History Main / IntroducedSpeciesCalamity

* 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, but it's their difficulty adapting to human biology that makes them so dangerous if a human gets infected.

* Australia has some of the most infamous examples of introduced pests, many of which are so adaptable that they have proved a serious threat to Australian biodiversity, ecological stability, and in some cases, even to the economy.

* ''Franchise/StarWarsExpandedUniverse'': The Republic hosts a strong exotic animal trade, which markets alien animals from throughout the galaxy to the core worlds' idle rich as pets and decorative animals. As is the case with this trade's real-life equivalents, these animals are frequently mismanaged and escape captivity, sometimes establishing stable populations on alien worlds. Coruscant in particular has served as the crux of this trade for millennia, and the deep bowels of its global urban sprawl are home to considerable populations of feral alien animals. This is often a considerable problem, as many of these creatures are dangerous predators and are the last sort of things anyone would want to be wandering around the neighborhood or nesting near important infrastructure.

* Among ComicBook/LexLuthor's many reasons for hating ComicBook/{{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]].
* ''ComicBook/WonderWoman1942'': 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.

* Played with in the Fanfic/TriptychContinuum story ''[[Recap/TriptychContinuumGoosed Goosed!]]'': after spending a millennium trapped in the Empire, Crystal Geese are reintroduced to Equestria -- which doesn't know how to deal with them any more, especially as all of the ones which were trapped ''outside'' went "suspiciously extinct". Fluttershy quickly figures out that the geese could do more damage through returning, because the local ecosystem has adapted to go on without them. [[spoiler:However, once the hostile migration stops fouling Ponyville, it starts heading towards Protocera and its griffon ''omnivore'' citizenry -- implying the species may be about to go extinct again.]]

* In ''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 [[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 the short story ''[[https://dailysciencefiction.com/science-fiction/biotech/alex-shvartsman/invasive-species_DSF Invasive Species]]'', a scientist discusses the possibility of using introduced species against an alien race called the Hauch'k, reasoning that certain Earthly plants and animals could irreversibly damage their fluorine-based atmosphere. Unfortunately, the Department of Defence turns him down, believing that they'll be able to win the ten-year-long war through conventional methods. [[spoiler: The ending implies that the Hauch'k have successfully embarked on a similar program, for the air outside is starting to smell of fluorine...]]
* ''Literature/JurassicPark'' eventually reveals that several smaller dinosaurs have already managed to escape from the park thanks to the [[IncompetenceInc incompetent management]], some even making their way to the mainland. With the predators that would normally keep them under control contained back on Isla Nublar, they flourish as pests and opportunistic predators -- eventually gaining attention when a Procompsognathus swarm kills a baby. [[spoiler:The novel ends with the reveal that several velociraptors have managed to escape the napalm-bombing of Isla Nublar, and are now thriving in Costa Rica, overcoming their implanted lysine deficiency by stealing from local farms.]]
* ''Literature/PerdidoStreetStation'' is based around one of these: [[AnimalisticAbomination Slake Moths]] are a [[SuperToughness 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]] [[DealWithTheDevil risks]] just to kill or capture the Slake-Moths before they can reproduce.
* Long before "The Trouble with Tribbles", Creator/RobertAHeinlein's novel ''Literature/TheRollingStones'' feature 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.

* Creator/DavidGerrold's ''Literature/TheWarAgainstTheChtorr'' series. An unknown alien race infests the Earth with off-planet life forms to wipe out most of humanity and [[HostileTerraforming replace Earth's entire ecosystem with their own]].
* In the ''Literature/{{Worldwar}}'' 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.
* This is effectively what happens in ''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.

* The documentary series ''Alien Empire'' discusses real world cases of this in detail, most prominently cockroaches. However, the episode "Replicators" discusses a hypothetical example just to show what happens when humans unwittingly introduce insects to perfect breeding environments: here, a fisherman decides not to get rid of the maggots he's been using for bait, and keeps them in his fridge while he goes on holiday, trusting that the cold will keep them under control. However, [[SpannerInTheWorks a fuse blows while he's out]]. As a result, the fridge -- with plentiful food, no predators and no competitors -- becomes the ''perfect'' environment for the maggots to metamorphose into bluebottle flies and start breeding. By the time the fisherman gets back, the fridge is now home to '''''thousands''''' of flies, which go on to infest the rest of the building as soon as [[WhatAnIdiot the guy makes the mistake of opening the door]].
* In ''Series/TheGoodies'' episode "Scatty Safari", the Goodies have started [[ItMakesJustAsMuchSenseInContext a celebrity zoo]] and are in search of a new star attraction. They eventually find it in the form of the last remaining Rolf Harris in Australia... and then pair it up with another Rolf kept in a Siberian zoo, resulting in the breeding pair and the result cub becoming their new attraction. Unfortunately, all three escape from the zoo, and due to their ability to both move ''and'' [[ExplosiveBreeder breed like greased lightning]], they quickly overrun their new environment -- resulting in a Pied Piper of Hamelin conclusion to the story.
* Invoked on ''Series/{{Leverage}}''. The team destroys a mark's business by dumping an invasive species of clam into the waterworks of the mark's dam, forcing the dam to shut down operation to get rid of them before they have a chance to reproduce.
* In the famous ''Series/StarTrekTheOriginalSeries'' episode "[[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.

* The Ak'ab of ''VideoGame/TheSecretWorld'' are a monstrous race of [[BigCreepyCrawlies giant insects]] imported from Guatemala by Mayan cultists to use as [[BeastOfBattle living weapons]] in the Darkness War on Solomon Island. The Buzzing specifically states that the native Wabanaki had no defence against the Ak'ab, nor did any of the magical beings on the island until the arrival of Excalibur. Unfortunately, the Ak'ab escaped the counterattack and hid underground; awakening in the 21st century, the insects emerged to find themselves with no masters, no predators and no competitors adequately equipped to stop them. As such, it's not long before they begin devastating the already-beleaguered environment, dominating local forests, pushing the Sasquatch to the brink of extinction and [[CurbStompBattle overwhelming any human efforts to oppose them]].

[[folder:Web Comics]]

* Occurs twice in ''WesternAnimation/TheSimpsons'':
** 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.

* In ''WesternAnimation/TheLegendOfTarzan'' episode "The Seeds of Destruction", Jane plants a sweet-smelling non-native flower near the elephant pond, but the vine grows out of control, driving the elephants out of their home and forcing them to share with the gorillas. When tensions between the two threaten to lead to all-out war, Jane must find a way to fix her mistake.

* This is effectively what happens in ''Literature/TheDayOfTheTriffids''. They were created by SovietSuperscience for their superior vegetable oil which can be used as an alternate fuel source, but an attempt to steal them goes wrong and leads to the seeds being scattered around the world. 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.

* Argentine Ants. In their native habitat, the floodplains of the Parana river in South America, their numbers are kept in check by the fierce competition from two other native ant species, fire ants and army ants, and because whenever they establish a new colony, genetic mutations result in the different colonies seeing each other as rivals and competing with each other, and their survival hinges on them being highly aggressive. When a small number of queens stowed away on human ships and set up new colonies in Madeira and New Orleans, there were no species that could compete with them, and lack of genetic diversity meant that the mutations that make them compete with themselves didn't establish as quickly, meaning they were more likely to co-operate together and form mega-colonies. Today, they're the most numerous ant species on earth, have established colonies on six continents, and are displacing and devouring many native ant, invertebrate and plant species in their new environments. As an added bonus, they also know how to co-operate with aphids, and aphids that ally with them also profit from their success, growing into swarms that kill off human crops.

* Argentine Ants. In their native habitat, the floodplains of the Parana river in South America, their numbers are kept in check by the fierce competition from two other native ant species, fire ants and army ants, and because whenever they establish a new colony, genetic mutations result in the different colonies seeing each other as rivals and competing with each other. When a small number of queens stowed away and set up new colonies in Madeira and New Orleans, there were no species that could compete with them, and lack of genetic diversity means that the mutations that make them compete with themselves don't establish as quickly, meaning they are more likely to co-operate together and form mega-colonies. Today, they're the most numerous ant species on earth, have established colonies on six continents, and are displacing and devouring many native ant, invertebrate and plant species in their new environments. As an added bonus, they also know how to co-operate with aphids, and aphids that ally with them grow into swarms that kill off human crops.

* Argentine Ants. In their native habitat, the floodplains of the Parana river in South America, they face fierce competition from two other native ant species, fire ants and army ants, and because whenever they establish a new colony, genetic mutations results in the different colonies seeing each other as rivals and compete with each other. When a small number of queens stowed away and set up new colonies in Madeira and New Orleans, there were no species that could compete with them, and lack of genetic diversity means that the mutations that make them compete with themselves don't establish as quickly, meaning they are more likely to co-operate together and form mega-colonies. Today, they're the most numerous ant species on earth, have established colonies on six continents, and are displacing and devouring many native ant, insect and plant species in their new environments. As an added bonus, they also know how to farm aphids, which pose a threat to human crops.

* ''Literature/PerdidoStreetStation'' is based around one of these: [[AnimalisticAbomination Slake Moths]] are a [[SuperToughness 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 of hazards 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]] [[DealWithTheDevil risks]] just to kill or capture the Slake-Moths before they can reproduce.

* In ''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 small number of yellowfin cutthroats remain preserved in a block of ice, until that block of ice is acquired by the Extinctionists, a club for [[EvilPoacher hunting enthusiasts 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.

* In ''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 small number of yellowfin cutthroats remain preserved in a block of ice, until that block of ice is acquired by the Extinctionists, a club for {{Egomaniac Hunter}}s 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.

* In ''Literature/ArtemisFowl: The Time Paradox'', the introduction of rainbow trout into Twin Lakes, and the resulting extinction of the native yellowfin cutthroat trout, is used as a minor plot point. A small number of yellowfin cutthroats remain preserved in a block of ice, until that ice is acquired by the Extinctionists, a club for {{Egomaniac Hunter}}s 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.

* In ''Literature/ArtemisFowl: The Time Paradox'', the introduction of rainbow trout into Twin Lakes, and the resulting extinction of the native yellowfin cutthroat trout, is used as a minor plot point. A small number of yellowfin cutthroats remain preserved in a block of ice, until that ice is acquired by the Extinctionists, a club for {{Egomaniac Hunter}}s 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 ConspiciousConsumption.

** Prickly Pear cactus was introduced to serve as a fence, but quickly spread over 15,000 square miles, rendering the land useless for grazing. The Cactoblastis moth was introduced as the caterpillar eats the cactus (hence the name) and quickly brought it under control, so it is a fairly rare species today.

* In ''WesternAnimation/TheLegendOfTazan'' episode "The Seeds of Destruction", Jane plants a sweet-smelling non-native flower near the elephant pond, but the vine grows out of control, driving the elephants out of their home and forcing them to share with the gorillas. When tensions between the two threaten to lead to all-out war, Jane must find a way to fix her mistake.

->'''Spock:''' Surely you must have realized what would happen if you removed the tribbles from their predator-filled environment into an environment where their natural multiplicative proclivities would have no restraining factors.
->'''Cyrano:''' Well, of cour- what did you say?
->'''Spock:''' By removing the tribbles from their natural environment, you have, so to speak, removed the cork from the bottle and allowed the genie to escape.
-->--''Series/StarTrekTheOriginalSeries'', "The Trouble With Tribbles"

!!Examples

[[folder: Comic Books]]

[[folder: Fanfic]]

* Played with in the FanFic/TriptychContinuum story ''[[Recap/TriptychContinuumGoosed Goosed!]]'': after spending a millennium trapped in the Empire, Crystal Geese are reintroduced to Equestria -- which doesn't know how to deal with them any more, especially as all of the ones which were trapped ''outside'' went "suspiciously extinct." Fluttershy quickly figures out that the geese could do more damage through returning, because the local ecosystem has adapted to go on without them. [[spoiler: However, once the hostile migration stops fouling Ponyville, it starts heading towards Protocera and its griffon ''omnivore'' citizenry -- implying the species may be about to go extinct again.]]

[[folder: Literature]]

* ''Literature/JurassicPark'' eventually reveals that several smaller dinosaurs have already managed to escape from the park thanks to the [[IncompetenceInc incompetent management]], some even making their way to the mainland. With the predators that would normally keep them under control contained back on Isla Nublar, they flourish as pests and opportunistic predators - eventually gaining attention when a Procompsognathus swarm kills a baby. [[spoiler: The novel ends with the reveal that several velociraptors have managed to escape the napalm-bombing of Isla Nublar, and are now thriving in Costa Rica, overcoming their implanted lysine deficiency by stealing from local farms.]]
* ''Literature/PerdidoStreetStation'' is based around one of these: [[AnimalisticAbomination Slake Moths]] are a [[SuperToughness 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 of hazards 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]] [[DealWithTheDevil risks]] just to kill or capture the Slake-Moths before they can reproduce.
* Long before ''The Trouble With Tribbles,'' Creator/RobertAHeinlein's novel ''Literature/TheRollingStones'' feature 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.

* In the ''Literature/{{Worldwar}}'' 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.

[[folder: Live Action Television]]
* The documentary series ''Alien Empire'' discusses real world cases of this in detail, most prominently cockroaches. However, the episode "Replicators" discusses a hypothetical example just to show what happens when humans unwittingly introduce insects to perfect breeding environments: here, a fisherman decides not to get rid of the maggots he's been using for bait, and keeps them in his fridge while he goes on holiday, trusting that the cold will keep them under control. However, [[SpannerInTheWorks a fuse blows while he's out]]. As a result, the fridge - with plentiful food, no predators and no competitors - becomes the ''perfect'' environment for the maggots to metamorphose into bluebottle flies and start breeding. By the time the fisherman gets back, the fridge is now home to ''' ''thousands'' ''' of flies, which go on to infest the rest of the building as soon as [[WhatAnIdiot the guy makes the mistake of opening the door]].
* In ''Series/TheGoodies'' episode "Scatty Safari," the Goodies have started [[ItMakesJustAsMuchSenseInContext a celebrity zoo]] and are in search of a new star attraction. They eventually find it in the form of the last remaining Rolf Harris in Australia... and then pair it up with another Rolf kept in a Siberian zoo, resulting in the breeding pair and the result cub becoming their new attraction. Unfortunately, all three escape from the zoo, and due to their ability to both move ''and'' [[ExplosiveBreeder breed like greased lightning]], they quickly overrun their new environment - resulting in a Pied Piper of Hamelin conclusion to the story.
* In the famous ''Series/StarTrekTheOriginalSeries'' episode "[[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.

[[folder: Tabletop Games]]

* 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.

[[folder: Video Games]]

[[folder: Webcomics]]

[[folder: Western Animation]]

** "[[Recap/TheSimpsonsS10E3BartTheMother Bart The Mother]]" has two Bolivian Tree Lizards hatching in Springfield, where their population explodes and they end up eating almost all of Springfield's pigeons, much to the delight of the population of Springfield (who view pigeons as disease-ridden "flying rats"). When Lisa points out that now Springfield is full of Bolivian Tree Lizards, Skinner outlines Springfield's solution; first, they will import large numbers of lizard-eating Chinese Needle Snakes, and then when the snake population becomes uncontrollable, they will import snake-eating gorillas; they don't need any animals to deal with the gorillas, because the gorillas will freeze to death when winter comes.

[[folder: Real Life]]

** Rabbits, once introduced to Australia as game for shooting hunts, have since proved to be one of the single biggest nuisances in the country. With local predators being wiped out by the settlers, their breeding rate proved extreme enough to endanger native species like Bilbies, and then to native plants, and then [[LaserGuidedKarma to the crops of British settlers]]. Centuries onwards, Rabbits are still a major problem in Australia - to the point that an attempt to wipe them out via germ warfare ''failed'' once they started adapting to the Myxoma virus.
** Foxes were also introduced as game for foxhunting. Unfortunately, with dingoes learning to avoid larger urban centres, they quickly became apex predators and began preying on smaller native animals - to the point that they've been observed climbing trees in pursuit of koalas and sugar gliders, and may have actually played a part in the extinction of several species.

[[/folder]]

Natural ecosystems exhibit a very distinct balance of populations: predators, competing species, disease and another natural causes all play their part in ensuring that animals don't end up breeding to the point of overwhelming the local environment, especially in the case of {{Explosive Breeder}}s. True, it's not unknown for animals to migrate to areas without the environmental elements that keep them suppressed and become an ecological threat to their new habitat, but this ''usually'' only happens under very special circumstances...

** Played for tragedy in the case of the Krogan. Deliberately uplifted to serve as a trump card in the war against the Rachni, things started going wrong once the war was won: the [[HealingFactor main]] [[ExplosiveBreeder traits]] that had [[HadToBeSharp allowed the Krogan to survive]] on their home world of [[DeathWorld Tuchanka]] soon proved highly dangerous once they ended up on less-hostile worlds: numerous accounts exist of Krogan overwhelming the natural environments of the planets they were allowed to colonize, eventually forcing them to expand further. Worse still, Krogan are not only [[ItCanThink intelligent beings]] but also a ProudWarriorRace, so it didn't take long for tensions between an overpopulated Krogan army and a stubborn galactic government community to erupt into conflict. Consequently, a new war started - one that only ended when the Salarians and the Turians infected the Krogan with the [[SterilityPlague Genophage]]. Krogan still exist by the start of the series, but as a demoralized DyingRace reduced to squabbling over any female capable of consistently bearing live young.

* 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, 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.