Scientists Study Amazing Flight of Flies

ByLee Dye

May 1, 2003 -- The ordinary fruit fly can change the direction of its flight by 90 degrees in about 50-thousandths of a second, a feat that has long puzzled scientists and bedazzled engineers who, it turns out now, were mistaken in their understanding of how Drosophila melanogaster performs that magical maneuver.

Until now, it had been thought that the fly uses air friction generated by its flapping wings to change its direction at an astonishing rate of 2000 degrees per second.

But new research shows the animal is far more sophisticated than that. It uses torque to rotate its body in the direction it wants to go and then flaps its wings furiously to speed off in the new direction.

The maneuver is analogous to a hovering helicopter that rotates from north to west, and then zips westward. Tiny critters weren't supposed to be able to do that.

"But the fly has to do this whole little ballet in about one-fifth the blink of a human eye, and the only way it's capable of doing that is with some rather spiffy neuro-circuitry," says Michael Dickinson, professor of bioengineering at the California Institute of Technology in Pasadena. Dickinson's lab, equipped with sophisticated video equipment, has caught the fly in the act, and the images show its intricate maneuvers in great detail, according to research published recently in the journal Science.

Dickinson is a leader in the field of insect flight, and his motivation for the research is pretty basic.

"Figuring out how the world works is motivation enough," he says.

Toward Tiny Flying Spies

But there's more to it than that. Scientists are increasingly looking at the world of plants and animals to solve some of our most pressing problems, and the lowly fly could play a critical role in that effort.

Dickinson is working with physicists and engineers at the University of California, Berkeley, to develop tiny robots that could fly through the air like a fly, and perform some task that might be too dangerous for humans.

Researchers at Vanderbilt University in Nashville, and other labs around the world, are plowing that same field and have actually built some robots that mimic the movements of insects. Someday, it may be possible to send these mechanical devices into a building, or onto a battlefield, to sniff out chemical or biological hazards before the first humans enter the area.

If scientists can figure out exactly how the fly works its magic, Dickinson says, they will be much closer to realizing that goal.

"For every problem, there is a model system out there that's well suited for it, and by studying animals that have to make a living by understanding complicated physics, we can gain a lot of insight," he says.

A Mighty Mini-Model of Motion

It's hard to find a better example than the fly.

"It has the fastest visual system on the planet, and the most powerful muscles on the planet," he says. "And it's all being coordinated by a brain the size of a sesame seed."

The power-to-mass ratio is great enough for the fly to master flight, "the most costly form of locomotion [in terms of energy]," Dickinson says.

No wonder his research assistant, Rosalyn Sayaman, has become so awed by flies that she says she "can't even swat them anymore."

Such a complex biological system lends itself well to Dickinson's field of research.

"I'm interested in how brains work," he says. "Flies are a very important model for understanding how brains process information, and what a brain has to do is critically dependent on the physics of the fly's motion itself."

Flight Lessons

Using three cameras, the researchers created three-dimensional images of flies inside a large free flight arena, which they dubbed the Fly-O-Rama. It had been thought that flies performed quite differently than larger flying critters, like birds.

But the videos show that a fly that wants to change its direction first accelerates, then goes into a banked turn like a bird, then accelerates again on the new course. But instead of using aerodynamic drag, like an airplane, to change its direction of flight, it somehow rotates itself through the generation of torque. And that's somewhat of a physiological achievement. Try jumping up into the air and twisting, and yet stopping the twisting motion at exactly the right moment.

"How does it [the fly] make the decision that it's turned enough, and it's now time to start counter-turning?" Dickinson asks. "It is rotating so fast that its visual system is blind during the rotation."

And it does all that within an extraordinarily short period of time.

Dickinson thinks there might be many applications for that technology, if we can just figure out how the fly does it. Those little pests might be able to teach us a lot, and many scientists have picked up on that theme.

"There's an old principle in physiology," Dickinson says. "If you want to understand something, study an animal that does it really well."

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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