How the Zebra got its stripes
Stripes are easily a zebra’s most recognisable feature, and each zebra has an individual pattern like a natural barcode—but what purpose do the stripes serve? Hypotheses include camouflage, confusing predators, allowing zebras to distinguish and recognise others…but now a team of Hungarian researchers propose that they may have evolved to deter bloodsucking insects, especially the voracious, disease-carrying horseflies, or tabanids. Like many insects, horseflies are instinctively attracted to horizontally polarized light (polarization being the orientation of the vibration pattern of light) because it’s a telltale sign of light reflecting off water, which is where they mate and lay eggs. But interestingly, females horseflies also use linearly polarized light to find animal hides to feed on. Research had previously proven that dark-coated horses attract more horseflies than white ones as a result of light reflection, and since zebras are completely black as early embryos and only develop white stripes closer to birth, the researchers hypothesised that the stripes existed to disrupt their dark coats and deter horseflies. They then tested sample hides of different black and white patterns, varying the width, density and angle in order to change polarisation. The results show that striped patterns attract the least amount of flies, and as the stripes become narrower, the number of flies decreases even further. “Zebras have evolved a coat pattern in which the stripes are narrow enough to ensure minimum attractiveness to tabanid flies,” the team concludes, because the dark and light stripes each reflect different polarizations of light.