The Long-worms lived in the barren wastes of the Far North and in the Grey Mountains during the Third Age. They terrorized the Men and Dwarves that lived in the area for many hundreds of years capturing great hoards of treasure and were a blight. After the war with the Dwarves and the death of Scatha at the hands of the Éothéod lord, Fram, they had begun to wane and had apparently become extinct into latter parts of the Third Age.
Long-worms were serpent-like and may have had no legs and some may have had wings. They were silver to rich gold to deep red or even black and breathe mist and flame. They possessed the ancient power of the Black Speech.