Why Do Zebras Have Stripes? Riddle Finally Solved

By April Reese | April 2, 2014 9:48 am

zebra

Ever wonder why zebras have stripes? Scientists have too, and now they have an answer.

Researchers going as far back as Charles Darwin have offered a number of theories about how stripes might benefit zebras. Did they develop their unusual multi-hued coats as camouflage to help deter predators? To keep cool beneath the harsh African sun? Do their stripes help them identify each other? A new study topples all of those theories, leaving just one still standing. As it turns out, stripes are an excellent bug repellent—at least for zebras.

Biting Flies

Researchers from the University of California at Davis knew that certain flies avoid black and white surfaces, so they wondered: Could zebra stripes have evolved to keep the animals free from suffering the bites of those very same flies, which can carry fatal diseases? To tackle that question, the researchers examined the distribution of zebras and the locations of the best breeding grounds for the stripe-averse flies. Sure enough, they found that they overlap. The same was true for other animals in the horse family that had stripes on various parts of their bodies.

“I was amazed by our results,” said lead author Tim Caro, a wildlife biologist at UC-Davis. “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 study, published yesterday in Nature Communications, builds on a 2012 study by researchers at Sweden’s Lund University that used horse models painted black and white to test whether flies would avoid stripes.

Stripe Avoidance

But why are stripes anathema to flies? It turns out that flies find stretches of water to mate and lay their eggs in by looking for the horizontally polarized light it reflects. Zebra stripes, however, are vertical and reflect polarized light differently, which makes them unappealing to horseflies. Unlike other African mammals, zebras have shorter hair that flies may be able to penetrate more easily to bite into the skin.

Researchers have yet to test their bug repellent theory in the wild, however. Zebras have striped insect armor, but they also emit odors that may attract flies, potentially canceling out the benefits of their striped coats.

 

Image by  jurra8 / Shutterstock

CATEGORIZED UNDER: Living World, top posts
MORE ABOUT: animals
  • Spiritdove Smith

    why not spots and checkers and not stripes.. its just the great mother with a paint brush. :D

    • Brian Jeffs

      It answers that in the article.

  • http://www.facebook.com/j.m.p.cloke Jon Cloke

    Fantastic! Now, why are the stripes vertical and not horizontal? Is it to make them look slimmer…?

    • Facebook User

      And of course taller.

    • EllaSilverYeah!

      article answered all that.

  • Hibernia86

    The idea isn’t to blend in with the grass. The idea is to blend in with the other zebra and make it harder for the lion to focus on any one zebra to take down.

    • Jason L Coleman

      That’s good enough for me. Great theory :)

    • http://blogs.discovermagazine.com James Morton

      i think lions are color blind.
      i bet the running herd is a natural strobe effect.

    • Facebook User

      Best theory I’ve ‘heard’ and you know what, I think that you are absolutely right, and imagine looking at all those vertical stripes, you wouldn’t know where one Zebra began and another ended.
      Good job!

      • Hibernia86

        To be fair, I wasn’t the one who thought of it. I read it on other scientific sites.

  • Hibernia86

    If this is true then why don’t all African grazers have stripes?

    • August Berkshire

      The article answers that. Says other mammals have longer hair to ward off the flies.

      • Emkay

        the largest predators in the world ‘siberian/bengal tigers have stripes…actually have striped skin too..

    • Don’t Even Try It!

      …because they would all be zebras! OMG that almost sounds racist!

  • howard

    Just for humor (it is a few days past April 1) our guide said it is easy to tell male and female Zebras. Males are white with black stripes and females are black with white stripes. My thought is that because Gnus have such terrible vision but a good sense of smell and Zebras have keen eyesight and terrible sense of smell that the very visible stripes are part of the synergy for both animals as they attend to their massive migration through the Serengeti.

  • evodevo

    I’ve raised and been around horses for 50 years. The biting flies they are talking about are tabanids, the same family as the tsetse fly. The big tabanid horseflies (green-eyed and black) I am familiar with are attracted by large, moving objects (they will alight on your white car, for instance) . Only when they alight will their other sensory systems kick in. They home in using sight from a distance, and then use smell after they land. They are not attracted to horse poop, like stable flies. Stable flies breed in horse manure, so smell attracts them.

    • Heimdall222

      Well, OK, but what does all that have to do with zebras?

      Details, please!

    • Don’t Even Try It!

      Yes, I used to live a couple miles down a gravel road and every day when I went down the road a whole swarm of those Horse flies would chase my car. Those little suckers can fly pretty darned fast, too. They’d chase the car the entire 2-miles if I stayed around 20 mph. The wife thought I had them all trained!

      • Emkay

        your wife sounds like the kind of person who would study why zebras have stripes!

  • Truth Teller

    God wanted them that way.

    • Heimdall222

      The researchers, or the zebras?

      • http://blogs.discovermagazine.com James Morton

        the researchers, silly…..

    • Facebook User

      Yes of course he did but he was running low on spots that day, the Leopards wanted the Lions share and the Giraffes, Hynea and Lady bugs all wanted their share so the poor Zebra had to settle for… ‘Stripes’.
      It’s a designer thing.

  • Don’t Even Try It!

    If a zebra had no stripes, it would be a horse!

  • Don’t Even Try It!

    Are zebras half white or are they half black?

    • Facebook User

      No Man, they is multiracial.

  • Max Friedenberg

    Why didn’t they evolve with bags of water all over them?

  • tralf

    Ok, so “flies find stretches of water to mate and lay their eggs in by looking for the horizontally polarized light it reflects. Zebra stripes, however, are vertical and reflect polarized light differently.” I’ll take your word for that.

    All that tells me is that flies won’t mistakenly take a herd of zebra for a body of water when they’re looking for a place to mate and lay eggs. Unfortunately, I suspect those same vertical stripes would then make the zebra rather more obvious to flies when it comes to feeding time. Which is, like, only 90% of their adult life?

    I’m behind the guy that mentioned the stripes acting as not camouflage but an illusion. For distant predators the stripes help hide the size of a herd and distinguishing individuals in the herd much more difficult.

  • tikitools1

    what about at night?

  • Francis Paul John McAnarney Jr

    it is probably the result of Caucasian horses mating with negro horses.

  • Alan

    Just read an article about how ships during WWII were painted in essentially zebra stripes, not for camouflage, but because when viewed through a periscope, the stripes confused depth perception, so they couldn’t tell how far away they were and properly calculate torpedo trajectories.
    Regarding the stripes conveying some evolutionary advantage, the question I’ve always had is “if it is so beneficial, why don’t other grazing animals have them too?”

    .

    • Rex Caprorum

      They do. Look at okapis, for instance – though whichever committee designed them just threw the whole lot at them – water chevrotain, the young of many species of wild pig, and various deer, among others, are all striped to a greater or lesser degree

  • Emkay

    Yessiree, another bunch of costly studies that help to eliminate world hunger, lack of fresh water, and AIDS prevention…

  • disqus_z3W1aYpBP3

    oky dokey

    • disqus_z3W1aYpBP3

      hi

  • calkan

    People who believe in creation just do not understand that (though modern educated humans cannot fully agree on why they have stripes) zebras without stripes figured out millions of years ago how to keep flies off of them. They either told their dna to make these stripes or the dna figured out the problem and solved the problem themselves. There is seemingly nothing evolution cant do. I love science and believe it will eventually help atheism find a way to gracefully move on. Then, no more propping up failed theories to back a world view.

  • Vicki Acton

    The real question is are Zebra’s white with black strips. If the strips a further apart does that make a difference. They are protected from the
    tsetse fly which kills solid colored horses unless they a vaccinated. The
    fly can not see the Zebra because of the black and white stripe that because of their eye the fly do not see them. I don’t believe in evolution
    I do believe in creation and the adaptability of every living creature for survival purposes.

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