Tyranids

Tyranids are a parasitic and powerful alien menace from the popular table-top game Warhammer 40,000 as well as its related universe - which has been expanded into books, videogames and more over the years - of all the countless enemies of the Imperium it is said the Tyranids are the most alien as they can't be intimidated nor reasoned with and don't want things like money or power: instead they seek only continual expansion of their own species.