History Main / IntroducedSpeciesCalamity

** "[[Recap/TheSimpsonsS34E20TheVeryHungryCaterpillars The Very Hungry Caterpillars]]" has Dutch leaf-slurper caterpillars suddenly swarming Springfield in numbers so great, it forces the town into lockdown, and Ned took it as a sign of the apocalypse. [[spoiler:Five days later, they pupated, freeing the town from the menace... Until they became butterflies later that day, that is.]]

* Bacteria and viruses that are lethal to humans are a variation of this. They're typically suited to life inside a specific host species, and they try not to kill the host that provides them with warmth, shelter and nutrition for the same reason humans don't burn their own houses down. Measles, tuberculosis and smallpox, for example, are minor nuisances to a cow because the inside of a cow's body is their natural habitat - it's their difficulty adapting to human biology that makes them so dangerous if/when a human gets infected. And that's just transmission from animals to humans. With modern air travel, diseases can spread quickly around the world. The UsefulNotes/COVID19Pandemic is a spectacular modern example.

** However, it turns out the Metroids were created by the Chozo to combat an even ''bigger'' threat to the galaxy known as the X-Parasites, organisms native to [=SR388=] who consume their prey on a cellular level and take on modified versions of their forms, being just as unstoppable as their former predators.

-->-- ''Series/StarTrekTheOriginalSeries'', "The Trouble with Tribbles"

** ''ComicBook/{{Superman}}'': Among ComicBook/LexLuthor's many reasons for hating Superman is that he views Superman as an invasive species that, if left unchecked, will eventually supplant normal humans. Depending on the author, this perspective is either utterly unfounded, [[VillainHasAPoint technically accurate]] in the case of Kryptonian villains with HostileTerraforming in mind, or [[TheExtremistWasRight bang on the money]].
** ''Franchise/WonderWoman'' [[ComicBook/WonderWoman1942 Vol 1]]: The Rykorn manages to overlap with AlienKudzu as their rapidly growing birthing stalks are of questionable sentience and the Rykorn themselves are PlantAliens with a HiveMind and connected to their stalks. In the course of a single night they overtake acres of land and require military and superpowered intervention in order to destroy the stalks before they overtake Texas and beyond.

** While the original episode is played for comedy, it gets a CerebusRetcon in ''Series/StarTrekDeepSpaceNine''; as it turns out, Scotty transporting the tribbles to the Klingon ship ultimately led to an ecological disaster for the Klingon Empire, which in turn led to the Klingons hunting the tribbles to extinction.

** ''VideoGame/PokemonScarletAndViolet'': TheProfessor's TimeMachine created [[ParadoxPerson Paradox Pokémon]], which are supposedly past/future versions of contemporary {{mons}} brought to the current day and absurdly powerful (if you see a robot Delibird when battling online, forfeit immediately). The PlayerCharacter has to shut down the machine in order to prevent them from overrunning the region, displacing the native {{mons}}, and potentially destroying their civilization.

In this case, humans (or some other form of intelligent life) introduce a new species to an environment without the usual elements that keep it in check. The reasons for this vary: this can be a deliberate attempt to [[HostileTerraforming alter the environment in their favour]], an ill-advised effort to bring pets and livestock to a new land, an effort to [[CreatingLife create a new species]], or it can have occurred entirely by accident - a spore stuck in the treads of a shoe, for example, or an animal stowing away aboard a ship.

* In ''Film/GodzillaKingOfTheMonsters2019'', King Ghidorah is at first thought to be a rival Alpha Predator to Godzilla. But upon further researching legends and myths, Monarch soon learns that Ghidorah is not from Earth, but is actually an invasive entity from another planet. After Godzilla is nearly killed by the Oxygen Destroyer, Ghidorah takes over as Earth’s Alpha and commands the Titans across the Earth to awaken and wreak havoc upon [[KillAllHumans both humanity]] [[EnemyToAllLivingThings and the world's global ecosystems]].

* ''Literature/ArtemisFowl: The Time Paradox'': The introduction of rainbow trout into Twin Lakes, and the resulting extinction of the native [[https://en.wikipedia.org/wiki/Yellowfin_cutthroat_trout yellowfin cutthroat trout]], is used as a minor plot point. A flash freeze leaves a small number of yellowfin cutthroats frozen inside a block of ice, which is later acquired by the Extinctionists, a club for [[CruellaToAnimals people with a perverse obsession with killing endangered animals]], so they can serve the yellowfins to the guests at a banquet they're hosting in a display of SnootyHauteCuisine. The Extinctionists consider this a tragedy not because of the extinction itself, but because the fish has a unique flavor which no-one will ever be able to enjoy again.
* ''Literature/TheDayOfTheTriffids'': Triffids were created by SovietSuperscience for their superior vegetable oil which can be used as an alternate fuel source, but an attempt to steal their seeds and sell them in the West goes wrong and leads to the seeds being scattered around the world when the airplane carrying them is shot down over the ocean. (Maybe, this is all second and third-hand information supplied to the reader by the novel's protagonist..) Even then mankind is able to keep control of the situation by hunting down wild triffids and confining them in farms, until social collapse from mass blindness allows them to break out. With humanity no longer the apex predator keeping them in check, triffids soon reproduce out of control.

* ''Literature/PerdidoStreetStation'' is based around one of these. [[AnimalisticAbomination Slake Moths]] are a near-invincible [[AbstractEater mind-devouring]] predator species with the ability to mesmerize prey with their wings, but are normally kept in check by the many hazards of their native environment -- a DeathWorld heavily polluted by the [[ToxicPhlebotinum Torque]]. However, five larvae are brought to the city of New Crobuzon for use in producing [[FantasticDrug Dreamshit]] for a crime syndicate... and when they get loose, the same traits that allow the Moths to merely survive their native environment make them damn near ''unstoppable'' in the city. With no competitors to stop them and no chance for the heroes to bring in competitors from their homeland without causing an even bigger disaster, the Moths are free to feast at will; worse still, [[ItCanThink they're smart enough to pick locks]] in pursuit of their prey. After seeing the [[EmptyShell bodies]] of their victims piling up over the next few days, both the heroes and the government are forced to take [[GodzillaThreshold insane risks]] just to kill or capture the Slake-Moths before they can reproduce.

* ''Literature/{{Worldwar}}'': In the sequel series ''Colonization'', the Race's colony fleet brings along animals from their homeworld. As they're adapted to their homeworld's arid environment, they devastate Earth flora in the regions controlled by the Empire and all the remaining human not-empires can do is shoot any that cross the borders.

* ''Series/StarTrekTheOriginalSeries'': In "[[Recap/StarTrekS2E15TheTroubleWithTribbles The Trouble with Tribbles]]," the ''Enterprise'' first makes the acquaintance of the eponymous creatures, initially believing them harmless pets. Unfortunately, Tribbles are a prey species on their native homeworld and have developed [[ExplosiveBreeders an incredible breeding speed]] to compensate; once aboard a spaceship with plenty of food and no predators, they quickly reproduce in such numbers that the crew is almost overwhelmed.

* In ''TabletopGame/Warhammer40000'', the Orks technically started out as this: having been created by the Old Ones to serve as warriors in their wars against the Necrons, the Orks were engineered to not only possess great strength, psychic power and reality-warping technology, but also to reproduce via ''spores''. This not only gives them an incredible advantage in numbers, but allows them to begin a planetary infestation again once they've apparently been exterminated. However, the Old Ones died out -- in some versions of the story, helped along by their rebellious creations -- and without masters or their traditional enemies, the Orks began to expand beyond all control: having been introduced to an environment ill-equipped to naturally repel them, the Orks soon become a persistent menace to civilizations across the universe. These days, however, it's most common for Orks to "[[AlienInvasion introduce]]" ''themselves'' to a new environment.

* ''VideoGame/{{Dishonored}}'': The Pandyssian rats were introduced to Dunwall by [[spoiler:Hiram Burrows]] in an attempt to KillThePoor. Pandyssia is a DeathWorld full of nasty predators that keep the [[ExplosiveBreeder rat population]] manageable, but the biggest creatures in Dunwall are humans and hounds, both of which can be ganged up on and eaten by rat swarms. It wasn't long before the perpetrator lost control of the rats, who quickly broke free from quarantine and colonized the island. The icing on the cake is the plague the rats transmit to humans, creating a PlagueZombie [[ZombieApocalypse Apocalypse]].

* In ''VideoGame/KnightsOfTheOldRepublic'', a visit to Tatooine results in the ''Ebon Hawk'' being suddenly infested with [[FantasticVermin Gizka]] after a spaceport official accidentally loads a crate of them onto the ship. With no natural pests or environmental threats to keep their numbers down, the creatures soon fill just about every single corner of the ship, and killing one only results in another appear to replace it. The player has the option of using Gizka poison to clear the infestation, convincing a buyer on Manaan to take them away, or just leaving them alone (they'll leave the ''Ebon Hawk'' when the ship crash-lands on the penultimate level).

* ''VideoGame/PokemonSunAndMoon'': Rattata were introduced to Alola after stowing away on cargo ships, quickly establishing themselves as vermin. As a result, Yungoos was imported from another region to help control their population. However, the Rattata adapted by becoming nocturnal and moving to urban habitats, thus creating a [[UndergroundMonkey new variant of the species]]. Meanwhile, Yungoos itself would go on to become a scourge in Alola.
* In ''VideoGame/PokemonScarletAndViolet'', TheProfessor's TimeMachine created [[ParadoxPerson Paradox Pokémon]], which are supposedly past/future versions of contemporary {{mons}} brought to the current day and absurdly powerful (if you see a robot Delibird when battling online, forfeit immediately). The PlayerCharacter has to shut down the machine in order to prevent them from overrunning the region, displacing the native {{mons}}, and potentially destroying their civilization.

* Shortly before the events of ''VideoGame/{{Temtem}}'', Digital Temtem were invented in Cipanku, who then escaped into the wild and started displacing the native Electric Temtem from their natural habitats. In a sidequest, some scientists introduce [[VoluntaryShapeshifting Mimit]], which can breed with most species, into the highlands of Iwaba in an attempt to rectify this.

* ''Literature/GreenAntarctica'': Pretty much any Antarctic species that makes it to the rest of the world becomes horribly invasive, some of them managing to thrive even in the tropics. Interestingly, it seems to not work the other way, since while rats, pigs, and dogs have been introduced to Antarctica, the native wildlife is more than a match for them.
** Devils[[note]]imagine a wolverine mixed with a piranha[[/note]] were introduced to China to control rat populations, unfortunately, by 1936, their population had [[ExplosiveBreeder skyrocketed]], leading to large parts of Shanghai being firebombed to destroy the swarm. It's been theorized that the government never fully exterminated them, [[NightmareFuel and a mega-swarm is predicted to break out around 2012-2014]].

** Fire ants (that is, ants that can start small fires) have been introduced to other continents, where they cause wildfires.
* ''WebOriginal/HamstersParadise'': When the isolated continent of Borealia collides with the continent of Nodera multiple species were able to cross over the connecting landbridge. The most devastating of which was the Borelian saberleaf grass crossing into Nodera, the plant incorporated silica into its blades which makes it [[TheHedgeOfThorns razor sharp]] and too dangerous for herbivores to eat or even just walk through and its prolific breeding outcompeted native grasses and drove several species of Noderan grazers into extinction or forced them into other habitats. However, an [[InvertedTrope inversion]] of this trope happened when the ungulope, another native of Borealia, entered Nodera, their mouths, throats and stomachs were designed to safety consume saberleaf and when they fed on it they reduced its numbers and allowed the native grass and herbivores to recover.

* The Season 1 finale of ''WesternAnimation/CentralPark'' concerns an invasive fish that everyone tries to catch before it reproduces.

** In "[[Recap/TheSimpsonsS6E16BartVsAustralia Bart vs. Australia]]", Bart brings his pet bullfrog to Australia; this results in a population explosion later on in the episode. At the end of the episode, a koala is seen hanging onto the skid of the helicopter taking the Simpson family to a ship that will take them back to America, implying that America will soon have the same thing happen to it with koalas[[note]]A layer of the joke is that this could never happen as koala's diets are so specialized they won't even eat eucalyptus leaves from a tree different from the one they learned to eat from.[[/note]]

%%** Even the dingo, an Australian icon, is one of these, brought to Australia by the first humans to settle there. Competition with dingos, as well as diseases transmitted from them, may have resulted in the extinction of the Thylacine (or Tasmanian tiger) on the Australian mainland, although it survived in Tasmania until 1936.

%%** Even the dingo, an Australian icon, is one of these, brought to Australia by the first humans to settle there. Competition with dingos, as well as diseases transmitted from them, may have resulted in the extinction of the Thylacine (or Tasmanian tiger) on the Australian mainland, although it survived in Tasmania until 1936.%%

* In ''Film/GodzillaKingOfTheMonsters2019'', King Ghidorah is at first thought to be a rival Alpha Predator to Godzilla. But upon further researching legends and myths, Monarch soon learns that Ghidorah is not from Earth, but is actually an invasive entity from another planet. After Godzilla is nearly killed by the Oxygen Destroyer, Ghidorah takes over as Earth’s Alpha and commands the Titans across the Earth to awaken and wreak havoc upon humanity.

* ''Literature/TheDayOfTheTriffids'': Triffids were created by SovietSuperscience for their superior vegetable oil which can be used as an alternate fuel source, but an attempt to steal their seeds and sell them in the West goes wrong and leads to the seeds being scattered around the world when the airplane carrying them is shot down over the ocean. Even then mankind is able to keep control of the situation by hunting down wild triffids and confining them in farms, until social collapse from mass blindness allows them to break out. With humanity no longer the apex predator keeping them in check, triffids soon reproduce out of control.

Compare FantasticVermin, which may result from this; compare OutsideContextProblem and NormalFishInATinyPond. See also AlienKudzu, which explores botanical examples of this trope.

* ''Literature/ArtemisFowl'': In ''Artemis Fowl: The Time Paradox'', the introduction of rainbow trout into Twin Lakes, and the resulting extinction of the native [[https://en.wikipedia.org/wiki/Yellowfin_cutthroat_trout yellowfin cutthroat trout]], is used as a minor plot point. A flash freeze leaves a small number of yellowfin cutthroats frozen inside a block of ice, which is later acquired by the Extinctionists, a club for [[EvilPoacher people with a perverse obsession with killing endangered animals]], so they can serve the yellowfins to the guests at a banquet they're hosting in a display of ConspicuousConsumption. The Extinctionists consider this a tragedy not because of the extinction itself, but because the fish has a unique flavor which no-one will ever be able to enjoy again.

** In "[[Recap/TheSimpsonsS6E16BartVsAustralia Bart vs. Australia]]", Bart brings his pet bullfrog to Australia; this results in a population explosion later on in the episode. At the end of the episode, a koala is seen hanging onto the skid of the helicopter taking the Simpson family to a ship that will take them back to America, implying that America will soon have the same thing happen to it with koalas[[labelnote:*]]A layer of the joke is that this could never happen as koala's diets are so specialized they won't even eat eucalyptus leaves from a tree different from the one they learned to eat from. Also eucalyptus trees don't exist in America.[[/labelnote]].

** While the original episode is played for comedy, it gets a CerebusRetcon in ''Series/StarTrekDeepSpace9''; as it turns out, Scotty transporting the tribbles to the Klingon ship ultimately led to an ecological disaster for the Klingon Empire, which in turn led to the Klingons hunting the tribbles to extinction.

* An example that had nothing to do with humans occurred about 3 million years ago when North America connected to the once isolated South America and caused what's known as the Great American Interchange. Species from both continents would cross into the other but it was definitely more one-sided in favor of the north as many of the native predatory marsupials, terror birds, giant rodents and native ungulates were outcompeted and replaced by canines, big cats, camelids and elephants. However there is some debate on whether it was as simple as competition as some ground sloths, terror birds and giant armadillos managed to make it all the way into North America, some theorize that the extinction of the South American megafauna was more to due with the ice age that was starting up adversely affecting the southern ecosystems and the northern animals just took advantage of the now vulnerable natives.

* Some paleontologists suggest that this led to the extinction of the dwarf sauropod ''Europasaurus holgeri'', found in the Langenberg Quarry of northern Germany. During the Late Jurassic, Europe was covered by the ancient Tethys Sea and made up of variously-sized archipelagos. While other sites from that time, like Portugal and Britain, are known to have been inhabited by large dinosaurs, Langenberg seems to have been an ecosystem of dwarfs (initially), with the rhino-sized ''Europasaurus'' living alongside lion-sized theropods. But footprints located 5 m above the deposit where the ''Europasaurus'' fossils come from, show that some 35,000 years later, there was a drop in sea level which allowed new wildlife to invade the environment, including a large 26-30 foot long theropod (likely similar to Allosaurus or Torvosaurus), which could have wiped out the native ''Europasaurus''. If true, this would have been akin to lions or tigers invading an island where the largest land herbivores were gazelle.

* ''Literature/TheRollingStones'' features a species known as Flat Cats. Essentially a RidiculouslyCuteCritter, one is brought aboard a spaceship as a pet... only for problems to arise when the Flat Cat starts reproducing, aided by the lack of predators and environmental threats.