Needs More Examples, Needs An Index, probably Needs A Better Description.
It belongs in Tropes In Space, Speculative Fiction Tropes, Alien Tropes and Cosmic Horror Story. Any more?
Most parasites use a single living being as their host, which they use to grow, develop their bodies, anf finally create a offspring of new parasites which will invade another person.
These guys, however, will employ a whole planet
as their host. Just us our parasites feed on our nutrients to grow, these guys will deplete the planet of its natural resources. This is likely to bring bad consequences for the planet inhabitants.
Compare Planet Eater
, where the parasite doesn't bother to progressively feed off the planet's resourced and directly eats
it, and Planet Looters
, which are more similar to thieves than to parasites.
Anime And Manga
- The Big Gete Star from the Dragon Ball Z movie The Revenge of Cooler probably counts, since it was a mechanical life form that was trying to absorb New Namek.
Live Action TV
- 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 Fifty Two, 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.
- Blakes Seven: 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 indestructable creatures who devastated entire planets, but whose eggs couldn't hatch unless seared by a supernova first, limiting their spread.
- 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.
- 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 we get to fight some of the offspring before they're launched to other planets.
- The Old Gods from Warcraft are planetary parasites that merge themselves to a planet and slowly corrupt it. Whether this would eventually destroy the planet is unknown, as the Old Gods on Azeroth were sealed away by the Titans (they could not be killed, having already corrupted the planet to such a degree that removing them would've required the destruction of Azeroth).
- Jenova from Final Fantasy VII.
- Metroid Prime 3 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.