Wraith

The Wraith are a vampiric hive-based species that harvest the 'life-force' of humans and other humanoids in the Stargate Universe. Countless worlds in the Pegasus galaxy live in constant fear of the Wraith, who return periodically to cull their human herds. After taking their fill, the Wraith hibernate for centuries, watched over by Keepers, before they wake and feed again. It was possible that when the Lanteans seeded Pegasus with humans, it was originally an 'Iratus bug' that fed on humans and evolved into the Wraith.

They are involved in many wars with the Lanteans, Asurans and Tau'ri using inferior technology, but their numbers and powerful hive ships often allow them to turn the tide in battles and eventually dominate the galaxy.