Board Thread:Warhammer 40k General Discussion/@comment-7186329-20130329201743/@comment-6078851-20130410172342

"The Tyranids are not native to our galaxy. They have travelled through the bleak intergalactic space between galaxies for countless millenia. Wether the Tyranids made this perilous journey because they had already consumed everything of worth in their home galaxy or in flight of another, even more fearsome race, is unknown. It is possible that the Tyranids have been preying on galaxies since time immemorial and ours is but the latest to feel its predations. Whatever the truth, for the Tyranids to have endured such an epic voyage must have required both the greatest of single-mindedness and unimaginable amounts of energy."

"The Hive Mind holds all Tyranid creatures in a psychic bond that enables them to act together as one gestalt organism. it is a single co-ordinating sentience formed from untold billions of individual conciousnesses, each of which is a Tyranid."

"The Hive Mind's influence is strongest in the vicinity of creatures such as Tyranid Warriors and the feared Hive Tyrants. These beings are able to comminicate with their kin, not through language, but by an instinctual telepathy through which they channel the will of the Hive Mind. Under the command of such creatures the tyranids operate in perfect unison, slaved to the psychic imperatives of a single communal intelligence."

this is a couple of passages from the most recent tyranid codex.