In the beginning of chapter six of J.R.R. Tolkien's The Hobbit, Bilbo Baggins, a hobbit, manages to escape the goblins and rejoins the rest of his traveling companions. They are surprised but overjoyed to learn that he made it through the mountain, and he tells them all about it (except for his using the ring to make himself invisible).
Gandalf knows the group cannot travel as fast as their enemies, now that they are on foot, so he hurries the group along. At nightfall, the group nears some woods and prepares to settle in for the night--until they hear some evil growling. The growling belongs to a pack of wolves called Wargs. Since the Wargs cannot climb trees, the group all quickly hoist themselves into trees; however, Bilbo is unable to climb.
Poor little Bilbo was very nearly left behind again! He just managed to catch hold of Dori's legs, as Dori was borne off last of all; and they went together above the tumult and the burning, Bilbo swinging in the air with his arms nearly breaking.
The Wargs below them are large, demonic wolf-like creatures who are allied with the goblins and can be ridden like horses; when they discover Bilbo and the others, the Wargs immediately report their location to the goblins. Gandalf knows from experience that the Wargs will never let their prey go, so he uses his magic to light pine cones on fire and then throws them at the Wargs. Several of the creatures' fur is on fire, and the chief's nose is singed. When the goblins arrive they cruelly laugh at the Wargs' misfortunes before lighting fires which will burn down the trees. A dramatic rescue involving an eagle follows shortly thereafter.
The goblins and the Wargs are infuriated by this and follow the band for a bit, but soon they stop their search. The Wargs appear again in the novel, ridden by Orcs into the Battle of Five Armies.
While Tolkien does not spend much time describing the Wargs, Gandolf gives us a clue about them when he refers to them as "ngaurhoth," which can be translated "werewolves."