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  • Indrima Das

How the Butter ‘flies’

We have all tried to catch a butterfly that caught our eye at least once and utterly failed. However, butterflies aren’t the strongest fliers. Instead of flying in direct paths, their large wings cause them to flutter about. Luckily that fluttery flight makes it hard for predators to catch them. Well, then how exactly do they fly out of our reach so fast? A recent study by the evolutionary ecologists, Christoffer Johansson and Per Henningsson from Sweden, tests how they use jet propulsion to make quick getaways.

Johansson and Henningsson are involved in the study of how flight has evolved in animals. They caught six butterflies in a meadow near their lab. To analyze their flight, the butterflies were placed one at a time inside a wind tunnel. The tunnel had smoke made of small, harmless droplets of oil. When an object is placed inside the tunnel, the air and smoke has to flow around it. This lets researchers test the aerodynamics of the object. During the experiment, fans were used to move the air just enough to keep smoke evenly distributed in the tunnel. Lasers were used to light up a layer of smoke in the tunnel just behind the butterfly. Four high-speed cameras were placed around the feeding station to capture the movement of the butterfly and the smoke as the butterfly was taking off. For each trial, the researchers placed a butterfly at the feeding station in the middle of the tunnel. They began recording when the butterfly took flight on its own. They analyzed a total of 25 takeoffs by the six butterflies.

The photos showed that the wings’ downstroke pushed air down and it swirled in a vortex as the wings moved. This created a force that pushed the butterfly up. When the wings moved up to clap, they made an air pocket. A strong jet of air was created behind the butterfly by the pocket between the wings and it propelled the insect forward. Thus, the butterflies rise as their wings move down and shoot forward as their wings move up. This is the physics behind the speedy takeoffs made by the butterflies.

A monarch’s daaid sitting on a flower

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