Board Thread:Warhammer 40k General Discussion/@comment-46.162.84.254-20130704080553/@comment-6078851-20140706133150

there's only one hive-mind. so every single tyranid is united under a single conciousness (so long as there's a synapse bio-form nearby). source - codex: tyranids.

as for a war of attrition the tyranids are the one race that could dominate everyone, even orks. as long as there's bio-mass at hand then tyranids can potentially not lose any war: 'nids attack a heavily fortified position and get trashed, but all the bio-mass from the recently killed swarms is right there and as long as they have access to bio-mass, any bio-mass, then their numbers won't diminish by a single troop/organism (plus any fortified position is limited by the ammunition at hand and tyranids are very capable of making enemies run out of ammo from sheer volume. when it come to utilizing numbers even the ork race doesn't compare). even if it's a straight melee of attrition against orks or imperial guard then every single enemy that dies becomes bio-mass to produce more organisms, and the speed with which tyranids can produce more tyranids is insanely high.

i totally agree that the necrons could, potentially, effectively combat tyranids, but even necrons would lose a war of attrition.