Pet Peeve -- Big Underground Monsters

I realize that this is a classic image – the giant monster from beneath the ground, often a dragon or something. That it’s from a dark and shadowy underground lair just adds to the aura. Where would The Hobbit be without Smaug snoring away atop his mountain of gold (inspired by the dragons in Beowulf and the Nibelung stories?

But life underground is tough. There’s no sun to input energy into the system. And unless you’re in some comparative rarity like Mammoth Cave, most caves are pretty small and cramped, with bottlenecks preventing free movement.

So cave creatures tend to be few, isolated, often not fast and sometimes blind. There’s not much to eat and not much space to turn around.

Nevertheless, horror movies keep giving us improbably large things living in caves. Worse, they sometimes freakin’ fly, which seems a singularly pointless ability in most caves (bats notwithstanding – but they live in caves where they have access to the outdoors).

The Descent (2005) – I have lots of other problems with this film about six women spelunking, but my biggest problem comes when the encounter the blind albino underground “crawlers”. Really? The women have been descending a long time before they find the crawlers – and there are quite a lot of them. The question “…and what are they eating?” is supposed to be answered by a den full of human and animal carcases, but that just leads to the question “So where did those come from?” Are therte spelunking cows? Ultimately, of course, the questions are irrelevant – it’s a horror movie that needs a thread-thin justification for the Evil Bad Things that pursue and threaten Our Heroes. But I can’t turn off my doubt for this and just coast.

The Cave (also 2005) A group exploring a cave in Eastern Europe encounter a group of man-sized things vaguely like the H.R. Giger-designed Alien in the cave. They eat people, and they fly. Underground. Right. The film instantly lost me.

2005 must have been a good year to underground-dwelling people-eating things, because it also gave us The Cavern, which I haven’t seen. This turns out to be a feral human being. But, again, what’s he been eating all that time? I never saw this one.

Related to this is the Giant Earth-boring Underground worm-like thing. I have to admit, although I love Frank Herbert’s stuff, his Sandworms of Arrakis never made a bit of sense to me. Any large creature in a desert environment makes no sense – to feed its bulk, simply to keep existing, requires a huge intake , preferably of unresisting herbivores. A Sandworm really needs something like huge herds of elephant-sized shmoos to survive. Only there isn’t anything like that, because Arrakis is a desert planet, with negligible vegetation and small creatures like the Muad-dib sand mouse. Arrakis’ ecology doesn’t make much sense even without the sandworms, unless Herbert hasn’t told us everything, but the sandworms take the cake. Even if they’re torpid all the time they’re impossible. But having them burrow deep underground is beyond impossible. Moving that much bulk through highly resistive earth would require huge reserves of energy. No animal on earth does anything comparable (burrowing creatures on earth either do so relatively slowly, or only burrow through a very shallow surface layer)

Similarly, the worm-things in the Tremors movies and TV show are beautifully imagined and make for clever films. But they don’t make an awful lot of sense, either. What the hell do they eat most of the time? Where do they get the enormous amount of energy needed to burrow – at high speed, no less – under packed dirt?

That’s the example I thought of when I read the thread title. I imagine Smaug just crashes in the cave and uses it to stash his gold. When he wants to go out for a meal and stretch his wings he spends his day outside. Though, yeah, if you’re a young dragon just starting out, it must be hard to find good cave real estate of a proper size and remoteness.

You mention giant worms, which are implausible. I think of giant worms as another example of the B movie tradition of taking a bug and enlarging it to terrifying size. Which is always scientifically implausible-- a giant spider, or any big-ass critter with an exoskeleton, would not be able to move.

Other than that, your examples are mutated humans or human-sized things living in caves. Which on the face of it is not so implausible. Humans are small enough to move around comfortably in many cave systems, and caves often have rich ecosystems with bats, insects and even blind cave fish that could provide plenty of good eatin’ for your average feral blind albino mutant.

I think you’re right and you’ve just ruined a whole bunch of movies for me…

I guess hypothetically I could imagine a cave that was rich with organic materials; e.g. it periodically gets flooded and silt drains through. But it wouldn’t be a largely sterile environment plus apex predator, it would have a whole ecosystem.

Regarding the worms, I guess you just have to think really outside the box. Like on another planet, species have evolved a mechanism that can move them quickly through the soil of their planet, in a way that nothing on planet Earth ever evolved (or our soil is unsuitable for the technique). And, furthermore, there is essentially a soil “ocean” of many creatures and ecosystems (although, I guess if the worms can move efficiently through the ground very fast, maybe just munching on billions of earthworms would be sufficient).

The biggest problem with the sandworms of Arrakis is that the sandworms are the ecology. The entire ecology is made up entirely of the sandworms, and the sandworms fill every niche at once. Sandworms eat sandworms. They produce the oxygen which they also breathe. All of the water and element cycles go through sandworms to sandworms.

Well there you go. There’s good eating on a cake.


I don’t know if this counts as spoilers, and it’s been a while since I’ve seen it, but I thought the monsters were all in their heads and the main lady was actually killing them all herself. So they weren’t supposed to be real.

No, you don’t get it: the sandworms take the cake!

Yes. And eat it. Thus, their food source.

Yes, these movies do require a large suspension of belief - just like any inner world “Pellucidar”. But that’s part of the tension. The monster is out there lurking in the darkness. And there’s almost nowhere for the protagonist to run. (Latter reason why “crisis on an airplane” movies are so popular.)

At least Star Trek made it plausible with their Horta.

Nitpick: while Mammoth Cave is quite long, its entrances and passageways, while larger than the average cave, are still not comfortably dragon-sized width or radius-wise (although a smallish dragon might be able to fit in the natural entrance).

Whereas Carlsbad Caverns, amongst a very few others in the world, does have an entrance where most traditionally-sized dragons would be able to enter and exit without having to contort themselves.

Oh. I thought you were going to eat the cake.

Not that plausible., especially if you’re really cut off from the outside and the sun.

I propose to you the example of Injun Joe in Mark Twain’s Tom Sawyer – trapped in a cave and starved to death. He reportedly took as a model a case of a guy ho WAS trapped in the local cave. He didn’t starve to death before he was found, because he ate bats and the like. But bats come in from foraging outside. If he’d had to stick to undeground grub (heh!), he’d likely have starved, too.

Gotta admit, the Horta bothers me in a way, too.

Sure, they eat rocks, basically*. Likely they dissolve it with an acid mix, of which hydrofluoric acid must form a main component. I wouldn’t want to be in a cave where HF had been used recently. The stuff is nasty – gets in your skin and eats down through it into your bones, which it attacks. And ypou don’t even know it, because it numbs you. They have to cut away affected flesh. I had a lab co-worker missing sections of flesh because he’d gotten HF burns. I’ll bet if you’re around hortas, the atmosphere is full of HF vapor or droplets, and if you breathe that…

*Kid joke: What’s big, red, and eats rocks? Answer: A big red rock eater.

I wasn’t considering dragons --mdragons don’t bother me – they go out of the cave and eat outside, coming back to sleep. So not having an entrance big enough for dragons doesn’t invalidate my complaint.

Yeah, Smaug and his ilk aren’t really “underground creatures”: They may sleep underground, but the ecosystem they’re a part of is mostly the surface ecosystem, with cows and lake-fish and humans and other things to eat.

Now, some dragons in fantasy are ecologically subterranean, but then, you have to make some level of allowance of “because magic”. In D&D, for instance, many varieties of dragons can subsist entirely on various minerals, even minerals which are chemically inert in our world, because their metabolisms aren’t subject to the mundane rules of our world.

Though, of course, it’s always hard to tell how far to take “because magic”. Those same D&D worlds have underground cities of drow and duergar, who subsist on fungus-based agriculture… which glosses over the question of where the fungi get their energy from. Are the fungi themselves magical? Are they grown in caves with other magical energy sources? Do the occasional surface raids by the underground dwellers somehow bring back enough Calories to meet the whole system’s needs?

He tried; at least a little bit. Sandworms are filter feeders, eating bacteria that live in the sand. Sounds good, lots of real life examples of giant filter feeders. But the bacteria survive by eating spice, and spice, of course, comes from the worms, and is the waste produced from eating the bacteria. It’s unclear to me where external energy enters the system.

Arrakis has barely any plant life, and obviously no oceans with photosynthetic plankton. So, the oxygen comes from the sandworms, and is a byproduct of the mechanism they use to dissipate the heat from the friction of moving through the sand. Still no good explanation of where the energy required to move that fast through the sand comes from.

The monster from The Lair Of The White Worm gets at least some of it’s sustenance from human sacrifices. Also, it arguably has the best theme song of any underground monster.

I thought they preferred Bacon.

Sandworms not only both bake the cake and eat it, but they make the cake ingredients from their own excrement. And their offspring. Which they eat. And they use their own waste heat to fire the cake oven.

Soylent Dune is WORMS! It’s WORMS!

The thing that always bugged me about the worms, even before I understood their life cycle violated the laws of thermodynamics, is, how deep are these deserts? Getting sand both unpacked enough for worms that large to move through, but deep enough for them to move undetected from the surface, should be impossible.