Naturalists have long wondered how brightly colored butterflies manage to evade the attention of birds that feed on other insects. New research from British ecologists suggests it’s not simply a matter of good luck, but rather a visual illusion created by the flapping of its wings. The study by researchers from the universities of Exeter and Essex concluded that the spots and stripes found on many butterfly wings, combined with their dancing flight, alter the predators’ sense of speed and direction. George Hancock, from the Center for Ecology and Conservation at the University of Exeter in Cornwall, said very few European butterflies were toxic or unpleasant and they were relatively easy to spot in flight, so they needed something special to keep them out of harm’s way. “Illusions interfere with the predator’s most basic visual guidance system and disrupt the final ballistic attack,” Hancock said. “As a result, birds and other predators often fail.” George Hancock of the University of Exeter says swallowtails deploy illusions to alter a predator’s sense of speed and direction. Photograph: George Hancock Jolyon Troscianko, also from the University of Exeter, said: “Butterflies’ wings deform as they fly, colliding with each other on the upward movement and peeling apart on the descent, so their stripes change angle and point in different directions as they flap their wings.” “Experts compared the mechanism to the ‘barber pole illusion’: the red and white stripes appear to travel upwards even though the pole only rotates in place. The breakthrough came when Troscianko showed a slow-motion video of a butterfly flying upwards through a ‘bird’s eye’ computer model. It appeared to indicate, mistakenly, that the butterfly was moving downwards. Troscianko said: ‘I first checked that it wasn’t a coding error, that there was swapped up and down somehow, but then I realized that this would be a perfect way to confuse attacking predators.” The team looked at hundreds of types of European butterflies and found that different patterns created different effects. Swallowtail butterflies were found to be among the best at using motion confusion. Troscianko said: “They are also thought to be the closest to ancestral butterflies, suggesting that motion confusion might have existed right around the time that butterflies evolved away from night-flying moths.” “This fits with our model showing how wing markings should deflect attacks to the sides and behind the butterfly’s vital body and inner sections of the wing.” To test how the patterns could affect attacks, 100 human volunteers acted as “predators,” trying to catch virtual butterflies on a touch screen. They struggled. The study found that the mostly white butterflies also managed to dodge the predators. The researchers believe that when They fly appear to move more quickly than they actually do because of the stark contrast they make with their surroundings, which can alter the timing of predator attacks. Troscianko said the discovery could be used to begin to explain how other animals used motion confusion. “We think it is likely to be much more widespread in nature than previously thought, from the flapping of birds’ wings to the flicking tails of lizards and fish. “It opens up a new and interesting avenue of research.”
