A swarm of small creatures existed in the Time Vortex.
When Polly prompted Ben and Jamie into trying a Ouija board in theTARDIS control room, the swarm contacted them via the board, asking if they were in a TARDIS. Polly said "yes" and asked when they were, to which they responded "VORTEX," before quickly spelling out "WE WILL DEVOUR YOU." They possessed the board and sent it wildly through the room in an effort to hurt them, but Ben managed to break it.
Afterwards, the swarm possessed Jamie through his subconscious and used him to manipulate the console controls. While Ben and Polly held him, the Second Doctor read ancient Gallifreyan while making a sign with his index and little fingers, causing the swarm to pour from Jamie's mouth and manifest in the control room before returning to the Vortex through the telepathic circuits. (PROSE: Something at the Door')