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Interviewees: Michael Dickinson and Gwyneth Card, Caltech
Even if you’re missing the warm days of summer, you probably don’t miss those swarms of flies that are annoyingly hard to swat. Caltech’s Michael Dickinson and his graduate student Gwyneth Card have finally found the secret to why flies are so good at evading swatters.
“As soon the fly sees the swatter falling towards it doesn’t just jump into the air,” explains Dickinson. “It actually sort of, rather coolly, over the next one-hundred-thousandths of a second, moves its leg and reorients its body in preparation for the jump.”
The Dickinson lab, one of the top fly research labs in the world, was uniquely qualified to investigate this problem. They’ve devised a number of sophisticated instruments for studying fly flight behavior, including a fly flight simulator game.
But none of their discoveries so far has been as pressing to the public as the issue of how to nail a pesky picnic-spoiler. Prior to this research, Dickinson and other scientists thought flies’ escape response was a simple reflex. To study fruit fly escape, Dickinson created an elaborate fly swatting apparatus hooked up to a high-speed video camera and a high-powered microscope. One by one, the flies are put into a dark tunnel and then lured to the end with a light. When they exit the tunnel, the flies find themselves on a platform, a prism, designed so that their movements can be studied from different angles. The "swatter" is a simple disc that drops along a rod towards the fly and triggers the camera to turn on. Fly fans may be gratified to know that the apparatus stops short of striking any blows.
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In real time, a fly’s response looks instantaneous. But when Dickinson and Card studied it in slow motion, they found that a fly uses most of the time to carefully reposition its legs and body. Then, at the last possible moment, the fly jumps in the opposite direction of the swatter. And I mean LAST possible moment! The time it takes from the start of the swatter’s descent to the fly jump off is only about 288 milliseconds. The fly uses 287 of those 288 milliseconds to plan its movements and, at the very last millisecond, it jumps off the platform.
Dickinson says that of the six legs, the middle two called the “jump legs” are the most critical for the precision takeoff.
“For example, when the fly needs to jump backwards because the swatter’s coming from the front it puts its jump legs forward so that when they extend they’ll push the body backwards,” says Dickinson.
Dickinson adds that if the swatter comes from the side, the movement is mediated by the jump legs, but also, in part, by the moving of the whole body. He points out that the motor planning is distributed across all six legs, a sophisticated behavior.
“They have tiny brains but they can do extraordinary things with those brains,” says Dickinson. He adds, “Most flies have a roughly panoramic field of vision so they can see nearly as well behind them as they can in front of them, and that’s one of the ways they’re so good at evading predators and fly swatters.”
So is he going to build a better fly swatter? Dickinson smiles and says that he’s really interested in how brains work, but adds that his results suggest that swatter design is not the problem. He suggests people should, instead, use the swatter more effectively by aiming for where the fly is going to jump in response to the swatter, not where it is at the beginning of the swing. So there you have it—the science of swatting flies.
This research was published in Current Biology, August 28, 2008, and funded by the National Institutes of Health and the Nation Science Foundation
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