Evolution Intelligent Design

The real reason why zebras have stripes: To shoo away flies

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Which horse was less pestered by flies?/T. Caro

This theory sounds like a strong contender.

There are so many theories out there about why zebras have stripes. Some enterprising researchers put cloth coats on horses, some striped and some not, to investigate the question. From ScienceDaily:

The stripes of a zebra deter horse flies from landing on them, according to a new study published February 20, 2019 in the open-access journal PLOS One by Tim Caro of the University of California Davis, Martin How of the University of Bristol, and colleagues.

Zebra stripes have been posited to provide camouflage, visually confuse predators, signal to other zebras, or help control heat gain, but none of these hypotheses have withstood rigorous experimentation. An alternative, that stripes somehow reduce the likelihood of being bitten by predatory flies, has gained adherents, but the mechanism has been unclear.

In the new study, the authors compared behavior of horse flies as they attempted to prey on zebras and uniformly colored horses held in similar enclosures. Flies circled and touched horses and zebras at similar rates, but actually landed on zebras less than one-quarter as often. When horses wore a striped, black or white coat, flies landed far less often on the striped coat, but just as often on the uncovered head. The authors found that while flies decelerated prior to landing on horses, they approached zebras at a faster clip and failed to slow down as they closed the distance, often bumping into the zebra before flying away again.

Additionally, zebras were at greater pains to keep flies off through tail swishing and running away.

Taken together, these results indicate that stripes do not deter flies from approaching zebras, but do prevent effective landing, and thus, reduce the number of flies successfully feeding. This finding provides further support for the hypothesis that the evolutionary benefit of zebra stripes is to reduce biting by predatory flies. Paper. (open access) – Tim Caro, Yvette Argueta, Emmanuelle Sophie Briolat, Joren Bruggink, Maurice Kasprowsky, Jai Lake, Matthew J. Mitchell, Sarah Richardson, Martin How. Benefits of zebra stripes: Behaviour of tabanid flies around zebras and horses. PLOS ONE, 2019; 14 (2): e0210831 DOI: 10.1371/journal.pone.0210831
More.

Zebras, we are told, are especially vulnerable to flies:

Scientists have been puzzling over the role of zebra stripes for more than 150 years. But, one by one, the most commonly proposed explanations have all been refuted. Some researchers have suggested that the stripes act as camouflage—they break up zebras’ outlines or resemble fields of tree trunks. But that can’t be true: Amanda Melin of the University of Calgary recently showed that lions and hyenas can’t even make out the stripes unless they get very close.

Another hypothesis says that the black stripes heat up faster than the white ones, setting up circulating air currents that cool the zebras. But a recent study showed that water drums cloaked in zebra pelts heat up just as much as those covered in normal horse skins. Ed Yong, “The Surprising Reason Zebras Have Stripes” at The Atlantic

Put another way, Darwinian theorizing isn’t anywhere near as useful as a combination of horse sense and experiment.

Now, another question arises: Why don’t more life forms show colorful patterns to deter flies? Are there costs and drawbacks as well?

Hat tip: Ken Francis, author with Theodore Dalrymple, of The Terror of Existence: From Ecclesiastes to Theatre of the Absurd.

See also: Stripes Confuse People But They Do Not Cool Zebras

Study: Zebra stripes neither hide nor flaunt

Stripes offer no advantage to zebra?

How the zebra got its stripes, this time really

How the zebra got its stripes, maybe

How the zebra did NOT get its stripes?

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2 Replies to “The real reason why zebras have stripes: To shoo away flies

  1. 1
    EDTA says:

    >The stripes of a zebra deter horse flies from landing on them, according to a new study…
    Of course horse flies land less often on zebra: they’re HORSE flies. Did they do the experiment with zebra flies?? (Sorry; I had just read the post about determinism, and I couldn’t resist.)

  2. 2
    vmahuna says:

    OK, so again, the guys in the lab came up with this zebra stripe thing and installed it on zebras. They NEVER installed it on any other equine. So the idea that horses (or donkeys) SHOULD have EVOLVED stripes is of course silly. Their design specs don’t include the Zebra Stripe option package, so they ain’t NEVER gonna get stripes.
    But I like the flies thing. Watch “Big Cat Diary”, which shows real live African animals with minimal human intervention. And what you see are VAST herds of zebras, antelope, and wildebeest and such and they all have DIFFERENT coloration. Now if there was ANY survival advantage in any PARTICULAR coloration (e.g., Zebra stripes) one would expect there to be more UNIFORMITY in the camouflage schemes.
    I’d also note that apparently giraffes simply got their custom paint job on a whim. Adult giraffes can KILL a male lion with 1 kick, so giraffes aren’t hiding from ANYONE. But the custom paint job does look neato.

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