Board Thread:Warhammer 40k General Discussion/@comment-25618639-20150406151006/@comment-6078851-20150424161058

they do have bacteria, but like every facet of their race it's symbiotic tyranid bacteria and is all part of the single 'whole' which culminates in the hive mind. i'm pretty sure they have used viral warfare though, but i don't remember where i got that from so maybe they havn't.

squigs were not created by the hive mind and are not tyranid - they are in the ork codex and don't even get a mention in the tyranid codex. squigs were created by the old ones as an integral part of the orkoid self-sustaining ecosystem, and have been part of that system for over 60 million years. tyranids only began to get to our galaxy around 10,000 years ago, and even being lenient no more than 20,000 years ago. squigs somehow have tyranid dna within them but the presence of that dna is relatively new.

as an additional explanation on the celestial orrery - it was sufficiently explained but i love it so shall expand :) it appears as a holographic-ish galactic map of every star (according to the previous necron codex anyhow), and to detonate a star simply requires a press of the corresponding star on the map. but despite the threat necrons pose to other races the orrery is currently controlled by a relatively compassionate necron who doesn't want the orrery used, or at least used as infrequently as possible. exploding a single star requires millenia of 'stellar micromanagment' to prevent a destabalisation of neighbouring systems, and that's a hassle even for necrons :)  but to destroy the entire tyranid race with the orrery would require waiting for them to all be within the boundries of the galaxy, by which time the galaxy's biomass will be half eaten, and it would require a significant volume of stars to be detonated to wipe out all tyranids. the orrery's an end-game weapon though, even if it worked the volume of newly popped stars would cause a galactic destabalisation and not even the necrons would be able to prevent it. but if they wanted to, then they could take out the tyranids with a wave of a hand, literally, as well as the galaxy :P