Tyranids are not native to the galaxy; they journeyed across inconceivable distances, risking the unspeakable cold and nothingness of the void for countless millennia to reach the rim of the galaxy. Such a voyage must have required utter single-mindedness and unimaginable energy. Now they have arrived, they have awoken from their frozen hibernation, and they are hungry.
Dedicated solely to their own survival, propagation and evolutionary advancement, Tyranids are the ultimate predators. The hive fleet overwhelms its foes with sheer numbers, reproducing deadly organisms and biomechanical creatures from the genetic soup of biospheres they've already consumed. Entire worlds fall to their insatiable appetite, leaving only dead husks in their wake