Stripes on butterfly wings may disorient predators — TimesLIVE

Researchers have found that contrasting stripes on butterfly wings, combined with wing movements, can create a visual illusion that makes it harder for predators to judge the insect’s speed and direction of flight. One of the study’s leaders, Professor Jolyon Troscianko of the University of Exeter in England, United Kingdom, explained the findings published in the journal Nature. The study was reported by TimesLIVE.

Movement illusion during flight

According to Troscianko, wing patterns combined with flapping can create a false signal about the butterfly’s direction of movement. During flight, the wings not only close and open but also move forwards and backwards along a figure-eight-like trajectory.

A stripe on the forewings during a downward flap may appear to shift slowly downward. By contrast, as the wing moves upward, it quickly disappears and returns in the direction of flight. As a result, the downward movement becomes more visually noticeable to a predator, although the butterfly is actually flying upward.

Experiments with virtual butterflies

To test the hypothesis, scientists combined high-speed filming of real butterflies, computer modelling, evolutionary process simulations and touchscreen experiments. The tests involved 100 volunteers, who made 3,000 attempts to catch virtual butterflies by touching the screen after watching videos.

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Participants directed their taps farther behind butterflies whose patterns were predicted by the models to cause stronger visual disorientation. Troscianko noted that stripes particularly strongly affect visual mechanisms for perceiving movement. As an example, he cited the “barber pole” illusion, in which stripes moving sideways may appear to move upward or downward.

Limitations of the study

The authors examined only bird vision. They suggest that a similar effect could potentially occur for predatory insects, including dragonflies and robber flies, but their vision works much faster, so the illusion may be less effective for them. According to Troscianko, butterflies with predominantly brown or red colouring usually cause the least visual confusion: such species may rely more on camouflage or warning colours.

The scientists also believe that their models of visual motion perception could find practical applications, including improving aviation and combat simulators, as well as developing patterns for moving objects that become visual targets.