On the fly means doing something without stopping and with little or no preparation. When circumstances abruptly change and you have to deal with them, that's doing things on the fly.

It was created in the 1950s by Charles Borrelli and Roger Courtland. The original version didn't even contain the words "fly, Eagles fly." Instead, it went "fight, Eagles fight." It was first ...

For two and a half days, 11 people — including Kuhn, three park employees, and seven fly specialists — spread out through two rooms in the science center, sorting through drawers of dried flies.