Smaug Breathes Fire Like A Bloated Bombardier
Beetle With Flinted Teeth
What does a narcissistic flying reptile that loves the taste of crispy dwarves have in common
with a beetle that shoots hot, caustic liquid from its butt? More than you think.
A few weeks ago, audiences were finally
treated to the Cumberbatch-infused reptilian
villain from J.R.R. Tolkien’s classic The
Hobbit. Smaug (pronounced and interpreted as
if you smashed together “smug” and “smog”)
is a terrible dragon that long ago forced a
population of dwarves from under a mountain.
He laid claim to all their treasures. He burned
all their homes. The titular character of the
book is then tasked with helping a company of
these displaced dwarves take back the
mountain from the beast. It wouldn’t be easy—the most common descriptor of a dragon is “firebreathing,” after all. But unlike other aspects of the book and now the film that are wholly magic,
Smaug’s burning breath is actually one of the least magical, and can be wrangled into
plausibility. Doing so involves looking inside a beetle’s butt, a Boy Scout’s satchel, and a bird’s
throat.
Even though they don’t exist, dragons, like all other real organisms, have evolved over time.
They weren’t always so huge. Dragons were once the size of cattle in popular depictions. And
some of them didn’t have wings, or breathe fire. Today’s dragons are uniquely terrible lizards—
massive, spiked, voracious, flame-spewing beasts. If even mythical beasts evolve, how would a
real dragon evolve its most recognizable ability?
First, a dragon needs fuel.
This aspect of dragon fire is the easiest to imagine. In fact, you are probably producing dragon
fuel as you read this sentence. Methane—a highly flammable gas that is produced naturally by
bacteria in the gut—is constantly bubbling up in your stomach as microbes munch on your food.
With a large stomach or even a separate organ to house this gas, a dragon could easily eat
enough food to produce a large amount of methane.
If methane isn’t the fuel, another more exotic liquid might be. Take the bombardier beetle. This
incredible insect evolved (yes, evolved) a way to harness the chaos of chemical reactions in a
defense mechanism. When under threat, the beetle excretes two chemicals from two separate
reservoirs that mix in a third, producing a very hot liquid and the gas needed to propel it into the
face of some would-be predator.
When two liquids come together, react, and spontaneously combust, they are called
“hypergolic.” The bombardier beetle isn’t the only organism that takes advantage of hypergolic
chemicals; we use them in rocket fuel. (You can see a nice small-scale demonstration of a
hypergolic reaction here.) A dragon could do the same. It wouldn’t be the first fiction animal to
do so either. Who can forget (or maybe remember?) the giant, fire-spewing “tanker” bug from
the ironically classic sci-fi movie Starship
Troopers?
A barrel with hypergolic fuel for loading into
the MESSENGER spaceprobe in background. In
other words, potential dragon fuel.
If a dragon convergently evolved chemicals that
combust upon mixing, like the explosive
bombardier beetle, the reaction it harnessed
could result in fire…terrible, terrible, fire. But
these chemicals aren’t cheap, biologically
speaking. A dragon would have to make a large
biological investment to produce them. That
would at least be consistent with dragons’
voracious appetite for dwarves, men, and
livestock—the winged beasts need to produce
more rocket fuel.
The next step in fire breathing is the spark.
Before you see a dragon’s flame you see the
teeth. Terrifying spears and stake knives that
click and clamor inside gigantic mouths—giant
flints. Some dragon lore speculates that dragons,
like modern birds, ingested rocks and stones to aid in digestion. Over time, stories say, the
minerals would coat dragon teeth. Or maybe the dragons could hold some minerals in their
mouths. Either way, quickly biting down on these minerals could produce a spark. Like a Boy
Scout’s trusty flint, clicking dragon teeth would provide the ignition for either a glut of methane
gas or a gush of hypergolic liquids (if needed).
Another possible spark could come from more detailed physics. If dragon teeth had piezoelectric
properties—where mechanical stress produces small jolts of electricity—a combination of
methane exhalation and teeth grinding could light the fire. Or maybe the crushed stones and
minerals could vaporize in the air ahead of the methane and combust, as metals do on helicopter
rotors in the Kopp-Etchells Effect. Perhaps the dragons could expel the liquids or gases so
quickly from their bellies that static ignition would occur. (When cleaning out supertankers, for
example, all the flammable vapors first must be vented. The high-pressure water jets used in
cleaning can generate sparks that ignite the gas.) Could a dragon evolve an organ that produces
its own spark like a kaiju from Pacific Rim? Science has many sources of ignition to choose
from, it’s just a matter of what the fiction allows.
Dragons are basically our pipe-dreams of what birds would be if they still looked liked ancient
dinosaurs but followed evolution’s flight plan. Dragons’ similarities with birds (themselves in
fact dinosaurs) could provide the last critical link to flame flinging. With multiple stomachs
aiding digestion, birds—and by extension, dragons—could evolve a specialized sack for storing
either methane or combustible chemicals. Birds also eat stones and rocks to break up tough
material in these stomachs, so Smaug munching on minerals isn’t that far-fetched either.
There are still a few problems. Dragons are huge, undoubtedly heavy creatures that would likely
rip their own wings to shreds when attempting to stay airborne. Also, holding both a large
amount of methane or hypergolic chemical internally is explosively problematic. Breathing out
fire is a problem in and of itself. A dragon would need specialized tissues in the mouth to deal
with the incredible heat, and lungs large enough to force the flames a significant distance (unless
it was a dragon from Skyrim, which specializes in powerful blasts of voice). I imagine that a
more scientifically plausible dragon wouldn’t be the slender, monitor lizard-like monstrosity we
see in the latest Hobbit film and more like a flightless, bloated flame-thrower.
What does this mean for The Hobbit, a universe already filled with magic? Nothing at all. The
film has its own problems to deal with. Nonetheless, I found Smaug’s fire breath to be one of the
least distressing suspensions of reality. Whether a “true” fire-breathing dragon is filled with flint,
gas, or rocket fuel, one thing is for sure: Where there is Smaug, there is fire.