Butterflies are master illusionists, and this is what helps them survive

Butterflies confuse predators using the elaborate patterns on their wings. When they move forward, they appear to be moving backwards. Scientists said that this is why they are hard to prey on, as the birds often miss the target.

Scientists have figured out why butterflies, despite being one of the most eye-catching creatures, do not fall prey to predators as much. Researchers from the universities of Exeter and Essex have found that the patterns on their wings serve a crucial purpose. They throw predators off course by creating an optical illusion. This causes the predator to misjudge the butterfly's speed and direction.

The study published in the journal Nature described exactly how this happens. The patterns on the wings create an illusion by appearing to move in a different direction than the butterfly. So when the insect moves forward, a white bar would seem to be moving backwards, generating the wrong visual signal for the predator. The wings twist and fold during the upstroke and are invisible, minimising the amount of forward movement that is visible.

"The stripes and spots on many butterflies' wings interfere with the way visual systems try to guess the direction and speed of moving things," Dr George Hancock, of Exeter's centre for ecology and conservation, said.

The complex movement of the insect's wings adds to the illusion. During the deliberate downstroke, the wings unfold and flex, and in doing so, flash bold colour patterns, and the movement masks the insect's actual flight path. The upstroke is even faster. The twisting and folding wings hide and blur the high contrast bands.

For the study, the researchers created a simulation of how the butterflies would appear to the birds. Dr Jolyon Troscianko said that he watched one butterfly in slow motion through bird vision. The winged insect appeared "glowing with downwards motion even though the butterfly was moving up".

At first it appeared to be a coding error in the computer model. However, he later realised that this is exactly how the butterflies confuse the predators. They tested it through human "predators" who were asked to catch butterflies on a touchscreen. Some of the butterflies used "false motion signals", and these were the ones the participants found hardest to hit. They regularly struck behind the butterfly, something that would be expected if its speed is misjudged.

The researchers also identified the wing patterns that created the most confusion. A total of 57,600 artificial wing patterns to "evolved" inside the computer, and the one that emerged as the clear winner resembled the actual patterns seen on butterflies.