Tyranid

Tyranids are an alien species which are believed to have originated in a different galaxy.

Tyranids are generally insectile but consist of an almost infinite number of species which evolve incredibly fast to deal with any threat. They travel from planet to planet in living ships and strip each planet of all resources before moving on (many Imperial Texts refer to the Tyranids as the Great Devourer or Shadow on the Warp). Several Hive Fleets have been reported so far in Imperial history and have been stopped by the Imperium (Hive Fleet Behemoth, Hive Fleet Kraken, and Hive Fleet Leviathan), however the total number of fleets in the Galaxy and beyond is unknown.