The whimsical, wafting flight of butterflies may not give the impression of top aerodynamic performance, but research published on Wednesday suggests their large flexible wings could be perfectly designed to give them a burst of jet propulsion. 

Scientists at Lund University in Sweden set out to verify a decades-old theory that insects "clap" their wings together, squeezing out the air between with such force that it thrusts them forward. 

Some of the UK's most beautiful butterflies in flight and taking off from flowers. Photo: VCG

In their aerodynamic analysis of free-flying butterflies published in the journal Interface, they showed that the clap function does generate a jet of air propulsion. But they also found that the butterflies perform this move "in a far more advanced way than we ever realized," said coauthor Per Henningsson, a professor in the department of biology at Lund University.   

At the moment the wings beat together they "were not just two flat surfaces slamming together," he told AFP.

Instead, they form a "pocket" shape believed to trap more air. When the researchers recreated this using mechanical wings, they found that those with butterfly-like flexibility that form this pocket at the moment of impact were 22 percent more effective in the amount of force created and 28 percent more efficient in the amount of energy used compared with rigid wings.