My aliens are little symbiotes (think Venom from Spider-Man) who appear to be like crown-of-thorns starfish when not attached to a host. They have general mimicry and camouflage similar to an octopus or cuttlefish, and can survive on their own. However, when attached to a host (willing or otherwise), they grant information to the host, but only as the host shares information back. Slowly, they grant the host enhanced body abilities through a chemical mix the symbiotes produce (although the symbiote is currently [slowly] dissolving the host’s brain). Understandably, the host generally doesn’t want to give up these powers, until it’s too late and the symbiote has taken over.

If they can’t identify each other, then they could accidentally bond with a symbiote (which then leads to them killing each other trying to maintain dominance of the host and not good for the symbiotes). Additionally, from a casual glance from Ned, the next-door neighbor, Joey seems the same day to day, even after the symbiote has taken control.

The symbiotes need a way to identify each other, without being seen as insane or not a human, so how can they identify each other?

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    $\begingroup$ With due respect to marvel you’re not describing symbiotes. Symbiotes wouldn’t take over. These are parasites. The only reason anyone would call them symbiotes is because they haven’t figured that out. $\endgroup$ Commented Oct 10, 2022 at 21:27
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    $\begingroup$ @candied_orange, that’s the whole point. They never figured out they were parasites until it was too late $\endgroup$ Commented Oct 10, 2022 at 23:56
  • $\begingroup$ It would maybe help them if they could cooperate - temporarily live in the same host in order to infect more humans by personal contact. $\endgroup$
    – Juraj
    Commented Oct 12, 2022 at 11:33

5 Answers 5


Smell (and/or taste)

Gllrpt, the symbiote, sees Billy, the neighbor boy. Gllrpt oozes and scabbles across the ground, ready to touch Billy, to hack into Billy's nervous system and make Billy the offer of undreamed-of knowledge and power.

Then Gllrpt catches the whiff (undetectable to human noses, but very clear to many animals) of the alien chemistry of Gllrpt's kind. It's Snrfllt, Gllrpt's crèche acquaintance!

And even if Gllrpt can't catch a whiff of one of its own kind, Billy, the already-attached, won't taste like a pristine human, not with all those symbiote-chemicals already flowing through his body.

Better luck next time, Gllrpt. Or wave at Billy, who may direct you to his still-pristine mother. (Dad's already taken in Prlaggt.)

Incidentally, the subtle odor may contribute to the unusual reactions of dogs, cats, moose, etc, when a possessed person is upwind.

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    $\begingroup$ Pheromone is commonly used term for chemicals used by wide range of organism for communication. The range of communication allowed by them is surprisingly vast and could also be used for other purposes between symbiotes. $\endgroup$
    – Ekaros
    Commented Oct 11, 2022 at 8:30

Hosts have only one orifice suitable for a symbiote.

And if a newcomer arrives and finds the orifice taken, it is considered good manners to move on.

Occasionally a symbiote might explicitly negotiate with an occupied host (usually from the vantagepoint of a temporary host) to explain why the services of the interested party would be better than those of the host's current partner. The host may opt to trade up. That involves the departure of the current symbiote, either voluntarily or not.


I'd argue that these aren't really symbiotes since they destroy the host's brain over time in order to fully take control, but that's just a nitpick that doesn't answer the question. What does answer the question is... complex.

First, smell. The chemicals the creature produces will be metabolized by the human body and some of the original chemicals or their metabolites will be expelled from the body via the sweat glands. Clearly this will be something that humans can't detect, but your creatures will be able to smell that someone in the area has been taken, and from up close it should be fairly clear who it is. You could take control of the process more directly and produce pheromones, if that's your thing. That will give you a much broader range of expression through the scent.

You can use the same basic mechanism via 'taste' once you make physical contact with a human: the skin will taste of the chemicals and byproducts, and if you enter the body it will be unmistakably inhabited.

But what about at a distance? Humans use sight a lot, your creatures probably not so much since they rely more on their host's sense organs, but they have to have some way of tracking potential targets and sight is one of the best options. Nothing says that they have to use the same visual spectrum as humans though, so perhaps they see things we can't: long infrared or short ultraviolet for instance. All you have to do then is change the UV 'color' of the host's visible skin in some way. Patterns of UV coloration on the face for instance will make it immediately clear to any creature seeking a host that this one is taken. And if you have enough control over it - which I assume these things do - then maybe it contains extra information like name, clan, rank or whatever.

Of course you could just ask. In your own voice of course, which happens to be pitched way up in the 200kHz range where no land animal is going to hear it. You have to 'shout' a bit because it doesn't travel well through the air, but it's a fairly binary thing: if they react at all then you know they're already taken. Oh, and it also comes in handy for messing with ultrasounds when they're trying to scan for parasites. Just saying.

And that's just the senses that humans generally work with, which are certainly not the only ones available. Electrical senses work pretty well under water, not quite as well in air though. Biological radio isn't impossible, especially if the creatures have been uplifted or otherwise enhanced in some way. Natural extension into a 4th spatial dimension that allows for communication somehow?

If all else fails - or you're feeling particularly lazy - you can always pull the classic get-out-of-jail-free 'telepathy' card.


Ok so, infected humans look the same to other humans. Then I assume acting and talking the same as well. It is either there isn't nay indicator or, Humans can't detect the signs.

There is a change, but it is undetectable.

Imagine the symbiote, while fusing with the host and taking over, makes a small adjustment to vocal cords and each time host says something, there is a distinct tone for symbiotes, but the frequency is either too high or too low. So, there is a chance. But humans can't detect it.

Same idea can be applied to skin like reflecting a certain light or light polarization human eyes cannot see.

Change is actually obvious. But humans lack the organ for it

Instead of going completely fictional, you can add a few properties some animals have in our world. Many birds, bats, and I think sharks (Not sure) have ability to sense the magnetic field of a planet to follow the lines in order to go to north or south, to find way home.

Imagine the host, and symbiote inside the host emitted some kind of signal that could be sensed by other symbiotes. Works as both "I am here." message, and an identifier. Kinda like a unique smell.

Countless blood spills created deals and rules

Terratories, dividing different people types to different group of symbiotes, or making very small signs that will have a meaning to the symbiote.

"Oh look! Jake became much stronger after that trip to the forest. It is okay if he wants to plant a few plants. He was kinda like a nature guy anyways."

Different coloured plant combinations, adding small signs to life style like adding a sigil under the doormat or chimney's top. Kinda like how dogs pee to mark their terratory. And if there are certain attack or interaction methods/paths symbiotes prefer, these signs can be effective.

You can add further division focusing on gender, height, body structure etc... World is diverse but not evenly mixed around all parts. Different group of symbiotes can divide the human world among each other to prevent bloodlust.

Reprogrammed Biology

Lets say, symbiotes developped a way to reprogram the host's immune system to reject any and all other symbiotes except itself as long as it was connected to the host. So, another symbiote can try to take a host, but immune system will attack and damage the symbiote heavily so it has to leave or die.

This way, any kind of conflict can be resolved with ifrst come first served second were killed on the spot logic. Maybe you can expand this like altering immune system to create resistance against viruses and such.

Same logic can be used in a bit different form like, maybe symbiote changes the host's organ structure and occupies all the connection points and other symbiotes are just slipping through host's organs, unable to connect and simply fall off. Like closing all sockets of a computer. Or like those water-proof pants that won't have stain.

Duels, fight between individuals

Let the symbiotes fight among each other but the moment a fight starts, winner is the owner and loser will die. Instead of triggering large scales of war, let individuals kill each other and prevent large scale conflicts. If a symbiote, despite being attacked by another symbiote, stil ltries to take a host over, then it was dumb and that guy can die so that the symbiote factions can keep the peace.


Pheromones/chemical traces is probably the simplest. When a symbiote has found a host, it releases a chemical that pervades the host's body and is constantly being released from the skin and body fluids, so if another symbiote doesn't get a whiff of it from the air as it approaches, it will absolutely detect once it touches the host. You could even have a situation where the chemical actually makes an unhosted symbiote physically ill so avoiding infected hosts is something that an unhosted symbiote has evolved to do.

If you're looking at it from a story standpoint, this also creates several possibilities. It gives the humans (or whoever) the ability to detect hosted symbiotes if they become aware of the chemical, and you could imagine it also being deployed as a defense like an insect repellent. It also creates some interesting possibilities as it could explain why someone is detected as having the chemical on them.

"I'm not infected! I use Symbiote-B-Gone all the time as a precaution!" says the symbiote currently occupying what's left of Chuck's brain.


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