Instead of another pair of wings, flies possess a small set of stabilizers, called halteres, which act like gyroscopes and give them a great degree of maneuverability. The first insect fossils date from 400 million years ago, whereas the first fly fossils are thought to be 240 million years ago. It is thought that during evolutionary history, flies turned one of their pairs of wings into the stabilizing halteres. In this beautiful colored drawing by drawing by A.J.E. Terzi, you can see the small halteres growing from the abdominal segment just behind the wings.