"The truth is Earth citizens are no longer willing to do these dull, labor-intensive tasks. We tried using illegal aliens instead, but they kept bursting out of people's chests."Body Horror where an alien parasite or a Fetus Terrible within someone else decides it's about time to move out and find a body of its own. This is achieved in a messy, painful, and almost always fatal manner. Related to Orifice Evacuation (where the alien leaves not quite as violently), Orifice Invasion (where an alien wants in), Face Full of Alien Wing-Wong (how these alien pregnancies start), and Spawn Broodling (often the point of this, and the weaponized version of this). Sometimes preceded by a Painful Transformation. Not to be confused with Chest Blaster or Chest Monster.
— Plan 7 of 9 from Outer Space
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- Parodied in the 2004 Nik Naks advert where the eater of the Nik Naks (crisps) has a giant one explode out of his chest, as everybody around him is splattered with dusty cheese. After an awkward moment they all start dancing.
Anime & Manga
- HUMANOID Szayel Aporro Grantz does this in Bleach. He impregnates the victim with himself, being "reborn" fully grown upon death.
- The Six Gates World franchise is fond of this. In Mon Colle Knights, Oroboros does this to its host, the Dread Dragon. In Majuutsukai No Shoujo, Kashe uses her own body as host for a demon, which ends up growing through her skin from all sides and eventually around her. After overcoming its mindrape from the inside, Kashe then chestbursts from it.
- This is how Yuca Collabel resurrects himself after a two month gestation period. He probably wouldn't have fit out the normal way since he had already aged to the form of a prepubescent boy in utero.
- Several of Berserk's nastier monsters such as the trolls of the Qliphoth and Emperor Ganishka's demonic Daka soldiers reproduce like parasites whose offspring kill the host. The former are conceived through rape of human women, the later by immersing pregnant women in a vessel connected to Hell so that their children are corrupted in the womb. What both have in common is that once developed, they exit the host in the most gory and violent way possible. Young trolls grow quickly in the woman, until they claw and rip their way out of her stomach, then eat her still warm body. Baby Daka burst out of the abdomen, leaving the woman to bleed out, and get collected in cages by attendants.
- The USBM from BioMeat.
- Parodied in the final episode of Bobobo-bo Bo-bobo.
- Parodied in one of the omake for Blue Exorcist. Rin hides his tail under his shirt and uses it to mimic the chest burster scene around Shiemi, who passes out from shock. Yukio is not amused.
- In Hunter × Hunter the Chimera Ant King bursts out of his mother the Queen this way, shredding most of her internal organs in the process. The Queen eventually dies despite the Hunters' medical intervention but Colt is able to save her last unborn child who turns out to be Kaito reincarnated.
- Played With in Hakkenden Touhou Hakken Ibun as Murasame bursts out of Shino's arm. And that's more to do with that is where he resides as Shino is his vessel.
- In one episode/chapter of Soul Eater, Soul did this to Maka. However, it was All Just a Dream.
- Coffin Princess Chaika has possibly the first time this trope has been combined with Only Mostly Dead. Frederica "dies," but some time later a Fun Size version explodes out of her abdomen.
- In one of the first issues of Spawn, the hellion comes up against a heavily armored cyborg. As Spawn notes, that armor is like a safe: meant to keep people out, not in. And now he has an array of reality altering powers at his command....
- In the Accursed volume of The Darkness, Jackie creates a woman out of The Darkness to satisfy his needs. She ends up becoming pregnant with a child made of pure darkness, which, naturally, emerges by ripping her stomach apart.
- Vampirella vs. Aliens: Vampi is one of several people who get a Face Full of Alien Wing-Wong and subsequent baby Xenomorphs bursting out of their chests. Notable in that she actually survives thanks to her durability as a vampire and Healing Factor. Though this does lead to a winged Xenomorph later on...
Films — Animated
Films — Live-Action
- The Xenomorph life cycle in Alien is the Trope Namer and Trope Codifier in modern media.
- Spoofed in Spaceballs, when a spoiled sandwich in a greasy spoon diner resulted in a chestbursting alien that then grabbed a top hat and cane and made a further parody of Michigan Frog from Looney Tunes. Made even funnier by the fact that the guy it happened to was played by the same actor.
- Species II had a scene with a woman who just had sex becoming visibly pregnant almost immediately, and splitting open.
- Happens to Jesse in A Nightmare on Elm Street Part 2: Freddy's Revenge, when Freddy cuts his way out of his body.
- The first Xtro has a woman being impregnated by an alien entity, with the offspring (a fully grown man) exploding out of her the next day.
- This is oddly the method in which The Devil possesses people in The Dark Side of the Moon, leaving a perfect triangle-shaped hole in their lower torso when he exits.
- The Deacon skips the Xenomorph's Chest Burster stage and rips its way out of the Engineer's chest already a humanoid.
- And that thing came from a squid-like creature that very nearly killed Shaw had she not quickly gotten it removed- made all the worse by the fact that her crewmates actively refused to help her, and she had to resort to the use of a machine programmed for men which cut her open and removed it while she was still fully conscious.
- And before that there's a strange, facehugger-like creature apparently coming from mutated worms. When confronted, this thing will latch onto its victim, and much like the facehugger, getting it off is easier said than done, since attempting to remove it only causes it to tighten its grip, and cutting it releases a highly corrosive acid. Then the creature in question actually works it's way into the victim's mouth and in the process causes them to suffocate to death while it does... something in their body- probably reproduce.
- In both the 1980 version of Humanoids From the Deep and its 1996 remake, the women impregnated by the Humanoids die horribly as the babies rip out of their bellies.
- Nightwish: The students go looking for ghosts in an abandoned mansion situated on top of of an abandoned mine, which turns out to be a breeding place for alien worms. They don't just burrow in people's chests, but all over the body, like a spider implanting hundreds of her young into a larger insect.
- The Void: Two women are impregnated with extradimensional monsters that later come violently bursting out of their stomachs.
- The "shit-weasels" in Stephen King's Dreamcatcher have a particularly nasty exit: chewing out of people's butts.
- In The Cat From Hell, a cat crawls into a hitman's mouth, and then is seen the next day having clawed a hole out of the stomach.
- Reneesme from the Twilight series. An odd version given that she is the daughter of the two lead characters. Yep. Pure. Unadultered. Horror. Written for teenaged girls. The character from whom she burst survives only by Emergency Transformation.
- Implied of A. E. van Vogt's Ixtl in The Voyage of the Space Beagle.
- The Dresden Files: In the first book Harry has to investigate a series of murders in which the victims' chest cavities exploded and their hearts flung out.
- In Speaker for the Dead, it is revealed that infant piggies eat their way out of their mother's body as a natural part of their reproductive cycle. This is actually one of the less weird aspects of their biology.
- The eponymous "Rawhead Rex" from Clive Barker's short story anthology Books of Blood Vol 3 was mentioned as having a reproduction cycle that involved impregnating human women and having their young burst out of their bodies. The way it's phrased, it's not clear if this is actually necessary for it to reproduce, or just something it does because it's misogynistic to the extreme and considers this a form of punishment and expression of power. Oh, and the rape dynamics in that description are definitely intentional.
- Given a Shout-Out in both the novel K-PAX and its film adaptation when prot[sic] first tells Dr. Brewer he's from another planet.
- '50s science fiction author Zenna Henderson is best known as the creator of The People, full of Christian ideology and sugary goo, but she could write psychological horror with the best of'em. In "The Last Step", she almost casually described alien invaders with zap guns that give you a little prick. In a few hours it swells up to the size of an orange and is extremely painful. Cutting it open relieves it, and also releases a zillion tiny creatures with pointy little feet — which scramble out and run everywhere, pricking your skin (and everybody else's) on the way. And then those pricked places...
- One of Brian Aldiss's stories has a non-lethal example: the crew of a spaceship are horrified when a parasitic worm burrows its way out of a man on a planet they're visiting. The victim is pretty sick, but survives.
- genetically modified tapeworms from The Troop.
- This is apparently how Puppeteers reproduce in Ring World, though unlike most examples, they apparently can't do it to humans, instead being obligate parasitoids of a single particular species native to their home planet (which they refer to as a "third gender" for PR reasons).
- One episode of The X-Files contained a parasitic fungus that made its victim burst open, spreading spores to surrounding people. All the scarier, since because this was an early episode, the concept exists in Real Life. Admittedly, it parasitizes ants, but...
- This is how the Magog reproduce in Andromeda
- The TV Show Fringe really enjoys this one, and in just one and a half seasons has featured monster larva, monster parasites, giant slug/monster viruses, and monster babies all bursting out of unwitting human hosts.
- Done at least once on Stargate SG-1 with a Go'auld which had to exit one host and transfer to another in order to survive. (Tanith, the seeming Double Agent turned triple agent.)
- Stargate Atlantis: In the episode "Doppelganger", an alien entity is plaguing the expedition members with vivid nightmares. It does this to Dr. Keller by creating a dream where an Iratus Bug bursts through Teyla's chest and kills her.
- Stargate Universe had these in "Time," repeatedly popping out of the away team's bodies after burrowing in to eat their juicy insides. They got better.
- Happened in CSI, of all places. It was a rat that burst out of a drowned body's squishy chest (freaking out Grissom and Doc Robbins) and ran amok in the lab. Robbins initially thought it was the gas that normally builds up during decomposition, but it wasn't.
- Similar to above, an escaped pet boa constrictor emerged from its owner's corpse on Bones, having curled up inside the mangled body's chest cavity because it was warm in there.
- Angel: The episode "Lonely Hearts" had a parasitic demon that lept between victims, coming out of the chest of the old host, and burrowing into the back of the new one, after it had sex with the next victim.
- Invoked in Sanctuary. Abby is infected with an abnormal parasite that will soon take over her body entirely. Magnus concocts a risky solution: Implant another abnormal into Abby's body which will cause the parasite to stop trying to convert Abby and jump to the other abnormal. It then escapes Abby's body chest burster-style.
- Good ol' Zeus has survived more than his fair share of this trope: first, when Athena sprang (fully formed and clad in armor) out of his head, and another time, when Dionysus was born out of his leg (though in this case Zeus had actually stitched him up in there beforehand).
- SCP Foundation
- SCP-150 ("The Prosthetic Parasite"). After SCP-150 has removed all of a human victim's limbs, it will infect the victim's torso. The torso will swell up and large numbers of SCP-150 larvae will emerge, killing the victim.
- SCP-371 ("Macrovirus"). After SCP-371 infects a victim with its genetic material, new SCP-371 specimens are created inside the victim's abdominal cavity. Once the specimens grow to a length of 20 centimeters they burst out of the victim's body, causing severe trauma (including internal injuries, serious bleeding and death).
- SCP-632 ("Intrusive Thoughts About The Many Spiders Forming Inside Your Head"). After the baby SCP-632 inside the victim's brain have grown large enough, the victim will repeatedly hit their forehead with great force to relieve the pain. When the victim's forehead shatters, the baby SCP-632 will leave the skull through the hole.
- SCP-695 ("Eels"). After SCP-695 eggs have grown to juvenile size inside a female human host, they may escape by erupting through the wall of her abdomen.
- SCP-751 ("Organ Eater"). After eating its victim's internal organs and increasing in size, SCP-751 swells up and causes the victim's skin to stretch and burst, releasing it from the body.
- SCP-834 ("Marked"). A researcher used a SCP-834 marker to drew reptilian scales on their chest. Six months later their internal organs were converted into a reptile-like monster and burst out of their chest.
- SCP-845 ("Liquid Polecat"). If SCP-845 is swallowed while in liquid form, it will change back into its animal form in the victim's stomach and burrow its way out of the victim's body through the abdomen.
- SCP-867 ("Blood Spruce"). After an SCP-867 seed is injected into a living creature's body, it grows throughout the creature's circulatory system, eventually killing it. SCP-867 then bursts out of the victim's body and grows to full size, consuming the body as it does so.
- SCP-1092 ("A Species of Fish"). After SCP-1092 inside a mammal's body grow to adult size, they bite their way through blood vessels and the skin and expel themselves from the body.
- SCP-1294 ("The Laughing Fox"). After SCP-1294 mates with a normal female fennel fox, the fungus will grow inside the fox and eventually burst out of its chest. Once outside it will assume the standard shape of a SCP-1294.
- SCP-1325 ("Easter Frog"). When the SCP-1325 growing inside the victim's stomach are large enough they release an emetic toxin that causes the victim to throw up, expelling the SCP-1325 out the victim's mouth. This has a 25% chance of rupturing the victim's esophagus (Boerhaave's syndrome). The chance is higher if the victim is elderly or a child.
- SCP-1407 ("DJ's Headphones"). SCP-1407 creates more instances of itself inside a human body, such as in the stomach, head and intestines. When enough are created the internal pressure will cause them to be expelled from the body through its orifices or through the skin.
- SCP-1429 ("Organoid Organisms"). When SCP-1429 infects a human body it settles into a specific randomly chosen organ, grows to large size and exits the body, sometimes through the victim's skin.
- Warhammer: The alien scene is spoofed in adventure Castle Drahenfels.
- Warhammer 40,000:
- Had rules in earlier editions that allowed genestealers (think xenomorphs minus the acid blood) to implant eggs into models in close combat. A young genestealer could hatch from the model on later turns, presumably Alien's style. This rule was later incorporated into a different Tyranid, the Hero Unit called the Parasite of Mortex, after the nature of the genestealers was tweaked.
- The Barbed Strangler weapon which, in early rules, would instantly kill the target due to a seed pod instantly growing into a sentient mutated vine cluster from inside the body and scything through people nearby.
- Dungeons & Dragons:
- One breed of Slaadi reproduces in this way (the adults have eggsacks in their finger and can implant an egg through a successful claw attack. The new slaad then grows inside the victim).
- Carrion crawlers also lay their eggs inside other creatures, though they kill the creatures immediately prior to doing so. Typically, they paralyze their victims a couple days before laying eggs, and kill them right before the laying so the corpses will provide a reasonably fresh meal for their spawn.
- One prestige class called the Blood Magus has, as it's most powerful ability, the power to teleport between the locations of any two living beings, with the option to deal damage to the destination creature. Guess how?
- The Ixtl-expy xill and an obscure creature called a gryph have a similar modus operandi.
- In the Monster Manual II, there was also the Neogi, strange spider-like evil slavers whose method of reproduction involved laying eggs in aged demented Neogi called Great Old Masters. Said masters exist in constant rage and pain until they start spitting neogi spawn, which eat their way out of the thing's body.
- The phaerimms from the Forgotten Realms setting reproduce like some wasps. They paralyze the target with a sting, then inject an egg.
- In Deadlands, Prairie Ticks are giant ticks which somehow have mouthpieces too weak to penetrate skin. So, they crawl down a person's mouth into their stomach to suck blood from their softer innards. And seeing as how the basic tick is about the size of a fist and, like a normal tick, they expand to 200 times their original size, when they detach and crawl back out, it usually kills the host.
- Be very afraid if your GM for the BattleTech RPG Mechwarrior decides to bring in some of the various wildlife that inhabits the setting. The crana is essentially a giant isopod partaking of this trope, thanks to its spike-like claws, paralytic venom, blood sucking feeding methods, and their tendency to lay eggs in victims that require highly advanced medical care to remove. Oh, and they're immune to poison and never appear alone or in small numbers, so the only way to handle a crana swarm without being overrun is lots of fire.
- In Hc Svnt Dracones Whispers can liquify and "dive" into a potential host, seconds later either the host explodes and two Whispers emerge, or the host simply explodes.
- In The Bible: The Complete Word of God (abridged), Eve emerges from Adam's ribs in this this manner.
- One of Q-Bee's EX Special Attacks in the Darkstalkers series has her sting the enemy and encase them in a cocoon, whereupon she dies (she's a bee, after all) and another Q-Bee bursts out of the victim's back and continues the fight.
- Parodied in Splatterhouse: Wanpaku Graffiti, the NES-only Super-Deformed sequel to Splatterhouse. At one point Rick encounters an unconscious girl on an operating table: suddenly, the girl's belly inflates and bursts, releasing lots and lots of little spiders. When Rick kills all of the spiders, the girl wakes up, being perfectly fine, and goes away!
- In the first level of Splatterhouse 2 a boreworm enemy ejects itself from a zombie's chest in this fashion, effectually re-killing it.
- In Resident Evil 2, either Ben or Chief Irons gets one of these from the mutated William Birkin. Canonically speaking, it winds up being Irons.
- In Resident Evil 6, we get the Rasklapanje, a creature similar to the Regeneradors from Resident Evil 4. They infect others by drilling a hole into the victim's face and planting a parasite, which, in seconds, bursts out from the victims chest, fully grown.
- Don't get kissed by the Xenomorph-lookalike in Space Quest II: Vohaul's Revenge, or it will impregnate Roger with one of these, hatching out of him near the end of the game.
- Chryssalids. First, they inject you with an egg, which zombifies you and makes you attack other humans. Once zombie you has been killed, or the Chryssalid inside you matures enough, your entire body splits open, revealing a Chryssalid. The only way to prevent this is to kill the zombies with fire.
- Tentuculats in the sequel work the same way. Except they're flying brain squids, but worse.
- Devil Survivor has the boss battle with Belzaboul and his maggot minions, who spawn eggs in your party members and their demons. It's implied that this trope is at work when an egg hatches, because not only does a squad of maggots spawn next to the victim, the victim takes massive damage.
- In Eternal Darkness, Bonethieves have a disgusting habit of forcing themselves into the body of a victim and using it as a cheap suit to attack the bearers of the Tome of Eternal Darkness. When the host bodies have taken enough damage, the Bonethief will blow its way out in a shower of gore, greatly damaging your Sanity and proceeding to attack you. It kills you, it gets a new host. Maximillian's ravings and paranoid fear of the Bonethieves are quite justified in-game, as it's revealed that at least one of the servants he slaughtered was indeed a Bonethief host.
- In Fate/Stay Night Heaven's Feel route, True Assassin comes to being by "eating" Assassin from inside.
- One of Guile's special attacks is to teleport his wand into the enemy's stomach and then cause it to fly out.
- Zuul reproduction in Sword of the Stars can result in this. They are marsupials, and the mothers' milk is a potent narcotic. As long as the mother is alive and produces milk, her children are in dreamland inside her pouch. If she dies, or becomes unable to produce milk... She becomes their first meal. More commonly (and less fatally to the Zuul), the Zuul mother removes the children from the pouch and leaves them near a suitable source of meat.
- In Conker's Bad Fur Day, Heinrich bursts out of the Panther King's chest in the final.
- The facehuggers in Alien: Resurrection implant the player character with these, just like in the films, and you have only a short time to find an Auto Doc before they hatch.
- The Good Ending of Covetous ends this way, with the parasitic twin emerging from its brother's stomach, killing him.
- Starcraft II Heart Of The Swarm: in one mission Kerrigan implants a Zerg larva into a Protoss prisoner then allows her ship to "rescue" her. Once it's on board the larva bursts out of her chest and starts sneaking around the ship infesting and bursting out of several lab animals until it accumulates enough biomass to mutate into a Brood Mother.
- The third game in Don't Escape has the mysterious crystal being capable of doing this if it infects a human being's insides, eventually growing too large to contain.
- It is revealed in Jurassic Park: The Game that this is how the Troodon reproduce. Note that there is absolutely no evidence for this happening in real life.
- A taunt in Team Fortress 2 does exactly this, and it's aptly named "Burstchester". The merc's reactions to the alien coming out of their chest vary, from the Medic being fascinated by it, to Soldier trying to strangle it.
- Broforce, an indie platform shooter/80's action movie homage features Xenomorph lookalikes/parodies as enemies. No points for guessing what happens to you if a facehugger latches on your face.
- Aylee from Sluggy Freelance. Not surprising, given the fact that she was introduced as a parody of the alien from Alien. And then later parodied in a... rather interesting way. Let's just say Bun-bun is quite badass.
- This Cyanide & Happiness strip. Rather odd example.
- Saturday Morning Breakfast Cereal uses this combined with Heart Is an Awesome Power and Precious Puppies.
- Homestuck used this to parody Alien in conjunction with Pokémon.
- The World Is Flat depicts this here.
- Even Doctor Octogonapus does this.
- This part of the Black Helicopter life cycle.
- In the Burgrr.com Terms and Conditions ARG eating Burgrr's food causes the eater to serve as an incubator for the Brainflies, which then go on to be processed and sold to another dimension.
- In Mortasheen, this is the creature Depraven's main attack.
- Ace Ventura:
- In the crossover episode with The Mask Ace thinks an Alien is inside him, but it turns out Spike was in his clothes.
- In the "Halloween Special," Ace does this with Spike and scares a high school principal.
- In the first episode of Hi Hi Puffy AmiYumi after Ami & Yumi get to the moon to ditch their Number 1 fan,she ends up bursting out of the front of Yumi's shirt.
- Parodied in the "Itchy & Scratchy" segment in The Simpsons episode "Deep Space Homer"
- Parodied in Family Guy, a video about talking about gay people had scene where a gay man was syringed by a doctor he suddenly spouted acid blood, and a full grown Xenomorph burst out of him, attacking the doctor.
- Parodied twice in the "Summerween" episode of Gravity Falls. Firstly, Grunkle Stan tries to pull one of these in his attempt to scare some snarky Trick Or Treaters, but it turns out unsuccessful; the fact that he used a cute and cuddly pig might have something to do with that. Later on, Soos eats his way out of the Summerween Trickster and comes out in a similar fashion.
- The title characters of Sanjay and Craig fake this as a distraction to sneak into a hospital, with Craig (a snake) bursting out of Sanjay's shirt.
- Robot Chicken has this happen to Elroy in a sketch where an alien invades The Jetsons' house.
- Parodied in the Codename: Kids Next Door episode "Operation: L.I.C.E.", in which a giant lice parasite bursts though Numbah Five's hat.
- Bread Winners : happens to Buhduece three times in the episode "Space Ducks" the bursters include Swaysway (who snuck onto the space ship) Jelly (who Swaysway brought with him) an actual Xenomorph.
- The Real Life scientific term for a creature (usually an insect species) that does this to other species is a parasitoid.
- Several insects reproduce in this way, planting their eggs inside another insect.
- Some species of wasps have a special larvae that acts as a Puppeteer Parasite, turning the empty husk of the caterpillar into a zombie-like Meat Puppet guardian. Like the Chrysalids from X-COM.
- Or worse, spider wasps. They paralyze one or more spiders with their sting and store them in a safe place. Before closing the entrance, an egg is laid inside the victim. Once it hatches, the larva will feed on the paralysed spider(s). To make this more terrifying than the Xenomorphs, the spider is still alive while being eaten alive from the inside out; not only that, but the larva avoids killing the spidernote as long as possible to keep it from decomposing. At least spiders can't feel pain. It's stated they were the inspiration for this trope.
- According to some stories, Charles Darwin was so horrified by finding out about the habits of parasitoid wasps that it destroyed his faith in a benevolent God.
- Spider wasps aren't the only that use spiders as hosts too. Some worms enter the spider's interior -without bothering to paralyze them- and fest on their innards (including to castrate them eating the reproductive organs). Not content with this the spider often becomes controlled by the nemathod going close to a source of water before the parasite leaves its host. Needless to say, the poor spider usually dies just before or after the worm bursts out.
- Phorid flies breed by using ants as hosts for their young. The flies lay eggs in the ants, and when the larvae hatch, they slowly make their way toward the ant's head to "zombify" them. The horrifying part comes from the larva emitting a chemical that causes the ant's head to fall clean off, and eventually a full-grown phorid fly bursts out of the ant's decapitated head.
- If that qualifies.... Look up scabies. Mites burrowing into your skin and laying eggs which hatch to produce more mites that lay more eggs... also they periodically fall off and get all over everything, spreading them to everyone who dares to set foot anywhere you've been.
- While not nearly as violent as some of the other examples, the Human Bot Fly certainly qualifies. As do a few other parasites that use human hosts.
- The mouse botfly plays the trope a little straighter. Its a lot like the human bot fly except it lives over a much greater range and is MUCH bigger in proportion to its host. Wile they prefer to live between the skin and muscle, they often get big enough that their anchoring spines tear holes that expose their poor hosts organs. If this happens, the cavities they leave upon erupting will indeed give the mouse a lethal infection.
- There is a story about a man who became attached to his little bot fly. He decided to "carry it to term," so to speak, instead of having it removed. Then it started tearing its way slowly out and he said, "Get this thing outta me!" Leaving the thing in is actually often the better option, as killing it is likely to cause the wound to be infected unless the entire maggot can be removed (while alive it secretes antibiotics that keep the wound clean).
- An urban legend speaks of a woman who went vacationing in South America and came back with what appeared to be a boil on her cheek. When the boil was lanced, it was revealed that a spider had laid its eggs in her cheek, and hundreds of newly-hatched spiders crawl out of the wound and across her face. Thankfully, no species of spider lays eggs in people. Which was the basis for one of the stories in Scary Stories to Tell in the Dark.
- Viruses essentially do this to their host cells. Diseases are a side effect.
- There is a type of fungus called Ophiocordyceps unilateralis, which possesses ants and controls them so it can make them crawl into a good spot to grow and reproduce in. After it forces the ant to go into a suitible spot it uses the sugars in the the ants body to live on and eventually leaves the ant as a husk. It will then grow out of the ant's body, ripping it open. Several ant species have developed counter-measures to this by observing ants with unusual behaviour and quickly guiding them far away so that the doomed ant won't infect the whole hive. It's quite efficient too.
- Sea louse larvae do this to their mother.
- The guinea worm is another example of this trope.
- When a female Surinam toad lays eggs, the male fertilizes them and presses them into his mate's back. The eggs form pockets under the skin, and when they hatch, the tadpoles develop into mature frogs in these pockets. Eventually, the frogs burst from their mother's back. (WARNING: Not for the faint of heart.) Oddly enough, this is a completely benign example of the trope.
- Tasmanian Devils have been known to burrow inside large carcasses while feeding and sleep inside them for some time before eating more. Although that's less reminiscent of Alien and more reminiscent of that scene in The Empire Strikes Back when Luke crawls inside a dead Tauntaun for warmth.
- The most common creature capable of pulling off this trope in the developed world is the ordinary house fly, but fortunately such an event would actually be a good thing. Flies typically lay their eggs in rotting meat, and the larvae proceed to devour the whole thing. If a living creature is so badly injured that they have a gaping wound, and if human are unable to get to medical attention, but are still able to survive for an extended period of time, the flesh at the edges of the wound will almost immediately start to rot. Flies will become attracted to this and lay their eggs, however the larvae cannot consume living flesh. As a result, they end up doing you a huge favour by eating dead flesh before it can finish rotting and become infected with dangerous bacteria, thus extending your remaining lifespan drastically. In that time, you can hopefully find help so that the wound can be properly treated. This type of parasitic action is how two women survived a plane crash that left them injured and stranded in the middle of the South American rainforests, as without the fly larvae nibbling away at skin that started to rot, their wounds would have been infected by the many, many nasty microbes that lie in the soil and waterways of the area.