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So, this is another part in a lot of my questions for something I'm making. Our protagonists are unfortunately stuck on an alien planet. They end up going into a cave, which is a bad idea because some caves here are full of exploding fungi(called creeper, because it creeps in the shadows), that explodes in fireproof spores and fire, killing (or injuring) the animal and then growing on it. For plot reasons, it only lives in caves with a stream running through them, nowhere else.

Things to know:

  • they must not instantly kill a human, only injure because they target smaller creatures
  • preferably has fire, although an explosion of something like acid works too
  • touch activated
  • i'm asking if its plausible to work and how, not if it could evolve
  • preferably hard to spot
  • size and shape can be anything
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  • $\begingroup$ Well, there are beetles that can spray a caustic mixture. So why not? But when you say it creeps, you mean the fungus itself is motile? $\endgroup$ – DKNguyen Sep 15 '20 at 19:02
  • $\begingroup$ @DKNguyen when i say creep i mean grows along all over and it wouldn't be able to fully kill larger animals immediately, and wouldn't need to, since now they are injured in a cave and cant really get out $\endgroup$ – Topcode Sep 15 '20 at 19:07
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    $\begingroup$ If the fungus it kills the prey right there, then the new spores might have to compete for space and resources with its parents or its parents siblings. If the explosion just wounds the target and sticks the spores to it, and the target limps off somewhere and dies, the new spores have a new place to grow, possibly someplace where more of the prey creatures might come by later. $\endgroup$ – notovny Sep 16 '20 at 0:04
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What we need is a a way to justify a biological specimen naturally creating nitrogen triiodide

Which, when I was in high school coating books with the stuff before tossing them onto tables, was lovingly known as contact explosives. It's an unstable compound that goes "boom!" with enough jostling around.

And the really cool thing about this is that it would easily justify why the fungi grow in caves — to avoid the wind, rain, hail, and even charging water buffaloes of nature that would make them go boom! before their prime.

Nitrogen is easy. It's in the air and the soil. But here on Earth, Iodine is uncommon in the soil and (I don't believe) doesn't exist in the air. However...

Fertilizing with iodine derivatives has been shown to aid in biomass production and increase the antioxidant levels in plants which provide drought and stress resistance. (Source)

Which is really useful since your fungi live in caves where there isn't regular rainfall, yes?

But, iodine is a bit of a problem for normal plant growth (as it's understood here on Earth), so you really don't want it in the soil. Cool!

I propose that your planet's bedrock is naturally rich in iodine. As that rock erodes into gravel and finally soil, the iodine is released and washed into the sea (making it both salt and iodine rich, but like Earth's oceans which are too salty (and in this case iodine-rich) for land-based plant life yet capable of supporting substantial life). But the bedrock, found conveniently in many caves, allows the fungi to naturally create nitrogen triiodide, a contact explosive.

Boom!

The consequence is that your adventurers might not be able to eat seafood....

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  • $\begingroup$ How about azides? en.wikipedia.org/wiki/Azide These are the propellants in many air bags. Organic azides are explosive ehs.ucsb.edu/files/docs/ls/factsheets/Azides_FS26.pdf , and if the environment has a lot of lead, they could even form lead azides (used as shock detonators). Azides are toxic to bacteria, and a species could have evolved them for that purpose. Storage for these is below room temp and in the dark! $\endgroup$ – DWKraus Sep 15 '20 at 21:44
  • $\begingroup$ @DWKraus Dude! Make that an answer. Be sure to indicate some believable way the ionization can occur in nature. That's a cool reference! $\endgroup$ – JBH Sep 16 '20 at 0:13
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There are already plants that produce flammable vapors so that much is highly plausible. The plant could concentrate the vapor into vesicles that were isolated from the air, allowing the concentration of the gas to build up. Once the vesicles are broken and the gas contacts the air, the high concentration of the gas relative to the oxygen in the atmosphere could cause it to spontaneously combust, creating an explosion. There's be a bit of a delicate balance here---you need vesicles strong enough to contain the gas, but that burst when touched---but that is hand-wavable at least, or could be explained with a spring-loading mechanism, like jewelweed. The fact that they grow in caves is another point in favor of this mechanism, as there is unlikely to be any weather that could cause them to burst without an animal triggering them. If you need a little bit more activation energy for the reaction (can't get the concentrations high enough) you could have a brief exothermic reaction caused by contact trigger the explosion.

To adjust the impact of the explosion, you can just adjust how much of the gas there is in each plant. More gas = bigger explosion.

There will be fire.

It is touch activated.

You don't care about evolution.

As for hard to spot and size/shape, its really whatever your heart desires---you'll want vesicles on the outside, but other than that go wild. The mechanism doesn't have any big requirements for shape, size is controlled by the size of the explosion you want, and color is completely irrelevant to the mechanism.

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Azides:

Anyone who works in a biology lab knows there are lots of compounds with azides added to them to prevent bacterial growth. The discarding of these materials is touchy (pun intended) because if they are discarded down the drain, the pipes can explode. Demolition teams have been called in to remove pipes in old buildings.

Azides are generally toxic compounds used as the explosive inflators of air bags. Sodium azide is the most common version, but organic azides are used as transitional compounds in chemistry and are also explosive. And I mean impact explosive. Plumbers would have pipes explode on them because azides precipitate out in pipes, especially with heavy metals, and become contact explosives. Lead Azide is used as a shock-sensitive detonator.

I could see an organism that evolved azide compounds as a toxin to kill bacteria, in much the same way penicillin was made by mold. Azides are stable at room temperature and below, and can be light sensitive, which is no problem for a fungus in a cave. As the fungus scattered spores due to inadvertent explosions, it spread. Animals killed by explosions would be food, and animals surviving explosions would flee and spread spores. Evolution would select for those that had better scatter and explosions. Big animals would need to survive as spore carriers, so the booms couldn't get too big. A lure like a scent would draw small animals to attempt to eat the azide-containing fungus, which would then explode inside the mouth of the poor rodent biting down on a sweet nugget to get a free meal.

If the fungus favored environments with heavy metals, the effects of the explosions would be magnified. They could either favor lead-bearing rock OR simply have more bang in such places.

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Ballochory

There are plants that explode right here on earth. Its purpose is to disperse seeds, so your spores that grow on the killed creature fit right in. The Impatiens plant is known as "touch-me-not" because it explodes on contact.

So, the fire.

The plant will have to project the inflammable substance with the seed. It could be kept protected from air until that point, but be so easily burned that it will ignite owing to the explosive friction once oxygen is present.

Note that your spores will have to be tough to survive the fire. Probably, like most fire-resistance seeds, they will be unable to sprout without going through it.

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