Why do zebras have stripes? To keep the flies off, say scientists

Scientists have discovered that zebras have stripes in order to ward off blood-sucking flies, who get dazzled by their colours and have trouble landing.

The animals’ distinctive coats help them keep off the insects that try to feast on them and carry deadly diseases.

Researchers put striped coats on horses to see how many insects landed on them and compared the results with horses covered in plain, single-coloured coats.

They filmed the horse flies as they tried to prey on captive zebras and horses kept on a domestic farm in Somerset, and found that the insects approached the animals at similar rates.

But once they began to circle them, the flies managed to land on zebras less than a quarter as often as they did on the horses.

Tim Caro, lead author of the report which was published in the journal PLOS ONE, said on approach, the flies “fail to decelerate properly, and so fly past them or literally bump into them [zebras] and bounce off”.

University of Bristol biologist and study co-author Martin How, said stripes may dazzle flies once they get close enough to see them with their low-resolution eyes – much like how pilots can become dazzled by the sun.

“In addition to stripes that prevent controlled landings by horse flies, zebras are constantly swishing their tail and may run off if horse flies do land successfully, so they are also using behavioural means to prevent flies probing for blood,” Mr Caro said.

Among the other theories about why zebras are striped are that the stripes provide camouflage to avoid large predators or that they have a social function like individual recognition.

It was also speculated that the stripes aid body warmth by setting up convection currents along the animal’s back.

But the one that is most feasible is the theory that they thwart fly attacks.

“Most biologists involved with research on mammal coloration accept that this is the reason that zebras have stripes,” Mr Caro added.

Zebras are highly susceptible to a variety of fatal diseases, including trypanosomiasis, African horse sickness, and equine influenza, that are spread by horseflies and tsetse flies.

Their short-haired coats also make them very vulnerable to insect attacks, as flies can more easily find blood vessels with their piercing mouthparts.

Close cousins to horses and donkeys, the world’s three zebra species, known for their black-and-white striped bodies, roam Africa’s savannas eating a variety of grasses.

Their stripe patterns vary among individuals, with no two alike.

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