[[quoteright:350:[[TabletopGame/DungeonsAndDragons http://static.tvtropes.org/pmwiki/pub/images/49128.jpg]]]]
[[caption-width-right:350:A "Bugsucker" is a symbiotic creature of Bugbear (host) with Stirge (guest)]]

-> ''"Of all the parasites I've had over the years, these worms are among the -- hell, they ''are'' the best!"''
->-- '''Fry''', ''WesternAnimation/{{Futurama}}''

In biology, a symbiote (or symbiont) is a living organism that lives in symbiosis with another organism. Symbiosis literally means "living together," and it comes in three variations:

* [[SymbioticPossession Mutualism - both organisms benefit from each other's presence.]]
* Commensalism - one organism flourishes, the other isn't affected.
* Parasitism - one organism is harmed, the other flourishes.

In fiction, all types are very frequent guests in ScienceFiction and {{Fantasy}}. The HeroicHost specifically gets their powers from such an arrangement, though the specifics vary.

Compare PuppeteerParasite (parasites that control other organism's brains) and FaceFullOfAlienWingWong (parasites who use our bodies for reproduction), which could be subtropes of this. Also compare ChestBurster. See also HeartDrive for a similar phenomenon involving biological {{Soul Jar}}s.

For details on hosts for symbiotes, see BodyAndHost.

For a version of Mutualism particularly common in ScienceFiction, see TranslatorMicrobes.

When TheSymbiote covers the host's body as some sort of costume, whether for [[ClothesMakeTheSuperman good]] or [[ClothesMakeTheManiac bad]], it's almost invariably a ClingyCostume.

----
!!Examples of Mutualism:

[[foldercontrol]]

[[folder: Anime And Manga ]]

* In ''Anime/KurauPhantomMemory'', the [[EnergyBeings Rynax-entity]] merged with Kurau's body benefits from the protection for her recuperating pair, while giving Kurau immense powers in return. It's not quite clear though whether the original Kurau is still in control of her own body or simply a "bystander" in the process.
** The finale (in the dub at least) makes it pretty clear the original Kurau was just a bystander. After the Rynax leaves her body, Kurau tells her father she can remember everything that happened when the Rynax was controlling her, and when she talks to Christmas she says she's not the Kurau Christmas knew, and that even though she isn't the Kurau Christmas knew, she saw everything the "other" Kurau and her went through together, which means the original Kurau was just an observer, watching the Rynax's life in her body until it left. Though, she did seem to have fond memories of the experience.
* In ''Anime/{{Pokemon}}'', a Shellder latches onto a Slowpoke permanently to create a Slowbro or Slowking.[[note]]This is not true in the games; Slowpoke evolves sans Shellder.[[/note]] The Slowpoke gets stronger by way of evolving, and the Shellder gets to snack on the Slowpoke's dinner scraps. Or something.
* In ''Anime/MacrossFrontier'', the Vajra have a special kind of bacteria in their intestines that maintains the telepathic connection between them. If the bacteria gets in humans (rare, as it requires ingesting of bodily fluids), it slowly kills them as a disease known as a "V-Type Infection". [[spoiler:It's eventually revealed that Ranka Lee has these same bacteria in her intestines, and due to contracting them ''in utero'' she is fully symbiotic with them. They allow her to tap into the Vajra HiveMind, making her the only human being who can communicate with the Vajra. At the end of the series, she uses her connection to cure Sheryl's V-Type Infection by influencing her bacteria into a similar symbiotic relationship.]]
* ''Anime/KillLaKill'' has the Kamui, sentient clothing that feed on their wearer's blood, and in return give them superhuman strength and resilience. May overlap with parasitism, as Kamui can cause exhaustion [[spoiler:and BodyHorror]]. [[spoiler:Episode 16 reveals that this applies to all life fibers; They're aliens that feed on humans and have helped them evolve so they would eventually wear clothing made of life fibers]].

[[/folder]]

[[folder: Comics ]]

* The color entities of ''GreenLantern'' feed on emotion and allow their hosts to manipulate solid light on a much larger scale than power rings. Unfortunately, some of them affect the behavior of their hosts, which can vary from subtle influence to full on PuppeteerParasite.
* In ''TheIncredibleHulk'''s "[[http://www.comicbookgalaxy.com/troublewithcomics/2009/10/flashmob-fridays-002-incredible-hulk.html Crossroads]]" arc the Hulk went to a planet where the food is poisonous to animals unless they have a symbiote attached.
* The Symbiotes from ''Comicbook/{{Spider-Man}}'', although they have a tendency to turn their host ''evil''. The ones in the [[UltimateMarvel Ultimate]] universe are parasitic, though.
** The core universe Symbiote species is as well (at least, after 90s retcons). The Comicbook/{{Venom}} Symbiote and its spawn are considered mutants by the others. Or they were, before they completely wiped out their AlwaysChaoticEvil brethren.
** Venom is coming back to this, after bonding with Flash Thompson, realizing that they must rely on each other to survive.
** Toxin, when bonded to Patrick Mulligan, had a relationship similar to that of a father and a naughty little child. [[spoiler:Not so much when Toxin is bonded to Eddie Brock.]]
** Carnage, when bonded to its first host [[SerialKiller Cletus Kasady]]. The symbiote and Cletus genuinely seem to care for each other and feel incomplete unless they are together. It's a body controlling parasite to anyone else, whom it only uses to help it reunite with Cletus whenever they are separated. Cletus tells someone who tried to steal the symbiote from him that he and Carnage were pretty much made for each other.
** Venom truly wants to be this for Peter Parker, its first human host. It wants to be with Peter and it wants to make him stronger. While Venom has the same corrupting influence on Peter as it does on other hosts, it does so not out of a desire to control him but because it genuinely believes it's doing Peter a favor by getting rid of his compassion.
* The symbiotes from Comicbook/SpiderMan may have inspired the eventual revelation that {{Spawn}}'s distinctive costume (which is standard issue for all [[HumanoidAbomination Hellspawn]]) is actually a living, sentient demon in its own right. How the "costume-demon" benefits isn't made clear, possibly from being able to passively feed off of the necroplasmic energy of its undead host. The host definately benefits from having a ''very'' protective live-in partner which not only provides flight/gliding (the cape functions like wings because, in its natural form, they are wings), offensive shapeshifting and CombatTentacles (via the chains and cape-tendrils), but will fight to protect its host even if the host is unconscious.
** Said symbiote feeds of negative emotions and pain, being around Spawn of all people is giving it plenty of that.

[[/folder]]

[[folder: Film ]]

* Midi-chlorians in ''StarWars''.
-->'''Qui-Gon Jinn''': Without the midi-chlorians, life could not exist, and we would have no knowledge of the Force. They continually speak to us, telling us the will of the Force. When you learn to quiet your mind, you'll hear them speaking to you.
* ''AndYouThoughtYourParentsWereWeird'' has Matt, a ghost, possessing Newman, a robot. Matt needs Newman's body to interact with the world, and Newman benefits from having a smarter mental roommate.
* ''{{Growth}}'' has leech-like parasites that infect a human host with their larvae and make their hosts stronger and smarter. However, the larvae rapidly mature and take over the body, reproducing and making their hosts aggressive. They also cause salt to act like acid. Often, mature parasites will ZergRush humans when hungry. Rather than infecting and reproducing, they eat.

[[/folder]]

[[folder: Literature ]]

* The Iskoort in ''Literature/{{Animorphs}}''.
** The Yeerks too, who are like the Goa'uld in that they skirt the line between mutualism and parasitism. They forcibly take hosts, but it's just as beneficial for them, as in their normal states they're blind, powerless slugs. [[spoiler: The Iskoot are what happen when the relationship goes over to full mutualism, hence why the Crayak wants them destroyed before the ''other'' Yeerks find out and spoil its fun.]]
** The Yeerk resistance movement is kinda like the Tok'ra in that host and symbiote share the body equally.
* Similarly, the symbiote in DavidWeber's book ''Literature/TheApocalypseTroll'' kills over 99% of its hosts, though in this case it's [[JustifiedTrope justified]] since it was originally developed as a bioweapon, and intended to kill 100% of its hosts. Those who survive, though, gain effective immortality via HealingFactor (and [[ReallySevenHundredYearsOld eternal youth]] into the bargain), enhanced senses and reaction times, and generally superhuman abilities.
* The symbiote from Creator/AnneMcCaffrey's ''Crystal Singer'' novels has a low success rate for adaptation to human hosts. Those who survive, though, gain a HealingFactor that makes them virtually immortal, barring murder or immediately-lethal accident. [[spoiler:Too bad about the slow memory loss, dementia, and paranoia...]]
* In Creator/JohnVarley's ''Literature/EightWorlds'' series, there are the symbiotes; artificially cultured plant-based organisms that are bonded with humans to produce a single organism that has it's own individual animal/plant ecology. They don't breathe or eat, and spend their time in open space, usually touring the rings of Saturn.
* Likewise, the cave slug in F. Paul Wilson's ''Healer'' is believed to be 100% fatal, but the title character is [[MillionToOneChance one in a thousand]] and instead gains the "usual" benefits per the two examples above, along with a voice in his head (which he names "Pard", as in partner). His touch can also heal others of physical and mental illness, making him a figure of awe and legend.
* The Binod Union in ''ComicBook/{{Atavar}}'', so much so that they're considered a single race.
* ''Literature/TheHitchhikersGuideToTheGalaxy'''s Babel Fish, a living plot device as a Symbiote.
* The vampire-fungi from the ''Literature/{{Necroscope}}'' series technically fit here. The fungal-leech gets a host with sentience and opposable thumbs, the host gets enhanced psychic powers including shapeshifting), enhanced strength, enhanced senses, and a craving for fresh blood and human flesh...
* The Kualkua species in SergeyLukyanenko's ''TheStarsAreColdToys'' duology are shapeless creatures able to split by mitosis. They are used by the Conclave for anything from translating speech in real-time to piloting suicide ships. At first, the human protagonist is horrified (but not surprised) as to the treatment endured by the Kualkua at the hands of the Conclave Strong races. Later, he is horrified after learning the true nature of the Kualkua (that of a [[spoiler:HiveMind, which to him represents near-godhood]]). This also crosses over into Commensalism and Reverse Parasitism.
* ''TheWarAgainstTheChtorr''. A characteristic of the invading Chtorran ecology. For instance Chtorran gastropedes are covered in neural symbiotes (so-called 'worm fur') that vastly increase their senses, making them super-efficient predators. Shambler trees are host to over thirty different species of carnivore that can seek out and devour prey, passing on nutrients to the shambler via their waste products.
* The K'da from ''{{Dragonback}}''. Basically a tiger-sized dragon that can turn into a tattoo, and ''must'' do so at least once every six hours. The K'da gets a host, the host gets a powerful guardian, and both get the other's companionship.
* In OctaviaButler's ''Literature/{{Fledgling}}'', vampires (or Ina) are like this with humans. In fact, the humans they feed on are called their symbiotes. Ina feed on human blood, and humans are addicted to whatever chemical is in the Ina's saliva. The humans also get to live longer (but they can't be turned). There even is a HemoErotic part, with Ina often having sexual relations with their humans.
* This shows up at least twice in Creator/PoulAnderson's ''Literature/TechnicHistory'' series: one encountered briefly by Nicholas van Rijn, and the natives of Dido in ''The Rebel Worlds'', who are a combination of ''three'' species--the "hands," the "wings," and the "feet."
* The detective-creature in Creator/HalClement's books ''Needle'' and ''Through The Eye Of The Needle'' was a blob of protoplasm that entered a human host to survive and move around. It was a type 2 (commensalistic) in the first book as the host was not harmed, but shifted towards a type 3 (parasitic) when the host became ill in the second book. There was also another creature, the hunted fugitive, who'd taken another body and was a PuppeteerParasite type. Clement actually coined the word "symbiote" in ''Needle.'' He later apologized for this, after biologists pointed out to him that the correct word is "symbiont"; it was too late by then, as a number of other writers had copied his term.
* ''Literature/GalaxyOfFear: Eaten Alive'': Enzeen on [[IDontLikeTheSoundOfThatPlace D'vouran]], after TheReveal, are repeatedly called parasites. [[spoiler: The planet is alive and [[QuicksandSucks eats people]], and they feed from it.]] However, it's clearly mutualistic; the Enzeen make visitors feel welcome on D'vouran and help hush things up whenever people start to feel suspicious and might start figuring out what's happening.
* The Rhumians in the ''Literature/SectorGeneral'' novel ''Code Blue Emergency'' are almost inert brain-creatures who form a symbiotic relationship with a non-sentient species from their planet, but can link to almost any living thing in emergencies. The squickier elements of this are acknowledged in canon, with even the radically-accepting medics of Sector General initially mistaking them for evil {{Puppeteer Parasite}}s.
* The Nahel bond between human and spren(essentially a sentient idea) in ''Literature/TheStormlightArchive'' is a slightly odd example of this, since spren are incorporeal. The bond grants the human Surgebinding powers, and allows the spren to retain its sentience in the Physical Realm (Spren are native to the Cognitive Realm). If the bond is broken, the human loses access to Surgebinding, while the spren becomes mindless.

[[/folder]]

[[folder: Live Action Television ]]

* The Vindrizi from "Exogenesis," in season 3 of ''Series/BabylonFive''. A race of living recorders designed to preserve the memories and knowledge of their creators, the Vindrizi seek out voluntary hosts who have nothing of their own left to live for.
* In ''FraggleRock'' the Fraggles have an odd symbiotic relationship with the Doozers. Doozers build large structures and other constructs with a candy-like substance, which is soon eaten by the Fraggles. An episode shows that if the Fraggles don't eat the Doozer buildings they eventually grow out of control and are left with nothing else to build, and the Doozers actually like the Fraggles eating their buildings as it lets them know their hard work is appreciated.
* The Goa'uld and Tok'ra in ''Series/StargateSG1''.
** The Goa'uld surf between mutualism and parasitism, since the symbiosis can allow them to take over their hosts. The difference between Goa'uld and Tok'ra is largely the choice whether or not to do this. The host also benefits from an extended lifespan, HealingFactor, and boosted strength.
*** Made a little questionable when there have been a couple of rare, but still present, instances of a Tok'ra taking a host without consent (an act of desperation by the symbiote) and even taking over their host (deliberate, if extraordinary). [[NotSoDifferent Hmmm]].
* The Trill in ''Series/StarTrekDeepSpaceNine''. The host humanoid body keeps the Trill alive while the host enjoys the cumulative memories, including the skills, of all previous hosts.

[[/folder]]

[[folder: Tabletop RPG ]]

* Very similar to the Vindrizi, the Kergillians from the ''TabletopGame/OverTheEdge'' tabletop RPG (and related card game).

[[/folder]]

[[folder: Video Games ]]

* Peacebringers and Warshades in ''CityOfHeroes''. They're each a kind of Kheldian, EnergyBeings from outside our galaxy who can merge with humans; the humans get powers, and the Kheldians get immortality as long as they have a host; their "natural" lifespan is only ten years. They're an unlockable playable class (well, two [[AnAdventurerIsYou Archetypes]] to be precise), and their powers include ShapeShifting into their previous common forms, including a [[StarfishAliens floating tentacled]] GlassCannon and a large armoured StoneWall, [[FanNickname nicknamed]] the 'squid' and 'lobster' respectively.
* In ''KnightsOfTheOldRepublic II'', a psychic connection of this sort is formed between the player character and Kreia.
* The fierce [[ProudWarriorRaceGuy Harika]] and mouse-like Yorn in the third installment of ''{{Star Control}}''.
* ''{{Skullgirls}}'' has loads of examples of numerous different types of symbiotes, though they're all referred to as "parasites" in-game. Of the playable cast:
** Filia has a symbiote living in her hair named Samson, and he zigzags between mutualism and parasitism: while they do work together in combat, Samson has a tendency to take control of Filia in some of their moves, and it's hinted that [[spoiler:he wants to turn Filia into the next Skullgirl--a PersonOfMassDestruction who ends up being the main agent of the BiggerBad.]]
** Squigly, meant to be TheRival to Filia, has a symbiote who act as a rival to Samson: Leviathan, a snake-like creature who has a much friendlier relationship with his host than Samson does.
** Eliza is the host of a symbiote named Sekhmet, who is different from the previous examples in that she has ''entirely replaced Eliza's skeleton'' in exchange of granting Eliza eternal youth as long as she feeds on blood.
* The compacts between spirits and humans in ''{{Poacher}}'' are this.

[[/folder]]

[[folder: Webcomics ]]

* The Gnoph in ''{{Gnoph}}'' live inside human lungs, and grant their hosts a variety of superhuman abilities.
* ''TheAccidentalSpaceSpy'': One of alien spies have this, the real body is just a oval. Rest of parts such as hands, eyes, etc were parasites but later adopted to mutual status.
* ''Webcomic/WorkSucks'': Epicena has a symbiotic monster named Hatch hooked to [[AmbiguousGender his...her...its]] back that has the ability to inhale and capture people Epicena wants. Epicena says Hatch is harmless unless (s)he tells it otherwise.

[[/folder]]

[[folder: Western Animation ]]

* The Worms in the "Parasites Lost" episode of ''{{Futurama}}'' (see the page quote.)
* Symbiotes in the ''WesternAnimation/MenInBlack'' animated series. Basically, they were metamorphic heads which had to attach to other creatures to survive. Having one attached to you meant you got super strength, shape shifting, and highly powerful regeneration powers; unfortunately, the only one we see is ungodly annoying and clingy, and if you're bonded with one past a certain period of time, it becomes permanent.
* ''{{Transformers}}'' has Headmasters, Targetmasters, and Powermasters. The human partners are kind of like having a gunner in the first two cases, while the human partner gains the armor and weapons of a Transformer. With Powermasters, the human partner serves as the ''engine'' on a planet when all fuel sources were poisoned to keep the Transformers' battle away from them. The bad news is that both give up some autonomy.
** There are also cases where a Transformer forms part of a larger one. Being carried around by (and presumably getting to lap up some spare Energon from) a big guy like Trypticon, Metroplex, or anybody with Maximus in the name is really handy, and the larger TF gets a small army of normal-sized Transformers that are always at his side, and who can handle fine-tune work. On the rare occasions on which Trypticon actually ''doesn't'' want to break stuff, he can sit back and send in his little buddies. These guys' status as fully sentient characters vs. remote-controlled tools changes between incarnations.

[[/folder]]

[[folder: Real Life ]]

* You've got some in your intestines right now, people. They're gut bacteria that eat leftover fiber from your food, and pay their rent with the vitamins they excrete. Lose them due to radiation therapy, high-dose antibiotics, or other causes, and your doctor will make you eat live-culture yoghurt until their population levels are restored.
* A very particular case of real life symbiotes are [[http://en.wikipedia.org/wiki/Mitochondrion mitochondria]], which actually live ''inside the cells'' of practically all animals (including humans), playing an important role in the metabolism.
** Although calling them "symbiotes" is giving them too much credit at this point. Mitochondria have been part of other organisms for so long that they are not independent lifeforms in any real sense anymore, but rather an integral organ of the cell they inhabit (which is why they're counted among the "organelles"). They still have their own DNA, though, which you do in fact inherit solely from your mother.
* Plants have something not dissimilar in their chloroplasts, the organelles that photosynthesize. These too are theorized to have been symbiotes at one point, and which are now [[CantLiveWithoutYou completely interdependent]].
* It's also theorized that eukaryotic cells in general (cells with nuclei) are also the product of a symbiotic relationship.
* Those white lumps seen in pictures of humpback whales are actually this trope, as they're giant barnacles that grow nowhere else but on the hides of baleen whales. The otherwise-immobile barnacles get a free ride into plankton-rich waters, at which point they start waving their net-like appendages to feed. The whale can hear which flipper's barnacles are scooping up plankton more rapidly, and turn towards the direction where food (for whale and passengers both) is most abundant.
* Many "cleaner" species, such as tickbirds or cleaner wrasses, pick parasites (see below) from the surface of larger animals for a living. They get a meal, and the bigger animal gets a de-lousing.
** [[http://en.wikipedia.org/wiki/Oxpecker Oxpeckers]] walk a fine line between mutualism and parasitism, since their main diet is their hosts' blood--they get some of it from the fleas and ticks they eat off of their host, but they will also sometimes peck at their hosts, or reopen their wounds, to get them to bleed.
* One theory on the origin of complex life is that a bunch of single-celled organisms joined together and skin and bones/exoskeleton were a handy defense that developed over time.

!!Examples of Commensalism:

[[foldercontrol]]

[[folder: Anime And Manga ]]

* The [[PoweredArmor Guyver units]] from ''Guyver''.

[[/folder]]

[[folder: Comics ]]

* In ''ComicBook/BazookaJules'' the source of Jules' superpowers is a micro-robotic weapon called the symbiote that entered into Julie's body and permanently fused with her nervous system. It has two main functions. One is to enhance its host physical abilities with chemicals and hormones making them [[SuperStrength stronger]], faster, and [[SuperToughness more durable]]. The other is to provide its host with weapons and gadgets. It was has various detection systems, a radar, and can provide its user with tactical advice, hence the voices inside Julie's head.

[[/folder]]

[[folder: Video Game ]]

* This form shows up in ''Knights of the Old Republic II'' as well: [[spoiler:the Exile, having cut off his connection to the Force after all the death at Malachor, effectively re-establishes that connection by becoming a black hole in the Force, siphoning excess power from his companions. Taking advantage of this is what allows you to kill Darth Nihilus.]]

[[/folder]]

[[folder: Real Life ]]

* Remoras get transported along by their host animals, benefit from their protection, and possibly eat their leftovers. But they don't seem to do anything for or against their hosts.
* The [[http://en.wikipedia.org/wiki/Cymothoa_exigua Cyomatha exiguna]] kills and [[CognizantLimbs replaces]] a fish's tongue. The fish is no worse for wear, apart from now having a ''[[NightmareFuel tongue with its own eyes and brain]].'' It does use up a bit of blood, but usually not enough to matter.
* You probably have a ''lot'' of these on your body without knowing it, such as dust mites that eat shed skin cells or amoebas that feed on the bacteria at your gumline (the latter being a double example).
* Even a bird nesting in a tree can be considered this.

!!Examples of Parasitism:

[[foldercontrol]]

[[folder: Anime And Manga ]]

* The Parasitic Beasts in ''Manga/{{Parasyte}}''. They drill into people's heads and take them over by eating their brains. Shinichi, the protagonist, manages to get away with one taking over his right hand (it aimed for his head, but he pulled it away in his sleep and it took over his hand in desperation).
** Although, since the Parasytes already killed the host, they're more like a parasite on the ''species'', since they instinctively crave the host's species.

[[/folder]]

[[folder: Comics ]]

* The Venom symbiotes in ''Comicbook/{{Spider-Man}}'' are oftentimes portrayed as this.
** Incidentally, [[AlwaysChaoticEvil this was the original function of its species]]. Taking a host, driving them to an early death, and then finding another. The fact that the Venom Symbiote wanted to establish a life-time bond with one person made the rest of its race consider it to be [[MySpeciesDothProtestTooMuch psychotic]].

[[/folder]]

[[folder: Film ]]

* The Xenomorphs from ''Franchise/{{Alien}}'', who utilize human bodies to reproduce via FaceFullOfAlienWingWong.
* The giant crab monsters in ''Film/{{Cloverfield}}'' were initially parasites clinging to the big guy.

[[/folder]]

[[folder: Literature ]]

* The Yeerks in ''Literature/{{Animorphs}}''; who in their natural state are little more than breadloaf-sized gray slugs, who need [[GrandTheftMe our bodies]] to free themselves from their senseless prison. A branch of their species became the Iskoort (noted above) and it's stated that there is a chance they will follow that path as well in the distant future.
* In ''Literature/TheDresdenFiles'' short story ''Day Off'', [[OurWerewolvesAreDifferent two of the Alphas]] are afflicted with "supernatural fleas".
* The Black Worm in {{John Connolly}}'s ''The Cancer Cowboy Rides.'' An inhabitant of the EnemyToAllLivingThings, Buddy Carson, it grants its host the power to transmit fast-acting cancer at a touch- and enforces its use with agonising pain and the threat of infection. Though the Worm doesn't speak in the short story, Carson mentions a dream in which it tells him that his only purpose is to "Spread the Black Word."
* In ''Infected'' (the novel), the parasites are extra-terrestrial in origin and cause the growth of a new consciousness that encourages the host to kill and maim as much as possible. [[spoiler: That's just a side-effect. Their real purpose is to guide humans to an area, where the parasites are really "workers" - they use the humans to build an organic teleportation gate for the invasion of Earth.]]
* [[BigBad Lotus]] in ''{{Literature/Monster}}'' is one of these feeding off the ''universe''.
* In ''[[ScottWesterfield Peeps]]'', [[OurVampiresAreDifferent vampires]] are due to a parasite living inside the body of a human host. The entire book is all about parasites, even with tips about [[RealLife real]] parasites at the beginning of each chapter.
** Debatable. While the "parasites" do significantly alter your personality and body to aid themselves (you have strong cravings for meat, want to fight or sleep with everything you see, and hate everything you once loved), they do grant super strength, night vision, immunity to most other diseases, control over rats, and extreme longevity. [[spoiler: In fact, there are two strains of the parasite. While the first strain will turn you into basically a super powered living zombie, the second (actually original) strain can be controlled with a mixture of standard vampire preventatives (garlic and other stuff), basically making you an immortal superhero.]]
* ''AfterMan'' had a species of shrew-like mammals that evolved into a parasite, using their mouth to suck blood from their host like a giant mosquito.

[[/folder]]

[[folder: Live Action Television ]]

* Another example of the [[OurVampiresAreDifferent parasites turn you into vampires route]] is the dodo parasites in ''{{Primeval}}''.
* The original appearance of the Trill in the ''Series/StarTrekTheNextGeneration'' episode "The Host". They were given a makeover before ''Series/StarTrekDeepSpaceNine''. The relationship wasn't as bad as usual, but the character in question did refer to itself as a "parasite".
** Also, the host of the original Trill was apparently completely submerged - no sign of Riker in there when he was filling in as host. If the Trill hosts minded, it wasn't said, but the relationship between host and symbiote - symbiote is the person you're talking to, host is just a body it uses - is the same as with the villainous host-takers.
*** Then again, Trill symbiotes aren't meant to be placed in humans, perhaps explaining this effect. It wasn't long before Riker's body began to reject it. The ExpandedUniverse makes the original Trill less Goa'uld-ish (and more reconcilable with Series/StarTrekDeepSpaceNine.) They've got a different look thanks to the same virus from ''[[Series/StarTrekEnterprise Enterprise]]'' that de-ridged the Klingons during TOS and a different culture due to having lived apart, and though it isn't said explicitly that this is what happened with Riker, an unprepared host of ''any'' kind of Trill symbiote runs the risk of being submerged, and not letting that happen is part of the training a potential host goes through. Therefore, if a Trill symbiote took a totally unprepared human instead of a trained Trill initiate as a host, you get what happened with Riker.
** ''Film/StarTrekIITheWrathOfKhan'' had parasitic eels native to Ceti Alpha IV, which Khan used to control several Star Fleet operatives.
* The Black Oil a.k.a. Black Cancer a.k.a. Purity from ''Series/TheXFiles'' is an alien virus that gets into your body through [[EyeScream your eyes]] and [[OrificeInvasion mouth]] and assumes complete control over it, optionally [[BodyHorror using it as a host for gestating a baby alien]].
* [[BigBad Anubis]] in season eight of ''Series/StargateSG1''. He is a Goa'uld (see above) who figured out how to AscendToAHigherPlaneOfExistence. The other Ascended didn't like that, so they kicked him halfway back down to the lower planes [[spoiler:to punish Oma Desala for helping him ascend]]. He now exists as an EnergyBeing which needs either a force-field suit or a host to interact with the material world. In the latter case the host has no control over the body and reacts to him as if he were a disease, breaking out into lesions and gradually dying. (Mind, ''most'' Goa'uld qualify for parasitism, though they can choose to let the host out to play. Being half-ascended is what makes Anubis burn out his host; a lot of other Goa'uld hosts [[FateWorseThanDeath would consider that getting off easy]].)

[[/folder]]

[[folder: Video Games ]]

* The "Zombees" in ''DeadRising''. The cause of the [[ZombieApocalypse zombie outbreak]] is a natural species of Colorado wasp that injects a host with larvae that travels into the brain and takes it over, turning the host into a zombie in which the larvae develops.
* The Necromorphs in ''Franchise/DeadSpace''.
* The various types of headcrabs in ''VideoGame/HalfLife''.
* The X Parasites in ''{{Metroid}}''.
* In ''VideoGame/{{Prototype}}'', Alex Mercer gets infected with a [[TheVirus virus-specific]] parasite, which debilitates him until he finds a cure.
* The Magatama in ''VideoGame/ShinMegamiTenseiIIINocturne''. Notable in that, despite being in name a parasite, it has many beneficial effects and only few drawbacks that can be cured or outright prevented with some foresight.
* Las Plagas in ''VideoGame/ResidentEvil4''.
* The Zerg Queens in ''{{Starcraft}}'' love this trope. They have ''two'' kinds of nasty parasites at their disposal, ones that crawl inside the host and [[TheMole feed information back to the Zerg]], and another that [[SpawnBroodling grows inside a biological unit and then emerges Chest Burster fashion.]]
** And a subtype of both that infects an entire Terran command center, turning the humans inside into something between zerg and suicide fanatics.

[[/folder]]

[[folder: Web Original ]]

* ''WebVideo/VaguelyRecallingJoJo'': Like the [[Manga/JoJosBizarreAdventure original manga]], Empress is a parasitic Stand trying to devour Joseph Joestar's body. To make things worse, it is immune to Hamon because it is part of Joseph's body. [[spoiler: Joseph defeats it with the help of Ceasar Zeppeli's ghost.]]

[[/folder]]

[[folder: Western Animation ]]

* The Big Tick in ''WesternAnimation/{{Ben 10}}'', who is a parasite that eats ''planets''. Unfortunately, [[EarthShatteringKaboom the planet does not usually survive]].
* Parodied with "Brain Slugs" in ''{{Futurama}}''; unlike most versions of TheVirus, which are typically capable of a bit of subtlety, Brain Slugs are blatantly visibly attached to the infectee, and make statements such as "Your mission for today is to go to the Brain Slug planet and stand around without wearing hats", in a stilted monotone.

[[/folder]]

[[folder: Real Life ]]

* And in case you were wondering by this point, yes, you have these as well, although generally a lot less than the mutualistic/commencialistic symbiotes as your immune system tends to wipe out the parasitic ones before they become too uppity. Most infectious diseases are caused by parasitic symbiotes and the immune response to them.
* Two words: ''[[http://en.wikipedia.org/wiki/Toxoplasmosis Toxoplasma]] [[NightmareFuel gondii]].''
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