Fruit flies could make some talented fighter pilots. Scientists who had the insects wing it through two laser beams watched the bugs make hairpin turns at blazing fast speeds, by banking in the same way that fighter jet planes do. The findings, published in the journal Science, shed light on these tiny critters’ remarkable ability to evade predators (and fly swatters).
[Updated at 5:15 p.m. PDT April 10: Tracking how these insects fly in response to a threat should help researchers understand the fruit fly's inner life, said Cornell University physicist Jane Wang, who was not involved in the research.
"The insects turn because they have some internal control circuitry, just like a pilot [who's] turning a plane," Wang said. "And by looking how the insects turn, we might be able to say what the 'pilot' is thinking."]
When trying to escape from a threat, the Drosophila hydei flies turn at a speed that’s five times faster than their normal turning speed, according to researchers from the University of Washington. Instead of turning right or left on the "yaw" axis, like a boat in the water, the flies execute banked turns, by rolling and pitching their bodies at the same time, which supercharges their turns. They can execute one of these within less than one hundredth of a second after seeing a threat, the scientists said. That’s 50 times faster than the blink of an eye.
“A lot of other people working in the field … would not have predicted the fly could rotate itself so quickly,” said study coauthor Michael Dickinson, a neurobiologist at the University of Washington in Seattle.
Dickinson and his colleagues captured 3,566 wing beats involved in 92 separate fruit fly escapes, which was no easy task. To capture such infinitesimally tiny movements, the scientists had to use high-speed cameras that took 7,500 frames per second -- that’s nearly 40 frames for each wing beat. They also needed flood the flight area with light to capture the motions in high detail -- but all that light would blind the flies, which wouldn’t be able to maneuver.
Instead, they had to use infrared light, whose wavelength is too long for human or fly eyes to pick up on. All the circuitry in those lights generated so much heat that the scientists had to run an air conditioner in the laboratory, forcing the researchers to dress warmly in already chilly Seattle weather.
There were, Dickinson said, “a whole lot of wool hats worn in the lab.”
The scientists watched the flies fly through two crossing laser beams, causing their own shadow to loom large like an impending threat. In response, the flies quickly executed their escape maneuvers, which the scientists were able to capture on camera.
The videos showed that the flies could roll to one side by 90 degrees or even more as they made these turns, almost bringing them upside down. And they could make these turns in less than two wing beats -- which is pretty remarkable, given that they typically flap their wings at 200 times per second, the scientists said.
“So it’d kind of be like a jet fighter pilot with a stick in his or her hand, only had to make a little bit of tiny change in the stick and pshooo, the plane goes off,” Dickinson said. “So we’re very interested in how the brain can control motion on such a fine scale.”
With all this high quality data, the scientists were able to pull out mathematical rules that governed the flies’ decisions on how to make a banked turn, and they then programmed them into a robotic fly that they tested in flowing mineral oil. (Because the robot was much bigger than the flies, the scientists had to adjust the viscosity of the fluid they were "flying" through so the physics would stay about the same, the scientists said.)
The next step, Dickinson said, is to understand the complex neural circuitry linked to the flight muscles that makes these daring maneuvers possible.