Study Reveals the Secrets of Butterfly Flight

The fluttering insects create tiny jets of air by clapping their flexible wings together, which may help them evade predators

Silver-washed fritillary butterfly
Silver-washed fritillary butterfly Per Henningson

The lilting, fluttering flight of a butterfly evokes whimsy rather than efficiency or purpose, but a new study reveals the mechanics of the insect’s less than linear flight pattern and suggests it may help them evade predators, reports Matt McGrath for BBC News.

"Butterflies look different from many other flying animals, compared to birds and bats. They have a very extreme wing shape—very large, short but very broad wings compared to their little body," Per Henningsson, a biologist at Lund University, tells Amy Woodyatt of CNN. "That is a bit of a puzzle, because that sort of wing is quite inefficient."

To tease out how the butterflies are using their inefficient wings, the researchers conducted an aerodynamic analysis of free-flying butterflies. In particular, the team wanted to find out whether butterflies “clap” their wings together in flight, as scientists hypothesized as far back as the 1970s, to generate a jet of air to propel the butterfly forwards, reports Agence France Presse.

Butterfly takes off (wind tunnel)

This week in the journal Interface the researchers report that butterflies do indeed clap their wings on the upstroke, but in an even more sophisticated manner than expected.

"When the wings go up during the upstroke, and they clap together at the end of the upstroke, we saw that they were not just two flat surfaces," Henningsson tells CNN. "Instead, they were bending, and due to their flexibility, [they were] forming a sort of pocket shape."

The researchers wondered if creating this pocket might capture more air between the wings and thus make the clap even more propulsive. To test this idea the researchers built tiny flapping gizmos with rigid or flexible wings. Per BBC News, the more pliable wings boosted the clap’s efficiency by 28 percent and the amount of force produced by 22 percent, which the authors say are massive improvements for such diminutive flyers.

Henningsson tells BBC News that butterflies may have evolved such short, broad wings to best utilize this unique clapping motion, which may in turn help butterflies evade predators by facilitating a faster takeoff.

"If you are a butterfly that is able to take off quicker than the others, that gives you an obvious advantage," Henningsson tells BBC News. "It's a strong selective pressure then, because it's a matter of life and death."

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