March 18, 2015

Fruit flies correct midair rolls in milliseconds

Researchers who study fruit flies to gain insight into in-flight stabilization have uncovered a particular detail on how these insects right themselves during a midair roll.

Postdoctoral fellow Tsevi Beatus, working with Itai Cohen, associate professor of physics, and John Guckenheimer, professor of mathematics, have discovered that flies stabilize themselves during flight using a control reflex that’s among the fastest in the animal kingdom. Their results were published March 11 in Royal Society Interface.

Flapping flight inherently is unstable, and insects must constantly be correcting these instabilities, including the in-flight roll, or rotation along the long body axis. Without a control mechanism for this movement, the insect would roll over and crash within just a few wing beats, the researchers say.

Tsevi Beatus/Itai Cohen
A fruit fly does a roll and correction. The three sides of the 3-D box show movies from high-speed cameras, and the 3D-rendered fly represents kinematic data of the body and wing positions in each frame. The movie is played three times to show the same maneuver from different views.

Their study involved gluing microscopic magnets to the backs of the flies. Magnetic pulses caused them to “trip” in midair, and a high-speed camera recorded how they recover using their wings.

They found that the flies managed to correct for large perturbations that roll them up to 100 degrees within 30 milliseconds; in the blink of an eye, the fly can perform this entire correction maneuver 10 times. The flies start to respond to the perturbation within 5 milliseconds – making this correction reflex among the fastest found in the scientific study of animals.

They make the corrections by flapping one wing harder than the other for between two and five wing beats, and the resulting force imbalance leads to corrective torque. In the paper, the researchers quantified this asymmetric wing motion using a controller model, called a proportional integral controller, that’s mathematically similar to those used in cruise control systems.

Finally, the researchers also tried to challenge the flies by sending them a series of pulses and rolling them over eight full turns. Still, the fruit flies managed to recover quickly, within just a few wing beats.

“We have not yet managed to find a perturbation from which flies cannot recover,” Beatus said. “Although these tiny insects are common and are often a nuisance, we now have a greater appreciation for what amazing fliers they are.”

The paper is called “Controlling Roll Perturbations in Fruit Flies,” and the work was supported by the Cross Disciplinary Postdoctoral Fellowship of the Human Frontier Science Program; a National Science Foundation Chemical, Bioengineering, Environmental and Transport Systems grant; and the Army Research Office.