Science might have finally figured out why zebras have stripes

Pablo Tucker
February 22, 2019

The mystery of why zebras have black and white stripes may have been solved as scientists find the pattern "dazzles" blood-sucking flies. To reach this conclusion, the researchers conducted an unusual experiment involving zebras and horses dressed in black and white striped coats. UC Davis Professor Tim Caro led a series of unique experiments for this study to better understand how stripes manipulate the behavior of biting flies as they attempt to come in for a landing on a zebra. When the flies would bump into the zebra in a failed landing attempt, the zebras swatted at them with their tails, ruining their chances of re-attaching and feeding on their blood.

"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.


The evolution of the zebra's black & white coat has intrigued scientists for years. Today, many scientists believe that the black-and-white stripes actually function as a fly repellant, but because it's hard to get close to wild zebras, it hasn't been clear how the pattern might deter the pesky critters from landing on the animals and taking a bite. He added that the most likely mechanisms for the deterrent effect are either that the "sudden reveal" of the stripes on close approach either surprised the insects and made them veer off, or interfered with their perception of how fast objects were moving past them, affecting their ability to land. Further, the scientists did not see a single tabanid probe a zebra's skin during 5.3 hours of direct observation, whereas the flies successfully did so 239 times on the uncovered horses during 11 hours of observing them. Stripes may therefore offer zebras vital protection, though the researchers aren't entirely sure why the pattern seems to confuse flies. While horses are more low-key about the presence of flies, merely twitching and occasionally swishing their tails to ward off the insects, zebras are far less tolerant.

Researchers think that zebras may have evolved this way because where they live.


Zebras are quite good at not getting bitten by flies. But the flies managed to land on zebras less than a quarter as often. The striped animals nearly continuously swish their tails during the day and will stop feeding if they feel bothered.


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