Tyranid are a Collective Body

• Devastation of Baal:

"The invader was Hive Fleet Leviathan, by Imperial designation, though the governing intelligence of the hive mind made no such distinctions between the component parts of its body. To its incomprehensibly vast intellect, Leviathan was a limb, a foot or an arm. If the hive mind regarded Leviathan as distinct from the other fleets devouring the galaxy in some way, it was by categories too alien for men to understand."

• 9th Ed Codex [Tyranids]:

"A billion times a billion tyranid stands at the rim of the galaxy, yet each one is no more than a single cell in the living body of the Hivemind, "THE DEVOURER OF WORLDS"."