Johansson and Henningsson caught six butterflies in a meadow near their lab. They placed them inside a wind tunnel. In a wind tunnel, fans blow air. The air flows around anything in the tunnel.
The scientists also added drops of oil to the air. This makes a harmless "smoke." It makes it easier
to see how the air flows around objects. The scientists then used a laser to light up the smoke.
The scientists then set up cameras in the tunnel. This allowed them to take pictures of the
butterflies taking off. This let the scientists see how they moved. The scientists made three-
dimensional (3D) pictures. They showed how the air moved as the insect flapped its wings.
The Vortex
During the experiment, the scientists watched six butterflies take off a total of 25 times. They saw
that the butterflies clapped their wings. The insects did this most often at the beginning of the
takeoff.
Then the scientists analyzed the pictures taken in the tunnel. They showed the air spinning. The
butterflies' wings created a vortex (a vortex happens when air or water spins around very quickly).
The photos also showed that the wings pushed the air
Jet propulsion
down. This created a force that pushed the butterfly
up (a force is a push or pull in a specific direction).
balloon upward
When the wings moved up to clap, they made an air
pocket. This made a strong jet of air. It shot out
behind the butterfly. That jet-propelled the insect
forward.
This is why butterflies flutter about when they fly. It
helps keep them from getting caught and eaten.
Scientists thought they knew how the clap worked
before. But Henningsson says it's "far more advanced
and sophisticated" than they realized.
Unbalanced air pushes
Air pressure equal
on all sides