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So I've been working on a low magic world where magic is actually just another form of energy that can be actualized, similar to alchemy in Full Metal Alchemist. Although development has taken a different course in this world, it resembles a late middle age to pre-industrial age period in time.

This world is slightly more dangerous than ours, with monsters running around here and there which may become a great pay day for an adventurer commissioned to clear it out, or a threat that jeopardizes an entire town despite them rolling out the entirety of their guards to stop it.

Among the various races and creatures that are in this world, I have one that still needs help figuring out. I would like to have slimes included as part of my fantasy world. I want slimes to work on a principle of acid digestion, in which stepping on one or having one latch onto your foot may compromise your leg, the bone in it, or even your life. They get to have the nickname "Farmers Bane" and are known as a threat to unsuspecting people who step on them.

So far I've envisioned my slimes as a type of extremely large protozoa, either single celled or a colony. When stepped on they encapsulate the foot and release a strong acid which greatly impacts the creature that has stepped on it. In particular, it's best if they can cause bone failure which has a potential for incapacitating their prey. Then, small deposited forms of the slime grow using the prey as nutrients once the flesh in the area is dead, or devouring the entire creature to form new cells if possible.

My question is simply this: Can a creature exist that can use hydrofluoric acid without destroying itself, and what kind of structures would it have?

I thought maybe a silicone based organism would work, but I don't know enough about chemistry to understand how hydrofluoric acid can or cannot react with something, and whether or not that something could be a living being.

I have other less important questions that I would love answered if the above is possible:

  • Is it possible to have a single cell organism that functions in this way, or does it need to be multicellular? (Or symbiotic with another organism)

  • Does chloroplast react to hydrofluoric acid?

  • If flesh is broken down by hydrofluoric acid can it still be used as nutrients?

Or if the above is impossible:

  • What are possible substitutes for hydrofluoric acid that I can look in to?
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    $\begingroup$ You may be interested in my answer here which touches on similar topics. $\endgroup$ – Dubukay Aug 17 '18 at 6:47
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    $\begingroup$ Why not have the slime be a magical creature whose brain and body functions are controlled via magic that is imbued into the acid itself? Every part of it contains this magic, so when its split into multiple parts, they can all act independently but when they are together they can still act as a whole unit. $\endgroup$ – Shadowzee Aug 17 '18 at 7:00
  • $\begingroup$ It's a very hard magic system which doesn't have such a function, though the idea of magical circuits that allow for a type of hive mind/colony effect might work as far as how the slime forms. $\endgroup$ – Clay Deitas Aug 17 '18 at 7:58
  • $\begingroup$ Not a duplicate but might still be very interesting for you: worldbuilding.stackexchange.com/questions/56710/… $\endgroup$ – dot_Sp0T Aug 17 '18 at 8:04
  • $\begingroup$ @Dubukay So if a slime was a siphonophore made of zooids that make amino acids that are absorbed by a core species that could make HF and not be digested, it might actually work? $\endgroup$ – Clay Deitas Aug 17 '18 at 8:37
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Hydrofluoric acid is not actually that acidic (pKa of HFaq ~ 3 vs. pKa of HClaq ~ -6). The main issue for, well, most multicellular creatures on earth really is that it can easily penetrate tissue and bind with Calcium in our blood and nervous system. Calcium Fluoride is highly insoluble in water. This effectively leaches out Ca2+ ions from the body which can lead to serious medical problems and even death (read about HF burns starting at e.g. the wikipedia article). Also; HFaq releases gaseous HF which can cause heavy eye irritation and blindness by attacking the cornea.

If your slimes biochemistry does not rely on Calcium (or Magnesium) you should be better off. The problem is that most fluorides are poorly soluble in water. You're basically limited to small cation compounds (basically only Sodium. Lithium binds strongly) or some fancy metal-ligand binding of your metals in the slimes' proteins.

If, however, your slime is not inherently water based, you might be better off. I could not find any studies about solubility of HF in solvents other than water (short of one rather dubious mention of it not being very soluble in liquid butane...), but from experience may I suggest something like methanol/ethanol (leaning towards he former)? They are both highly polar and will for certain support large dissolved concentrations of HF. The things to worry about then are: evaporation and envirenmental water leaching into the slime. The first is going to be a problem with slime design either way, and the second could be dealt with in a similar way to which many creatures living in slaty environment deal with large salt concentrations - actively removing it from the slime's body. Maybe some thick-yet-mallable skin on the slime which deals with both the evaporation of it's body and houses water pores? Polivinyl alcohol gloop e.g.?

Non of this of course touches on the most important part of the design: Why would a slime have an evolutionary need for HF in it's body(?) and how would it get it's (in this case) nutrient fluoride? These are your questions to answer, but if all you need is a tough enemy and not necessarily a species, then the easiest way to solve all these problems is to go with a "normal" water-based slime who's biochem is only very loosely based on insoluble-in-fluoride-form ions. The slime has been roaming under a chemical factory (or equivalent thereof in your world, e.g. in the swamps surrounding the age old tavern - The Alchemist's Refuge) and thus has absorbed a large amount of HFaq. The slime is slowly dying and is therefore enraged, at least to whatever degree the state of the slimes' consciousness allows.

Edit: Also; further to your comment: Even a large amount of HF does not act fast. It usually takes a day or so for the symptoms to arise. The pray could just wander away after stepping into the slime unless otherwise constrained. If you want to paralyse or disable living creatures there is a plethora of easy to make in cell nerve agents / fast acting poisons and toxins.

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    $\begingroup$ The idea of a bunch of alcoholic slimes running around is hilarious to me. $\endgroup$ – Clay Deitas Aug 17 '18 at 8:24
  • $\begingroup$ Sorry hit enter to space it and accidentally posted. Anyways the idea is that these slimes through some evolutionary BS evolved to produce some amount of HF, which makes them capable of killing most mammalian prey, which they can then digest/use to grow new slimes. As I haven't finalized their biology, I can't say whether they move or not, but the idea is that even a slow moving or stationary slime is very dangerous to step on or come into contact with. HF seems to be the acid which is best at accomplishing this goal. $\endgroup$ – Clay Deitas Aug 17 '18 at 8:32
  • $\begingroup$ They wouldn’t be delink as such. It would be they’re internal biology. Kindof like we’re not corroding in oxygen and don’t dissolve in water. Although I’d like to think that somewhere out there there are HF based intelligent life forms talking ok their world building heapexchange about a possibility of water based limboids which would make HCl in their guts... $\endgroup$ – MarcinKonowalczyk Aug 17 '18 at 9:00
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    $\begingroup$ Thats what makes it dangerous. If you step on one and don't realize it's dangerous it will slowly corrode and kill you. This makes it a lot harder for animals to avoid it, because they die a long time after contact, which makes it hard for others of the species to identify what caused it. Plus these slimes are brainless animals that rely on chance to bring prey to them, meaning something that can pass through the skin is the best. Also, slime's and acid seem to go together, so I wanted to try and include an acid as opposed to poison. $\endgroup$ – Clay Deitas Aug 17 '18 at 9:52
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    $\begingroup$ As for the prey wandering away, it's a good way for the slime to spread around, assuming a new slime is attached to the prey and will use it as nutrients. $\endgroup$ – Clay Deitas Aug 17 '18 at 9:54
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Our stomach uses hydrochloric acid for digesting whatever we eat. And, as you might notice, the stomach doesn't digest itself in the process (not in healthy subjects, at least).

This happens thanks to a layer of mucus covering the layer of the stomach in contact with the acid solution, therefore the same solution can be used by your slime, which also happens to be slimy, to it fits the character!

Not all the substances are digested by the acid alone, if I remember correctly lipids need a different environment to be broken down. Otherwise, the broken down molecules are exactly the expected outcome of the digestion.

In principle the same adaptation could be used with hydrofluoric acid. However, the main reason for not using hydrofluoric acid is that it is the weakest of the acids having an halogen: its acid dissociation constant is 11 orders of magnitude lower than hydrochloric acid. So, in light of this your slime could be easily outcompeted by other slimes using hydrochloric acid.

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  • $\begingroup$ Hydrofluoric acid has the advantage of corroding bones though, and is more likely to be fatal through minimal exposure. This is a question of an attack mechanism rather than a digestive one, though if the attack ruins the nutrients then it kind of makes itself pointless, which is why I included it. $\endgroup$ – Clay Deitas Aug 17 '18 at 7:53
  • $\begingroup$ @ClayDeitas, before reaching the bones you need to go through the skin and flesh. $\endgroup$ – L.Dutch Aug 17 '18 at 8:01
  • $\begingroup$ HF readily penetrates tissue (skin and flesh) and because it interferes with calcium channels (Ca ions) to form insoluble fluorite it impairs the nervous system so you won't feel it much when you are burned with HF. $\endgroup$ – GretchenV Aug 17 '18 at 8:13
  • $\begingroup$ You are correct acids won't break down fats, enzymes are needed for that. $\endgroup$ – John Aug 17 '18 at 14:05

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