Worldbuilding 104: Real and Alien Parasites
Greetings and sine! Well, no, today I am cosine! A bit of a math joke there. One thing everyone knows about me—the glorious Vivian!—is that I love biology, and no, not only about sex and reproduction; I just love freaky biology period, and what is more freaky than reproduction? Parasitism. I recommend reading my previous post on alien biology for this one, and the one on diseases.
Definition of parasitism
You know the drill, a good definition!
Parasitism is a form of symbiosis where one biological creature, the parasite, is positively gaining from the symbiosis, but the other creature experiences a negative gain.
I can hear many of you asking
Symbiosis? Parasitism? Those go against each other, you incredibly beautiful alien!
As always, you’re amazing in how you compliment me while questioning me, thank you! Despite the colloquial usage of symbiosis and its many derivations, it does not in any way actually imply it being mutually beneficial. When both parties benefit, it is called mutualism.
This beautiful chart describes the relations between species and their names.
As you can see in this image, parasitism is still where one gains and the other loses. There are many others like commensalism where one gains and the other is unaffected. Burdock plants are an example where the seed hitches a ride on a mammal's fur (positive as it spreads the seeds further), and the mammal gains and loses nothing. Humans experience this also with various small insects living on the skin that eat things and in no way affect the person.
Parasitism as a strategy
Given that parasitism gives a negative to the host, which I will refer to throughout the post no matter the exact nature of the symbiosis, it would seem reasonable that hosts will try everything and anything to avoid a parasite. And you, my brilliant reader, would be entirely correct in this assumption! Immune systems and much else are a response to parasitism! Yes, illness can be considered a form of parasitism that lasts not a long time because the disease agent is dealt with rapidly.
So, if other organisms absolutely do not want you as a parasite, why in tarnation's name would you ever evolve this strategy, given its obvious cost of everything trying to get rid of you? Because it is sooooo beneficial if you pull it off! You humans think of bloodsuckers as a negative, but think about it. What is in blood? You have blood cells, proteins, sugars, you have all the nutrients the body needs in its pure form so that all the cells can easily grab them. You don’t need to bother digesting other cells, other than blood cells, just pure biological joy!
Or, if you are in the intestines, it's all digested and ready to be absorbed, and you can be there to take it! Well, I think you get the point: parasitism is a popular strategy for organisms because while the risks are high, the rewards are worth it. Naturally, if they have nothing protecting against immune systems, they will be killed instantly. Which is why parasites are often highly specialised. It takes a lot of investment to deal with one species' immune system, so they often invest it all into surviving with one species.
Parasitic types
You have many kinds of parasites: spoiled people, men, lazy people, women, children, and I am messing with you! But yes, there are several types.
The first type are called endoparasites, and they are the ones that are the most feared, most disgusting, and the ones most people think of. They live on the inside of the host and have somehow gotten inside. It can be through a wound, like the screw-worm fly, or, more commonly, through the food that is ingested. Though take note that screw-worm fly does not count as an endoparasite, which I will explain in a little bit. Once inside, the parasite has the issue of the immune system. This is why, in general, endoparasites are the most specialised of all parasite types as they have to deal with highly specific immune systems and anatomies. An example of this is tapeworms and the likes in your intestines.
The second type are called ectoparasites. No, they are not ghost parasites; get that silly image out of your silly head! Anyway, despite not being ghost parasites–which we will get back to, trust me on this–they are parasites that reside on the outside of the host. So ticks, leeches, blood bats, and various others. I believe, given what I said before, it should be obvious why ectoparasites tend to be very fond of consuming blood and actively getting blood. These ones tend to be considerably less specialised, as you don’t need to deal with the immune system as much. You do need to deal with the hosts wanting to swat you away, but you know… How well can a sheep do that? Most mammals struggle, but not all. Some parasites might even have evolved to actively avoid species that can swat them off. Albeit, I don’t know of any, and the gain of avoidance might not justify the cost of figuring out who you’re going for in the long run.
Mesoparasites are considerably less well known but equally fucked up, if you ask me. They go into an orifice of an animal and… set up camp and live there. So they are partially endo and partially ecto. As the orifice is a natural opening, it is not something the host would actively patrol for anything harmful invading as you get stuff going in and out there regularly anyway. One famous one is the parasite that eats a fish’s tongue and replaces it, then eats part of the fish’s food constantly. Another example are the screw-worm flies; they will eventually plop out of the wound that they keep open and turn into a proper fly.
Epiparasites, or hyperparasites–I like epi more–are parasites that parasitise other parasites. This is some inception level shit. So yes, even parasites can get parasites. It is quite rare for an endoparasite to get an endoparasite, as endoparasites develop in the host from eggs often, but it’s not unheard of. There are viruses that infect viruses, for example, as much of a parasite as they can be classified, and I think to some degree, they can be. Wasps often show up here where they parasitise on each other's larvae… which is messed up.
The last one is what is called social parasites, and no, I am not talking about your cousin or my mother, I am talking about species that exploit the social behaviour of social species. Given not too many species are social, and most social creatures are, well, not dumber than a sack of hammers, exploiting them is not the easiest. But there are some social species that are dumber than a sack of hammers sat on by a donkey: eusocial insects. The insects themselves are dumb and only follow the social cues no matter who or what does it. They are so robotic that if you smear death pheromones on a live ant, other ants will come, grab the live one, toss it into the pile of ant corpses, and keep throwing it back until the pheromones are gone. Of course, some species find ways to use this; slaver ants are an example of this. They literally enslave other ants because they, the slavers, are so useless at doing any work other than raiding that if they don’t enslave, the colony will die out.
Get rid of parasites!
Hold on there, cowboy, cowgirl, or cowherm! I get that parasites are icky and BLERGH! But when it comes to nature, they are very important! Nature is a complex mess, and it tends to find equilibriums over time because nature is a patient bitch. When things are not in an equilibrium, it crashes and burns hard, and nature can keep trying until an equilibrium appears and stays.
The fact that humans are nature's latest attempt at crashing the game for shits and giggles is beyond the point, but with this in mind, parasites must be doing something to keep being around, right? Well, they do things! They fill niches that exist, and a filled niche doesn’t provoke any species to fill it. After all, as the rule goes, “Every niche in nature can only have one inhabitant.” I paraphrased it.
But over all, parasites of all stripes keep populations in check. Life has this bad habit to kill, consume, multiply, and conquer! If left to its own devices without anything stopping it, life would consume everything, multiply endlessly, and conquer everything within reach. You have probably seen this when there are spikes in populations of insects. Parasites help bring these spikes down by consuming the eggs and weaker individuals. You think it is bad for humans, but you know… it applies to insects you hate, too, so don’t be too hasty on dismissing parasites as a whole.
Image taken from Rational Animations’ video
Fictional parasitism
Alright, I have talked about the existence of parasites, but now let's make up our own!
Why would I?
You might be asking why in tarnation would you ever use parasites in a story, to which I say… Why not? They are dope 😀 Seriously, a lot of illnesses and issues and drama can be done with parasites. Many might not be aware, but a lot of parasites have destroyed societies, civilisations, and people. The vast majority of exploring Africa was halted by parasites that made it far too deadly to try. Malaria, the parasite, was actually a primary reason why Africa was originally left alone from colonisation. Then people figured out how to deal with malaria, and Africa got borked.
Fantasy parasites
We can start with fantasy parasites, and my dear, beloved sister Anne did a blogpost on fantasy diseases. And I have to say here that it's still amazing, but here what kind of parasite it is depends entirely on your magic system. Similar to how fantasy diseases have to be tailored to your magic system, your parasites will also have to.
For example, if you go with the system Anne and I use for fantasy with the different types of mana, you can have the parasite feed on manic that the body naturally produces. Imagine water mana people who naturally produce water magic, and there are parasites here that feed on that magic. So when they are going to use their water magic and woosh the foes away, it… fails, because they no longer produce enough magic. Or it goes completely wrong and crashes because the parasite is destroying the normal mana pathways, or whatever you imagine. I wish I could actually see these things in stories more, and that is why I make these posts.
Or, if you want to go the other way, what if the parasite produces mana as a side effect? Maybe it normally kills the host or severely harms them, but because the protag is humanoid and sapient, aka a sophont, they can adapt, and it is less of a parasite and more mutualism? Now, that would be interesting: a mix between the will of the protag and the parasite so powers are more unpredictable but still enough for the story.
Personally, I think the most interesting possible parasites lend themselves to harder magic systems, but they don’t have to. You can have soft magic systems and still do magical fantasy parasites that cause magical mayhem. (Anne: Find out about the difference between hard and soft magic systems in this post). I am now imagining Gandalf having a leech bite him on the ankle and suck out magic so his spell fails. I find it too hilarious. Anyway, you can do such to help nerf powerful soft magic users. Maybe the parasite took so long to find that attempting to remove it from the inside will cause a magical explosion or something. Your imagination is the limit!
Science fiction parasites
Boy, does science fiction LOVE parasites. While fantasy has a sore underrepresentation of them in any interesting fashion, science fiction has the opposite. You have parasites that cause vamprism, technically parasites that cause zombification, and I am drawing a blank on a third, damn Anne and her need for the rule of three!
But yeah, that is the most common use, but in space operas, they do occasionally pop up, as they are interesting things to explore. But what can you use for parasites in science fiction? Absolute insanity, and nature has already done a lot of the work. You can do the usual hijacking digestion and such, but there are also other interesting parasites, or more precisely, fungi. You have the fungus that zombify ants, and Last of Us made that one popular and very freaky.
There is another parasite, I do not remember its name, but it hijacks the brain of a spider similarly and zombifies it. So you can have the parasite do a lot of work on the brain. This really freaks people out because the sense of self and agency is important to them, and the idea that something could manipulate someone's personality freaks them out. There are already unicellular parasites that are thought to manipulate human brains to be more risk taking, so you know, they’re already here!
You can have them mutate the person to fit whatever criteria and so on you want. The options are quite literally endless to the point where it is close to magic. Sure, parasites are meant to be highly specific when they are on the inside of your body, so coming from random planet XYZ123 should mean you’re safe from it… but who cares when it is cool and fun?
While strictly technically not a proper parasite as it is not a living thing, nanites and ultra small machines could have a similar function after they run amok. An idea I had for a planet in my universe, and anyone is free to knick this one, is that in the distant past there was a society that got nanotechnology. It, however, did not end well for them, and the entire ecosystem got royally borked, but life didn’t die. Through some weird thing, it recovered with an extra organelle, a nanocondria! Okay, not the most creative name, so sue me! Wait, don't! Anyway, it allows a fused mix between life and mechanical. Run with it and create interesting parasites for it if you want.
Parasites and sophonts
Just so everyone knows, “sophont” is the technical term for any creature with human level cognition, sapience, sentience, the whole shebang. So how do parasites interact with sophonts?
Sophonts are the hosts
This is where you humans live now. Parasites infest your miserable boney bodies! And do their thing. Some you’ve lived with since ancient times, and your evolution and immune system are in a constant battle with them, so in most cases, no worries! Troublesome, yeah, but not an active danger to your species’ survival.
Most of the times… does imply that there are times where it could! GASP! Yes, as said, life wants to spread and destroy all if it could; it is the natural end for all life. Just as parasites have to deal with your immune systems and their own parasites and more, the issue comes if some parasite, alien, created, whatever, somehow suddenly has the key where none can fight against it.
HIV kind of got to this; it managed to find the golden ticket to cripple the body’s immune system so the system cannot attack the virus properly, and then it wreaks all the havoc it so desires. That was entirely accidental, and something a virus could do, but it is possible that other parasites can find similar keys to be unopposed. If they can do that and be certain to spread, humanity is borked… if it wasn’t for the sapience part. That makes it so that you can adapt your behaviour and see what works to deal with it, similar to during the Black Death! Which also illustrates you stumbling like headless chickens and not really doing much progress… but my point stands! You can have multicellular parasites become very slow plagues depending on the setting. Evolution is a war, and the only way to win is to always be at war.
Sophonts are the parasites
The issue with being a parasite is… well, as stated, you depend on something else regularly. Though if you think about it, you humans depend a lot on chickens, so in a way, you’re parasites to the chickens! 😮 PLOT TWIST!
Jokes aside, sophonts being parasites is theoretically extremely unlikely if not impossible. You generally need to be smaller than the host, and smaller sizes are not conducive to sapience and higher brain functions. A thing I didn’t explain above is that endoparasitism is strongly correlated with reduction of complexity. It is such a strong process of reduction in functionality, as the host does most of it, that many parasites have lost entire organ systems.
But one can still do it in science fiction. The most famous example I can think of is the Goa’uld from Stargate. Despite my hatred for needless apostrophes, which this has, because you don’t have a glottal stop or a contraction there—it’s there to look alien!—they have them be sophonts, but they use humanoids, which is 99.9% humans, as tools for their bodies. I honestly liked how the show explored them, even if they were cartoonishly evil, and the Goa’uld could have read my blog and understood even the most basic of things when it comes to actual ruling.
Summa summarum
Parasites are an important part of nature, and they will always exist because those niches are really well paying for the organisms despite the risks. But for fictional stories, they offer a great deal of story potential, too. Both in terms of small temporary problems to build up, but also in terms of problems to overcome. You can even make them the main antagonist like many scifi stories have done.
There needs to be more exploration of parasitism in fantasy, and I definitely do want more sapient parasites over all. I need to make a species of that—alright, it’s settled, I am going to do that for a practicum, but it will come when it is ready. Until next time!
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Copyright ©️ 2024 Vivian Sayan. Original ideas belong to the respective authors. Generic concepts such as parasites, the classifications, and the idea of nanocondria are copyrighted under Creative Commons with attribution, and any derivatives must also be Creative Commons. However, specific language or exact phrasing is individually copyrighted by the respective authors. Contact them for information on usage and questions if uncertain what falls under Creative Commons. We’re almost always happy to give permission. Please contact the authors through this website’s contact page.
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