Experts discover how zebra stripes work to thwart horsefly attacks | Hacker News Reader

Experts discover how zebra stripes work to thwart horsefly attacks

phys.org

174 pointswglb59 comments

I thought this was already known? What did this study add?

> The team found that tabanid horseflies are attracted to large dark objects in their environment but less to dark broken patterns. All-gray coats were associated with by far the most landings, followed by coats with large black triangles placed in different positions, then small checkerboard patterns in no particular order. In another experiment, they found contrasting stripes attracted few flies whereas more homogeneous stripes were more attractive.

The paragraph before this quoted paragraph seems to imply this study addresses the why, but for the life of me, I can't understand how this paragraph answers why.

Here's the end of the actual study, which sums up the "why" decently.

>Our working hypothesis now is that horseflies are attracted to equid hosts owing to a combination of odour at a distance, then size of the animal contrasted against the sky or vegetation at a middle distance. But at close range, where they can no longer see the body's outline, flies make a visual switch to local features. If these are small dark objects contrasted against a light or white background, the horsefly no longer recognizes this as a host target and veers away. The contrast of stripes and their relatively small size are therefore the key elements of how stripes operate to thwart fly landings.

Maybe they suffer from the barber pole problem. Since there is only an edge, and no corners, the flies cannot localise themselves when they are too close. Without corners, they wont be able to visually tell whether or not they get closer to the target, not if they move along the edge. If the stripes are non-homogeneous. They wont be able to tell neither how far they moved across them either.

I believe that was one of the things tested, and is tentatively being ruled out. They found that checkerboard patterns had a similar effect.

I could be reading the paper wrong though.

Me neither. But fly eyesight apparently is based on flicker, and movement plus spatial frequency equals temporal frequency.

Yeah I thought this rung a bell.

Here [1] is a BBC article from 2019 that refers to a 2014 study where they hung zebra-print coats on horses to observe the effect of flies landing on them.

[1] https://www.bbc.com/future/article/20191031-the-truth-behind...

This is interesting. I’d always assumed the stripes were camouflage, similar to a tiger’s stripes. Tigers look orange and black to us, but many prey animals perceive color differently, and the tiger’s stripes help it blend in among jungle foliage. The photos in this short article demonstrate the effect:

https://theconversation.com/why-do-tigers-have-stripes-14522...

I had always heard the stripes were camouflage not to blend in with the environment, but to blend in with the herd - to make it hard for a predator to single one out

Tigers are not herd animals that are preyed on by other predators, though :-).

Indeed.

Tigers have evolved stripes for camouflage in grass.

Specifically because the animals are dichromats and cannot see the colour of the tigers' fur against the green of the grass because their colour reception is not sufficient.

https://www.iflscience.com/we-now-know-why-tigers-bright-ora...

I meant zebras

Which is why we do science on things that seem obvious - because while the obvious answer to something is, quite often, the correct one, it isn't always.

I would imagine the orange with black stripes of a tiger are much more effective camouflage around dawn and dusk when the sun is low, shadows are long, and the colour temperature of light shifts towards the orange and red end of the spectrum.

This is not at all correct, simply because their prey cannot perceive orange at all. Tigers do not look orange to their prey. This is the same reason hunting vests are orange: The prey animals in question cannot pick orange out of a green scene.

Distracive camouflage.

Years ago, I started seeing transparent plastic bags full of water hanging in the doorways in my hometown, the given reason being that they prevented flies entering the bar or the house.

I thought that was some kind of joke, but... it seemed to work, at least when the bags were under direct sunshine. Flies weren't very happy flying in the vicinity.

Later people, emboldened, decided that strings of discarded CDs keep pidgeons away from balconies. I can't attest to that.

wait till you visit eastern europe where drivers believed strings or single CD handing on the rear-view mirror somehow makes the car stealth to a police radar.

I always thought the idea was that the reflection from the flash would overload the camera sensor and hide your face/numberplate when a speed trap strikes.

there certainly are reflective stripes you put around license plate which make very hard to take photo of license plate with flash

They also make sure you pay an extra hard fine when they do manage to identify you after all.

Maybe not radar but IR laser guns?

I don't think it'll actually work though.

The goal is not avoid detection, but that they can't record your plate number.

Trying to avoid flying too low over the water surface?

Water flickers when disturbed by slight winds and when under direct sunlight. This seems to disturb flies' vision and they tend to stay away from the area.

Sadly, where I live, this method would produce a gazillion mosquitoes and biting gnats.

Add soap to turn it into a mosquito trap

It's know as the "dissuasive effect", and it's well studied (see:

https://www.sciencedirect.com/science/article/pii/B978012088......

and

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1744-1617.......

)

Now, obviously it isn't a magic barrier/tarp, but as long as there isn't too much of a cost/impact to making use of it, there is a selective advantage to taking advantage of this effect.

I'm loving the upgraded horse blankets.

> Now the team want to determine why natural selection has driven striping in equids—the horse family—but not other hoofed animals.

Probably some flying stingers that transmitted a lethal disease that these past horses couldn't quickly build resistance to. It could also be that this sickness came in waves with only a few survivors every time, and the patterns on the zebras got amplified on every wave until it reached the current state. In the beginning it may have even been a coincidence that the pattern was there for individuals which survived the plague, but over time as it amplified it transformed into a evolutionary benefit on its own.

Wouldn't an all white coat be even better?

That was my first thought, and without seeing the paper all I can do is guess. My guess is when they say the horseflies like big dark objects they mean big and/or dark, with big being the top priority. So a big white blob would still be more appealing than several small white and dark blobs.

That, or the shade mean even white is sometimes a big grey blob.

Anecdotally, big isn't really necessary, though it helps (especially when designing traps, since there are going to be a lot of the suckers). Look up either the H Trap or the Bug Ball.

I've always thought black works best, but that might just be for horse flies- a quick google search seems to confirm that blue does work better than black for deer fly traps.

Blue does!

I even have a blue hat, to which I tape blue masking tape, and spread tanglefoot on. I catch endless flies, and am not bit!

Examples:

https://eagergridlessbeaver.wordpress.com/2021/08/04/blue-so...

Are deer flies a biting fly? We've got flies that bite, but I am only vaguely aware of the term deer fly.

> Are deer flies a biting fly? We've got flies that bite, but I am only vaguely aware of the term deer fly.

There are different. There's the horse fly (https://en.wikipedia.org/wiki/Horse-fly) and its related species deer fly (https://en.wikipedia.org/wiki/Deer_fly) And there's the black fly (https://en.wikipedia.org/wiki/Black_fly) which is a different family. They all bite.

I am unaware of the term deer fly. The name tends to suggest that they'll bite deer; it's possible they're not interested in biting humans.

Horseflies will happily bite humans, though they are pretty well guaranteed to die in the process.

Wikipedia says that deer flies do bite humans and their bite 'may be painful'. They are a type of horsefly, suggesting that the description of their bite is understated.

I wonder if we just call the "deer fly" a "horsefly" here. We (Missouri, USA) have the little horseflies (maybe a 1/2") and then the giant horseflies (biggest I've caught was 3").

Where I live, deer and horse fly are sorta interchangeable terms. Quebec.

We do have different breeds of them too. Early in summer, the head biting one.

Later, near August, there is one with a yellow back, and it goes for ankles!

That's pants in sock season time.

There are loads of bot flies too. They supposedly go for cattle, but I've caught mice with their larvae, so I worry about napping outside, during their season.

From upstream: Horseflies will happily bite humans, though they are pretty well guaranteed to die in the process.

Not sure this is a deer fly. The ones I hit, often just fall off, then fly away. You usually have to crush them with your foot to kill them. They are tough.

Ya our jumbo horseflies can take a lot before the don't get up. I use to go out and swat them off my cattle and they'd shake it off and come right back. I now pull a wing off and leave them on the ground. Their remaining wing buzzes really loudly and the spin in circles which attracts the chickens. I can get about a hundred in a 30 minute period at the peak of their season and the hens will circle around to grab them.

An excellent solution!

In my part of the woods (Wisconsin) horseflies are quite large, between 1/2 and 1 inch but mostly around 3/4. Deer flies are much smaller with a distinctive triangular shape made by their wings when they land.

Both have a very irritating bite, but the deer fly is a small sting of pain that goes away quickly while the horsefly tends to leave a large welt that sticks around for at least a day or two.

The horseflies I'm familiar with lived in a swamp in New Mexico. The bite felt like getting hit by a nail gun, but they'd explode when slapped.

I don't have time to read it, but the paper is linked at the bottom of the article.

https://dx.doi.org/10.1242/jeb.244778

Thanks, I assumed that was the start of the ads and ignored the gray square.

This particular experiment didn't test pure white but it sounds like a previous did.

Can we reduce mosquito bites by wearing striped clothing?

Horse flies, maybe. Mosquitos unlikely, they find you via smelling co2

Horse flies find by co2 as well, it is just their vision can thwart them...

They paint stripes on cows to keep the horseflies away, so it's worth looking into.

Few mosquitos in my neck of the woods, but I remember from childhood that raising a hand above your head was more effective than clothing choices. Raising a hand with a cigarette helped even more (I think the operating theory in my family was that they’re drawn to lower oxygen levels as it suggests a breathing being’s presence), but generally that was frowned upon while I was growing up.

what neck of the woods is that, as "i want to go to there". just one summer, i'd love to run around outdoors and not worry about mosquitos

Seattle! We have them, don’t get me wrong. But nothing like the swamps of northern Virginia I grew up in.

I suppose the swamps will fully flood and the mosquitos will move north in due time.

Not many in San Diego.

How did they distinguish whether it's pattern or the paint itself working? Obviously if you cover 50% of skin by paint, which horseflies don't like, they will land only on the unpainted skin. I wonder if they painted skin to 80% scale if it decreased attacks even more.

Who's painting anything? The link clearly shows horses covered in blankets. I'd imagine the comparison is done only between horses covered in blankets of various patterns, so the pattern is the only significant variable.

I confused it with different experiment when they directly painted cow (AFAIR) and measured number of mosquitos.

Yes, here with all blankets of equal size it seems to provide more relevant results about which pattern attracts insects, though not sure why they didnt test zebra stripes which they keep mentioning.

It's possible the black or white dye attracts or repels flies, but the contrasting triangles pattern should show if that were the issue.

How did they accurately measure how many flies landed on each horse?

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