Affinity

Ignorance: They cannot build a ship.

Infection: They only can infect planet near completely infected planet. Infection takes few turns. Once infection starts, owner of the planet should quarantine the planet using fleet. Quarantined planet acts as if they are being seized.

Toxic: Infected planet need to be excavated.

Consume: As they infects planet where people lives, the planet produces science.

Excavation: Other factions need scientific research which appears after encounter them. Excavation skills can be upgraded.

Evolution: Make Hive faster at infection, make other factions take more time to excavate them. Maybe they can penetrate quarantine.-by science

Story

As many factions interacts, their virus has interacted too. One scientist found that the viruses has highly evolved, he gave them a Hive-mind, which was illegal. So, the scientist got arrested and the virus has quarantined. As thousands of years passes, the planet where virus was quarantine has forgotten. But a young explorer has come and released the virus. The virus consumed the explorer and got human intelligence.

Sorry for my bad English and insufficient explanation :)

Maybe i can't response to your reply.