Most parasites use a single living being as their host, which they use to grow, develop their bodies, and finally create many new parasites that will invade another host.
These guys, however, will employ a whole planet as their host. Just as our parasites feed on our nutrients to grow, these guys will deplete the planet of its natural resources or its very life force (this is likely to bring bad consequences for the planet's inhabitants), and use them to complete its reproductive cycle, spawning more of its race. Once the cycle has been completed, the newborn will somehow leave the planet to find another one, where they will start a new cycle. Destroying the planet when leaving it is optional.
- Dragon Ball Z
- In Toriko, the entire Gourmet World was spawned by such a parasite. A meteorite infused with Gourmet Cells struck the original planet Earth long ago. The Gourmet Cells fed off the energy of Earth's mantle and grew new landmass. Gourmet World is a giant tumor that dwarfs its host.
- Kill la Kill: Life fibers ultimately cocoon the Earth to make it explode, spreading even more life fibers to other planets, which Ragyou Kiryuin facilitates.
- In the Marvel Comics Alternate future Earth X, it's revealed that Celestials gestate their young inside of planets, and genetically manipulate the dominant species to turn them into superpowered protectors for their child.
- In 52, one of the possible futures that Rip Hunter foresees (and successfully averts) involves Mr. Mind spawning 52 giant extradimensional parasites that feed off the mental energies of entire universes.
- Heavy Metal Volume 2 #5 (September 1978). In the story "Urban Renewal" by Stephen Bissette, giant insects attack a planet and lay their eggs in it. When the eggs hatch, it destroys the planet.
- Agent Smith in The Matrix describes humanity as this:
Every mammal on this planet instinctively develops a natural equilibrium with the surrounding environment, but you humans do not. You move to an area and you multiply and multiply until every natural resource is consumed, and the only way you can survive is to spread to another area. There is another organism on this planet that follows the same pattern. Do you know what it is? A virus. Human beings are a disease, a cancer of this planet. You're a plague, and we are the cure.
- Perry Rhodan has the Guan a Var or "sun worms", whose natural habitat is hyperspace. They drain entire stars of their energy at a frightening rate (three of them are seen to burn through the reserves of one star with an inhabited system in a matter of mere days, though that was admittedly after millennia of imprisonment and starvation), reproduce, and move on once the star has gone supernova or otherwise become useless (to both them and pretty much anyone else). They're also, despite being descended from once highly intelligent organic starships, basically just dumb animals that can't even perceive the effects of their actions because their senses no longer extend into normal space.
- H. P. Lovecraft (of course) had the Dholes, titanic worm-things which burrowed beneath worlds to slowly devour them from the inside-out and multiply until nothing but a shattered husk was left. Fortunately, the closest they got to Earth is the Dreamlands.
- A later addition to the Cthulhu Mythos, the Worm that Gnaws in the Night, was this to the planet Shaggai, except that it was doing it all by its lonesome; it's so massively powerful that when the Planetoid Abomination Ghroth arrived in its solar system (something which makes every other resident top-tier abomination fully active), the Worm's full awakening resulted in an Earth-Shattering Kaboom.
- The Star Trek novel Prime Directive gets points for parasitic complexity with a three-species symbiosis: Species A secretly bases on worlds which emit radio transmissions, feeds the Cold War paranoia of the locals through UFO sightings and signal manipulation until the hapless natives nuke each other, then seeds the newly-radioactive environment with Species B, an algae which uses gamma rays the way most plants use sunlight. Species A's signals eventually bring Species C, an immense spacefaring cloud which consumes the algae, and then provides A with transportation and life-support on the way to the next target. The unlucky world is left an irradiated wasteland with much of its organic chemistry sucked away. Spock identifies all three species as non-sapient, and determines that the time needed to evolve their incredibly complex behavior proves they are relics of a prior iteration of the universe.
- In the Star Trek: New Frontier novel End Game, the Great Bird of the Galaxy (which is also a nickname for Gene Roddenberry) is found to be gestating inside the planet Thallon. The Bird hatches, and a Planet-Shattering Kaboom ensues.
- The Worlds of Power novelization of Blaster Master portrays the Plutonium Boss as one of these. When it arrives on a planet, it burrows underground and feeds on radiation from the planet's core. Eventually, it destroys the planet from the inside-out, then moves on to another world.
- Blake's 7: Zil is one of a humanoid species of parasites who live on the surface of a living planet called "Host."
- The Giga Shadow of Lexx spent thousands of years regenerating under the surface of the Cluster world, as well as ruling the Light Universe through His Shadow and feeding on the Human Sacrifices given by his loyal followers.
- Doctor Who: The 6th Doctor episode "The Twin Dilemma" featured the Gastropods, a race of nearly indestructible creatures who devastated entire planets, but whose eggs couldn't hatch unless seared by a supernova first, limiting their spread.
- In Kamen Rider Gaim, the Helheim Forest proves to spread its seeds like wildfire, and there is a very real threat that if the dimensional portals aren't closed, this invasive species could end up turning Earth into a new Helheim. We know because this is what happened in the formerly-Earthlike world now known as Helheim. Oh, and the monsters used to be that world's people and animals, as anything that eats the fruit of the plants becomes an Inves monster and ends up spreading the seeds further still. Earth has ten years left.
- Call of Cthulhu boxed set Spawn of Azathoth. If a Seed of Azathoth strikes a planet, it can penetrate it and grow into a Spawn of Azathoth the size of a star. All that's left of the planet is shattered ruins. The former fifth planet of the solar system suffered this fate: its remains are the Asteroid Belt.
- Star Fleet Battles. Starswarm robots burrow into planets and use raw materials underground to create more robots. Once enough new robots are made, the swarm leaves the planet and heads into space.
- GURPS Space Bestiary'
- The alien species known as world worms travel between planets in pods. When a pod lands, the worms pour out and infest the planet, eating their way to the planet's core. By the time they've grown to full size (several miles long), they've done so much damage to the planet that it disintegrates. After mating, the worms split up and release pods, which begin their journey to find a new planet to destroy.
- Invader swarms are made up of thirty ton aliens that land on a planet in numbers of 200-1200. They breed prolifically, doubling their population every month, while eating all of the organic life they can find. When they reach their maximum population (in the trillions), they launch themselves into space and head for the next life-bearing world, leaving behind a dead planet.
- The Parasite from Evolva. A giant egg comes to the planet, develops lots of tentacles, creates an army of aliens, and uses the planet's resources to make new eggs, supposedly to send them to other planets.
- Lavos from Chrono Trigger. Similar to the previous example, but he doesn't create an alien army, is instead exploited by the planet's mages (doesn't end well), and the heroes get to fight some of the offspring before they're sent to other planets.
- The infamous Jenova of Final Fantasy VII, from the exact same company that developed the above Chrono Trigger. Jenova shares a few similarities, feeding on the collective life-force of the planet and being directly responsible for the downfall of the Ancients. When the Shinra Corporation tries to exploit the thing, mistaking it for one of said Ancients, they end up simply creating Sephiroth—a new form of Jenova that's smarter, stronger and a lot prettier.
- The Old Gods from Warcraft are planetary parasites that merge themselves to a planet and slowly corrupt it. They were created by the Void Lords to corrupt nascent Titans gestating within planets as part of their plan to destroy existence. The Old Gods of Azeroth are so deeply connected with the nascent Titan that outright destroying them would kill it as well, so they were instead subdued and sealed.note
- Metroid Prime 3: Corruption reveals that the origin of Phazon is a possibly-sentient planet known as Phaaze, and that it sends seeds over to other planets in order to infest them with Phazon.
- Master of Orion II had the space eel, a space monster that would target planets to use as spawning ground. Left to its own devices, eventually you'd end up with two space eels.
- The Dark Bramble and its seeds in Outer Wilds are heavily implied to be this. It's strongly hinted that the bramble was not always the form of the fifth planet in the solar system, and has, in fact, consumed and replaced the previous planetary body with its twisted, spawling Eldritch Location self. Were it not for the sun going supernova every 22 minutes in a time loop, it's likely that the seeds on other planets in the system might inflict the same fates on Timber Hearth and Giant's Deep.
- The Mycon's "Deep Children" from Star Control 2 are dropped from orbit, burrow their way down to the mantle of a planet, grow tendrils throughout the planet, then start tearing holes in the planet's crust, turning it into a lava world (or Juffo-wup as they call it). The whole process takes about a year.
- The over-arching plot of the UFO After Blank series revolves entirely around these. Their mating rituals, the chaos they've caused for humanity and other aliens whose planets they've infested and the attempts of various factions to control them for their own nefarious purposes.
- The Noizoids from Harmoknight, who arrive on Planet Melodia on a massive, spiky-green meteor and cause nearly every animal nearby to become violent.
- Stellaris occasionally spawns a habitable, completely inconspicuous planet that, after a random number of years, suddenly starts shaking, breaking up and releasing noxious gasses into the atmosphere. If you're lucky, these disturbances subside after a while and leave you with a damaged but still habitable world. The more likely outcome is that the planet cracks open like a giant egg and hatches a Voidspawn, a hostile Leviathan-class creature that looks like the unholy lovechild of a dragon and a dragonfly. If you leave it alone long enough, it'll eventually start migrating through the galaxy (probably looking for another planet to infest), laying waste to everything in its path.
- The Entities of Worm have centuries-long gestation periods after arriving on a planet where they adapt and learn via embedding shards into the dominant species, such as humans. Once completed they absorb all available nutrients in every dimensional version of the planet and detonate the planet. This propels their young into space, each of which will seek out another planet.
- The Dark One Worm from Super Robot Monkey Team Hyper Force Go. It's also implied that there are other members of its species on other planets.
- The Homeworld Gems in Steven Universe reproduce by draining the life force from a planet's crust to form new Gems. While their attempt to do this to Earth was stopped a long time ago, the equipment used is still sitting there, and is shown to work just fine. Just before they were driven off, they played this trope even more straight by burying a "Cluster" Gem near the Earth's core. It was planned to crack the planet open at the end of its millennia-long incubation.