Why Zebras Have Stripes: Flies New theory says horseflies hate them By John Johnson, Newser Staff Posted Feb 9, 2012 2:12 PM CST 9 comments Comments Zebras stand in the shade at the Dusit Zoo in Bangkok, Thailand. (AP Photo/Sakchai Lalit) (Newser) – A new theory offers a simple explanation on why zebras have stripes: Horseflies hate them. Researchers discovered that the flies will go after an all-black animal or an all-white animal more than a striped one, reports LiveScience. What's more, the zebra's narrow, vertical stripes seem tailor-made to ward off the pests. (The researchers have some important-sounding rationale involving "horizontally polarized light" to back up their theory.) "We believe that escaping biting flies, which are annoying to their hosts and transmit lethal diseases, would be a very important selection factor, which may have a much stronger effect than the benefits of striped coat patterns suggested previously," says one of the researchers.