Wirrn Breeding Colonies

The Breeding Colonies were a group of worlds controled by the Wirrn, in the Andromeda Galaxy. Though the wirrn lived most of their life in space, they needed terestrial planets to reproduce, so they could incubate animals, usually senseless herbivores limiting their technological progress.

When humans expanded into Andromeda, they started taking the breeding planets, and after a thousand years of fighting eventualy drove the Wirrn away from the galaxy. (DW: The Ark in Space)