Changing Planet

Mystery Solved: Why Flies Are So Hard to Swat

Why are buzzing flies so hard to swat?

It’s a question that’s vexed humankind for millennia, but scientists may finally have the answer.

Flies on the wing react to looming threats as if they were fighter jets—by banking away in a fraction of the blink of an eye, according to a study published April 10 in the journal Science.

Too fast for the swat, the airborne insects harness their aerodynamic force within a wingbeat or two to almost instantaneously change their course, the study of fruit flies found. (See “Video: Inside Look at Insect Flight.”)

Indeed, this happens so quickly—in less than one hundredth of a second—that scientists required three high-speed cameras, each able to take 7,500 frames per second, to capture it.

Not only that, but the escape maneuver—which sees fruit flies (Drosophila hydei) fling themselves into rotations of 90 degrees or more, flying almost upside down at times —is very controlled and specific.

A fruit fly flaps its wings 200 times a second during normal flight and even faster when taking evasive action. Photograph by F. Muijres and F. van Breugel, University of Washington.
A fruit fly flaps its wings 200 times a second during normal flight and even more when taking evasive action.
Photograph by F. Muijres and F. van Breugel, University of Washington

That’s according to study co-author Florian Muijres, a researcher at the University of Washington’s Dickinson Lab, Seattle, where the study took place.

Small differences in the beat of the wings generate the force needed for the fly to suddenly pitch and roll. The differences have to be very precise; otherwise, Muijres said, “the animal would constantly spin out of control.

“Based on the direction of the looming threat—whether from the back, the front, or the side—the flies perform a different type of escape maneuver that is very controlled,” he added.

Speedy Flies

That contrasts with the escape tactic of a resting fly, a topic previously investigated at the Dickinson Lab.

From a resting position, the fly performs a wild leap and stumbles through the air using the legs. “Only on the second phase will they gain control and start flapping their wings,” Muijres said.

The new study, which employed winged robots dunked in vats of mineral oil to better understand the flies’ lightning-fast movements, challenges recent studies that instead point to flies turning using a yawing maneuver.

Yawing is what the driver of a car feels when turning the vehicle, which is rather different from the face-flattening motion the pilot of a banking fighter jet experiences. (See videos: “World’s Weirdest: Flies and Maggots.”)

Yawing, or pirouetting around a vertical axis, is a sensible way for hovering insects to change direction, according to Graham Taylor, a professor of mathematical biology at Oxford University in the U.K.

For changing direction while flying, however, insects need to redirect their aerodynamic force to create the rotation needed to curve their flight path, explained Taylor, who wasn’t involved in the new study.

Time lapse images from a high-speed video shows how a fruit fly startled by a looming shadow (off camera at the bottom right) performs a rapid roll to bank away from the threat. Photograph by F. Muijres, University of Washington
Time-lapse images from a high-speed video show how a fruit fly startled by a looming shadow (off camera at bottom right) performs a rapid roll to bank away from the threat. Photograph by F. Muijres, University of Washington

“Airplanes, helicopters, and other insects bank to direct their aerodynamic force vector into a turn, so the fact that fruit flies do so too isn’t really a surprise,” he said.

What is a surprise, Taylor said, is the remarkable rapidity of the escape response, “and the subtlety of changes the flies make to their wingbeat when turning.

“The flies are responding to an approaching threat in half the time it takes to start blinking in response to a camera flash,” he said. “And the time it then takes to accomplish the turn after that is even faster again, so they are throttling up to full power in a 50th of the time it takes you to complete that blink.”

That flies can react so rapidly suggests they’re wired for it—with a neuron dedicated to such in-flight emergencies running down the body to the wings and muscles.

Robot Inspiration 

Understanding the workings of this control mechanism in an animal with a brain as tiny and limited as a fly’s could help in the development of mini airborne robots that can find their own way around obstacles.

Likewise, Taylor said, changes in the fruit flies’ wingbeat, which the study team measured using the winged robots, could provide useful insights into flight control for designers working on flapping micro-vehicles. (See “The Dream of Human-Powered Flight Takes Off.”)

Indeed, study co-author Muijres noted that Delft University of Technology in the Netherlands, to which team member Johan Melis is attached, is involved in such a project, a dragonfly-like autonomous flapper known as the DelFly.

But what about trying to swat the real thing? Should we just give up? It’s difficult, Muijres said, but the study did offer one tip.

When you come at it from the side, the insect flies straight away from you, “so if you keep your hand going in the same direction, you can catch the fly.

“Try it,” he said, “and let me know.”

James Owen is a journalist and author based in Stockholm, Sweden. After cutting his teeth on the news and features desks of several UK newspapers, he struck out as a freelance writer, specializing in life sciences and natural history. His fish biography 'Trout' (Reaktion Books) was published in 2012.
  • Jim

    If you make a clap with both hands slightly over the fly you cannot miss

  • DespisesFlieses

    Reminds me of the movie: Epic.

    The little buggers are so fast, I often think I’m imagining them,
    but they’re stupid enough to keep coming back and they get
    The Spray.

  • Vivian

    Send me the grant money …simply strike toward the back of the fly they start off flying backwards a splat every time

  • Fred

    @Jim I actually saw this one in action. I was interviewing for a job and a fly was buzzing around. Without much thought, my future boss used the hand clap method and the fly dropped dead on the desk. I thought, “Wow, that’s impressive! Don’t mess with this person”. It was later explained to me that flies fly straight up. If you aim above where they are, your hands will meet them as they zoom upwards. Not rocket science or magic, but still impressive to see it happen. 🙂

  • craig

    I’ll team up with VIvian for the grant $. Wet rubber gloves. Surface tension. Dead fly every time.

  • Ima Ryma

    ‘Twas in the year two thousand nine,
    Prez Obama was on T.V.
    A house fly flew in a fly line.
    The Prez did swat. The fly dead be.
    PETA was very peeved of course.
    But politics the Prez assessed.
    Prez Obama had no remorse,
    Probably just a right wing pest..
    Four years later, another fly
    Did fly about the Prez’s head.
    But being a partisan guy,
    The Prez did not swat this fly dead.

    Repubbie flies – the Prez does slay,
    But lets Demmie flies get away.

  • Thermos


  • Fly ninja

    I have found that when a fly has landed, I can scoop it up from behind with my hand and catch it alive. No mess, no fuss.

  • Gary page

    But with fruit flies if u use both hands either side in a clapping motion they are easy to swat. I guess they cant handle the threat from two opposing sides at the same time ha 🙂

  • Lisa

    Making my skin crawl over here :'(

  • Sonny

    the link to science mag has problem. extra double quotes.

  • TheOtherRosie

    Flies are not hard to swat at all. Even cows & horses can swat flies. I’ve been swatting flies for long as I’ve been able to walk.

  • Glen

    Flies perception of time is different from humans. Flies avoid being swatted in the same way that Keanu Reeves dodges bullets in the film The Matrix – by watching time pass slowly.To the insect, that rolled-up newspaper moving at lightning speed looks like it is inching it’s way through thick treacle.Like Reeves side-stepping slow motion bullets, the fly has enough time to escape.

  • Raja

    Take a bazooka, Destroy fly without letting it dodge.

  • Manuel Ramirez Alvero

    Hahaha I seriously fought with fly once with spray hose inside the toilette. I was amazed! I didn’t won.

  • LIon

    If you slowly approach a sitting fly with a knife from above, if you manage not to scare it with your hand, it seems it cannot see the blade and you can even touch it slowly before it flies away.

  • Dave Borges

    Do you understand we pay grownup scientist to study crap like this

  • Christine Dell’Amore

    Thanks for catching the broken link to Science journal, Sonny!

  • Antonia Lazenby


  • Ashley Goldstein

    I used this article for a science project and I was wondering who the author of it was. thanks

  • James Owen

    Hi Ashley,
    It’s great you’re using this study for your science project. The study’s author (or, more correctly, co-author), if that’s what you mean, is Florian Muijres. You can get to his details by clicking on his name in the report above. I’m the science writer who wrote this Weird & Wild post – James Owen – but I guess you already knew that!

  • libby

    I love NG. Flies also see in slow motion. It’s a fact.

  • Tanweer

    In rainy season flies are even more fast and annoying. Why is that?

  • Christian

    So…. they have potentially incredibly amazing reflexes, yet they waste their time trying to antagonize people who can and will eventually squash them.

    Why have they not developed some sort of ability to detect predators/prey like most other species?

    We don’t run with the tigers or the lions, and we sling snakes around at each other. But flies, they have this “in-built” mechanic to avoid danger, but ironically try and put themselves in danger’s way ALL the time.

    They really are the perfectly built creatures meant for annoyance.

  • cdad

    Have learned if you move slow you can get close enough to a fruit fly to almost touch them. I wonder if they have trouble detecting slow movement

  • weird dude

    many people say that flies perceive time faster than other beings allowing them to dodge objects trying to squash them but that doesn’t make sense because that doesn’t allow them to move faster they just THINK* faster. *it’s in caps because there’s no italics;

  • weird dude

    also 2/3 times i can kill a fly(or any flying insect i see) first try barehanded, but i always kill it. so i’m wondering how fast does that make my perception time/ other related body processes?

  • Weyland Yutani

    I usually just grab them out of the air, it’s actually really easy with a little practice, the trick is learning how to move and close your hand without creating too much turbulence, otherwise said turbulence will move the fly out of your grasp.

    Alternatively if all else fails then use the good old fashioned rapid hand clap, if you do it right then it doesn’t matter how quickly that fly reacts as the closing speed of your hands vastly exceeds the maximum speed that a fly could achieve, so it simply can’t get out of the way quickly enough before it goes boom.

  • Nick

    I once worked in a factory that was static free…you had to wear special clothing and special things on your shoes…even the floor was made of anti-static material…thing is, if a fly came in the factory I could just pick it up, it never flew away was very odd. So my theory is they detect static electricity and that’s how they are always one jump ahead when something approaches

  • Kam Apin

    from your writing i can conclude that. flies manage to flyy steadily at a vacumm;i.e.: moving car because of that 7500 franes per seconds.

    I need help/explanation on this, how come when you see a moving ship. there is a fly, it flies the same speed as the moving ship.

    the same goes to a moving pick up. at the bucket, how can a fly flies in a palarell speed with the moving truck

  • Aaron

    The idea that a fly experiences time in slow-motion is pretty unlikely, if not downright implausible.

    If it were true then it would, in fact, be impossible to kill a fly. It wouldn’t matter how fast you moved or even if you cut off it’s route of escape; if that fly could see in slow motion it would dodge your strike no matter what. It’d be like a cat dodging a strike from a sloth….the sloth will never touch that cat.

    However, this is not the case with flies because we can kill them using certain methods, I.e. “The Fly Swatter”. If flies actually saw the world in slow motion, then they would easily be able to dodge a fly swatter being swung by a human. It would move at relatively the same speed as a human hand, so why is it that a fly can dodge a hand but not a fly swatter?

    The answer is simple, and way more logical than “it can see in slow motion”. You see, flies have an ability that humans do not possess; the ability to sense changes in air pressure.

    When you swing your hand in the direction of a fly, it can immediately sense the nearby change in air pressure created by the movement of your hand. It can even sense the general direction of that change in air pressure, easily maneuvering to avoid whatever is causing that change.

    A fly swatter works because it is highly perforated( full of holes ); because of this, a fly swatter creates practically no change in air pressure when it moves, or at least not enough for a fly to detect. The fly doesn’t even know what hit it because it can’t sense moving objects fast enough if they don’t cause changes in air pressure. If a fly could see in slow motion, it would easily avoid a fly swatter every time.

    It is much more logical to assume that, rather than seeing the world in slow motion, insects and smaller animals perceive the world exactly as we do….but the rate at which they can process information is much faster. For example: imagine two men who process information at different rates, one fast and one slow. If you were to throw a dodge ball at each man, one would dodge the ball with ease while the other would most likely get hit.

    In this scenario it is most probable to assume that both men, being human, experience time at the same speed. If humans could experience time at different speeds, then two people looking at a clock would see two different times. Most likely those times would only be off by a couple seconds/milliseconds, but still, two completely different times would be visible to each person at any exact moment in time. So, given that both men must be experiencing time at the same speed, why is it that one man can dodge the ball while the other can’t? The answer? Reaction time.

    The rate at which we experience and perceive time does not change, but the amount of time it takes for us to process information does. Both men see the ball moving at the exact same speed, but one man can react just a few milliseconds faster, and that makes a huge difference. Flies don’t experience time in slow motion, they can simply process information about 4 times as fast as a human can. This makes it seem like we must be moving really slow to them, but the reality is their brains just work at a much faster rate. They can react at speeds that seem impossible to us simply because we can’t comprehend such an expedient rate of processing information. It’s like trying to imagine what it’s like for animals to use senses humans don’t even possess. Nearly impossible because it’s beyond human comparison.

  • J

    If your driving in a car 75mph, and there is a flie in your car flying around, does that mean the clue is flyin at the same speed of your car????

  • Bill

    Try approaching the fly directly at the head once it has landed, move in reasonably slowly with your finger already in the flick position, 10/10 times if your aim and distance is correct the fly will be stunned and hit the deck.
    Simply pick it up and toss it out, or do with it as you will.


    must be sweeping bins loads of flies up after standing ovations

  • Steve Benson

    The reason why a fly-swatter works is because it has holes in it? I’m not too sure, but I believe that part of the explanation is what has holes in it!!! I SWAT flies all the time with newspapers, magazines, paperback and hard-cover books, as well as any number of other items (“flip-flop” foot-ware works great). As matter of fact — believe it or not — a National Geographic magazine is the best fly swatter I have found to date, when it’s used correctly. To kill a fly at a distance, for example. Say there is a fly on the wall. All you have to do is position the National Geographic so that it hits the wall flat when you throw it, killing the fly every time without fail. Ironically, National Geographic is perfectly suited for such a task. Indeed, not more than a couple of hours ago, I used this very method to kill a fly that had landed on a small pile of clothes I was readying to be washed. Perhaps you need to re-think the whole “hole” part of your otherwise exquisitely well-thought-out commentary to re-determine whether or not that part of your explanation will or will not actually “fly”.

About the Blog

Researchers, conservationists, and others share stories, insights and ideas about Our Changing Planet, Wildlife & Wild Spaces, and The Human Journey. More than 50,000 comments have been added to 10,000 posts. Explore the list alongside to dive deeper into some of the most popular categories of the National Geographic Society’s conversation platform Voices.

Opinions are those of the blogger and/or the blogger’s organization, and not necessarily those of the National Geographic Society. Posters of blogs and comments are required to observe National Geographic’s community rules and other terms of service.

Voices director: David Braun (

Social Media