How Do Zebra Stripes Stop Biting Flies?

Christopher Davidson
February 23, 2019

To prove their point, the academics dressed up a domestic horse as a zebra, to show fewer flies land on them.

In Africa where zebras are native, horse flies carry unsafe debilitating diseases such as trypanosomiasis and African horse sickness which cause wasting and often death.

Researchers may have finally discovered why zebras have stripes, with new experiments showing that horse flies find it more hard to land on zebras than they do on uniformly coloured horses.

Compared to rates at which flies landed on the white coats and the black coats, hardly any landed on the striped coats.

To confirm that it was indeed coat pattern that was thwarting the flies' precision, the researchers kitted some of the horses out in three cloth jackets: one white, one black and one zebra-striped.

While horseflies circled or touched the animals at similar rates, landing was a different matter, with a lower rate seen for zebras than horses. Even Kipling would have struggled to construct a Just So story as unlikely as the discovery that the zebra evolved stripes to make flies go splat.

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School of Biological Sciences, University of BristolDr Martin How, Royal Society University Research Fellow in the School of Biological Sciences, added: "This reduced ability to land on the zebra's coat may be due to stripes disrupting the visual system of the horse flies during their final moments of approach".

Horse flies are a widespread problem for domestic animals so mitigating techniques, such as the development of anti-fly wear created to resemble zebra stripes, may, from this research, be an interesting outcome for animal health and wellbeing. While horses are more low-key about the presence of flies, merely twitching and occasionally swishing their tails to ward off the insects, zebras are far less tolerant.

As additional protection, zebras swish their tails nearly continuously to keep flies off, the study found.

"Once they get close to the zebras, however, they tend to fly past or bump into them", said Caro, a professor in his university's Department of Wildlife, Fish and Conservation Biology.

The study also showed stripes did not act as a long-range deterrent but appeared to "dazzle" the flies that got up clos. A possible explanation is zebras may be highly prone to infectious diseases carried by African biting flies, although that hypothesis requires further study.

Why do zebras have stripes? The zebra tail swishing, and at times running, means flies that land on zebras are tossed off more quickly.

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