How would the anatomy of a metal-eating bug work out?

Question

Background:

The creature is bug-like, and similar to an armadillo in size. Its diet consists of metal, and is found underground in large colonies. It uses the metal it ingests to:

• Enhance it's shell and claws, distributing as needed.
• Expel any excess/inferior metals as a refined alloy with a unique mixture of metals (depends on what they've eaten, and what their shell is made of).

They easily chew the metal, they are all born with super hard mandibles that shear the metal easily. However, the only issue I'm finding is how they would digest/distribute/retrieve metal in their bodies.

They live off of nutrients found in the rock around the ore, so they don't always eat to improve, but also to survive.

Restrictions:

This must be science based, and have backup claims stating (or showing!) that the system would work. I can stretch a little for some things, the systems don't have to be proven to work together, just individually.

Answer 1

I need to start with two frame challenges

• First, you haven't said so, but I agree with @L.Dutch: your creature must eat organics like every other creature on Earth or it simply won't survive. The critter needs nutrition! But, as is famously quoted, your armadillo-sized-metal-eating critter, (let's call him ASMEC) cannot live on bread alone!

• Second, as Gnudiff points out in his comment, armadillo-sized bugs aren't feasible. You can handwave this one, or convert the idea to an armadillo-sized animal. I'm approaching this somewhat from the animal side, but the answer could be read either way.

There is a glorious bacteria in the world, Cupriavidus metallidurans, that uses an enzyme to ingest toxic gold, convert it to a water-soluble condition, and then (*ahem*) poop it out as pure gold. That gives us a real-world basis for what you need.¹

Introducing Freezium Pheonixus Metallidurans...

A stomach enzyme that breaks down (name your metal here or NYMH) into a water-soluble version of NYMH, which is then secreted like sweat such that it coats claws and (probably) scales to create (as it dries) an ultra-hard shell around ASMEC. You could even assume that the metal additionally serves the same function as grit does for birds: to help with digestion by grinding up the organics ASMEC eats.

The sweating process is slow enough that as ASMEC moves around, it creates the necessary articulation between scales, etc., to not become a solid statue. At a guess, you'd probably find this guy violently shivering from time to time to both help distribute the sweat before it dries and to shuffle everything to preserve articulation.

Have you ever seen a dog rid itself of unwanted water? Yeah... something like that. It would sound cool.

I noted your restriction and, though I've done my best, I'm ignoring it. Whomever is placing such a restriction on you knows too little about biology. As I mentioned in my (now deleted) comment, we don't have the tech to create life and don't have an example of an animal that does anything like this other than with hardened hair — so I consider the requirement of showing that the system would work to be non-binding. Consider it a third frame challenge.

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_{¹ There is also a microbe, feroplasma acidarmanus, that eats iron. If you wanted an alloyed metal on the ASMEC, you could have the microbe live happily on its scales and let it bed down on iron ore. 😆 It's that much more to justify the believability of the ASMEC.}

Answer 2

They would use commensal metal-oxidizing micro-organisms.

First - metabolism has 2 duties. You need energy to make you go. You need the raw materials you are made of to build / repair your body. We humans use carbon containing compounds for both - we burn some for energy and save some for building our bodies.

Your bug would need to eat carbon like we do, to build its body because insects are made of carbon like we are.
But if it had a source of energy besides carbon, it could use all the carbon it ate for body building and use the other stuff for energy. That would be efficient!

There are plenty of micro-organisms that oxidize metals and get energy from them. Iron is the most familiar but pretty much any metal that can be oxidized is oxidized by something to get the energy out. Read more https://en.wikipedia.org/wiki/Microbial_metabolism#Other_inorganic_electron_acceptors

Having a gut full of microbes to do your metabolic work is a fine thing for a eukaryote to do. Termites use commensal microbes to metabolize cellulose. Shipworms have a gutload of anaerobic bacteria that pass them energy from sulfur metabolism. Your bugs would have onboard metal oxidizing bacteria and would pass them finely chewed metal (and oxygen), and receive energy in return. They would excrete oxidized metals - rust etc.

I think that if these insects wanted to store ingested metals for later use that would make sense. I store the Wendy's fries I eat for later use right here (pat, pat). Storing metals in jaws and shells is fine. Then during the lean times they could metabolize these metals for energy as someday I may do with these fries.

Excreting refined metals is a little more of a stretch. Excreting pure metal oxides and sulfides would be expected, and excreting contaminants would be expected as well. A pure metal oxide is almost as good as a metal for a metalsmithing savvy human, because all you need is to smelt off the oxygen and you have the metal again.