“Meddle not in the affairs of dragons, for you art crunchy and good with ketchup.” ― Anon
The fearsome Komodo dragon (Varanus komodoensis) is the world’s largest living lizard, weighing in at an average of 150 lbs, and measuring 3 metres in length. It is native only to five of Indonesia’s islands, including its namesake, Komodo.
The Dragon is both a scavenger and an ambush predator; capable of lying in wait for hours at a time until prey, such as buffalo, come close enough for it to attack. Of course, not all kills are clean and quick. Animals injured in attacks by Komodo dragons can survive only to die days or weeks later from their wounds. Dragons have even been known to follow wounded prey for days until they die in order to enjoy an easy meal.
Interestingly, being the dominant predator in their habitat, it is likely that a member of the species will benefit from a delayed kill; even if it isn’t the individual that caused the death. This is very possibly a demonstration of ‘altruistic’ behaviour whereby an individual’s actions benefit the population as a whole.
But what exactly do these injured animals die from? Certainly Komodo dragon bites can be sufficiently deep to cause fatal blood loss but this is not always the case. Something else must come into play. The nature of that ‘something’ has caused a lot of controversy in recent years as different studies have produced contradictory results. There are currently two major theories, the oldest of which is coming under increasingly heavy fire from supporters of its more contemporary rival:
The Original Theory: Harmful bacteria live in the mouth of the Komodo dragon and infect wounds the dragon inflicts upon its prey
This particular theory originated in Walter Auffenberg‘s book, ‘The Behavioral Ecology of the Komodo Monitor’, published in 1981. In order to understand why Dragon bites sometimes resulted in delayed fatalities, Auffenberg swabbed the gums of captured Komodo dragons and identified four bacterial species from the samples. Three were described as being common causes of infections in animal bites.
Around 20 years later, Joel Montgomery’s group repeated this test, but on a much larger scale and with far more sophisticated screening techniques. They identified 58 species, with considerably more seen in wild Dragons than captive ones. The group also injected Dragon saliva directly into the abdomens of mice in the hope that they might recover a bacterial culprit from any mice that died from these simulated ‘bites’.
Some, however, consider their results contentious. All of the bacterial species the group found are pretty common in soil, plants or on animals’ skin. One species – Pasteurella multocida – present in some of the infected mice, was assumed to play an important role in prey infection, since the Dragons themselves were immune to it. Unfortunately, the species was only present in 5% of Dragons’ mouths and it turns out it isn’t actually capable of causing fatal septicaemia at the rate seen in Dragons’ prey.
It is now increasingly thought that the bacteria found in Komodo dragons’ mouths are simply the bacteria that were growing on/in the reptiles’ most recent meals. This may explain why captive Dragons, which are fed fresh meat, have fewer bacterial species in their mouths than their wild relatives, which will eat rotting carcasses. This all makes for a conspicuous lack of compelling evidence to support the idea that Dragons have evolved to use bacteria as a ‘weapon’.
The Modern Theory: The Komodo dragon uses venom to incapacitate its prey
This idea arose from a 2009 study by Bryan Fry’s group in Australia. They noticed that prey wounded by bites from Komodo dragons show common symptoms; namely being subdued, bleeding heavily and finally going into shock. Interestingly, these are the same symptoms caused by venom released by members of a related genus of lizards called the Helodermatids.
With this in mind, Fry’s group performed a Magnetic Resonance Imaging (MRI) scan of a preserved Dragon’s head and discovered a large venom gland in the lower jaw. The gland was divided into 6 compartments, with separate ducts leading from each compartment into the mouth, opening out between the Dragon’s serrated teeth.
The team discovered that the venom contained 2,000 proteins, around a third of which were known toxins in related reptile species. Indeed, the Dragon’s venom composition was similar to that of snakes, containing anticoagulants and toxins that lower blood pressure, causing persistent bleeding and weakness.
Interestingly, unlike other venomous lizards, Dragons do not have teeth specially adapted for chewing and working venom into their unlucky victims’ wounds. Instead, Fry suggests that the Dragons, who don’t have particularly strong bites, use their serrated teeth to “grip-and-rip” flesh, forming deep wounds into which venom could easily flow.
The venom theory has more convincing evidence behind it than its predecessor and has become a far more widely accepted theory since its conception in 2009. It seems far more feasible that Dragons could have evolved effective venom, rather than evolving a co-dependent relationship with a variable bacterial population. The next steps in proving this theory may be to find evidence of Dragon venom in a prey animal, as well as physical proof that these venom glands actively work.
Despite all of this, however, the original theory still has a lot of supporters and has not yet been entirely ruled out. It is likely that the scientific community will remain split on the issue for some time to come. One thing we can all agree on, though, is that this fascinating beast has evolved a highly effective killing mechanism, which makes it both a powerful and intimidating predator.
Guest post by Ian Wilson
Learn a little more about Ian:
“I’m currently about to enter my fourth and final year of a PhD studying the genetics of the human parasite Entamoeba histolytica. I’m based at the University of Liverpool, which is also where I completed my undergraduate degree in Microbiology. I’m really passionate about improving the public’s relationship with science and I aim to become a full-time science communicator when I finish my PhD so I can really get stuck in!”
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