Board Thread:Warhammer 40k General Discussion/@comment-25618639-20150406151006/@comment-6078851-20150424162044

but tyanids have a LOT more bodies to feed than anyone else, and many of those organisms have high-grade carapaces that can equel power armour, plus they are the single most alien race in a galaxy full of alien life :)

i'm a believer of necron 'edibility' by tyranids, but as mentioned there doesn't seem to be any canon source which states explicitly one way or the other.