Quick-thinking helps flies

31 August 2008 02:30pm

Incredibly quick-thinking accounts for the maddening ability of flies to avoid being swatted, scientists have discovered.

High-speed imaging of flies in action revealed their amazing ability to plan and execute an emergency take-off in a split second.

Long before making the leap, the fly calculates the location of the threat, works out an escape plan, and positions its legs for a jump in the safest direction.

All this occurs within 200 milliseconds from the time the fly first spots the looming swatter.

In the US experiments, reported in the journal Current Biology, a 14-centimetre black disc took the place of the traditional flexible fly-swat or rolled up newspaper.

Scientists dropped the disc onto fruit flies standing on a small platform and filmed what happened.

They found that if the disc approached from in front of the fly, the insect 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, from the California Institute of Technology in Pasadena, said: "We were surprised to find that 'long' - in fly time - before a fly takes off in response to a predator or swatter it plans the direction of the jump by making a rather complex series of postural movements. 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 very rapidly, 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."

© The Press Association