"Why do Zebras have stripes?" is about as classic a childhood question as "Why is the sky blue?"...as fly repellant sounds v. interesting - but of course correlation does not equal causation, so I look forward to studies that test this idea...I just hope they don't involve being stuck in a cage with a bunch of biting flies!
Tim Caro of the University of California, Davis, has puzzled over contrasting colouration in mammals before. Now, in a new study published in Nature Communications this week, he and his colleagues have focused their attention on the zebra. They take a completely original approach, stepping back from one species of zebra and attempting to account for the differences in patterning across different species and subspecies of zebras, horses and asses. Is there anything about the habitat or ecology of these different equids that hints at the function of stripes? “I was amazed by our results,” says Caro. “Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies.” Where there are tsetse flies, for instance, the equids tend to come in stripes. Where there aren't, they don't. The idea that flies don’t like stripes dates back at least to 1930. Since then, there have been several studies that have provided experimental support, with flies preferring to alight on all-black or all-white surfaces rather than on stripes. The authors also stress the burden of blood sucking insects: both tsetse flies and horseflies are the vectors for significant and often-fatal diseases in horses; they are probably also capable of draining a significant amount of blood (several hundred millilitres in a day, apparently).