Now experts have discovered that the insects “clap” their wings together – and that their wings are perfectly developed for better propulsion.
Biologists from the Swedish University of Lund wanted to test a 50-year-old theory that butterflies ‘flap’ their wings and push out the trapped air to create a beam and push the animal in the opposite direction.
“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 small body,” said Per Henningsson, associate professor of biology at the University of Technology. University of Lund. told CNN. “That’s a bit of a puzzle, because that type of wing is quite inefficient.”
The biologists studied free-flying butterflies, and in their aerodynamic analysis they found that the creatures’ wings acquired a cup-shaped shape during the upstroke and ‘clap’, pushing the butterfly forward. Meanwhile, the downstroke helps support the weight.
They also noticed that the butterfly wings behaved in an unusual way – instead of slamming together, like two flat surfaces, the wings bent to create a “pocket shape” that would capture more air and improve propulsion.
“When the wings go up on the upstroke and they clap together at the end of the upstroke, we saw that they weren’t just two flat planes,” explained Henningsson.
“Instead, they bowed, and because of their flexibility, they formed a sort of bag shape,” he said, adding that the team thought that the butterflies caught more air between their wings in the process, adding flapping and improving performance.
The team tested their theory using a series of triangular robotic flaps and found that flexible wings the efficiency of the blow by 28% compared to rigid wings
Experts think the creatures evolved to favor this unusual wing shape to avoid predators.
“This flexibility may be one of the reasons why they have this unusual wing shape,” said Henningsson. “Butterflies take off very quickly – they do this as a safety measure, to minimize the risk of getting caught,” he explained.
The research was published Wednesday in the journal Interface.