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?