant would help predigest prey in the same way that mammalian amylase breaks down starch. Since no special delivery mechanism for these factors exists, calling them a venom would really be stretching the definition.
    Another aspect of the sensationalization of komodoensis deserves mention. Auffenberg always was careful to refer this species as the Komodo monitor, not dragon. The latter name is an invention of the popular press because of the monitor’s size (though salvator is impressively large too) and for better or worse is now entrenched. Herpetologists know that the true dragons are all agamids!

  23. Some myths are harmless and some myths, like “man made” climate change, are more dangerous than the consequences that would result if the myth were true!

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