- "Why are you torturing us?
We're researching you. Living fossils, surely you can understand that."
- ―Tate questions the Host Force[src]
The Host Force is a mysterious hostile entity or entities known to live on Carpathia. From what has been seen in episodes of season 1, is that it can project itself within somebodies mind, so that it is only visible to who they wish to see them. They are capable of duplicating carbon-based lifeforms, such as Josie Hunter. They are also capable of decresaing fertility within the population on Carpathia.
It has acted hostilely to life on Carpathia. It eradicated early Hominids a thousand years ago, the fossils of these creatures were discovered by the Carpathian Pioneers. (Episode 5) A thousand years later, when Humans from Earth landed on Carpathia, it is presumbed that it created the devastating C-23 virus that killed many. This caused the Humans to blame the Advanced Cultivars, an advanced breed of Human specifically designed to survive on the planet. (Episode 2) They also seem to have decreased fertility within the population on Carpathia. (Episode 6)
In Episode 7 the entity/entities tells Richard Tate their true intensions of killing all the Carpathians. When Tate comes to Rudi, leader of the ACs, for help. Rudi refuses, telling him that only his people are in danger, suggesting the Host force means the ACs no harm.