Flies get a jump on swatters, study finds

Ever wonder why it is so hard to swat flies?

It’s because they don’t just fly away from impending doom. They first jump in a direction that takes them away from the swatter, said Caltech bioengineer Michael Dickinson.

The neurochemistry of the fruit fly’s jump response has been thoroughly studied. So-called giant neurons in the insect’s brain, the biggest in the fly, sense the shadow of an approaching object and fire, propelling the fly into flight. Researchers had thought that was all there was to it.

But Dickinson and graduate student Gwyneth Card took high-speed digital movies of fruit flies as a black disk dropped toward them.

They reported Thursday in the journal Current Biology that, about 200 milliseconds before impact, the fly’s tiny brain calculates the location of the threat, then maneuvers its legs into the optimum position to jump out of the way.

If the threat is coming from the front, the fly moves its middle legs forward and leans back, then jumps backward. If the threat is from the back, it moves its middle legs backward and jumps forward. If the threat is coming from the side, it leans its body to the other side before jumping.

“It’s like a gymnastics maneuver,” Dickinson said. “It kicks into the air with its legs, then the wings take over.”

When Card and Dickinson removed the insects’ middle legs, which provide jumping power, the insect still leaned in the direction it needed to go before lifting off with only its wings. If they removed the wings, the flies could still jump out of the way of the threat.

As for practical applications, Dickinson said fly swatters should lead the fly like a trap shooter, anticipating the jump. The knowledge of how they launch could also help the many labs trying to build robot insects.

 thomas.maugh@latimes.com