((Eh, without the 100% mass energy thing (which I'm not sold on), the vast majority of the biomass is lost in transit because the space between galaxies is really really really huge.))
((1% of the biomass and such of several galaxies is still a lot of biomass.
And given how much every faction in WH40k ignores/breaks the laws of physics on a daily basis, a 110% matter-to-energy conversion wouldn't surprise me.))
((Most of the Tyranids are melee oriented, with some ranged forms. If the Altered do absorb biomatter on contact, then the Tyranids wouldn't have a chance to bring flesh back to the hive. The Tyranids do conform to most biological guidelines, but the Altered have shown no qualms about ignoring biology altogether. Simply put, the Tyranids need time to assimilate things, and the Altered do not. You can't beat a cheating enemy without cheating yourself.))
((Um, I disagreee, strongly, with that final "can't beat cheaters without cheating" principal. It may be true in this case, but I've knowingly competed against cheaters and won while still playing fair. It's hard, but if you keep your mind open and figure out not just that they're cheating, but what exactly the cheat is, then you can act to counter it.))
((Well, it's a lot harder when the cheaters are cheating the laws of reality.))
((On that topic, I just wanted to note:
Tyranids are essentially 'beaten' through war, bullets and manpower.
The Altered, as far as we can tell, were killed out through war, bullets and manpower.
Hell, even the MassEffect universe's reapers (Massive capital-ship sized AI which created new troops out of their fallen/captured enemies) were pushed back pretty far by bullets, war and manpower.
((Really? Those seem like the most pointless and wasteful strategies to use against all three.))
But something like the flood with the only solution being "eliminate their food source" is a different scale of threat, canonically.
((Not really. I mean, the way you kill a vampire is different than how you'd kill a werewolf, but they're roughly the same "scale" of threat. And you need to look past "How do we kill it" do determine scale. Don't look at how you win--look at how you
lose.))
tl;dr, The Zerg on crack
((Technically, it's more like the Zerg being Tyranids with withdrawal issues.
Fun fact: Starcraft was originally supposed to be a WH40k game. They couldn't get the licensing for it, though, so they made the Tyranids Zerg, the...Eldar, I think, Protoss, and I've comedically "forgotten" who the Terrans were.))