No Fly Zone
While it's obvious that zebras' stripes help them blend in with tall savanna grasses, a recent study offers compelling evidence that the stripes serve a secondary evolutionary function: scrambling the vision of bloodsucking horseflies.
Evolutionary ecologists, including Susan Akesson - the author of this study - already knew that horseflies are drawn to polarized light, which is reflected better by black fur than white. Until now, they merely assumed that zebras' black and white stripes made them less appealing than if they were entirely black. But after further experiments counting horseflies trapped by sticky boards and horse-models painted with zebra stripes, Akesson's team garnered sufficient evidence to indicate that the particular striped patterns of zebra coats are stunningly effective fly repellent. What's more, repellent efficacy increased with the stripes' narrowness. This helps explain why the zebra's skinniest stripes are on their heads and legs, locations with the thinnest skin. The alternating black and white stripes reflect a cacophony of polarized and non-polarized light, which quickly confuses hungry horseflies and keeps the zebra's blood on the right side of its exotic coat.
Like any humble professional scientist, Akesson cautions that her team's findings aren't the final word on the herd – the tests were conducted in Hungary, rather than Africa, and experiments with models don't entirely mimic flesh and blood beasts. For example, a living zebra's body heat or breath could act as a horsefly lure overriding stripe defenses. Nonetheless, the team's findings merit further inquiry into the zebra's striped style.
"Behind the zebra" by Cybaea on Flickr courtesy of Creative Commons Licensing.