This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A bird attacking a butterfly will often find its beak snapping at thin air. According to new research, that split-second miss isn't just bad luck.
It's caused by a visual illusion from the butterfly's wings. The new study, published in the journal Nature by researchers at the University of Exeter and the University of Essex, provides the first evidence that a butterfly's flight and wing pattern work together to create powerful visual illusions. The illusions scramble a predator's sense of speed and direction, causing it to misdirect its attack.
The finding helps solve a long-standing puzzle: Butterflies have striking patterns that make them stand out, yet remarkably few predators specialize in catching them midflight. Moths, by contrast, are hunted by a wide range of visually guided aerial predators. "The stripes and spots on many butterflies' wings interfere with the way visual systems try to guess the direction and speed of moving things, boosting false motion cues while hiding the butterfly's true heading," said Dr.
George Hancock of the University of Exeter's Center for Ecology and Conservation on the Penryn Campus in Cornwall. "The illusions interfere with the predator's most basic visual targeting system and disrupt the final 'ballistic attack' in the tens of milliseconds when it commits to grabbing its prey, with no time to change course. As a result, birds and other predators will often simply miss." The underlying mechanism works much like the "barber-pole illusion"—the red-and-white striped pole outside barber shops, where the stripes appear to travel upward even though the pole is only spinning in place.
"Butterfly wings deform as they fly—clapping together on the upstroke and peeling apart on the downstroke—so their stripes shift angle and point in different directions as they flap," said Dr. Jolyon Troscianko, also of the University of Exeter. "Combined with their unpredictable flight paths, this patterning creates misleading motion illusions just like the barber-pole, causing a predator to miss entirely, or to strike a less vulnerable part of the wing, such as the hindwing or tail.
"The first slow-motion video of a butterfly I put through our bird-vision computer model was glowing with downwards motion even though the butterfly was moving up. First I checked this wasn't a coding error, that I'd swapped up and down somehow, but then it dawned on me that this would be a perfect way to confuse attacking predators." The team combined multiple lines of evidence. They used a high-speed camera to film real butterflies taking off at over 1,000 frames per second to capture how their patterns behave in flight, as seen through the eyes of a bird.
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