Why do zebras have stripes?

Have scientists finally found the answer to why zebras stand out from the crowd? Maybe, but it’s not all black and white.

ZebrasLong before the pattern was turning heads on the catwalk, people were speculating about the reasons behind the zebra’s iconic black and white stripes. Charles Darwin took a crack at the monochrome mystery, theorising that the stripes were used in the selection of mates. He based this idea on the curious case of a female zebra in captivity that rejected the advances of a donkey – until, that is, the amorous fellow was painted black and white. Darwin’s contemporary, Alfred Russel Wallace considered his theory ‘poppycock’. Wallace hypothesised that the zebras striking striae might offer camouflage against predators such as lions, wild dogs and hyenas. It turns out they were both wrong.

Scientists from the University of California Davis have definitively shown why zebras have stripes, and, yes, it does have something to do with predators – really tiny ones. It turns out that certain nippers, such as tsetse flies, hate landing on striped surfaces.

The finding was reached by comparing all existing theories against one another. One theory thought that the pattern offered protection against the heat through the creation of convection currents. Another theory was based on a form of visual disorientation known as the ‘motion dazzle confusion effect’. The scientists created a map of where striped equids are located in the wild, and then compared it to information on temperature, predators, forests, population sizes and, of course, biting flies.

“Not only did we find that flies explain the striping really well, but the other hypotheses were explaining it really badly,” said Tim Caro, the leading author on the study who has been studying zebras in the wild at Katavi National Park in Tanzania for over eight years. “I wasn’t really thinking that one particular hypothesis would work better than the other, so it came as quite a surprise to me.”

But why aren’t all animals on the savannah sporting stripes? Well, zebras are less thick-skinned than their companions at the watering hole. Caro and his team compared zebra pelts against those of impala, buffalo, waterbuck and roan antelope and found the zebra to be far more susceptible to attacks from biting flies.

Like everything when it comes to science, the answer leads only to more questions. Why are flies so opposed to this particular pattern? And why are zebras so concerned with flies? Flies can spread fatal diseases like equine anaemia, influenza and sleeping sickness. “But it could be something as simple as blood loss,” said Caro. “If you’ve got hundreds and hundreds of biting flies on you, you can lose a lot of blood – almost half a litre a day.”

But before you pack your favourite black-and-white-striped blazer for your next safari, you should remember that, while they may be quite eye-catching and fashionable, stripes probably aren’t going to protect you from airborne pests. “Flies see in polarised light – which we cannot see – and the pelt of a zebra gives off a very different sort of polarised light than cloth does,” said Caro.