Wing ‘clap’ solves mystery of butterfly flight

Butterfly sitting on a flower

A new study shows that butterflies evolved an effective way of cupping and clapping their wings to generate thrust that helps them avoid dangerous predators.

Researchers at Lund University in Sweden studied the aerodynamics of butterflies in a wind tunnel. During the upward stroke, the wings cup, creating an air-filled pocket between them. When the wings then collide, the air is forced out, resulting in a backward jet that propels the butterflies forward. The downward wing beat has another function: the butterflies stay in the air and do not fall to the ground.

This theory was described by researchers almost 50 years ago, but is only now being tested on real butterflies in free flight. It was commonly thought that butterfly wings were aerodynamically inefficient, however, researchers disagree. “That the wings are cupped when butterflies clap them together, makes the wing stroke much more effective. It is an elegant mechanism that is far more advanced than we imagined.”

These findings could help improve performance and flight technology in small drones.