Quick-thinking flies are one jump ahead of the swatter

Astonishingly quick thinking accounts for the ability of flies to avoid being swatted, scientists have discovered. High-speed imaging has revealed an ability to execute an emergency takeoff in a split second.

Within 200 milliseconds of spotting the looming swatter, the fly calculates the location of the threat and positions its legs for a jump in the safest direction.

In the US experiments, reported in the journal Current Biology, a 14cm (5.5in) black disc took the place of the traditional swatter or rolled-up newspaper. Scientists dropped the disc on to fruit flies standing on a platform and filmed what happened.



They found that if the disc approached from in front, the fly moved its middle legs forward and leaned back. It then raised and extended its legs to push off backwards. When the threat came from behind, the fly moved its middle legs slightly backwards before leaping forwards. Danger from one side caused the insect to keep its middle legs stationary, lean its whole body in the opposite direction, and then jump.

Professor Michael Dickinson, of the California Institute of Technology in Pasadena, said: "Those movements carefully position the fly's centre of mass relative to the jumping legs so that leg extension propels them away from the looming threat. These movements are made within about 200 milliseconds, but within that time the animal determines where the threat is coming from and activates an appropriate set of movements to position its legs and wings.

"This illustrates how rapidly the fly's brain can process sensory information into an appropriate motor response."