In a crisis, fruit flies do stunt turns

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With a brain the size of a salt grain, a fruit fly can do Top Gun maneuvers in about one-fiftieth of the time it takes to blink a human eye.

That a fruit fly manages to do fighter-jet banked turns in midair contradicts some earlier ideas about how tiny insects maneuver, says Michael Dickinson of the University of Washington in Seattle. Other researchers had suggested that turning flies “use their wings almost like paddles to sort of row themselves around,” he says. Yet an elaborate fly-filming arena he and his students created reveals deft and quick banking, they report in the April 11 Science.

The Drosophila hydei fruit flies that Dickinson’s lab studies have neither a lot of mental processing power nor fancy muscles for flying. But being able to do sophisticated moves with minimal equipment only makes them more interesting. “We don’t really understand miniaturization,” Dickinson says. But “insects do small very well.”

To film fruit fly flight required years of refining a 3-D video monitoring setup. Filming them at high speed means each exposure lasts only one thirty-thousandth of a second and needs brilliant light. Powerful illumination in the visible spectrum would blind the flies and end meaningful behavior, so Dickinson and his colleagues used infrared cameras, with wavelengths flies can’t see. The cameras require so much lighting that the setup has to include its own refrigerator to prevent overheating.

To startle the fruit flies into making their most panicky moves, a lab version of a stadium Jumbotron shows a shape looming at the fly from various directions. Then came the computing challenges. “You have just ridiculous amounts of data because you’re capturing images at 7,500 frames per second,” Dickinson says.

What the cameras showed were emergency turns much faster than the ones that flies make when no menace appears. Also, an alarmed fly doesn’t reorient in the same plane like a rowboat turning on a lake surface. Instead, the fly abruptly rolls its whole body to one side like a plane, raising one wing as it banks. The fly then rolls back and zooms off in its new direction.

Researchers would not have been surprised if a life-or-death escape turn prompted a fly to make drastic and not necessarily economical adjustments, like ceasing to flap with one wing. But Dickinson says, “When you look at what they’re doing with their wings, it’s remarkably subtle.” Wing-motion shifts, some barely detectable, are very precise. “It’s like someone playing the violin,” he says.

Yet those barely detectable shifts work. The researchers mimicked the effects with an oversized robotic fly flapping in a container holding several metric tons of mineral oil.

“Exciting work,” says Robert Wood of Harvard University, whose lab has developed beelike robots. The fly paper’s information on the speed and motions of the extreme turns will be “quite useful,” he says, for helping design fliers inspired by nature.

FLIGHT OF THE FLY  Filming flies at 7,500 frames a second, scientists found that the insects bank and turn quickly to escape danger. Credit: Florian Muijres, Dickinson Lab, University of Washington; produced by Ashley Yeager