They can be warded off with fire and will return to the Spirit World when the Veil is closed.
In the time of the Old Religion, on Samhain Eve, the High Priestesses would gather on the Isle of the Blessed and perform a blood sacrifice to the ancient gods, tearing the Veil between the worlds. This would allow the Dorocha to enter the world of the living and the High Priestesses would gain magical energy from them.
When Morgana sacrifices her dying sister to open a split in the Veil, the Cailleach and the Dorocha come forward. The Dorocha spread throughout the land and attack villages before reaching Camelot. According to the Cailleach, Morgana's enemies will rue the day the Veil was torn. If the Dorocha were allowed to remain in the world of the living, they would have caused massive devastation.
However, the Dorocha are sent back to the Spirit World when Lancelot sacrifices himself to repair the Veil instead of Arthur (or Merlin, as he wanted to take Arthur's place) (The Darkest Hour).
|Series 4 Enemies|
|The Darkest Hour: Morgana • Morgause • The Dorocha • The Cailleach • Agravaine • Wilddeoren • Wyvern|
The Wicked Day: King Odin • Morgana • Agravaine • The Gleeman • Geldred
Aithusa: Julius Borden • King Odin
His Father's Son: Morgana • Agravaine • Queen Annis • King Caerleon • Derian
A Servant of Two Masters: Morgana • Agravaine • Fomorroh • Merlin (indirect)
The Secret Sharer: Morgana • Agravaine • Alator • Orn
Lamia: Lamia • Agravaine
Lancelot du Lac: Morgana • Lancelot (Shade) • Agravaine • Dochraid
A Herald of the New Age: Shrine Boy • Elyan (indirect)
The Hunter's Heart: Morgana • Agravaine • Helios
The Sword in the Stone: Morgana • Agravaine • Helios • Aithusa • Nathair