As much of a blessing as the internet is, in these days of easy access to information, it’s hard to tell what is factual and what is complete fabrication. Thankfully serious scientific papers, accredited books, and generally authors who want to be taken seriously won’t cite internet sources as references.
However, the speed at which one can disseminate information across the internet often means that the first inkling we have of a scientific breakthrough is web-based. Or at least through twitter or some-other social media platform. Someone catches wind of something, posts about it, and the information goes viral in the blink of an eye. It can take months after the initial announcement for the real scientific evidence to be published and become readily available.
The above introduction is really an attempt to cover myself here, as the information discussed below was certainly not gleaned from any scientific paper. It was from a random tweet that was shown to me by one of the camp managers, which, if true, goes a long way to answering one of the age-old questions of the African Bush: why do zebras have stripes?
We’ve covered this topic a couple of times over the years, but any discussion of the matter generally just involves a recitation of a number of theories. This tweet (see picture below), if true, might go a long way towards answering the question, while – of course – posing many new ones.
Funny picture, right?
Well, according to the tweet (I eventually found the article after initially typing this), scientists in Japan apparently found that painting cows in zebra stripes dramatically reduced the number of insects that were biting them, by roughly 50%!
If this is really the case (it’s not always that simple, as evolutionary features like this often have multiple benefits, and therefore evolved for multiple reasons), it will make the task of guides a whole lot easier in future, as an extensive discussion about the stripe evolution won’t be necessary.
Or will it?
The issue now – at least for me – is why didn’t other animals evolve similar anti-fly mechanisms?
I don’t know how many of you have been bitten by a Tsetse fly, but it’s unpleasant, to say the least. It’s very similar to a horse-fly bite, except the horrible little buggers can’t be killed! You’ll swat one as you’ll swat a normal fly, and it will drop to the ground, seemingly on its way to fly Heaven, but give it a minute or two and it will be buzzing around again, looking for any exposed areas of skin you may have. Fortunately there are no Tsetse flies at Londolozi, but having travelled further north in Tsetse country, I can emphatically agree with zebras that evolving a mechanism to defend against them would certainly be in one’s best interest.
But why would wildebeest not develop stripes to defend against them? Or Thomson’s gazelles, or giraffe?
I don’t know.
Maybe zebras emit a different pheromone type that is more attractive to the Tsetses, or biting insects in general (the tweet didn’t focus specifically on Tsetses, I’m just taking the opportunity to vent my dislike for them). Perhaps there was some sort of specific habitat co-existence between the equines and the insects in some long-forgotten time. Maybe the nagana – a type of disease that can kill horses and cattle with ease, and essentially left vast tracts of Africa unexplored because early settlers couldn’t venture into the interior as they were almost guaranteed to lose their valuable herds – affected Zebras the worst, so it was imperative that over time they developed some extra barrier against transmission.
Herein lies the rub (and the appeal), in that with every question answered, 10 more get asked.
We could sprout theories here about why stripes are unique to zebras until the cows come home, and why do different zebra species have different strip densities, but I’d rather close off here.
As I said earlier, I’ve only read an article that discusses the cow-painting experiment; I’ve yet to read a scientific paper with anything conclusive.
Any thoughts on the matter…?
I have heard all the various theories concerning zebra stripes over the years, and my inclination is that several could be true at the same time, as you pointed out. Insect repellant, dazzling predators, allowing foals to identify mum’s uniquely striped bum. In any case, wearing dark blue or black clothing when touring in tsetse fly areas is a certain way to attract those pesky beasts, so I wonder…
I thought Zebea has got stripes to confuse predators. The fly theory is a new one to me. As you mention James, why don’t all animals not have stripes then. Maybe stripey clothes will help us humans.
James, it is not possibly the type of paint they used that deter the biting little buggers? But interesting theory none the less. 🙂
Interesting point Gawie.
It would be great to see the experiment repeated with a different type of paint…
The Japanese scientists actually considered the paint! They painted some cows just with entirely black stripes, and some cows with black and white stripes.
The black-striped cows had flies settle on them and bite them at the same rate as unstriped cows, whereas black and white stripes confuse flies. Interestingly, this only works up close. All of them attract flies from a distance, but fewer flies settle on stripes.
The U.K. experiment on horses tested 3 captive zebras vs. horses, and then also horses wearing white, black or striped coats. Again, flies approached them a similar amount, but they didn’t slow down near the zebras and striped coats. Basically they just bumped into the animal, then decided not to settle. The stripes seem to confuse them that the striped being is actually an object/animal.
Last, zebras react more than horses when they have a fly on them. They swish their tails, bite at the fly, and even run away. Horses don’t do that as much, which suggests zebras live in areas where it’s more important (from a disease point of view) that they don’t get bitten.
I think Wildebeest have stripes too, only not as obvious as zebra……
Hi Irene,
This is a very good point which I didn’t actually consider…
James..good stuff as usual..can’t tell you how many times I’ve absolutely nailed a Tsetse with what I thought was a death strike..only to have it look at me with disdain and attack me again. Hang in there.
There is actually a scientific report on this topic, from which the tweets etc. come: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6776349/
Japanese scientists found 50% fewer biting flies landed on cows painted with zebra-like stripes.
A separate bunch of white coats in England put striped coats on horses, and found that just like zebras, biting flies settle less often on “striped” horses:
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0210831
These guys in an earlier paper noted that the tsetse fly range and the range of zebras overlap to a great degree.
So there’s mounting evidence stripes do indeed lead to fewer bites. The scientists in Britain also noted zebras swish their tails a lot, and even run away from flies, so there are other reasons they get bitten less than horses (and presumably cows)!
Personally I buy more into the idea that when you’ve got a herd of zebra running away from a predator, it’s very confusing for them to see, particularly if predators see less colour than we do.
Could be both, though, right? The stripes confuse lions, and flies!
It’s an excellent question why all other species don’t have stripes, if they occur in the same location as zebra fleeing fangs and claws as well as flying biting beasts. Equids do appear susceptible to some diseases spread by flies (according to a 2014 study by the guys who coated horses with stripes). Zebras have shorter coats than other horses because they live in hotter weather, and some wild horses have mild stripes on their legs.
Presumably the reason we don’t have striped impala is they have their own cat defenses … and maybe don’t feel the flies as much?!
Hi Alex,
Thanks for this, some great info! I agree to a certain extent on the confusing pattern theory, and I”m fairly confident that the stripe evolution was a result of multiple benefits that reinforced them, rather than a single reason…
Perhaps it’s one of nature’s mysteries that is best left to be discussed and/or debated around the campfire, holding a beer, gin and tonic or a glass of wine. … thanks for the bit of humor on Halloween!
James, wonderful blog – I don’t know why zebras have stripes
Perhaps there IS no reason and doesn’t need to be! Just as 2 people don’t look the same, perhaps the stripes are nothing more than a characteristic that helps zebras identify each other! I surely don’t know but it makes for an interesting discussion!
Or perhaps it is exactly that.. you are known by your stripes!
I suspect that most Zebra are killed in the pitch dark by Lions. It could be that Zebra could get away without stripes given any available light. A fair analysis of the camouflage theory might have to take account of typical light conditions afoot when kills are made. Not that stripes prevent Zebra from being killed in the pitch dark but that it
could be the only time when it makes a difference. Ok – my own wild pet theory. : )
I think all the theories have good merit.