A fluttery flying technique

For decades, scientists unfairly maligned the humble butterfly as an inefficient creature. Now, with the help of a wind tunnel, scientists in Sweden are proving the opposite is true.

In the early 1970s scientists first noticed the insect claps its wings during flight. At first, the discovery seemed to help cement the creature’s reputation as a clumsy flier. But Swedish scientists on Jan. 20 published a paper in the Journal of the Royal Society Interface showing slapping its wings at the top of the upstroke helps the butterfly produce forward thrust by capturing a pocket of air and jetting it backwards. The discovery demonstrates that, far from being inefficient flyers, butterflies are fearfully and wonderfully made.

Biologists Christoffer Johansson and Per Henningsson of Sweden’s Lund University began by catching six silver-washed fritillary butterflies in a meadow near their Stensoffa, Sweden, field station. The pair of scientists hoped to use a wind tunnel to monitor how the butterflies use their flexible wings to create thrust and lift. But in order to study butterfly aerodynamics, the team needed to see the air interacting with the insects’ wings. By releasing visible gas called a tracer into the wind tunnel, the team could observe the butterflies creating vortices or even capturing pockets of air with their wing flaps. “When the wings clap together at the end of upstroke the air between the wings is pressed out, creating a jet, pushing the animal in the opposite direction,” the scientists wrote in their report.

Animals with rigid wings could achieve the same effect with a wing clap. But according to the Lund University scientists, butterflies’ flexible wings are 28 percent more efficient in creating the thrust because they can contort them into the perfect shape. The trick allows butterflies to take off faster, giving them a better chance at surviving a predator.

Henningsson even suggested that further study of the technique could “inspire improved performance and flight technology in small drones.”

This isn’t the first time scientists put butterflies in a wind tunnel to understand their flight mechanics. In 2011, a pair of University of Oxford zoologists published a paper attempting to explain how butterflies generate so much lift on each downstroke of their delicate wings. After coaxing red admiral butterflies to fly to and from synthetic flowers in a wind tunnel, the Oxford scientists reported the insects use a veritable bag of tricks to stay in the air. The red admiral butterflies created a variety of vortices and then used their own wings to capture the wake they just created.