At breakneck speed, a fruit fly veers off course and rolls into a precise bank. As the fly dips and dives around a miniature arena inside a laboratory in Seattle, three high-speed cameras shooting at 7500 frames per second capture its every twist and turn.

Michael Dickinson, biologist and fruit fly expert at the University of Washington, has spent years studying insect flight, and converting static images into dynamic models. "I'm obsessed with flies and how they work," he says.

Now, Dickinson and his team have revealed the physics behind how a fruit fly escapes from threats, be they predators or rolled-up newspapers. His work, published in today in Science, shows that flies escape danger with a specific sequence of rapid wing beats and sharp turns. And soon, engineers may use Dickinson's basic research to build smarter, smaller flying robots.

"The results were very exhilarating," Dickinson says. "We found that flies indeed use visual information to generate evasive maneuvers, and perform very rapid, banked turns away from the threat."

The Neuroscience of Flight

Dickinson wondered how flies, despite their small brains, manage to dip and dive with such precision and speed. "I liken it to the precise motor skills that we need to play the violin or the guitar," he says. "It's quite a behavioral feat."

Dickinson and his team examined 3566 individual wing beats from 92 different fruit flies, and found that it takes only a few quick wing beats to send a fly pitching and rolling away from a threat. The flies' high-speed rotations, which far outpaced their normal flight, were especially surprising given the insects' relatively small brains and primitive musculatures.

"This means that the fly's brain and skeletal system have the ability to create extraordinarily subtle changes," Dickinson says.

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Mega Robo-Flies

Once Dickinson and his team filmed flies in flight, the next step was to figure out the physics behind their sharp turns. But seeing all the details of a tiny fruit fly in flight proved to difficult. To examine some those mechanics, like a fly's banks (angled turns), up close, Dickinson built a giant robotic fly with a two-foot wingspan. "It is certainly already known that insects generate banked turns, but we replayed those changes on a dynamically scaled robo-fly," he says.

Dickinson borrowed the principle of dynamic scaling from boat and airplane engineers, who test their prototypes by placing a scale model into a large swimming pool, which mimics the sea or the sky. "We played that trick in reverse," Dickinson says. "Instead of making an aircraft conveniently small, we made an insect conveniently large."

The team programmed this giant robotic fly to flap its wings through several metric tons of mineral oil. At that size, and in such dense liquid, the robotic fly could flap slowly but produce the same forces generated in mid-air by a tiny insect. "By playing with viscosity of the fluid, we set up a situation where the physics was identical to that of a small fly," Dickinson says.

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Microrobotics

Dickinson's research may inform the young field of microrobotics, where scientists still struggle to produce reliable, tiny robots. "People are definitely trying to build insect-sized robots," Dickinson says "I can't know whether our work will specifically be used in the future, but certainly there is a conduit of information between biologists like myself and engineers."

Robert J. Wood, a bioengineer at Harvard University who specializes in microrobotics, agrees.

"There are many fascinating aspects of this work," Wood wrote in an email. "The quantification of how rapidly these animals can turn, and the mechanism that they employ to make such rapid turns, is quite useful for thinking about bio-inspired strategies for achieving similar performance in engineered systems."

Time-lapse image of four escape maneuvers made by fruit flies. Credit: Florian Muijres

Flying Onward

Next, Dickinson hopes to study how flies respond to gusts of wind and odors, and to learn more about how sensory information is translated into deft flight maneuvers. Ultimately, he plans to dissect a fly's brain and study the specific mechanisms behind insect flight.

"It's no longer a pipe dream to be able to inspect the actual circuitry in this tiny brain, to see the hardware that the fly uses to produce these behaviors," he says.

But until then, Dickinson will continue to delve into fly brains, and learn as much as he can about what makes them tick. "Understanding how this tiny drop of neurons can work so elegantly is a huge intellectual challenge that will lead to insights in computing and robotics," he says.

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