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I have an alien species similar to a caterpillar, the original idea was that the creature could eat different materials, digest them then combined with a very sticky liquid created in its body, it could spit it out in strings to form different structures.

Other than eating wood I originally wanted it to be able to eat metal ores to create really strong structures and pieces, eventually with a precision almost like a 3d printer.

This creature will also have the ability to generate electricity from a symbiotic relationship with electric bacteria or I may choose another method but that isn't too important for this question.

With the creatures ability to produce electricity and spit wires of material I then thought of carbon nanotubes, similar to spider silk covered in carbon nanotubes to conduct electricity.

I have trouble with either option 1) strong enough mandibles to break down rocks with iron, maybe with the help of acid to dissolve it then suck it up as it would have to have strong stomach acid or acid that doesn't replenish itself too regularly to dissolve the metal, and could this metal combined with the spit even conduct electricity 2) the creature naturally creates carbon nanotubes, I don't think this is possible in a living creature but it could be a good solution to add to the creatures sticky strings to both build strong structures and conductive wires.

So my question is what is the most possible situation, a creature that can eat and digest metal from rocks or a creature somehow naturally creating carbon nanotubes?

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    $\begingroup$ Reducing ores to metals in any quantity sufficient for building macroscopic structures requires vastly more energy than a non-magical living being can generate. Go with the nanotubes; they are carbon, after all, and living things already have exquisite metabolic pathways for manipulating carbon chains. $\endgroup$
    – AlexP
    Dec 31, 2019 at 17:44
  • $\begingroup$ @AlexP thanks do you know what kind of organs or biochemical process I should give the creature so it can make nanotubes? $\endgroup$
    – user69935
    Dec 31, 2019 at 18:02
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    $\begingroup$ Carbon nanotube spinnerets? I don't see how arranging carbon atoms in interlocked hexagonal cycles is fundamentally different from arranging them in interlocked chains; we just don't know how to make them in low-temperature low-pressure processes. $\endgroup$
    – AlexP
    Dec 31, 2019 at 18:17
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    $\begingroup$ For your option 1, I recently read something that mentioned looking for yellow oozy iron-rich deposits along riverbanks, etc - formed by bacteria. Something like that could be a workaround for needing strong mandibles to break up iron ore, it'd likely be easier for some creature to find and use these deposits like other creatures find salt licks... the shortcut: let something else do the work, of course :) $\endgroup$
    – Megha
    Jan 8, 2020 at 8:44

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Carbon nanotubes and metallic iron both require new biochemistry. Could you use wood and gold?

Eating wood then spitting it out to build things is a real thing. Some wasps do that to build their nests.

To have a thing that makes carbon you could process the wood. Wood is a fine source of carbon and biological organisms do carbon chemistry. However nothing to my knowledge processes carbon containing molecules like cellulose all the way to carbon alone - something like graphite or carbon nanotubes or diamond. That would be your fiction, but carbon chemistry is not fiction.

Having something biologic produce metal is trickier. I do not know of anything that makes iron, and one could argue that metallic iron is not a good thing in close contact with biologics - we are wet and salty.

But gold is a different matter. Gold is fine in contact with tissue. It does not easily oxidize. If you are looking for a conductor, it is an excellent conductor of electricity. And you can make metallic gold with biochemistry.

These Bacteria Eat Toxic Metal, 'Poop' Gold Nuggets

The problem arises when the bacteria encounter gold ions, which are gold molecules that have lost one or more of their electrons and are thus unstable. These ions are easily imported past both cellular membranes into the interior of the cell, where they can cause damage on their own. The ions also inhibit the CupA pump that gets rid of excess copper and, as such, can compound damage from copper ions that make their way into the cells.

Fortunately for the bacteria, they have a workaround: another enzyme called CopA. This enzyme steals electrons from the copper and gold ions, transforming them into stable metals that can't easily pass through the interior membrane of the cell.

"Once the metallic gold nanoparticles [are] formed in the periplasm, they are immobilized and less toxic," Nies said.

Your organisms chew up wood and spit it back out to make their structures. The structures are laced with copper and gold, courtesy of their commensal microbes able to pull off this biochemical feat. Your structures are as strong as a wasp nest, and they conduct electricity because of the metals. Plus they would look really cool.

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    $\begingroup$ keep in mind these bacteria produce very small quantities, you need huge masses of them and a lot of time ot get significant amounts. $\endgroup$
    – John
    Jan 1, 2020 at 6:06
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    $\begingroup$ The bacteria don't make gold - they collect it, atom by atom. While there is more gold in ordinary rocks than people think, it's still not a common material and these organisms are going to have to eat a lot of rocks to collect enough gold to do anything useful. $\endgroup$
    – IndigoFenix
    Jan 1, 2020 at 8:06
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    $\begingroup$ @John - that is because they are lazy layabouts. Once they grow up and go to work they will be kicking out gold like Rumplestiltskin., $\endgroup$
    – Willk
    Jan 1, 2020 at 17:25
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    $\begingroup$ Carbon nanotubes may not need as new a biochemistry as you think, there are already biological nanotubes of other compounds and bacteria abre being used to shape and assemble carbon nanotubes. nature.com/articles/s41598-017-09692-2 $\endgroup$
    – John
    Jan 1, 2020 at 18:29
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    $\begingroup$ Hey JRams. The idea with the wood is to stretch the rare gold further. Kind of like meatloaf to stretch your meat further. The gold can therefore serve as just a conductor and not a structural role. If you want "spit", what is in the spit to serve as structure once it dries? You could just use environmental minerals - so instead of wood wasps, you have mud wasps. Or if these are carbon based creatures use their carbon-containing wastes as building materials. Frass wasps? $\endgroup$
    – Willk
    Jan 1, 2020 at 18:33
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Goethite

Credit really goes to Mephistopheles's question which has the topic on my mind, but limpets are a deep sea dweller that use shards of a mineral called goethite to strengthen their teeth, similar to composite fibers. Thus, a creature which intakes a naturally occurring hard material (technically a mineral, though it is made from iron) already exists.

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    $\begingroup$ Goethite is made of iron in the same way that water is made of hydrogen... (That is, iron and goethite are very different substances with very different physical and chemical properties. There is no relationship whatsoever between the chemical and physical properties of an element and those of a compound which contains that element.) $\endgroup$
    – AlexP
    Dec 31, 2019 at 18:49
  • $\begingroup$ If you're going to be that technical, you mean 'no correlation between the elements's properties and a compounds properties'. There is a relationship, just not the traditional one of 'combine two hard things to make another hard thing', the relationship is that both are caused by the same base atomic interactions, but under different structures and rules. (Also, goethite isn't as different from iron as water is from hydrogen gas.) $\endgroup$
    – Halfthawed
    Dec 31, 2019 at 19:25
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I think carbon nanothreads are more realistic. Not carbon nanotubes or graphene. Both of those are pure carbon. Carbon nanothreads are a hydrocarbon. Most cells are between 10 to 250 micrometers. Many cells have little hairlike things in the nanometer range as well as nanometer range organelles. Many parts of the body is non living engineered material. A lot of connective tissue and bone is not actually alive, just constantly repaired by living cells. Using a hydrocarbon nanothread as a protein bonded material isnt as much of a stretch as a pure carbon material or refined metal materials. Perhaps this creature eats charcoal? The charcoal is mostly carbon, the carbon becomes hydrated and gets incorporated into the cell. Eventually over many generations the cells do this themselves without needing charcoal. The charcoal origin may come from lightning or volcanoes. Volcanic soil is highly fertile, butterflies fly and have baby caterpillars. Close as I can think up anyways.

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