This is a point of debate.
Some people are firmly entrenched with the idea that Balrogs have wings and can fly.
However, this statement is preceded by the description given above that its darkness was LIKE wings. Tolkien was very particular on the use of words. It would seem that the Balrogs were running with the lava flow although not as fast. We also know that Glaurung was a Great Worm and not a dragon which could fly. Find out all about Balrogs on this page.