A bird attacking a butterfly may often miss its target due to a visual illusion created by the butterfly's wings, according to new research. The study, published in the journal Nature by the University of Exeter and the University of Essex, provides evidence that the flight patterns and wing designs of butterflies create visual illusions that confuse predators about their speed and direction, leading to misdirected attacks.
This research addresses a longstanding question regarding why butterflies, which have prominent wing patterns, are not commonly preyed upon mid-flight, unlike moths that are targeted by various aerial predators. Dr. George Hancock from the University of Exeter's Centre for Ecology and Conservation stated, "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."
Dr. Hancock explained that these illusions disrupt the predator’s visual targeting system, causing them to miss their target during the critical moment of attack. Dr. Anna Hughes from the University of Essex noted that the striking patterns on butterflies' wings are essential for their survival, as they create confusing motion signals that hinder predators' ability to launch accurate attacks.
The study likens the mechanism to the 'barber-pole illusion,' where stripes appear to move in a different direction than they actually do. Dr. Jolyon Troscianko from the University of Exeter elaborated that as butterflies fly, their wings deform, altering the angle of their stripes and creating misleading motion illusions. The research team utilized high-speed cameras to capture the flight of butterflies and analyzed the patterns of around 400 European butterfly species, finding that motion illusion patterns are prevalent.
To further investigate, 100 volunteers acted as “predators” attempting to catch virtual butterflies on a touchscreen, and a computer simulation was used to evolve wing patterns that maximized motion confusion. The results indicated that these patterns closely resemble those found in nature, suggesting that the ability to create visual illusions has significantly influenced butterfly wing evolution.
Dr. Hancock remarked on the apparent paradox of butterflies evolving to be highly visible despite few being toxic, stating, "Our study reveals the wide variety of different patterns butterflies can use to create illusions that confuse predators." The research also highlights that while butterflies and moths use camouflage while resting, their vibrant colors serve a different purpose when in flight, providing an alternative defense mechanism against predation.
Dr. Troscianko added that while the dazzling stripes of zebras and snakes have been theorized to confuse predators' motion perception, this study offers new insights into motion vision analysis, suggesting that motion confusion may be more widespread in nature than previously understood. The research was funded by the Biotechnology and Biological Sciences Research Council.