Vortex Wraiths were chaotic, quasi-biological life forms indigenous to the Time Vortex. According to River Song, they clustered around disastrous events, "making things worse". (AUDIO: R&J)
The Time Lords built defences into their TARDISes to prevent the Wraiths from noticing them. (PROSE: The Slow Empire)
After Gallifrey was destroyed, the Wraiths were forced to evacuate the Time Vortex due to the Council of Eight. (PROSE: Anachrophobia)
The transference network of the Slow Empire once allowed a group of Wraiths to penetrate the Doctor's TARDIS. (PROSE: The Slow Empire)
A group of Vortex Wraiths once gathered in 1941 London. They kept the air raid sirens from sounding, and fed off the resulting "bonus" deaths. River Song, accompanied by Jack Harkness, spared the humans by striking a deal with the creatures. (AUDIO: R&J)