How Do Zebra Stripes Stop Biting Flies?

Horse dressed in a striped coat in order to resemble a zebra. Credit Tim Caro  UC Davis

Horse dressed in a striped coat in order to resemble a zebra. Credit Tim Caro UC Davis

The scientists filmed flies as they approached zebras and as they approached horses wearing zebra coats. While flies slowed down substantially before landing on horses, when they approached.

"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.

While horseflies circled or touched the animals at similar rates, landing was a different matter, with a lower rate seen for zebras than horses.

In 2014, researchers showed the ranges of the horsefly and tsetse fly species and the three most distinctively striped equid species (Equus burchelli, E. zebra, and E. grevyi) overlap to a remarkable degree.

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Stripes might also be visual markers for group bonding or to direct companions to particular parts of the body for grooming.

As a result, the exact cause of stripes in zebra remain unknown.

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In a similar way, human pilots can be dazzled when attempting to land into the sun.

More recent research has suggested that somehow the stripes reduce the chances of a zebra being bitten by flies.

The objective of zebra stripes has always been a mystery.

There had been 4 main hypotheses about the advantages zebras accrued by evolving stripes: camouflage to avoid large predators; a social function like individual recognition; thermoregulation, with stripes setting up convection currents along the animal's back; and thwarting biting fly attacks.

The researchers videoed horse flies as they tried to prey on captive zebras and domestic horses at a livery in North Somerset, England.

As additional protection, zebras swish their tails nearly continuously to keep flies off, the study found. The striped animals nearly continuously swish their tails during the day and will stop feeding if they feel bothered.

In contrast domestic horses chiefly twitch to flick away flies and only occasionally swish their tails. They add, "The selection pressure for striped coat patterns as a response to blood-sucking dipteran parasites is probably high in this region [Africa]", researchers wrote in the journal Experimental Biology.

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