From the edge of the Eastern Fringe, the vicious Tyranids have come to the galaxy. Rather than a single species, the Tyranids are an alien ecosystem composed of countless bioforms which are variations on the same genetic theme. Their numbers unknown, the Tyranids are dedicated solely to their own survival, devouring all organic material on every planet in their path. Despite their appearance, these creatures are very intelligent, forming a single Hive Mind. Many enemy commanders have fallen underestimating the Tyranids. The Tyranids travel the galaxy in Hive Fleets, each of which serves as the vanguard of the primary invasion force.