I'm thinking about creating a creature that can eat anything. Perhaps a rock, if it looks "tasty", or a chunk of a spaceship, or even a piece of itself if it wishes. Of course, it seems silly, so perhaps there are some materials that are impossible for it to eat (its stomach?), and the question is:

How small the set of types of non-edible matter can be and how to explain it?

I'm not saying that it has to be sentient, e.g. it might be a gel that just turns the matter it encounters into its own. The only requirement is that, when it eats something, that thing becomes a part of the creature, so it becomes movable. To explain this further, the creature can certainly excrete, digestion is not necessary (e.g. if it can incorporate the matter as it is), but it cannot act like a box/container (I would not consider a safe to be such a creature despite the fact it could "eat" anything that fits in it and then "defecate" its contents later when asked to).

My approach was via some mouth-like organ that would transform matter into something the creature could eat, but I had no idea how to solve the energy requirements.

  • $\begingroup$ unless there is a fission/fusion reactor in the creature he would need to be more selective than eat anything, it would also need some specific materials more than others $\endgroup$ Commented Oct 20, 2014 at 12:39
  • $\begingroup$ “The only requirement is that, when it eats something, that thing becomes a part of the creature, so it becomes movable.” – I am not sure that I understand this. Everything the creature eats has to become part of it? So the creature does not excrete anything? Also, while we are at it: Does the creature only have to be able to ingest everything or does it also have to digest it? $\endgroup$
    – Wrzlprmft
    Commented Oct 20, 2014 at 13:36
  • $\begingroup$ @Wrzlprmft I've added some clarification. $\endgroup$
    – dtldarek
    Commented Oct 20, 2014 at 13:53
  • $\begingroup$ @dtldarek: I meant digest in the broader sense of using it in some way. With other words: Is it acceptable if the creature ingests something, does nothing with it that is of use to the creature, and then excretes it? E.g., we can ingest small balls which are made of a material that does not react with our biology and thus are excreted more or less intact. Would you consider this as eating for your question? $\endgroup$
    – Wrzlprmft
    Commented Oct 20, 2014 at 14:07
  • $\begingroup$ @Wrzlprmft Yes, as long as the creature could, if it wanted, to eat half of that thing (i.e. to split it, perhaps into very small pieces). For example humans with their teeth cannot do anything to a small platinum ball, so I wouldn't consider "eating" it. On the other hand, if a creature found a big piece of metal and took a bite, and then excreted that piece more-or-less intact, that would still work for me. One intention is that such a creature would be unstoppable by conventional means like walls etc. $\endgroup$
    – dtldarek
    Commented Oct 20, 2014 at 14:24

5 Answers 5


The closest thing that I have ever read about is the Dreen from John Ringo's Looking Glass series.

The Dreen use biological based technology rather than mechanical technology. A Dreen "Tank", for example, is a living creature with heavy weapons and armor. Even Dreen spaceships are alive and grown.

Obviously, to produce items such as tanks and spaceships, the Dreen would have to consume a tremendous variety of minerals and such, so the can "eat" pretty much everything. Most of the actual eating is done by a rapidly spreading complex mold-like organism that can break down any material. It is part of a vast collective consciousness and so can be controlled (so that it does not, say, try to eat the walls of the spaceship carrying it). Because their technology is biologically based, it does focus first on consuming organic products, such as human bodies.

It also contains the genetic programming to produce all of the Dreen biological forms. This means that if even a small amount of the Dreen "mold" escapes containment (and remember, it can eat anything), it can eventually produce an entire new Dreen colony entirely from scratch.

The Dreen are probably one of the nastiest and most fearsome creatures that I have ever read about in science fiction.

  • 1
    $\begingroup$ Sounds to me like the Flood (Halo) or the Zerg (Starcraft) figured out how to use non-organic materials just as effectively as organics. I will have to pick this series up. $\endgroup$
    – BlueBuddy
    Commented Oct 21, 2014 at 0:09

An organism that does this would most likely need to have been designed specifically to do it, that means genetic engineering and possibly even cybernetic enhancements.

In general when digesting things you want to pull them inside yourself so you can control the environment. You could then have a snake-like creature that unhinges it's mouth and engulfs the object to eat within itself. It then has a series of digestive systems as the object moves through.

To break down larger items it would also be able to secrete digestive enzymes and generate a certain amount of brute force, enabling it to break up objects into smaller chunks that can then be consumed.

Each stomach would have a series of mechanisms both chemical and mechanical to break down a specific substance or set of substances and then retrieve anything useful that it finds within.

First it might dissolve and consume any organic material, then another stomach might break down plastics, then another extracts metal, and so-on through the process.

A recycling worm might be engineered that you released into a ruin, it then consumes every it finds and separates it out. Growing scales made of individual types of metal, consuming organic matter and plastics to fuel itself, etc.

You would most likely need to supplement its diet though, as there is not very much nutritional value in reinforced concrete.


I would break the concept up into levels of "eating." Obviously the most complete version of eating is the one we are used to: between the mechanical crushing of our mouth and stomach, and the chemical reactions in the stomach and intestines, it turns the "food" into simple component molecules that can be transferred to anywhere in the body where they are needed.

For a different version, consider the human consumption of gold foil (why not?). We mechanically tear it into pieces which can travel through the digestive tract, but our chemical digestion does not occur with Gold. Instead it travels through relatively unharmed to be eliminated, with much of its physical layout intact.

The deciding factor between these is whether the creature actually gains from eating the material, or if it merely find its way into the digestive tract, to be eliminated later.

A third case would be to view "eating" as a defense mechanism. Instead of having a stinger or similar defense mechanism, if a creature could render its attacker inert by consuming it, it would be more than comfortable doing so, even if it did not gain any energy from it.

I think anything could be fair game along these lines, especially if you include defensive binge eating. A creature that can withstand massive massive heat could quickly disassemble and oxidize just about any compound (5000 degrees would be sufficient for everything shy of perhaps Tungsten). It would be an energy inefficient eating process, but it would work.

The only thing I think it could not eat would be a toxin crafted to take advantage of any digestive weakness it may have. For example, the creature would need to decide if something is food (using food processing mechanisms to acquire energy) or an enemy (using destructive mechanisms, which may cost energy). An enemy which appears to be food could subsist long enough to do internal damage. Such a toxin would have to be highly specialized.

One interesting direction to take is that "interesting" things would happened to try to eat exotic things. For example, if there was a way to turn a creature inside out without killing it, what would happen if one creature ate its inside out breatheren? (This is similar to the argument in DnD about turning a bag of holding inside out). A specialized toxin might try to emulate the sensation of eating its bretheren in hopes of preventing a destructive digestion from occurring.


The sentient crystalline formations in Anne McCaffrey's Crystal Line, called Jewel Junk by Killashandra Ree, were capable of metabolizing almost any material they came into contact with provided there was enough energy available to the particular node to perform the molecular disassembly. It even eats through rock. The only thing it can't (won't?) manage is Ballybran Crystal which is a quartz-like material with some very strange properties that may not be strictly 3-dimensional.

In The Vortex Blasters by E. E. "Doc" Smith the loose atomic vortices are eventually discovered to be incubators for energy-based creatures. The vortices destroy pretty much everything in their surroundings until ultimately they form a molten crater. Part of the destruction appears to be the conversion of matter into energy to "feed" the incubating life. In this case not the life-form itself but the artificial (from our perspective) life support unit.

But if you want something scarier, try any of the various Grey Goo stories - Drexler's Engines of Creation, the Replicators from Star Gate, the nanoswarms in Michael Crichton's "Prey", etc. These are a form of created pseudo-life that disassemble anything with the requisite elements for reproduction, converting it to new copies of the "cells" of the goo. Add some sort of computronium to the mix and you have a potential hive mind scenario. Check out the noocytes from Blood Music by Greg Bear for a slightly more biological basis for this. Still engineered, but biologically so.


Robert Forward's Camelot 30K.

It's not quite your description because what I'm thinking about is a plant, not an animal. The plants will process anything that's a solid in their environment (and as the "30K" in the title refers to the temperature, that's most things). While they don't actually have a use for many of the elements they process them into berries that are desired by the species that farms them.

While we never find out the true origin of the aliens it seems to me that they must be the product of some very advanced genetic engineering as there's simply no path by which they could possibly evolve. I would think the basic idea could apply to an animal as well, though--something engineered as a mining tool. Such a creature would be designed with metabolic pathways to handle as many elements as possible.


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