The Scourge are a race of telepathic beings which inhabit an octodimensional realm and feed on the emotions of fear, angst and despair generated by the Human mind. They usually manifest themselves in the form of large blue insectoid creatures, whose minds are all interconnected. The symbol of the pentagram seems to facilitate their transition into our own realm.
The Scourge have existed since the dawn of humanity, having preyed on Australopithecus and its descendants. They are nearly always unseen: nothing more than a strange presence that inhabits the mind in a subconscious level. While they usually behave as parasites - both stimulating and feeding off the host's negative emotions - they are also able to overtake their victims' minds and even physically possess them and transform them into Scourge if they wish.
To what extent the Scourge are a physical species is not known, as they have also claimed to be a manifestation of fear. It is possible that the emotions of fear and despair are nothing else but the way the Human mind interprets and reacts to the presence of the Scourge.
- Doctor Who audio stories - The Shadow of the Scourge (2000)
- They (perhaps along with the Dæmons and the Beast) are the main source behind demon legends in the Doctor Who universe.
- Curiously, the Scourge apparently need or prefer to have signed surrender papers before invading another dimension. This is likely based on the folkloric notion that demonic entities are not able to enter a home unless invited.