Secret of bees' flight revealed
Ian Sample, science correspondent
Tuesday November 29, 2005
The Guardian
The flight of the humble bee was once so baffling that mathematicians famously concluded it was impossible. But using high-speed cameras and a scale model robot scientists have at last worked out the secret that helps bees stay aloft.
Most flying insects flap their wings using long, sweeping strokes, but honeybees take a less efficient approach. Even though it is a less stable way to fly, honeybees flap their wings more furiously and with a shorter stroke than other insects, producing just enough force to lift their bodies. The scientists believe bees developed the unusual style to cope with the varying demands they face during flight. When foraging for nectar, they are at their lightest, but when laden with pollen, or carrying larvae, they can weigh twice as much. By switching from rapid, short wingbeats to longer beats, bees can vary their lifting power considerably.
The scientists unravelled the bees' flying tactics by diverting them into a clear plastic box fitted with three high-speed video cameras which took 3D snapshots of the hovering insects 6,000 times a second. They found that a honeybee typically flaps its one-centimetre-long wings 240 times a second, each beat covering an arc of only 90 degrees. Other insects flap at no more than 200 times a second, with each stroke beating over a 165-degree arc. Using a scale model winged robot, the scientists measured how the different wingbeats produce lift. Instead of producing a steady, powerful upward thrust, the bees' flying style generates peaks of lift at the beginning, middle and end of each beat.
To test the bees the researchers, led by Michael Dickinson at the California Institute of Technology, pumped a mixture of helium and oxygen into the box, making the air as thin as at 9,200 metres above sea level. The bees responded by opening out their stroke to around 140 degrees, in effect switching their flight behaviour to that used by other insects, they report in the journal Proceedings of the National Academy of Sciences today.
