Some of D&D’s most iconic monsters and villains make their homes deep underground. There’s entire dark cities, Duergar fortresses, and Mindflayer laboratories all connected by a near endless network of tunnels, caverns, and cave systems. In this nefarious subterranean system they make their evil plots and wage brutal campaigns of conquest, unbeknownst to the surface dwellers above. For all the life and activity down there, there sure isn’t a lot of information about what fuels these creatures. Specifically I’m talking about their food.
I’m going to be taking a campaign setting agnostic perspective here, so you can run with this wherever your game happens to be set. Also, I don’t want a bunch of people emailing me to tell me that in some obscure corner of Forgotten Realms cannon Drizzt mentions some delicious underground pear. But even still, Forgotten Realms is guilty of most of the things I’m going to talk about.
So, what is there for all of the creatures to eat underground? Aside from numerous civilizations, every D&D Monster Manual regardless of edition has an abundance of giant carnivores: Beholders, Darkmantles, Formian Giants, and Hook Horrors just to name a few. With just a fifth grade knowledge of food chains, you know you need a large base of plants for herbivores to eat and the herbivores are then eaten by carnivores. Most material I’ve seen boils down to one organism: mushrooms.
Since mushrooms can grow without light, they seem like an easy choice to fill the plant niche. I have two problems with this. First, it’s boring. Second, it doesn’t actually make that much sense. Although many species of mushrooms can be grown entirely in the dark, they’re decomposers and thus need to feed off of organic matter. There are some rare fungi like Talaromyces flavus that can feed on rock (and even iron), but these are microscopic and don’t resemble whitecap mushrooms most of us picture. If we’re already taking some liberties and allowing for mushrooms to draw nourishment from solid rock, why limit it to mushrooms?
Let’s make a more interesting ecology, shall we?
We’ll keep mushrooms around, but they’re just going to be a small part of the larger food chain. Drawing on another organism that doesn’t need light to grow, let’s bring in some tube worms. Tube worms are chitinous cylindrical creatures they grow near the ocean floor and can reach heights of nearly 8 feet. They live so deep that light can’t reach them and survive through a process called chemosynthesis wherein the worm’s gut bacteria gets its nutrients from hydrogen sulfide. Let’s imagine a version of these guys down underground feasting on vents of natural gases. Let’s also make them edible… but barely. While maybe monsters underground can snack on these guys, the humanoid creatures have to prepare them in a very specific way to make them digestible. Perhaps they have to be slow cooked and then brined. Maybe if some player characters are captured by dark elves, they have to survive exclusively on a diet of disgusting pickled tube worms?
OK, let’s add one more thing to the bottom of the food chain before moving on. Burrowing animals like rabbits often feed on roots. So, let’s take this and take it to its most extreme endpoint. Since no carrot is going to grow down to a mile below the surface, we’ve got to find something that goes way farther. In Africa, we have a species called the Shepherd’s Tree that has roots that can extend beyond 200 feet deep. How about a tree that’s roots grow ten times that amount or more? Maybe on the surface there’s a grove of trees that have silvery or copper tinged leaves. None of the locals know exactly why, but you and I know that their unfathomably deep roots syphon vital minerals from far below. Their massive root systems might even be considered a nuisance by miners who notice them feeding on the veins of metal they’re trying to extract.
As I write this, I’m starting to realize I could go on about this for quite awhile, so I’ve decided to make this into a series. I think next time I’d like to get into food sources found in caves in our world. Specifically, I want to talk about how everything feeds on bat guano…
But my larger point to all of this is that people often ask how they can make their world’s more immersive. I think taking a moment to think through how living things interact in your setting is logically the best place to start. When players are exploring the deadly, alien reaches of the Underdark, it’s not super memorable or engaging to describe one mushroom patch and call it a day.