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Parasitic Horror

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Parasites are organisms which depend on feeding off living hosts for their survival. For sapient creatures such as humans, this is an inherently horrific concept as it violates all our ideas about bodily autonomy and how we interact with other creatures. While "normal" predation is at least intelligible to a species of former hunter-gatherers, parasitism seems to us both pestilential and insidious, not an acceptable part of the circle of life but some abberant perversion of nature.

In fiction, this often takes on far more extreme forms, being infected by parasites the size of your fist, ones that take over all of your motor functions, or horribly mutate your body. It may be the offspring of some other lifeform implanted into you against your will, based off the similar behavior of parasitic wasps. Sometimes they will get inside your body through Orifice Invasion, otherwise they'll just burrow into your skin. In some cases the parasite might even be both intelligent and malevolent.


Sub-Trope of Body Horror.

Super-Trope to Puppeteer Parasite, Chest Burster, Parasite Zombie, Parasites Are Evil, and Womb Horror.


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    Fan Works 
  • Abraxas (Hrodvitnon): In this MonsterVerse fanfiction, two of Ghidorah's "children" cause this. When the Many are being injected into their first human victims, it looks like something is slithering under the body's skin. One of the unborn Zmeyevich kicking like a regular baby against its mother's belly is just a little bit more visible than is human.

    Film — Live-Action 
  • The Bay is a Found Footage Film that starts out as a documentary of the Fourth of July celebration at Claridge, Maryland, only for the town to succumb to a plague of a mutated species of Cymothoa exigua spawned from the polluted bay. They infect the people through the water supply and eat them alive and spawn until they die, where they escape their host and jump to a new one. By the end of the film, nearly everyone in the film had died after the US government quarantined it, the footage leaked by the reporter that survived.
  • Growth, which provides the page image, is about an island that unwittingly hosts a secret government laboratory studying parasites. While they're intended to produce extremely big, shiny pearls, this is only a proof-of-concept. They are accidentally released, first infesting a creepy kid (who, does, as a matter of fact, have them swarming out of her eyes), then overrunning the whole island. The Cruel Twist Ending of the film shows that those pearls are actually their eggs, and they're hatching...
  • The Mummy Trilogy: Scarab beetles can quickly burrow into a person's skin and eat them from the inside out. They are especially fond of human brains.
  • The Ruins: The evil vine not only eats people (or drinks their blood), but it also infects them with spores which then proceed to grow inside the victim. One of the main characters ends up killing herself as she tries to cut them out.
  • Sputnik. The alien lives in the host's oesophagus and stomach, and secretes a toxin that knocks out the host and relaxes his muscles so the alien can exit via the mouth to hunt and feed, which it does every night. Once outside the body and ingesting oxygen it grows from a snakelike form to a multi-limbed Starfish Alien 1.5 metres in length. It's speculated that the alien is using the host as a spacesuit until it becomes fully adapted to Earth's environment, whereupon it will discard the host like a cocoon (turns out the relationship is symbiotic).
  • The Thing (both 1982 and 2011): The titular villain is an extraterrestrial single-celled organism that can infect its victims by mere touch and hides inside of them. If its cover is blown, the Thing creates a horrific pandemonium of meat, tentacles, and mouths out of its host's body. To hide and hunt efficiently, the Thing orchestrates paranoia to the heroes, causing them to accuse each other for being the alien menace.
  • Venom (2018) is a reconstruction of this. While Eddie is initially terrified by the Venom symbiote using his body as a host, and is especially horrified by his new diet, Venom is actually sentient and able to be reasoned with—and, as consolation, being his host also grants Eddie all kinds of cool superpowers. They grow to genuinely like and trust one another, to the point where Venom is hurt and angered by being called a parasite, insisting their relationship is mutually beneficial. By the end, Eddie's grown to like having Venom around, and offers the compromise that they only eat bad people, to which Venom agrees, allowing them to become a full-on Horrifying Hero.

  • All Tomorrows: On one world that resisted their invasion, the Qu punished the people living there by transforming some of them into an array of parasites. Some were tortoise-sized and ambulatory, others were fist-sized and lived attached to hosts, and there was even one variety that infested the wombs of its victims. Most of them went extinct after the Qu left, but one variety subverted this, as they went on to regain sentience and formed a symbiotic relationship with their hosts.
  • The Troop involves a parasite-based bioweapon created as a side-gig to a genetically engineered tapeworm diet aid. While the diet aid was meant to become The Symbiote, the bioweapon took all the bad things about them and cranked them up, and added a few more besides.
  • Things Have Gotten Worse Since We Last Spoke: The last parts of the book involve Agnes being convinced by Zoe to consume raw insect-infested meat, willingly giving herself a tapeworm in order to fulfill her desire to be a mother.

    Live-Action TV 
  • Babylon 5: Season 3, "Exogenesis," features giant centipede-looking alien critters who are shown sinking into the flesh and bonding to the spinal columns of assorted lurkers in Downbelow, where they seem to take control of their hosts' bodies. Contrary to what Marcus and Doctor Franklin initially think, the Lurkers aren't victims, but volunteers, and the alien critters are actually symbionts, sharing their memories with the Lurkers in exchange for the ride. Basically what the Trills from Star Trek would be if the Federation didn't know about Trills.
  • One episode of Earth: Final Conflict introduces a parasitic worm that burrows into the body of its host, making them completely unafraid of everything, up to and including death. However, after an hour, the parasite will kill the host.
  • The Expanse: In season 4, Holden and Amos are trapped on an alien planet with the other colonists and have sought refuge in the ancient artifacts. It later turns out that the water contains parasites which nestle inside their eyes, slowly causing them to go blind.
  • In one episode of Primeval a flock of dodos manages to escape into a building in the present day. The dodos themselves are about as dangerous as you might expect, but they bring with them a highly infectious worm-like parasitoid that can also transfer to humans.
  • Stranger Things: The Mind Flayer manages to leave a bit behind when it injures El, which starts wriggling and painfully crawling around under her skin later. Jonathan has to cut her leg open and try to dig it out with his fingers while they're all hiding from the Mind Flayer.

    Multiple Media 
  • Star Trek:
    • Star Trek II: The Wrath of Khan features Ceti Eels, which burrow into their victim's head through the ear canal and attach themselves to their host's brain. This has the side effect of making their victims extremely susceptible to suggestion. Khan uses this to hijack the starship Reliant and force Captain Tarrell and Commander Chekov to lure Enterprise into an ambush. When Khan orders Terrell to kill Kirk, he's able to resist the eel's influence just enough to eat his phaser before Khan can force him to murder the Admiral.
    • In Star Trek: The Next Generation, the episode "Conspiracy" plays the parasites for various types of horror: firstly, they change people's personalities, secondly, they make people violent and super strong, thirdly they themselves look pretty gross with their appendages sticking out of the person's neck, and fourthly, some of them breed in somebody's stomach, causing him to explode.
  • Ultra Series:
    • Ultraman: The Next: Beast the One, the Big Bad of the film is a parasitic, space demon who merges with a human host and slowly overrides their mind, body and finally, kills them altogether, absorbing its host into itself. It can do the same with other living creatures for the sake of augmenting itself.
    • Ultraman Z: Celebro, Big Bad of the series, is a space entity that takes possession of various organisms to carry out his evil plans. His possessions are shown to be rather unsettling as his body language shows signs of twisting the bodies and actions of those possessed to suit his needs and his possessions are shown as rather painful.

    Video Games 
  • The plot of Baldur's Gate III concerns the protagonists being implanted with illithid tadpoles, seeking a cure before the parasite eventually consumes their brains and transforms their bodies into mind flayers. The opening cutscene demonstrates the implantation of these tadpoles, showing them entering their victim's skulls by crawling around their eyeballs in a manner similar to the page image above.
  • Destiny has the larvae of the Worm Gods, which are in each and every single member of the Hive race. The larvae give their hosts immortality and, when supplied with enough death and destruction, the ability to bend reality to their whim. However, if they are not sustained with enough death, destruction and wanton murder, they feed on their hosts. The Hive have turned this grotesque relationship into a religion.
  • Endoparasitic sees Cynte infected with a parasite that he is only able to keep at bay with vaccines syringes scattered across the research facility.
  • The Last of Us revolves around a Zombie Apocalypse caused by a mutated strain of the Cordyceps fungus, which turns people into bloodthirsty zombies and, over time, covers the victims in fruiting bodies, starting with the head.
  • Resident Evil 4 and Resident Evil 5 involves a mutative Puppeteer Parasite known as Las Plagas. They often reveal themselves as carnivorous worms growing on people's spines after their host gets decapitated.
  • In Skies of Arcadia, when the crew reaches The Empire, a certain enemy is a homeless man being piloted by a gigantic cockroach-like insect.
  • Sid Meier's Alpha Centauri: Mindworms. Just Mindworms. The dominant native lifeform of Planet, Mindworms are small, maggot-like creatures that attack in massive swarms and paralyze their prey with psychic terror before laying their eggs inside the brains of their conscious, screaming victims. And they always make a beeline towards the biggest sources of pollution. Fun.
  • StarCraft's Infested Terrans are stuffed so full of alien parasites they (both the poor space marine and all his new passengers) are bursting out of their spacesuits.

    Web Original 
  • A certain Creepypasta involves a man on a bet to lose weight take anabolic steroids and a tapeworm pill together. The tapeworm begomes giant and eats all his organs.
  • Mortasheen, a horror-themed Mons world heavily influenced by real-life biology, has too many parasite-based monsters to list individually. Wormbrains are Puppeteer Parasite flatworms that control genetically-engineered host bodies. Botanical monsters are cultivated as parasites of natural plants. The Genetimorph and Underfiend are dangerous parasitoid creatures whose offspring are Chest Bursters, whereas the Wrigglegeist is an endoparasite that lives harmlessly inside an unwary host. Still more Mortasheen parasites feed off of weirder things like genetic material and neural activity.