Many think that butterflies fly as if they are “drunk”, but the truth is that butterflies’ flight is studied well by them. According to Science Mag, butterflies soar by using big wings and slow wing-beats, about 10 beats per second, compared with about 200 in honey bees.
A new model shows how they control this jerky, erratic flight: good posture and a bit of waggle. Research on butterfly flight has been limited to studying tethered butterflies in wind tunnels, or simulations focusing only on horizontal motion. In the new study, researchers took high-speed videos of orange oak-leaf butterflies free-flying in the lab, and then simulated their unruly flight patterns, along with the intricate air currents they produce.
The team found that a body posture perpendicular to the ground helps the insects fly upward, especially when combined with a large rotation of their body timed with each flap of their wings. By toning down this waggle or the angle of their body, butterflies can move forward instead of upward, according to a study to be published in Physical Review Letters E. The researchers say that butterfly flight would make a good model for developing tiny flying vehicles that could be used for surveillance and rescue operations. Frenzied fliers like bees are hard to mimic, but a butterfly’s slower, waggling flight might be more manageable for the rescue robots of the future.
So, butterflies are master flight manipulators. Their erratic bobbing and weaving has a purpose.
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”.
