Why flies evade the swatter

Few things are more irritating than the persistent drone of a fly unable to work out why it cannot fly through a window.

One thing that is more irritating is the fly's ability to evade a rolled up newspaper.

But at least scientists now believe they have discovered how the insects do it.

Biologists had long realised that flies had reaction times measured in thousandths of a second, but were unable to work out why. Now researchers at the University of Berkeley in California have discovered that scientists were looking in the wrong place.

Researchers had tried and failed to find a direct nervous system connection between the part of the brain that deals with what a fly sees and the muscles powering its wings.

The research, published in the current edition of Science magazine, says that the fly's evasive talents are located in a pair of tiny club-shaped structures by the insect's wings called halteres.

For many years, scientists had recognised them as the fly's equivalent of an aeroplane's gyroscope, keeping the insect stable in flight by stopping it from wobbling from side to side.

The university researchers have discovered nerves which directly connect the fly's brain to the halteres. The nerves are activated when the fly sees something moving in its surroundings.

They found that when the fly spots something moving, messages are fired at high speed from the brain into muscles of the millimetre-length halteres.

Now the researchers are testing their theory that those muscles relay messages to the steering muscles of the wings - saying turn right or left.