The Tyranids are without doubt the most alien race encountered by humanity. They have been likened to a galactic locust swarm, remorselessly hungry and too numerous to stop. They are a nomadic, space-dwelling race which has migrated from beyond our galaxy in search of new resources to assimilate. These they have discovered in abundance in the Imperium of man and the assorted alien races now in their path. Tyranids only descend onto planets to totally strip them of bio-mass before moving on, leaving nothing but a ball of scoured rock in their wake.