A particular style of metamorphosis commonly found in butterflies, moths, wasps, bees and certain other flying insects, pupation is often the most dramatic change that can be undergone: unlike molting insects, who simply shed their skin and transform into a much larger variation on their original form, a pupating insect either spins a cocoon for themselves out of silk or converts their outer layer of skin into a chrysalis - in either case allowing them to undergo a much more intensive transformation. Consequently, the imago that finally emerges from the pupa will likely be unrecognizable compared to the original insect.
As such, it's perhaps not so surprising that fiction takes this relatively simple process and plays it for suspense, mystery and even horror: a pupa or pupae of an unknown species are discovered, and immediately questions will be raised as what will emerge when the creature's metamorphosis is complete — and given the focus on the pupa, chances are it will be complete at some point in the story. A form of Chekhov's Gun, once a cocoon is given sufficient focus, it's inevitable that it will hatch at some point. Regardless of whether or not the original larval form was encountered beforehand, the atmosphere will quickly turn anxious, and the tension gradually ratchets up as more shots are devoted to those ever-present pupae sitting in the background, just waiting to crack open...
The imago form of the creature will often be hostile in some way, either immediately attacking everyone in range or hiding in the shadows and slowly picking off characters one by one, depending on how intelligent the monster is. In extreme cases, it may even be intelligent enough to be a new villain in its own right.
On occasion, the fears of the audience will turn out to be completely unfounded, and what actually emerges will be harmless or even benevolent, but these cases are rare and typically deliberate subversions.
Compare and contrast Egg MacGuffin, which can be played for similar tensions but occurs at the beginning of the creature's life cycle. Contrast Metamorphosis Monster, in which the shock factor lies in how different the imago appears in contrast to the larval form, and All Webbed Up, which is when the victim ends up getting cocooned by the monster in preparation for a later meal (a completely different kind of horror).
- Dragon Ball Z: Played for Laughs in the Otherworld Tournament arc. After Goku escapes his opponent Caterpie's Tickle Torture, Caterpie, outraged that Goku hurt him, decides to transform into his "ultimate form". He weaves a cocoon around himself, ready to change... then the announcer states that the process will take several hundred years. Since no-one, even immortal gods, has the time to wait, Goku is declared the winner by default.
- Yu-Gi-Oh!: In Yugi's first duel at Duelist Kingdom against Insector Haga/Weevil Underwood, Weevil was able to set Larva Moth into the field: upon flip summoning it, he then equipped Cocoon of Evolution so that he could special summon Great Moth within 4 turns. Upon emerging, it was Weevil's strongest card (second to Perfectly Ultimate Great Moth) since it has an effect of scattering poisonous pollens that lower attack and defense (which is exclusive to the manga/anime since it doesn't have that effect in the TCG).
- Big Finish Doctor Who: Zig-zagged in "Enemy Of The Daleks": here, the Doctor encounters an insectoid species known as the Kiseibya, engineered specifically to kill Daleks. Starting out as parasitoid larvae, they eventually pupate and emerge as human-sized flying insects; however, though the emergence of the first Kiseibya is played for horror, complete with the scientist responsible for its creation forcing the Doctor to kneel before it as it hatches, the threat turns out to be non-existent: adult Kiseibya live exclusively on metal - and only become a threat to organic life when it's time for them to breed. However, it's played very straight when the Daleks find the now-empty cocoons... just in time for the entire swarm to ambush them.
- 52: The Shazam villain Mister Mind (a caterpillar-like creature from Venus) is exposed to artificial time particles known as suspendium, allowing him to finally escape his larval form. He uses Booster Gold's Robot Buddy Skeets as a makeshift cocoon, eventually emerging as a monstrous winged creature capable of devouring time itself.
- My Little Pony: Friendship is Magic (IDW): In "Ponies in Book Land", after the bookworm starts devouring its way through the stories in Twilight's library, a large number of colorful cocoons starts appearing around Ponyville. These cocoons, dubbed "schmarfelpods", end up covering a large part of the town and inspire a great deal of nervousness in the characters as they wonder what's going to come out of them. Once a schmarfelpod hatches into Daring Do, it's revealed that they contain fictional characters from the stories the bookworm ate, leading to increased apprehension about which characters exactly are going to come out of the hundreds and hundreds of cocoons scattered around town. Once the rest break open, the released characters promptly wreak havoc in the town, including a league of villains who try to forcibly take it over.
- The Fly II: Unlike his father, Seth Brundle, who underwent a gradual (and grotesque) mutation from human to man-insect monstrosity, Martin Brundle undergoes an insect-like complete metamorphosis. Late into the film, he cocoons himself and, unlike the pathetic final form of his father, emerges as a perfect man-fly fusion that has Super Strength, can leap great distances, shrugs off bullets, and spits acid. However, despite his now monstrous appearance, he retains his intelligence and morality, focusing his Roaring Rampage of Revenge against people who really had it coming.
- Gremlins: Mogwai that are allowed to eat after midnight encase themselves in creepy, Giger-esque cocoons as they begin metamorphosing into gremlins. This is played for much ominousness when Billy discovers that six of his five Mogwai are now cocoons clustered around his bed; it eventually results in an especially nightmarish moment in which the newly metamorphosed gremlins begin clawing their way out of their cocoons while a terrified Gizmo tries to hide.
- In Godzilla (2014), the male MUTO hatches from a huge, glowing, crescent-shaped chrysalis after feeding on the radiation of a nuclear reactor from within for fifteen years. While the larval form is never seen, the imago is a winged insectoid which immediately begins a trail of destruction across the Pacific.
- In Godzilla: King of the Monsters (2019), the direct sequel to the above, Mothra is introduced as a humongous egg from which her equally huge larval form hatches. A bit of non-lethal guard tossing later, she disappears from the plot for a while aside from a brief scene to show that she has spun herself a cocoon underneath/behind a waterfall. When she finally emerges as a bioluminescent moth the size of a 747, the spectacle is so awe-inspiring that everyone who witnesses it either stares or weeps at the sight. Unlike the MUTO example above, Mothra's metamorphosis is one of the rare benevolent examples as the Queen of the Monsters, just like her King, is firmly on the side of good.
- Much of the above echoes Mothra's arc in the earlier Godzilla and Mothra: The Battle for Earth, where the larval Mothra spins a cocoon on top on top of the Japanese National Assembly Building. The scene where she hatches in her butterfly form - while her fairy priestesses sing a hymn to her - is the high point of the movie, played for wonder and awe rather than terror. In contrast, Mothra's spikier, more threatening Spear Counterpart Battra skips the cocoon altogether, and transforms from caterpillar to imago in a flash of red lightning.
- Species has the alien Sil that Escaped from the Lab as a preteen girl, who boards a passenger train. In one of its compartments, she undergoes a Body Horror puberty that involves creating a cocoon. From this stage, she emerges as a young woman in her twenties. The other occupant of the compartment doesn't survive this process, and a conductor checking compartments sees way too much weirdness and simply turns a blind eye to it all.
- Perdido Street Station: Early in the story, Isaac obtains a mysterious grub along with all the other test subjects he requested; once he works out that it only eats Dreamshit, the grub begins growing at an impressive rate and eventually spins a large cocoon for itself. While Isaac continues his more optimistic experiments, the narrative segments focussed on the pupa quickly take a turn for the unsettling as it gets closer and closer to hatching. What emerges from the cocoon is a Slake Moth, an Animalistic Abomination with a hunger for living minds; Isaac isn't in his lab when it hatches, but one of his friends is — and quickly ends up becoming its first victim. From here on, the Slake Moths are the main villains of the story.
- Alien Empire, a 1995 documentary series, brings up a comparatively mundane example of this in order to demonstrate what happens when humans meddle with insects: in "Replicators," a fisherman has a tray of live maggots left over from his daily bait, but he doesn't want to get rid of them, so he puts them in the fridge — believing that the cold will keep them subdued until he gets back from his holiday. But while he's out, a fuse blows, the fridge begins heating up, and with nothing to stop them, the maggots begin eating through their food supply, then metamorphosing in a time-lapse sequence; by the time the scene cuts away, the fridge is full of pupae. And at the very end of this episode, the fisherman arrives home, realizes that the power's off, opens his fridge — and is greeted by the sight of several hundred bluebottle flies buzzing towards him.
- Babylon 5 has a downplayed example at the end of season 1, as the Minbari ambassador Delenn decides to enter a chrysalis for unknown purposes. A fair bit of suspense comes from the expectation of what, exactly, will emerge, even if nobody expects a horrible space monster.
- The Big Bang Theory: Conversed for laughs in The Cooper-Nowitzki Theorem, where Leonard explains his theory on how Sheldon reproduces to Penny.
- Doctor Who: "The Ark In Space" introduces the Wirrn, essentially parasitic wasps in space: having already demonstrated a breeding process replete with Body Horror, it's revealed that the Wirrn larvae resulting from this conversion process will eventually pupate into even more dangerous adults. Worse still, this also marks the point when they cease to require oxygen - leaving the Doctor and the others in serious danger when the Wirrn switch off life support.
- In Warhammer and Warhammer 40,000 feature the giant flying insects known as Rot Flies. These daemons started out as the puppy-like Beasts of Nurgle, but eventually grew frustrated with the fact that their new "friends" refused to play with them and eventually gave in to hatred after being banished from the physical world. Retreating to the depths of Nurgle's garden, they eventually develop a cocoon out of sheer resentfulness — in which they gradually metamorphose into the forms of giant insects so that they can take their revenge on the mortal realm.
- The World of Darkness:
- Vampire: The Masquerade: Members of the Tzimisce clan can use the discipline of Vicissitude to weave cocoons for themselves out of flesh. Effectively immune to damage from sunlight and (to a lesser extent) fire, these cocoons can be used as a safe place for a Tzimisce to rest during the day. Given that Vicissitude also allows them to alter their bodies in many weird and disturbing ways, it's entirely possible for them to transform themselves even further while in this state and — if their cocoon is found — immediately go on the attack once the cocoon opens.
- Werewolf: The Apocalypse: Individuals with a particular devotion to order can be accepted as servants of the Weaver herself, resulting in them being guided into the Umbra and cocooned deep within her domain. Inside, the subject is remade by being permanently merged with a Weaver spirit, their beings intertwined so thoroughly that no distinction exists between the two. What ultimately emerges from this cocoon is a Drone, a powerful embodiment of stasis that Werewolves often find more disturbing than even the Wyrm's Formori; for good measure, artworks depicting them play this for horror, featuring Drones emerging from their cocoons with eerily symmetrical faces and Black Eyes of Evil.
- In Borderlands 2, Varkids will sometimes turn into cocoons on being injured. Cocoons are fairly meaty, and if they aren't killed they emerge in a tougher form, making for a mad dash to destroy it before things get worse. If you're not careful, you might end up outright fighting a raid boss level form.
- The Breach: A recurring cutscene features the ship's medic begging the protagonist for help inside his head, transporting the protagonist into an endless void containing only a cocoon. The medic's pleas fade with time as the thing in the cocoon grows, and by the final scene she emerges as a fully mutated convert of the Eldritch Abomination that's taken over the ship.
- Deep Rock Galactic: Glyphid Dreadnoughts, basically the game's bosses, are usually found inside of cocoons that need to be actively popped. According to Mission Control, this is necessary because having them ambulatory and ready to crash other mining operations (as they sometimes do to you) is bad news, and because their cocooning means they're trying to turn into something even worse than the chitinous, fiery juggernauts themselves.
- Dragon's Crown: The battle against the Doom Beetle in the underground labyrinth has occasional grubs show up, and whichever ones that don't immediately attack the player will spin themselves into cocoons. The narrator outright tells the player(s) to destroy them before they can hatch into more Doom Beetles (albeit with significantly less health).
- In The Legend of Dragoon, while exploring the Divine Tree on their way to The Very Definitely Final Dungeon, the team ends up getting on the bad side of a giant caterpillar. Halfway through the ensuing boss battle, the caterpillar becomes a chrysalis; in this form, it can't harm your party but it's effectively immune to all forms of damage, meaning that this is a good opportunity to heal up and brace for the worst. Eventually, the chrysalis cracks open to reveal an imago, a significantly tougher opponent.
- Metroid: Multiple examples appear through the series:
- Metroid: Zero Mission: In the lower areas of Norfair, Samus encounters giant grubs that can only be defeated by attacking their weak underbellies. She later finds a stationary one that is strung up in some vines that she must sever, which drops the grub through the ground and lets her continue to Ridley's lair. The grub can be seen starting to pupate. Samus must double back to the grub's location, only to see the grub has left its pupa. The nearby tunnel leads to a chamber where Samus must fight the imago.
- Metroid Fusion has the Zeo enemies in Sector 2, slow-moving caterpillars that start pupating once you beat the boss. When you return during the blackout, they have become the flying Kihunters.
- In Metroid Prime 2: Echoes, the Chykka boss starts of as a larval monster that swims around the arena before pupating into a wasp-like flyer. Similarly, the Emperor Ing starts off as a stationary creature resembling an Inglet, seals itself into a spherical cocoon that Samus must bust open, and then emerges as a giant version of the Warrior Ing.
- Pokémon Gold and Silver: The Larvitar line is a unique non-insect example. As Larvitar, it starts out as a small baby reptile before evolving into the cocoon-like Pupitar. When it fully evolves into the Godzilla-esque Tyranitar, it drops the Ground sub typing for a Dark Type, as they're fearsome Pokemon that can destroy mountains.
- The Secret World: The Ak'ab are essentially giant insects based largely on moths, complete with cocoons. Situated out in the dark forests of Solomon Island, you most commonly encounter the cocoons of warrior Ak'ab, which are around six feet tall and found around trees deep within their territory; on the upside, they will not hatch until actually attacked — assuming you've managed to survive the waves of incoming attackers long enough to do that. The cocoon of the Queen is hidden in an underground hive and absolutely massive, giving you a good idea of the boss battle that lies ahead of you...
- StarCraft: The first missions of the Zerg campaign in the original game have the Overmind charge you with protecting a mysterious, fleshy chrysalis, which grows quite large as whatever inside develops. When it finally hatches, what comes out is Sarah Kerrigan, a human mutated into a frighteningly powerful Zerg hybrid, custom-made by the Overmind to be its champion, and who plays a central role through the rest of the series. The rest of the Zerg species is like this to a lesser extent, as many of their advanced units metamorphose from basic units that turn themselves into chrysalii.
- In Resident Evil 6, the J'avo type enemies have a chance (modified by difficulty and level) of randomly bursting into flames and then freezing into waxen-looking cocoons, from which they can emerge as any of a variety of different more powerful monsters. Additionally, the boss monster Haos, a creature designed to literally infect the entire planet with the latest Zombie Apocalypse plague, initially appears inside of an enormous cocoon that a closer look reveals is made up of tens of thousands of people melted together into a single mass of wax-like resin to provide the requisite biomass.
- Aladdin: The Series: In "Mission: Imp Possible", Mothias is first met while in its cocoon made of magical golden silk. The extremely greedy imp Nefir as well as Iago both instantly get the idea to steal the silk. The emerging giant moth has a well-known hunger for imps and instantly starts hunting Nefir. Only by tricking Mothias into a spider web made of it's own golden silk can the massive creature be subdued.
- Amphibia: In "The Domino Effect", Anne adopts a wild caterpillar that reminds her of her cat back home. It is later revealed that the creature is a "coastal killerpillar" which soon after pupates into a monstrous moth-like creature and tries to eat the Plantars.
- Camp Lazlo: In "Creepy Crawly Campy", Raj befriends a cute little elephant-like bug that ends up creating a cocoon on his head overnight. The next morning, it emerges as a giant, horrifying monster bug that scares the other campers, though Raj doesn't seem to mind.
Raj: It's okay you're not pretty!
- Dexter's Laboratory: In "Monstory", Dee Dee and Dexter are transformed into monsters over the course of their latest squabble. Unfortunately for Dexter, his initial form is rather unimpressive... up until he manages to find somewhere isolated enough to make a cocoon, resulting in a surprisingly creepy scene in which he gradually metamorphoses into something much more intimidating and capable of matching Dee Dee's height. However, neither Dee Dee nor Dexter are done transforming: they get so big that they end up levelling a city over the course of their fight.
- In The Dragon Prince, Aravos is able to interact with the outside world from his magical prison through a caterpillar. The last episode of the current season shows that the caterpillar has built a huge cocoon, which Aravos will presumably emerge from should the series continue.
- Men in Black: The Series: "The Quick Clone Syndrome" reveals that Alpha has been recovering from the injuries he suffered back in his first episode by wrapping himself up in a cocoon deep in the sewers. Having transformed into an even less human shape in the intervening time, he goes on the offensive as soon as J and K begin forcing his cocoon open.
- SpongeBob SquarePants: Played with in "Wormy", where the titular caterpillar confuses SpongeBob and Patrick by undergoing metamorphosis. After the duo leaves, we see live-action footage of Wormy's cocoon set to creepy music, eventually emerging into a live-action butterfly. Normally this wouldn't be too scary, but the episode portrays Wormy as a monster from SpongeBob and Patrick's point of view, with some horrifying buzzing close-ups of the live-action butterfly's face.
- Teen Titans: Subverted in "Transformation". Starfire starts to exhibit all sorts of ugly deformations as a result of Tamaranean puberty that she tries to hide with bulky clothes. Eventually, she's unable to hide them anymore and flies off in fear that her teammates will think she's ugly. She ends up getting captured by a spider alien that feeds on Tamaraneans that go through this process, just as Starfire ends up immobilized in a cocoon. The other Titans show up to save her, with Robin reassuring Starfire that no matter how monstrous she might end up looking after the metamorphosis, she'll still be their friend. It ends up being moot, because Starfire looks just the same after emerging — the only difference being that she now has extra powers.
- In the case of bees and wasps, leaving the pupal stage of development is usually the point where they can actually start inflicting harm on humans. Plus, if you're actually close enough to an opening cocoon, you run the risk of being stung - either by the occupant or by the rest of the hive.
- Subverted in the case of parasitic wasps: despite their terrifying breeding habits and their habit of cocooning themselves not far from the corpses of their victims, the adult form is largely harmless to human beings, given that it rarely stings and actually lacks venom glands in some cases.
- Inverted with the puss moth (Cerura vinula). The adult moth looks beautiful with its black and white patterns, it's the caterpillar that is scary. It has a fake Nightmare Face around its head. To animals, it's meant to look like a big, intimidating beast. To humans, it looks more like a screaming Monster Clown.
- Although not a true pupa, some internal parasites such as trematodes have a semi-dormant "cyst" stage to their complex life cycles, in which form they ride out the transfer from a smaller host species to a larger one. Having them emerge from their cyst is not a good thing, if you happen to be that larger host.