Genestealers
Genestealers are peerless predators, swift vanguard organisms armoured in chitinous plates and possessed of terrifying strength and agility. Their broods move far ahead of the Tyranid hive fleets, to seek out fresh feeding grounds and spread their insidious genetic infection amongst the defenders. When the invasion swarms finally descend, the Genestealers burst from hiding to begin the slaughter.