Things of Middle-earth
Description:Gandalf mentions werewolves, and lists them separately from wargs:
"There are orcs and trolls, there are wargs and werewolves; and there have been and still are many Men, warriors and kings, that walk alive under the Sun, and yet are under his sway."
FotR, Book II, Ch 1, Many Meetings
What are they?
"... and Sauron brought werewolves, fell beasts inhabited by dreadful spirits that he had imprisoned in their bodies."
The Silmarillion, Ch 19, Of Beren and Lúthien
After Sauron conquered it, Tol Sirion was called "Tol-in-Gaurhoth, the Isle of Werewolves."
There are two named werewolves, both in the Silmarillion. Draugluin was killed by Huan; Carcharoth who bit off Beren's hand with the Silmaril inside, fought with Huan and both died as a result.
Contributors: Lyllyn 1.22.04