The riddle of zebras’ stripes

Zebra

Why zebras have black and white stripes is a question that has intrigued scientists and spectators for centuries. A research team led by UC Davis, has now examined this riddle (in a very systematic way).

Many hypotheses for zebra stripes have been proposed since Alfred Russel Wallace and Charles Darwin debated the problem 120 years ago. These include:

  • A form of camouflage
  • Disrupting predatory attack by visually confusing carnivores
  • A mechanism of heat management
  • Having a social function
  • Avoiding ectoparasite attack, such as from biting flies

After analyzing the five hypotheses, the scientists ruled out all but one: avoiding blood-sucking flies. The scientists found that biting flies (such as horseflies and tsetse flies) are the evolutionary driver for zebra stripes.

Why would zebras evolve to have stripes whereas other hooved mammals did not? The study found that, unlike other African hooved mammals living in the same areas as zebras, zebra hair is shorter than the mouthpart length of biting flies, so zebras may be particularly susceptible to annoyance by biting flies.

Yet in science, one solved riddle begets another: Why do biting flies avoid striped surfaces?

Read more →

11 thoughts on “The riddle of zebras’ stripes

  1. Jessica-Lee Bown (14021138)

    After reading this article, I realised that there may be many good reasons as to why the black and white patterning on a zebra accommodates to the prevention of biting flies from attacking them. Physical positioning of their stripes, as well as other physical attributes (such as where it was suggested, in the article, that because their hair is shorter they would need something else to prevent parasites) make more sense now that it is known why they have stripes.

    Essentially, biting flies find it harder to land on black and white stripes, although it is not clearly known why. The geological distribution of black stripes on a zebra, however, make sense in comparison to the conclusion of the investigation – the stripes on a zebra are particularly thin towards the bottom of the leg and are narrower by the head, which suggests that because their legs and head spend a lot of time in the grass, especially when grazing, those parts may be more vulnerable to biting flies.

    There may be other reasons to show the link between their patterning and prevention of biting flies, but the other theories also cannot clearly explain distinguished features, such as why the patterning is narrower on the head. In comparison, the conclusion in this article can provide a logical explanation to such a feature.

  2. Molebogeng

    Its really amazing how nature works. Who would have thought that zebras are striped to protect them from annoyance from small insects? I thought it was just to make them seem different from other hooved and domesticated animals such as mules, horses, donkeys etc.
    Another interesting thought or more of a question is, why is it that zebras have shorter hair compared to other animals? Is it because of the fact that they had to evolve in order to adjust to their new environment?
    Another perplexing question is, do they stripes have to have a particular co-ordination or are they just formed in anyway?
    As a student that’s interested in veterinary studies, I find this blog quite informative and maybe at some point it could help zoologist as well as vets to combat problems experienced with regards to zebras.

    Molebogeng Nkagisang
    Student No: 14105528

  3. Tanya Strydom (14104262)

    As a horse rider and thus naturally a huge fan of equines this article has really opened my eyes to a lifelong conundrum as to why zebras actually do have stripes while close family members such as horses and donkeys don’t.
    This could actually help explain why horses who are in the same families as zebras look so vastly different. The domestic horses have obviously not had the need to develop stripes as the are not affected by biting flies. Whereas it could also explain why some wild horse have some striping present on their legs along with the African Ass. Are they starting to develop a fly repulsion mechanism?

    This has also opened doors to a whole new array of questions.
    Such as why do different zebra species have different striping patterns? Is this possibly to do with the fact that different species of biting flies are ‘put off’ by different striping patterns?
    And one that is possibly easier to answer, do giraffes have spots for that same reason or are theirs purely for camouflage, the colours are neutral enough I guess…

    Awesome article and I hope they will keep us updated on the actual reason as to why flies avoid striped surfaces and why zebras have not just developed a thicker coat?

  4. Kedibone Scheppers

    u14121876

    This research is amazing. I’ve been going on holiday to places with many wild animals, including zebras, for a long time. I always thought that the stripes on zebras were for camouflage. now that that assumption has been thrown out the window, I would really like to see why zebras have the stripes and why biting flies avoid them because of their stripes

    1. Devan Winterton (14011426)

      A long mystery being solved, very interesting work. I’m sure many people,myself included, did not know why zebras have stripes; nevertheless, know how they came to be. Research such as this is quite fascinating and I’m sure many people have their questions answered. I did have a few questions though: Are the zebras’ stripes caused by the skin being coloured and then showing through the hair (such as a tiger’s stripes) or is their hair actually coloured in those patterns, or maybe both? Also, are their stripes determined by anything in particular, such as genes and environment, or are they just undeniably random.

      Yours faithfully
      Devan Winterton
      14011426

  5. 14109094

    This is most interesting, as the origin and function of zebra stripes is a phenomenon that I have pondered for a long time. From a scientific viewpoint one can appreciate why the black and white striping may deter biting flies. Black and white surfaces reflect light at different intensities, but more importantly, they also reflect different sorts of polarised light that is visible to flies but not to humans. The degree of reflection of the polarised light depends on the surface of incidence ( this can be observed through the difference of gloss paint when compared to matt paint). Thus one may deduce that the zebra hairs reflect the polarised light at different intensities and in different ways.
    Looking at the seven living species of the equine group (horses, zebras, asses, and the 20 subspecies which derived from them), you can see that most have striping on their bodies somewhere. I find it interesting that the range of striped species, and the intensity of stripes among zebras, increase in areas which overlap where biting flies are more active. This serves to convince me that there is indeed a connection between the two.
    Could this new-found information have applications to humans? Would wearing striped clothing protect locals and holiday makers from mosquito and fly bites?
    However the other 4 hypothesis are not well studied and too little of them is known to fully discount their role in the evolutionary drive that created the stripe patterns we see in zebras and other members of the equine species.
    One other possible hypothesis that seems very plausible is the possibility of it being a mechanism of heat management.

    14109094

  6. Carien(u14093792)

    I first came across this research article online whilst browsing through “Australian News”.

    Having recently spent my holiday looking at various natural ways (with no success) on how to get rid of flies and after being bitten endless times by Biting flies, I decided to extend my research in the upcoming summer months to include overalls painted zebra-style. Student 14109094 also commented on using this information as an application to humans. The only way to prove this hypotheses would be to carry out an experiment. Therefore, if you should see a zebra walking on two legs – have no fear and please do not shoot, it will only be me in my zebra overall trying to prove the above hypotheses. If I include an all white and an all black overall in the experiment, I may even be able to prove the hypotheses of it being a mechanism of heat management as mentioned by student 14109094. I do find his/her elaboration on the reflection of polarised light most interesting and will be reading up more on this subject as I had also come across tips that involved using light reflection as a mean of deterring flies. Apparently the light refraction distorts the fly’s vision. What I do find interesting is if one looks at the above video of the running zebra , one will notice that the legs are distinctly whiter compared to the rest of the body. However, looking at pictures which involve no movement, the black and white distribution on the zebra legs are similar to that of the body. Could this be an example of light reflection?

    Although I am not a horse expert, there are various articles revering to horse biting flies (Labanidae) and methods of reducing their numbers [http://www.idph.state.il.us/anvhealth/pcbitingflies.html]. The one most annoying to me is the Black fly (Simuliidae). Therefore area will dictate where these pests are more active as mentioned by Jessica-Lee Brown (14021138). Tanya is lucky to live in an area where they have no problems with these flies.

    This article gives much food for thought.

  7. 14038880

    All African grazer’s are irritated by biting flies. The question is why did zebra evolved stripes where as other grazers are single coloured. The researchers ruled out four other hypothesis. I think it is a contribution of different factors leading to the evolvement of zebra stripes. For example: the idea is that one zebra’s stripes blend in with the stripes of a lot of zebras creating confusion on the predators side. Thus I think it is several factors which lead to evolution of stripes and not one factor alone.

  8. Carmen Britz (14040752)

    Isn’t nature one of the most amazing things in life? The way that animals adjust to their environment and evolved through natural selection, and for survival of the fittest.
    The big question, why do zebras have black and white stripe, led to a new questions that we have to investigate, the moment we found a scientific reason for the first question. The closer we live to mother nature, the more answers we will get and the more we will understand why that was the specific outcome. We have to respect our wonders in nature are appreciate their complexities, because without it, our animal kingdom wouldn’t have survived.
    One thing we, as scientist, just have to accept is that we are never going to know everything. There will always be something new and more complex, that we discover with new inventions, but that we don’t understand yet.

  9. u14026784

    White striped surfaces reflect different sorts of visible light and some sorts of polarized light which we cannot see but flies can. Therefore the different hairs of the Zebra’s pelet are important in preventing flies from landing on them. Out of all the reasons given for why Zebra’s have black and white stripes, the most outstanding reason is that of avoiding blood sucking flies.

  10. u14093741

    I think that this is a really interesting discovery , as I would never have thought that avoiding blood-sucking flies was the main reason behind a Zebra’s strips. It is truly amazing to realize how certain animals have different features which serve as different defence mechanisms . It is however strange that only Zebra’s have such features compared to similar animals. It is also amazing how the Zebra has managed to evolve these characteristics .

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