This is going to be my attempt to flesh out the Khrave xenos as an army for 40K. They are a major threat the Imperium has faced since the Age of Strife and are noted to be psychicly gifted. One battle that I read about them taking part in described them as chiropteran and I'm perfectly happy to run with bat-like, brain eating aliens. Their technology is Warp based but apparently can still be used by non-psychics too. They can descend upon a planet and wipe it out as food or stay for centuries, carefully feeding off it.

There are a lot of details that can be filled in, which will make them a fun creative exercise. I intend to run with them being highly social apex predators who view everyone else as food (space vampires). I also want to make their sentience entirely based on feeding off of other sentient beings. The young and starving will be nothing more than humanoid pack predators. They will get bigger and stronger based on their age and the minds they eat. I'm also working on the idea that they do have a psychic community that, unlike the Tyranid hive mind, each individual retains their own individuality. This would be why their fleets are known as shard webs or nest webs, as each nest forms a psychic nexus that can link to other nests, allowing them to navigate and communicate across space.

The Khrave view Chaos as an infection capable of corrupting entire nests but their communal link allows them to resist it or at least detect it in other Khrave. The young/starving will not have this psychic connection and can suffer mutation, which the Khrave are intolerant of. Unlike the Imperium, I'm thinking they turn their mutants into biomechanical war machines rather than destroying them. I'm also considering only giving them access to the psychic phase level of psychic powers as a special group of Khrave that feed very carefully on psykers so they can use those powers as a group, but not as individuals as an individual can be easily corrupted.

That's it for now. More musings to come.

My major sources come from the following:
http://wh40k.lexicanum.com/wiki/Khrave
http://warhammer40k.wikia.com/wiki/Khrave