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Mystery of Zebra Stripes Unraveled

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When it comes to nasty bites of insects, the black and white striped zebra seems the lucky one. New research shows that bloodsucking flies are less attracted to the striped coat of the zebra, than they are to the solid white or black coats of horses.

Horseflies are attracted to polarized light. It resembles light reflected off water, where they lay their eggs. In a previous study, it became clear that since white does not reflect polarized light, black horses attract more horseflies than white ones. The researchers therefore assumed that zebra coats, with their mixtures of light and dark stripes, would be less attractive to flies than those of black horses but more than those of white horses.

To test their theory, the researchers traveled to a horsefly-infested horse farm in Hungary, where they tested the insects’ attraction to gluey boards with different types of black and white patterns. The team found that the striped board which most resembled the coat of the zebra attracted by far the fewest flies, even less than the white board. The team then measured the number of horseflies on sticky 3D model horses of different colors and patterns, and found again that a striped coat functions as the best fly repellent.

‘We conclude that zebras have evolved a coat pattern in which the stripes are narrow enough to ensure minimum attractiveness to tabanid flies’, says the team and they add, ‘The selection pressure for striped coat patterns as a response to blood-sucking dipteran parasites is probably high in this region [Africa]’.

Source: National Geographic, New York Times

Egri, A., Blaho, M., Kriska, G., Farkas, R., Gyurkovszky, M., Akesson, S., & Horvath, G. (2012). Polarotactic tabanids find striped patterns with brightness and/or polarization modulation least attractive: an advantage of zebra stripes Journal of Experimental Biology, 215 (5), 736-745 DOI: 10.1242/jeb.065540

Photo: Wikimedia Commons

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