The Tyranids are the most alien of races to infest the galaxy. An elemental force, they mass in void-swimming shoals, remorselessly hungry and too numerous to stop. The Tyranids are believed to have migrated from beyond the known galaxy in search of new systems to consume, ravening swarms descending upon planets and stripping them of all life. Every living thing is consumed, brought back into the hive ships and dissolved into a rich biological gruel from which new Tyranid organisms are grown. Tyranids do not make their weapons and starships out of metal and plastic, but use gene-splicing and bioengineering to grow them from the living organic material harvested from the worlds they have devoured. When the Tyranids move on in search of fresh prey, they leave nothing but a ball of scoured rock in their wake.