Locust Wings Designed for Marathons

Locust wings are built for long hauls, possibly inspiring engineers to be more flexible with their designs.

A new study may inspire aeronautical engineers to be more flexible with their designs. That's because the bends and twists in locusts' flexible, flapping wings power the insects' extraordinary long-distance flights, a Sept. 18 Science paper reveals.

Even though researchers have been studying how insects and other creatures fly for a long time, "we still don't completely understand the aerodynamics and architectures of wings," comments Tom Daniel of the University of Washington in Seattle, who was not involved in the new study. The new work, Daniel says, uncovers the flight signatures of flapping, flexible wings.

The research focuses on the flight of the pestilent locust, an insect renowned for its efficient flying style. If dragonflies are like fighter jets, then locusts are like continent-spanning 747s, says Adrian Thomas of the University of Oxford, coauthor of the new study. What locusts lack in agility, they make up for in distance: the four-winged insects are built to fly hundreds of miles at a time.

Thomas and colleagues used high-speed cameras to capture the details of how wings of the locust Schistocerca gregaria deform as they flap by bending and twisting. (A similar twist with an extended human arm would start with the thumb pointed slightly up at the top of the flap, then the arm would turn so the thumb is parallel to the ground in the middle of the flap and continue down until the thumb is pointed toward the ground at the end of the downstroke, Thomas says.)

Data from the high-resolution flight images allowed the researchers to create a near-perfect mathematical model of how the flexible, twisting wings propel the insect through the air. With the model in hand, Thomas and his team could predict the shapes of the air currents around the flying locusts. Tiny packets of smoke released near a flying locust showed air swirls similar to swirls predicted by the model. "We can check whether it really works, and it does," Thomas says.

Next, the researchers tweaked their model to simulate stiffening the wings and, separately, to mimic straightening the wing's curved shape, to see how those changes affected flight efficiency. In the model, when the locusts had rigid or straight wings, flight performance suffered, the team found.

Most earlier models of insect flight relied on stiff, straight wings, overlooking the important effects of flexibility and shape, says Thomas. "Engineers like these things simple," he says. But this new study shows that wings with a little flop can actually get more air-pushing lift from each flap.

The study provides sound experimental evidence that flexible wings add to flight performance, comments Robin Wootton of the University of Exeter in England. "This is lovely work by the best team, in my view, currently working in this field," he says.

Figuring out the details of how locusts and other insects fly may help researchers design tiny robotic fliers. "There is a growing interest in the exploration of micro air vehicles," says Daniel. "Nature's designs may be useful in creating synthetic ones."