How butterflies control their twisty-turny flight

Butterflies are master flight manipulators. Their erratic bobbing and weaving has a purpose – to shake off predators – and now scientists have worked out how they control their trajectory.

Yueh-Han John Fei and Jing-Tang Yang from the National Taiwan University took high-speed video of butterflies in flight, and developed a model relating the insect’s body pose with its flight path.

Their work, published in Physical Review E, may help develop nimble miniature drones.

Unlike most insects, butterflies don’t fly with a constant body angle – that is, they’re continually rotating and tipping their body, even if they’re travelling in the one direction.

While erratic, their flight is useful for tricking predators. So scientists have tried to model butterfly flight behaviour in a bid to apply it to drones.

But studies have been undertaken in wind tunnels with tethered insects. Fei and Yang knew that to truly unpick a butterfly’s finer flight details, they would have to observe free flight.

So they captured 14 leaf butterflies – famous for their dead-leaf-like camouflage – on their university campus in Taipei and popped them, one at a time, in a transparent chamber.

Two high-speed video cameras recorded the butterflies’ flight, and the movies were slowed and analysed.

The pair found that a butterfly’s body rotation not only affects its horizontal trajectory, but also its vertical. In other words, tilting a butterfly’s body backwards so it’s almost completely vertical can cause it to “jump” in the air with a single wing flap.

Meanwhile, moving its body around means it tends to stay out of the way of downward forces generated with each flap. This means the butterfly is able to “bounce” in the air multiple times, and quickly, without losing altitude.

Now they’ve modelled how butterflies control their flitting, the researchers write, “the inspiration of flight controlled with body motion from the flight of a butterfly might yield an alternative way to control future flight vehicles”.

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