I have a creature or more accurately creatures that I have a problem with. I can't figure out why it is afraid of water.

They are land based tiny tiny little piranha like organisms that work in unison. Each individual organism is about the size of phytoplankton and plankton. They work together almost like a hive mind but have no evil queen to rule them.

Each individual creature is not intelligent and acts more on instinct and signals from others. Think of eusocial insects using chemicals and pheromones. Because you never see one alone and only in large clusters, they always appear like a low-lying mist or fog. Let's call a cluster of these creatures the Mistraille.

Mistraille can consume all living plants and animals by entering the victim through a cut/wound/tear etc. and leave behind a desicated husk (I believe they consume everything, bones, muscles, all plant matter except the outer covering/skin but this can be changed if necessary). The plant/animal can still be alive when the Mistraille enters. After a time the Mistraille can actually move the animal around like a 'meatsuit' (this could allow isolated cases of Mistraille in areas not normally associated with it).

A small amount of Mistraille enters the body, reproduces while consuming the body and emerges in greater numbers. The Mistraille therefore leaves a fairly desolate empty environment behind them. They appear to live in deserts — which came first, Mistraille or the desert? (rhetorical question).

I didn't want an entire desert wasteland of a planet, so I have tried to limit Mistraille range by giving it two major weaknesses; light and water. Mistraille normally take cover during daylight hours, either by hiding deep in the desert sands, deep shadows (like basements, caves, inside empty shoes etc.) or in their latest victim. They are also physically constrained by large water bodies and can be temporarily repelled by water sprinkled at them (more on this later).

EDIT I had already figured this would also limit their climate range as well. i.e. it would be limited to the dry, 'desert' mid latitudinal regions of the planet. Extreme variations in the day/night cycle, rain, humidity, and even soil moisture would hinder them. Equatorial regions would probably be too wet. High latitudinal areas can have deserts. If the Mistraille had managed to use a 'meatsuit' or darkness to travel there (by accident) it would then have to cope with the longer summer day cycles (only a brief dry night cycle) and the 'wetter' winter cycles. I still don't think high latitudes like tundra would be the best location. Same for the polar desert regions - 'eternal' day is not what this little critter is all about! EDIT

See this climate map from Wikipedia as a reference to habitat location (thankfully this creature is not on Earth, so sleep peacefully!) See this climate map from Wikipedia as a reference

Two minor restrictions are they cannot hide in or travel through rock/solid surfaces. Porous rock yes, solid rock no. Mistraille also cannot consume a victim from the outside. It has to get inside the body first. So any cuts, wounds, open sores are a way in. To further limit this I feel that natural orifices like mouths, noses, ears, bums, skin or plant pores should be off limits to entry (reasoning not completely worked out yet).

I need limiting factors to stop the spread and range of said Mistraille as well as some way to keep it at bay at night by 'intelligent' creatures.

Extra information in case it influences the answer

I have figured out several constraints and reasoning behind their light weakness.

  • Mistraille actually are in deadly danger to any length of exposure to the UV spectrum of light.

  • Due to their limited exposure to daylight they have an unfounded fear of the entire visible spectrum of light (almost a Pavlovian response).

  • They can be repelled at night by artificial light sources such as fire, or modern day torches (it is the light not the heat that they avoid). This won't prevent the Mistraille from crossing the barrier of light if it really decides to go at you.

  • I have figured that the parts of the plants that photosynthesize during the day would be off limits. Therefore Mistraille can only hideout during the day in deep shadows, animals and in the more solidish parts of the plants E.g. tree trunks. (I know that there are light and dark phases of the photosynthesis cycle, but hopefully you get my reasoning).

Related information to question

In working out the details on water I have figured out some constraints but not the reasoning.

  • I want to limit their spread, so I made them unable to cross large bodies of water; oceans, seas, rivers, and perhaps marshes. Mistraille could possibly create 'bridges' to cross little trickles or very tiny streams. E.g. ants working together to cross a small river but this might involve sacrificing those in the water.

  • At night or in the deep shadows you can temporarily 'repel' Mistraille by 'sprinkling' water at them. A deluge would also work, but you are in a desert so you don't want to use all the water at once.

What I can't figure out is why they are afraid of water! They go inside animal and plant bodies that are made up of a large proportion of water. How can I reasonably explain the fear of the one but not the other?

My question is: why are my creatures, Mistraille, afraid of water outside their victims but not when they are inside their victims?

I've been thinking that maybe the water would interfere with their hive mind communication, isolating each creature from the cluster. But how would they then communicate inside their victims?

Maybe something in the chemical makeup of the victims body fluids could trigger a delayed transformation to a form more adapted to the fluid environment. But with that reasoning it can't be related to the freshness or saltiness of the fluid and can't be plant /animal species specific.

Hopefully you see my conundrum. I'm not looking for idea generation per se, just a somewhat valid reasoning on how I can explain my creatures actions. And if necessary alternate solutions.


These are very tiny creatures, so their body structure would be fairly basic and not too complex. (I don't think they would be similar or based on felides. Sorry!).

Something along the lines of this image by Sanja Zamuda ... enter image description here

I had been toying with a caste structure but now think I will definitely need one. Highly eusocial creatures are defined as having a job role bases on the creatures body characteristics from birth. No changing a worker into a queen or a queen onto a worker. I believe Mistraille would be 'primitively eusocial' - their job roles aren't defined from birth, they can have multiple generations, shared care for the young, etc.

So using that basis I believe I can make Mistraille have different sets of body characteristics based on the surrounding environment.

When they are traveling outside any victims they could be fairly similar to each other. Each simple creature communicating via pheromones and the larger collective consciousness a sort of hive mind with no queen directing any actions. These outside Mistraille move by either crawling/hopping or 'flying' on very basic proto-wings. No swimming. The best image I have, in my head, is the classic sediment transport image by bouncing, rolling, dragging, and suspension etc. It is this 'outside' form that would be the most vulnerable to light and water (a holdover from their 'inside' forms?).

When they encounter a victim, they enter and then this would trigger a process of transformation to occur. This transformation would result in a better adaptation for 'liquid' interiors but the reasoning so far of narrow osmosis range/required toxin would still hold (or a similar reason not yet mentioned). They could transform into several specialised body types suited to what they are munching on E.g. animal or plant AND bone, muscle, organs, plant fibers etc. They would also lose any proto-wings they have and develop 'claws', 'razor sharp teeth' and 'swimming' abilities. The 'nests' where the Queens and child-rearing occur would be in locations safe from light (so in plants, in the protected areas not involved in photosynthesis).

As I mentioned before, this transformation requirement from 'travel' mode to 'attack' mode (as @Drenzel called it) would explain why they can't eat a victim from the outside. It could also explain why natural orifices are off limits.

They would still communicate by chemicals and pheromones but might be directed by several Queens. I don't believe the hive mind is as developed as each creature knowing and experiencing the others experiences (as these are very simple creatures) but rather each individual creature influencing and been influenced by the collective consciousness.

THANK YOU VERY MUCH FOR THE ANSWERS SO FAR I'll be taking a little bit from most of them.

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    $\begingroup$ How does the swarm move? Do they fly/crawl/float? You say that they appear like a low-lying mist or fog and are land based, but could possibly "bridge" across trickles of water. This suggests they crawl / have appendages to link together (I'm imagining tiny insect-like creatures). $\endgroup$
    – kwah
    Commented Jul 21, 2016 at 10:43
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    $\begingroup$ I got interested in the light part. Beware the Vashta Nerada. They stalk not in every shadow but ANY shadow. (You should watch Doctor Who S04E09-S04E10, "Silence in the library", if you haven't already. You should ALL do) $\endgroup$
    – xDaizu
    Commented Jul 21, 2016 at 12:06
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    $\begingroup$ Oh my! I hadn't even made the connection! That was a good episode. 'hey, who turned off the lights?!' $\endgroup$ Commented Jul 21, 2016 at 13:45
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    $\begingroup$ Perhaps the water is what triggers them from 'travel' mode to 'attack' mode. So if they come into contact without actually been inside a person, they would switch into attack mode.... then die on the floor. Would give them a reason to fear water that isn't inside what they want to feed on. Also this means any area with decent levels of humidity would be pretty much immune to them as their small size would mean even humidity would cause an issue. $\endgroup$
    – Drenzul
    Commented Jul 21, 2016 at 14:48
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    $\begingroup$ Distinction between porosity and permeability (very important to soft-rock geologists in particular): porous rocks have interstitial gaps in the structure, but possibly not connected; permeable rocks have connected interstitial gaps in the structure, allowing substances of sufficiently low viscosity to flow through the rock. Many rocks are porous without being permeable. $\endgroup$ Commented Jul 23, 2016 at 14:49

11 Answers 11


As a hive mind species, one of their greatest fears is isolation of the individual units from the rest of the hive, this would often mean death for the individual units, and if all of them are scattered, death for the hive.

Large bodies of water, especially flowing or moving water (rivers, waterfalls, waves) have tended to separate them from one another, killing or severely injuring those hives who encounter fast moving water. Over time they have developed an innate fear of all large concentrations of water, but especially indications of fast moving water. A misting of water, especially a directional spray, often corresponds to a large moving body of water, like a waterfall or river rapids. This signals one of their primal fears, causing them to contract as a group and retreat from the source.

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    $\begingroup$ Can I +2? I really like the directional spray idea. Thanks! $\endgroup$ Commented Jul 20, 2016 at 13:53
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    $\begingroup$ This could also be coupled with the rain if you want to keep them inside or cause them to act less predictably. $\endgroup$ Commented Jul 20, 2016 at 16:49
  • $\begingroup$ Just thought of a new scenario. Would an arterial spurt of blood scare them off to? It's fast moving directional spray! Could lead to some interesting scenarios. $\endgroup$ Commented Jul 24, 2016 at 13:24

Maybe something in the chemical makeup of the victims body fluids could trigger a delayed transformation to a form more adapted to the fluid environment. But with that reasoning it can't be related to the freshness or saltiness of the fluid and can't be plant /animal species specific.

Let's not be specific, then, and let's look at something that does kill some animals in our own real world.


The salinity of our bloodstream is different from that of most bodies of water. The same can be said for the sap in plants. That's because living beings accumulate many different ions in their organisms to some extent, but also eliminate excesses to some extent.

For example, our blood has as much salt content as saline - 9 grams per liter. For salinity purposes, our blood is within the range of brackish water (between 0.5 and 30 grams per liter). That's more salty than fresh water, but less salty than seawater.

So let's say that your Mistrailles have a bodily salt content like our own. But unlike many animals and plants, they can't regulate the salt in their organisms like we do. The range of salinity they can tolerate is narrower.

If they are immersed in drinking water, their cells will each individually absorb a lot of water and pop, just like our own red blood cells in a cup of drinking water. You could also see this happening to a sea jellyfish if you take it out of the sea and place it in a bucket full of drinking water, but if you do that you have no soul.

If they are immersed in seawater, the water will run out of their cells and they will die dehydrated. Just like our own red blood cells in a cup of seawater. You can also see this happening to a river hydra (poor cnidaria have very narrow salinity ranges they can live with) if you take it from a river and put it into a bucket full of salty water, but if you do that I am going to dennounce you to PETA.

And that's why they can't stand water, unless it has been carefully treated to have exactly the amount of saltiness they will tolerate. You should probably be really careful around your Saline IV storages.

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    $\begingroup$ Imagine accidently injecting someone with infected saline water! urghhhh, I just made myself shudder in horror! $\endgroup$ Commented Jul 20, 2016 at 17:44
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    $\begingroup$ I love that your answer is both scientifically based in the real world, and also made me chuckle! $\endgroup$
    – Taegost
    Commented Jul 20, 2016 at 20:34
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    $\begingroup$ A desert animal needs to keep the water inside of it, so just topic exposure to water won't trigger an osmotic damage any more than what a human (land animal) can survive in water with the head out. $\endgroup$
    – Davidmh
    Commented Jul 21, 2016 at 12:23
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    $\begingroup$ But this osmotic answer plus the directional spray answer could explain why the topical exposure DOES work. $\endgroup$ Commented Jul 21, 2016 at 13:55
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    $\begingroup$ @Davidmh the creatures described in the question are microscopic. What would be a topical exposure to us would be complete immersion for them. $\endgroup$ Commented Jul 21, 2016 at 14:01

They communicate through chemicals in the air, and I think this is the solution.

While flesh contains a lot of water, it mainly isn't in a liquid state, being stored in the tissues. Even though blood is liquid, it isn't an excessive amount.
Any chemicals that they release to communicate with each other and keep their hive mind like link going are going to be contained in their victims body.

But a river or a large body of water would dilute and wash away all of the communication chemicals cutting them off from the rest. Being a very social creature, this silencing effect is very disconcerting for them, causing a lot of fear, and so they avoid it instinctively.

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    $\begingroup$ The concentration/diluting of these communication chemicals could influence why it takes awhile to get to work eating the victims insides. Thanks! $\endgroup$ Commented Jul 20, 2016 at 13:41
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    $\begingroup$ You would also have to have them "go to ground" during a rain shower, though in their desert like environment this may be a rare occurrence. Heavy fog/mist may affect them as well. Might keep them down in the early morning when there is dew on the ground (so they are active in early to middle night, not pre-dawn morning). $\endgroup$
    – Jason K
    Commented Jul 20, 2016 at 13:50
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    $\begingroup$ @JasonK Going to ground during rain would definitely be a thing, since rain is good at clearing particulates out of the air. I don't know about fog though, if that's even a problem in the desert, since it's suspended in the air. It may mute the chemical communication, but it does that with sound to some extent too. I don't think dew would be a problem. They don't have a problem with small amounts of water, just larger amounts. $\endgroup$
    – AndyD273
    Commented Jul 20, 2016 at 15:38
  • $\begingroup$ My thoughts exactly! $\endgroup$
    – JDługosz
    Commented Jul 21, 2016 at 6:03

One option is that the water is mostly fresh and the Mistraille can not manage cellular integrity due to osmotic pressure. The salt in their systems would leach out and water enters in killing them if they are immersed. The blood of the host contains a similar amount of minerals / salts but entering the fresh water causes their cells to burst. Even sprinkling of water greatly weakens them, stopping them from entering the host. Salt water could be missing important salts / minerals or contain predators that like to eat them.

The water could also contain viruses or bacteria that are deadly to the Mistraille but that the host immune system destroys.

Either way this shall fuel my nightmares for some time.


Consider that, like their irrational fear of general light because of a vulnerability to a specific range of light wavelength, the Mistraille are only vulnerable to something commonly found in the world's water bodies.

In that event, any of the following could apply:

  • Natural predator lives in or near bodies of water (believability: low-moderate; why is a natural predator of a desert creature dependent on bodies of water?)
  • A toxin is released by flora or fauna that appears frequently around bodies of water, but the amount in the water is only a danger to very small organisms; larger organisms filter it out and/or tolerate it (believability: moderate-high; some creatures are immune to Mistraille because they let the toxin into their blood, others store the toxin in an organ they avoid)
  • Mistraille are dependent on a toxin that must exist in the right quantity within an organism and the toxin breaks down quickly in bodies of water, so organisms don't have a chance to absorb it (believability: moderate; kind of sounds like the Mistraille are an engineered creature run amok intended to clean up an industrial spill) [courtesy AmiralPatate]

These were off the top of my head. If I come up with any more, I will add them in later.

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    $\begingroup$ why is a natural predator of a desert creature dependent on bodies of water It may not be that they are specifically sought out, but rather that they happen to be not very distinguishable from plankton, and therefore get eaten before they can reach any destination. Or maybe they can't swim. $\endgroup$ Commented Jul 20, 2016 at 13:31
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    $\begingroup$ And since I'm full of comments, an alternative take on the toxin would be to flip it. Maybe they need the toxin and it can only be found in the desert. Whatever they eat must have the right amount of toxin. So a plant that produces the toxin would have too much of it and be left alone. Oceans wouldn't have enough and be left alone as well. Other plants or creatures would ingest/inhale toxin (no negative effect necessary) and become an acceptable treat. You're free to use that one in your answer. $\endgroup$ Commented Jul 20, 2016 at 13:39

They can consume all living plants and animals by entering the victim through a cut/wound/tear etc. and leave behind a desicated husk (I believe they consume everything, bones, muscles, plant matter except the outer covering but this can be changed if necessary).

They need a cut/wound/tear to enter victim but they can consume bones, that may be because they have two different "stances", lets say migration and feeding so when they are in migration mode they have a normal solid shell-type body, but in contact a liquid they dissolve like a slime which is useful to enter in other organism via circulatory system and just dissolve/control-it but not so when you just spread away in water with huge solubility and nothing to feed of.


Well, do your creatures crawl, do they fly? Can they swim? Can they "breathe" underwater?

Maybe they can fly but just short distances. Too short to cross a large body of water. They'd drown. So they don't even try. Just like a grasshopper (insert any short-range flying creature) wouldn't try to jump over a mile-wide river or an ocean.

Maybe they can fly long distances but they can't dive into the water (because they can't breathe underwater or because it hurts them otherwise), so they know that they would starve over a sea or ocean, like locust.

Maybe they can even swim/dive but they are really slow and it's hard to catch fish for them so why bother when there's easier meat on land.


A major plot point in the novel Fragment is that (significant spoiler warning!)

salt water is fatally toxic to the Henders Is. wildlife, seemingly on contact, due to osmosis action.

The novel is an interesting read in its own right, but may be especially useful for your project. Some additional thought or incorporation of other ideas suggested may improve this point to apply in your built world.


Maybe water makes them unable to move? Dry sand or flour can be even moved by wind, but it sticks together when wet. So when you spray water at them, they stick to each other and fall to the ground. And in the larger bodies of water they have trouble keeping together. But in the human body they either slowly move inside the muscles/other solid things (while eating them) or are transported by the blood flow.


They are a group, and they are small so they might not want to go in water because:

  1. They get split, and a single mistraille would probably die
  2. On land, they can easily see predators coming but in the water they move so fast they might accidentally land in the mouth of a predator

I think they might be scared because water is the only fluid that cleans their surface from hormones, or something like that, that they need to orient itself and that might cause death, while other fluids like blood don't do that. For example, scout ants leave a trace of hormones when looking for food, so when they come back other ants can follow the trace an bring food back, lets say this "cretures" have hormones all around its body that they use to find their own, or the hormones may do many things like give them a sense, for example if we don't have saliva, we lose the taste in our tongue, these are just some ideas without closing so you can do the rest

  • 3
    $\begingroup$ This is only a single sentence. Can you flesh out this answer some? $\endgroup$
    – kingledion
    Commented Feb 22, 2018 at 17:06
  • $\begingroup$ edited answer with some examples $\endgroup$
    – user32608
    Commented Mar 15, 2018 at 13:13
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