Scientists discover secrets of fly's flight

The secret of a fly's flight has been uncovered by scientists using high-speed cameras – revealing that its frustrating ability to change direction in an eyeblink is down to subtle movements of its wings.

But the experiment also turned up a surprise when it showed that the fly's inertia, rather than any friction with the air around it, limits its ability to switch direction. Until now, it had been thought that the insect's small size meant that the air would effectively act like a liquid flowing over its body, and so changing direction would be like swimming against a current. Instead, it is more like a footballer, using its wings to change direction in an instant as a player would his feet.

The studies, published today in the journal Science, investigated flies' ability to perform "saccades" – abrupt 90-degree turns that are part of the insect's innate flying technique when it is heading towards food or avoiding an obstacle. But saccades happen extremely fast, being executed in less than 50 milliseconds. Using sets of three cameras each taking 5,000 frames per second, or five frames every millisecond, Steven Fry and Michael Dickinson at ETH in Switzerland and the California Institute of Technology discovered that the fly can change direction in the space of just 10 wing beats, each lasting 5 milliseconds.

The change was achieved by "quite minor" changes in the shape of the wing – and the fly was achieving the change principally by altering the position of its body, "just as a helicopter increases thrust by pitching downward", the authors note. The discoveries, especially of the small effect that friction has, could help in the design of artificial flying "insects", the authors suggest.