Balrog wings
From Tolkien Gateway
There is some debate over whether Balrogs in general, and in particular, the Balrog of Moria, were winged creatures capable of flight. This perhaps stems from somewhat ambiguous descriptions in text. The first time the Balrog's 'wings' are mentioned in the encounter at the Bridge of Khazad-dum, the word is clearly used in a figurative sense: "His enemy halted again, facing him, and the shadow about it reached out like two vast wings". Later in the encounter, however, the creature's wings seem to be physical: "It stepped forward slowly on to the bridge, and suddenly it drew itself up to a great height, and its wings were spread from wall to wall...".
Points raised against the "flying Balrogs" include a text from the Silmarillion which compares the speed of rivers of flame that Morgoth had unleashed with that of a Balrog. "Then suddenly Morgoth sent forth great rivers of flame that ran down swifter than Balrogs from Thangorodrim ..." At least at first blush, this appears to suggest that Balrogs primarily move on foot. Another point is that some of these creatures were in the service of Glaurang, a land-bound worm.
