From the Mass Effect twitter:
(@mytwitter) When the full game releases, hi-res textures will be built into the game! #masseffect3
If this is a lie I will find you and kill you HarryHengst.
I either missed this altogether, or it left such a minor impression that I forgot it. What was the reason?
They apparently "liquefy" a large number of beings from a single species to reproduce, but I considered this to be separate from the reaper's scorch-and-burn policy of exterminating, well, everything. Was this what you were referring to?
While the specifics arent ever given, they need organic life to reproduce themselves in some way. But from what little was said, they do need a specific kind of organic life, since the Protheans were not suitable candidates for reaperization and thats why some were genetically re-engineered to become the Collectors we know and love. Which also explains the Collectors themselves, and their actions of collecting other species in an attempt to find the best suitable candidate for the Reapers to use for reaperduction.
Everything other species can go fuck itself as far as the Reapers are concerned so they just wipe them all out or they re-purpose them if they show any promise like the Keepers on the Citadel or the Protheans as Collectors. As well a lot of people speculate that generally there arent as many space faring species in the galaxy when the Reapers arrive as there are now in ME and some believe thats because of Prothean intervention on a lot of planets, explaining their outpost on Mars.