The fact that butterflies can fly has baffled scientists for years. Relatively speaking, their wings are short, broad and extremely large compared to their body size, and the proportions don't quite seem to add up (physics-wise) to enable flight. In theory these proportions should make the butterfly's wings inefficient. But lest we doubt Mother Nature, it turns out their wings have evolved perfectly for their use. And thanks to a recent study conducted by researchers at Lund University in Switzerland, now we know exactly how they work.
Turns out butterflies don’t actually flutter their wings. In the early 1970's, Danish zoologist Torkel Weis-Fogh published his findings on insect flight and what he dubbed a clap-and-fling mechanism. The method of lift generation was first observed in parasitic wasps and it was believed, but never thoroughly observed, that butterflies employed a similar technique. The scientists at Lund University set out to revisit this theory and apply quantitative measurements of aerodynamics to test the hypothesis in butterflies.
To perform the analysis, scientists captured free-flying butterflies (now we're imagining scientists in lab coats running through a field with butterfly nets) and created two mechanical clappers to simulate different scenarios - one was fashioned with rigid wings and the second with flexible ones. They discovered that the clap wasn't your typical round of applause. When butterflies perform an upstroke motion with their wings, it pushes out trapped air and creates a sort of jet, which propels the butterfly in the opposite direction. The study also found that the wings are more flexible and bendy than originally thought. When performing this upstroke motion, the tips of the wings curve together and touch in a clap-like movement forming a cup shape. Coupled with the wing's flexibility, this cup shape enables the butterfly to trap and push out air more rapidly, explaining their ability to take off quickly. The opposite downstroke movement helps support the creature’s weight during flight.
Testing this observation with the two clappers, the researchers found that the one with the flexible wings increased the efficiency of "the clap" by 28% compared to the one with rigid wings. The unique combination of the clap movement and their wings' flexibility makes butterflies extremely efficient flyers, able to take off rapidly and avoid predators in the process. Turns out, butterfly wings have evolved perfectly for their purpose!
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Image by Vincent van Zalinge