system
Given the following post, respond as if you're commenting on Reddit:
human
[Edge of tomorrow] How do mimics sustain themselves?

What do they eat? How are they making those missiles that shoot down the drop ships?
gpt
In the novel's universe [\/meta], It is speculated the Mimics are essentially an engineered weapon.  The "seed", well the one that wasn't recovered before it went active, hit the middle of the Pacific Ocean.  

Then it began "mimicing" the creatures it found under the assumption said creatures must be near ideal for the world.  That's why the the things look vaguely lovecraftian.  They encountered deep ocean floor creatures and then amphibians and then finally land creatures as they worked their way up the continental shelves.

So the Mimics are likely cyborgs, for lack of a better word.  They probably don't actually eat as eating would be inefficient for such designed creatures, but are crafted or spawned based on whatever materials are available.