Are Dragons an Invasive Species?

When fire breathing isn’t just cool and intimidating.

Apparently, I have far more to say on the subject of dragons than I thought I did. So I’m ploughing on with the subject for a few more posts and then I’ll move on. This time a broad consideration of the environments in which a dragon might actually live, and the impacts that dragons could have on those environments.  

In the film How to Train Your Dragon, ‘Toothless’ the protagonist’s dragon, is holing up in a cave in a forest. There’s moss and grass and trees all over the place. In the ‘befriend the monster’ montage, Toothless burns a circular patch of the grassy ground to sleep on.

Ok, mate, mate… before you even start; it’s a film aimed at kids. You can’t seriously be about to launch into a tirade on the environmental consequences of a dragon in a film aimed at kids. Just chill.

But, much like a dragon, I have no chill. Because that’s precisely it. What’s a film aimed at kids and families trading on? Stereotypes, archetypes, the cultural easy-access points and shorthand. Any bit of information that is available in the broader public consciousness. In this instance that shorthand is the link between giant fire-breathing reptiles and highly improbable surroundings. I argued in the original post of this impromptu series that the basic unquestioned received wisdom about dragons make very little sense. Forests are common enough, but it extends in every direction. If you’re writing a novel or a film with a dragon in it, are you thinking about the habitat in which a dragon lives? The relationships between dragons and the way that the interactions between them and their environments could occur, drastically alters the settings themselves, and thus the stories, that they are involved in. 

Take the most obvious home for a dragon: the fractal spines of snow-covered mountains. It’s very majestic. Mountains are a great place for offsetting the potential for continuous conflagrations that forests engender. Lots of rock, frequently a lot of snow, there’s not much there for them to set alight, therefore you’ve got plenty of room to be a dragon without accidentally killing your entire food supply in a bout of enthusiastic barbecuing. However, reptiles are cold blooded. They tend to hibernate during the cold months of the year. Ectothermic creatures have no internal heating capabilities and so they rely heavily on the sun for heat – hence they are notorious sunbathers. There’s no reason for a dragon to be immune to hypothermia. It’s the kind of situation that could create a sort of mystical take on the irony of what’s known as ‘paradoxical undressing’ – the phenomenon that drives people undergoing advanced hypothermia to strip naked. If you lack a way to heat yourself internally, you might attempt to heat yourself externally…

Caves are a common one and, broadly speaking, they’re a bad fit. There’s very little about caves that would suit a giant reptile – they’re too small, too cramped, too cold, and have far too little food. While you can theoretically get away with just sticking them in a relatively open surface-level cave, the general image is of a dragon having stashed it’s hoard fairly securely into the side of a mountain, using it as a kind of proto-Bond-villain lair-of-doom, so we can assume some level of depth, else why even make a big deal about the caves in the first place?  

The space issues you can offset with suspension of disbelief – nobody is going to question Moria-style cave systems. Cave systems can get pretty sodding big anyway, the Hang Son Doong caves in Vietnam are pretty spectacular in scale, and generally we’re not amazingly familiar with the subterranean bowels of the earth anyway, so there’s not generally a strong basis to start nit-picking like an ape on grooming day.  

However, much like the mountain peaks, it’s cold in caves. You could be forgiven for expecting that hundreds of thousands of tonnes of rock and earth would have an insulating effect, that heat would get trapped between the molten heart of the earth and the fatty layer of crust and soil. Not so, apparently. Most of the heat you experience above ground comes from the sun – that much is obvious. Moving below ground is just putting things between you and the sun, and you have to go pretty far down in order to heat up again.

The Mponeng gold mine in Gauteng, South Africa, descends more than 4 km below the surface. Down there the temperature of the rock reaches 66 C.  The deepest natural cave we know of, Veryovkina Cave, is more than 2 km below the earth at its deepest point. The water and air temperature is about 7 C at that point. At 100 m below ground, those temperatures are around 1 C. It’s thought that, owing to structural integrity versus pressure, the deepest a natural cave can be is about 3 vertical km.

While it’s not uncommon for reptiles to spend time underground, most of this is in burrows and other shallow subterranean habitats, well above even 100 m, let alone 2 or 3 km. Down at those kinds of depths there is zero light and significant tracts of cave networks are submerged. The animals that live down there are frequently eyeless and colourless. At the bottom of the world life is more HP Lovecraft than JRR Tolkien. For a dragon to be comfortable in subterranean landscapes they’d have to go all the way to the bottom for the environment to be hot enough. Even if we allowed them to keep their staggering size, dragons would somehow have to feed adequately for millions of years. In a habitat where feeding is generally not easy, the chances of a species of dragon surviving down there are zero. There just aren’t enough calories.

All this said, you can handwave the scale of the life in the deepest of pits. Given the broad unfamiliarity with the environment – fittingly, the rule of ‘here be dragons’ still applies. Just remember that the ‘dragons’ your deep cave environments are likely to produce, are far and away freakier than the giant scaled dudes that Beowulf and Bilbo were tussling with. One of the best parts of The Lord of The Rings is just Gandalf describing his time after his tandem skydive off the bridge in Moria with the Balrog: “Far, far below the deepest delving of the Dwarves, the world is gnawed by nameless things. Even Sauron knows them not. They are older than he. Now I have walked there, but I will bring no report to darken the light of day.

Where dragons are concerned, I’m not convinced that caves are their habitat. It doesn’t make a whole lot of sense. Sure, they could just go for a cave close to the surface, so they’re not dealing with frigid temperatures, but if that’s the case then why bother at all? Why not just find a plateau or a high enough open space and sleep there? It’s not like dragons have much in the way of predators and a difficult enough incline would give them ample ability to survey the surroundings for the odd idiot in a suit of armour, so they could watch at their leisure while the poor sods tire themselves out before being cooked, presumably in the name of the local nobility or something…

One reason you might find a dragon in a cave does jump to mind. A few paragraphs back I mentioned paradoxical undressing in hypothermia sufferers prior to death. The other part of that process is known as ‘terminal burrowing behaviour’. It describes the propensity for hypothermia victims, having squeezed themselves out of their clothing, to then attempt to squeeze themselves the most confined spaces they can find – beneath beds or into cupboards and shelves. They die like that. If you want an explanation as to why you might find a dragon high up in a mountain lurking in a cave, you might just be looking at the last instinctual attempts at self-preservation taken by a dying and desperate animal.

Dragons and forests do not mix. That much is obvious, but it seems like it bears saying. They don’t even have to live directly in the forest, they can be living on the stock forest-surrounded mountain. Anywhere with dense vegetation doesn’t work. Any dragon living around a forest or a jungle or just a grassland, is going to render the entire area into an Australian-style inferno sooner rather than later.

If these areas were to start out covered in thick vegetation, then they wouldn’t remain that way for long. Which, from a story perspective, is pretty good. How do you know there’s a dragon nearby? There is no life anywhere. The entire landscape has become an ash-coated wasteland. Anything that grows gets immolated. The environment of a dragon has to be fireproof. It it’s not it won’t last because the chances are that over a long enough timeline, anything that can be burned will be burned. Not necessarily purposefully, but dragons are just going to act like natural wildfire accelerants.

Deserts and badlands work as a reasonable site for nesting grounds. Open space, hot, little in the way of vegetation to set alight. Unfortunately, there’s also little in the way of large prey in a desert, so while a desert makes good sense for a dragon to live in, if they want to eat then they’d have to find somewhere nearby with a large population of large animals to hunt for food.

Volcanoes might actually be a good choice for a dragon’s lair. Somewhere hot enough to suit the external heat sources required by cold-blooded animals, but volcanic ash and mud left behind after eruptions can makes for nutrient-rich soil, and so perhaps the ground would be fertile enough to regrow any destroyed vegetation relatively faster than a less fertile environment. If the vegetation does regrow densely enough in relatively quick cycles following fire-related deforestation, then areas around volcanoes could be a seasonal source of food for migrating animals, which puts an interesting spin on the dynamics of dragon activity in a setting.

It turns out that dragons are just a lot easier to fit into a world when they don’t breathe fire. The fact that the archetypal western dragon can breathe fire makes their existence almost paradoxical. To quote Fight Club, “On a long enough timeline, the survival rate for everyone drops to zero.” That timeline becomes vastly shorter when dragons are involved. They are natural extinction machines.

I’m going on the presumption that, though clever or cunning, a dragon is still an animal. An animal with the ability to breathe fire is going to do so at some point or another, and the probability for fire being breathed in an environment containing flammable materials rises over time and with any increase in the total number of dragons in a theoretical setting. To be fair, I’d argue humans are just as likely to do the same thing. The ability to create massive amounts of fire at any time in a world full of things that burn, without the adequate limitations on resources or countermeasures against sudden outbreaks of fire, is likely to create a significant number of problems. In this scenario, the comparatively frequent ignition of massive wildfires isn’t a potential, it’s an inevitability. 

If a dragon sets an area on fire and reduces everything in it to ashes, it depopulates that area, either directly through the various problems of massive fires, or over time by depriving an area of vegetation thus depriving entire sections of the food chain of sustenance – and by extension the entire food chain of an area when the ecosystem collapses. Over time a lot of animals might evolve to migrate in herds, you might get an ecosystem that evolves to favour anything that travels in swarms. Mobility in an environment that is prone to conflagration would benefit the passing on of genes. If dragons do not adapt to this trend, they die of starvation when they run out of food because their food has either died in a fire or migrated to a not-burnt area. To survive, dragons would need to follow their food from place to place in order to be sure that they could reliably find the calories necessary to feed themselves. There are various evolutionary consequences for dragons following the same logic, but I’m going with the idea that the standard template dragon is the evolution that ‘won’.

So, knowing that dragons can fairly easily destroy an entire ecosystem and render massive chunks of land completely uninhabitable, it stands to reason that if they’re forced to travel around in order to feed themselves because they require food sources that cannot survive low-vegetation habitats, that they are also likely to chain-destroy environments over time. The total area of life-sustaining land is likely to be a shrinking one, as the environment is going to shrink faster than it can regrow. Even if all of the flora on the planet took on the characteristics of Japanese knotweed or some similar fast-regrowing plant life, the likelihood is that it’s going to replenish too slowly to sustain herbivorous and insect populations.

On a long and extreme enough timeline, dragons have the capacity to render entire continents, if not their entire planets, uninhabitable and inadvertently cause their own extinction by inadvertently causing the extinction of everything else. If your setting is a medieval fantasy and features dragons, consider the idea that there is a reasonable probability that mankind never has the chance to reach that point in history.


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