Scientists Say Zebras Have Stripes Because They Help Deter Biting Flies

Posted on April 2, 2014

Scientists have discovered that zebra stripes help deter biting flies, such as horse flies and tsetse flies. A research team led by the University of California, Davis came up with the reason why zebras have black and white stripes after analyzing five hypotheses. Other past theories for the stripes have included camouflage, confusing carnivores, heat management and social behavior. The scientists rule out these four hypotheses.

The scientists mapped the geographic distributions of the seven different species of zebras, horses and asses. They compared these animals geographic ranges with different variables, including woodland areas, ranges of large predators, temperature, and the geographic distribution of tsetse flies and horseflies. They then examined where the striped animals and these variables overlapped. After analyzing all the hypotheses only the blood sucking flies remained.

Tim Caro, a UC Davis professor of wildlife biology and lead author of the study, says in a statement, "I was amazed by our result. 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."

The scientists note that experiments have previously shown that these types of biting flies tend to avoid black-and-white striped surfaces. It is not known why the flies avoid these surfaces. This will have to be answered in a future study. Caro says that the evolutionary debate can now move "from why zebras have stripes to what prevents biting flies from seeing striped surfaces as potential prey, and why zebras are so susceptible to biting fly annoyance."

The study, "The function of zebra stripes," was published here in Nature Communications.

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