How to Swat a Fly

Some of this is not breaking news, but some is.  When I was watching someone in another classroom in futile pursuit of said dastardly, dirty diptera, I realised that there is a lot of interesting science behind successful swatting.

Flies are hard to swat for a number of reasons.  They avoid predation by both sensory detection and behavioral responses.  With its large eyes, a fly can see nearly 360°, including behind itself.  This means that it’s nearly impossible to “sneak up” on a fly. Because an insect’s flicker fusion frequency is 250 Hertz or more (compared to the human 50), they are vastly more sensitive to motion. Flies can see a flyswatter coming at them, no matter how slow or fast you move it. As anyone who has ever examined their prey has noted, flies are also hairy.  These “hairs” (setae) make them sensitive to changes in ambient air speed and direction — they can feel the acceleration of the air from the pressure wave created by the flyswatter.

Michael Dickinson and others at the California Institute of Technology have recently teased out other details to the flys’ success.  They used high-speed imaging to discover that flies will make changes in their body position (including limb angles) upon seeing the swatter.  These adjustments enable flies to take off at the appropriate escape angles when they leap into the air.  Dickson’s advice to fly killers is to aim the swatter to where the fly is going, rather than where it is.  This is of course good advice, but (unlike the details of fly posture) not breaking news to anyone who has hunted moving targets, whether shooting ducks, netting dragonflies, or intercepting soccer balls.

My own advice is slightly different, as it was built upon behavioural observations from several years ago.

Firstly, one can halt (though not immediately kill) a fly in mid-flight by fouling up its airstream.  This involves using not a flyswatter, but a piece of fabric, such as a kitchen towel or piece of random laundry from the washbasket or bedroom floor (you know who you are). You’re still trying to hit the fly, but instead of “snapping” it with a whip action, you’re trying to knock it out of the air.  The stunned fly plummets to a horizontal surface where you can quickly squish it with a tissue.

Secondly, one can outright swat a fly that has (finally!) chosen to land somewhere.  I usually do this with both hands, which naturally requires one to get over the learned repugnance of touching a fly. (But hey, we do have soap and running water, right?)

Now, we already know that the fly can see you coming, and can feel you coming.  Neither stealth by flyswatter speed nor approach angle will work.  What I do is to pluck a tissue from the box, set it nearby, and then “bookend” the fly by framing open hands (with fingers closed together) on each side of it.  I’m not trying to swat the surface (which then necessitates waiting for the fly to land on something both hard and washable), but rather the airspace several inches/ centimeters just above the surface.

When I clap my hands together, it doesn’t matter which direction the fly is positioned to take off — it’s still caught between my hands.  Because I have bony fingers, sometimes the fly is caught in the pocket between the base of two fingers and my palm, but a slight twist of my hands in opposite directions is sufficient to do the pest in. It’s not necessary to reduce the fly to a messy smear — just enough pressure to break the wings is enough to disable it so you can deliver the killing crack while picking it up with the tissue.

Having then rid the room of the rambunctious irritation, I then go to wash my hands of the whole affair.

P.S. See Bug Girl’s blog for a series of great posts about distinguishing between flies and bees, or my own series on the subject, “Garden Buzz: Bee or Not a Bee?”



  1. 4 December 2008 at 0:04

    OMG flies are so dam clever, I shall never kill one again!

  2. 28 October 2008 at 16:27

    I am very noise- and pitch-sensitive, and certain noises drive me WALL-CLIMBINGLY INSANE. The pitch generated by fly wings is one of them.

    One summer we had so many flies in the house that I took it as long as I could until just snapping and going bananas with the flyswatter!!! “Grrrrrrrrr!!!” I emoted! I swatted! There was carnage everywhere!!! Corpses littered the carpet!!!

    My bird-catching cat had the most clear-cut mammalian “Chill OUT, dude, jeez, they’re just flies!” expression on his face that I have ever seen on another living thing.

  3. diddums said,

    27 October 2008 at 20:35

    My cats are death to flies… I think they just exhaust them, and the flies eventually come within their reach when they didn’t have to. I’m not sure a fly can just get up high and stay there; it has to be constantly on the move… and eventually that brings it back within reach of those greedy paws.

    Both cats have been seen picking up flies in their mouths, carrying them around, and putting them down again, uncrushed, to see if they will move around and be entertaining. The flies sit looking stunned.

  4. Ettina said,

    27 October 2008 at 19:13

    My brother is another fly-catching kid.
    He tried to explain to me how he does it. Apparently, flies have trouble turning 180 degrees in midair very quickly, so if you put your hand in front of them they will fly into your hand. Even if they aren’t already flying, they’ll take off in that direction.
    Also, moving your hand closer slowly until the fly twitches, then staying still before sneaking a bit closer again can get you pretty close to a stationary fly and increase the chance of fly-grabbing. (I use a similar technique to catch my cats.)
    As for cats catching flies, I have occasionally seen them hunt flies, but it seems to me that only kittens try and they rarely succeed. Moths are more entertaining, it seems.

  5. qw88nb88 said,

    26 October 2008 at 2:14

    Our four cats seem to have selected for flies that maintain altitudes too high for feline reach. Alas, this leaves all of us laying in bed or sitting at the kitchen table, tracking the demons as they make noisy loop-de-loops around the ceiling.
    Being the resident entomologist (or even biologist) I am the default person in charge of pest control, no matter what the phylum!

  6. 26 October 2008 at 2:04

    Although this is very sound advice, I only have one thing to say:


    I cannot abide the thought of trapping a buzzy fly in my bare hands. Even if it is immediately stunned, the memory of that feeling will stay with me for ages. UGH!

    Therefore, I propose a completely different method. A young cat (or three). it is not always effective, and is extremely inefficient. However, it provides real entertainment for both cats and children (flies have not offered opinions on this) for quite some time. And there is no touching of hideous, dry, crackly files with bare hands needed as they are usually eaten in the process.

    One Sick Mother.

  7. qw88nb88 said,

    26 October 2008 at 2:03

    Now Maddy,
    If you keep killing all of the slow flies, then you’ll be selecting for the really quick ones that can evade your damp dishcloth! (-;
    Of course, all of your children are also above average.

  8. Maddy said,

    26 October 2008 at 0:16

    I must have listened to the same programme. I was also fascinated at how they came to that determination in collaboration with the film speed etc.

    I’m tempted to say that it’s nonsense for two reasons:-
    I am an expert swatter with a damp dish cloth
    All of my children can catch flies on the window without squishing them

    but of course that’s purely anecdotal and quite bizarre.


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