Study reveals why the zebra got its stripes


When uniformly coloured horses were dressed in "zebra coats" the flies made far fewer landings on the striped areas but were not kept away from the uncovered head. However, video analyses revealed differences in approach speed, with horse flies failing to slow down on approach to zebras, which is essential for a successful landing.

Previous studies have shown that bugs don't bite zebras at the same rate at which they attack horses, but it was unclear why that discrepancy existed.

The evolution of the zebra's black & white coat has intrigued scientists for years. They use their tails to bat them away and, when flies do land, they don't stay long because zebras move around a lot.

The researchers videoed horse flies as they tried to prey on captive zebras and domestic horses at a livery in North Somerset, England. But what about a zebra's stripes? Perhaps the animals' signature coats help them camouflage, facilitate social signalling, or keep zebras cool.

For a new study, which appears in PLOS ONE, researchers conducted a series of experiments to better understand how stripes manipulate the behavior of biting flies as they attempt to come in to land on zebras. They add, "The selection pressure for striped coat patterns as a response to blood-sucking dipteran parasites is probably high in this region [Africa]", researchers wrote in the journal Experimental Biology.

"Just like when you're flying on an airplane, a controlled landing is extremely important for flies", Tim Caro, lead study author and behavioral ecologist at UC Davis, tells Popular Science's Jessica Boddy.

Scientists conducted an experiment on a United Kingdom horse farm in Somerset that involved zebras as well as horses dressed in black and white striped coats.

Together with the striped patterns findings, this anxiety suggests that zebras evolved sophisticated defense mechanisms in order to avoid infectious diseases carried by biting flies. Horses, on the other hand, primarily twitch and occasionally swish to ward off flies.

"Stripes may dazzle flies in some way once they are close enough to see them with their low-resolution eyes", says study co-author Martin How. Zebras swish their tails nearly continuously during the day to keep flies off, stop eating when flies bother them, and run away if the flies are particularly persistent.

The bugs were still attracted to the zebras, and still pursued them from a distance, but couldn't nail the landing when they got close.