Watch a horsefly bite human flesh and drink the blood

To make this educational video, some stalwart soul offered themselves as food for a horsefly of the genus Hybomitra.  Like mosquitoes, only female horseflies drink blood, and they do so so with fearsome mandibles that contain six sharp blades, or stylets. Here’s a picture by Anthony Thomas of the mandible of a Hybomitra affinis horsefly, showing the stylets(“st”), and below that, one of the stylet blades.


Thomas’s paper also describes the way they bite:

Blood-feeding is accomplished by retracting the labella, the two lobes at the base of the labium [“la” in first picture above), to expose the fascicle of stylets. The long flattened sharp blades of the Mandibles (Fig. 5) are the first of the stylets that enter and cut through a vertebrate’s skin. With its body firmly anchored to the hosts skin/fur/feathers/scales the female fly thrusts its head downwards forcing the mandibles into flesh. Muscles attached to the base of the mandibles move the blades in a side-to-side scissor-like action thus enlarging the initial wound.

And some Fun Horsefly Facts from Wikipedia:

Tabanids are agile fliers; Hybomitra species have been observed to perform aerial manoeuvres similar to those performed by fighter jets, such as the Immelmann turn. Horseflies can lay claim to being the fastest flying insects; the male Hybomitra hinei wrighti has been recorded reaching speeds of up to 145 km (90 mi) per hour when pursuing a female.

In the video below, the bite itself takes place 54 seconds in, and then the hungry lady fills up with blood that will be turned into eggs.  I bet you’ll wince a little watching this!

And the YouTube notes:

Hybomitra horse-flies biting and sucking blood. Camera: Canon Powershot SX200 with a +12 diopter close-up lens (a doublet lens from an Elmo Super 8 camera).


  1. GBJames
    Posted June 18, 2020 at 2:02 pm | Permalink

    I don’t think I can watch this video.

    • Posted June 18, 2020 at 2:09 pm | Permalink

      Suck it up and watch! It’s not much worse than watching a mosquito bite you.

      • GBJames
        Posted June 18, 2020 at 2:16 pm | Permalink

        I don’t do that, either! I swat the damn things.

    • John Conoboy
      Posted June 18, 2020 at 2:21 pm | Permalink

      It is actually quite fascinating.

      • GBJames
        Posted June 18, 2020 at 2:29 pm | Permalink

        Its evil, I tell you!

    • Filippo
      Posted June 18, 2020 at 9:07 pm | Permalink

      Bet you were glad to get a trigger warning.

      • GBJames
        Posted June 19, 2020 at 9:21 am | Permalink

        I’m a snowflake.

  2. Diana MacPherson
    Posted June 18, 2020 at 2:04 pm | Permalink

    Horseflies hurt. I have had a hole left from the little assholes.

    • Posted June 18, 2020 at 6:05 pm | Permalink

      Deer fly bites are pretty painful too. And harder to defend against. Horse flies are so big and slow I can usually swat them.

      I hate all biting insects.

      • Diana MacPherson
        Posted June 18, 2020 at 6:50 pm | Permalink

        Yeah deer flies are undeterred by repellant sprays too.

        • Posted June 18, 2020 at 8:50 pm | Permalink

          The only redeeming feature of black flies and mosquitoes is that they are deterred by DEET.

      • Diana MacPherson
        Posted June 18, 2020 at 6:50 pm | Permalink

        Yeah deer flies are undeterred by repellant sprays too.

  3. ploubere
    Posted June 18, 2020 at 2:18 pm | Permalink

    That’s some real devotion to science. Those bites feel like electric shocks.

  4. sugould
    Posted June 18, 2020 at 2:26 pm | Permalink

    HOw much blood can they drink proportionate to their weight?

  5. Ken Kukec
    Posted June 18, 2020 at 2:29 pm | Permalink

    Vid needs narration by Bela Lugosi.

  6. Ken Pidcock
    Posted June 18, 2020 at 2:31 pm | Permalink

    I hadn’t thought of them as especially fast, but I guess they are.

  7. Randall Schenck
    Posted June 18, 2020 at 2:42 pm | Permalink

    Horse flies are really nasty. Very hard on livestock. I’m guessing the teet will keep them off as it does for other creatures after your blood.

  8. cicely berglund
    Posted June 18, 2020 at 2:45 pm | Permalink

    Well, up here in the wilds of Canada we get progressively. Black flies. Deer flies and then horse flies.
    I have gotten bit on several occasions and giant swellings appear- not kidding – giant.
    Eyes swollen shut- feet unable to be put in shoes- lips and face beyond recognition.
    I’m more careful these days.

    • Diana MacPherson
      Posted June 18, 2020 at 2:54 pm | Permalink

      Oddly enough I don’t react to these jerks other than missing chunks of flesh but the little black flies will make me swell up.

      • merilee
        Posted June 18, 2020 at 3:17 pm | Permalink

        Same here with black flies. I’ve also been bitten (including today) by tiny little red suckers which might be apider mites. The bites it h like hell for days.

    • garry vangelderen
      Posted June 18, 2020 at 3:05 pm | Permalink

      These bugger’s bite hurt like hell and then itch like the blazes. Fortunately not many around where I live in Ontario (Penetanguishene). But get plenty of black-flies and deer flies. Mostly itching reaction with me personally. Fascinating, though.

    • sugould
      Posted June 19, 2020 at 11:05 am | Permalink

      Have been stopped at a traffic light near our forest preserve, and they deer flies will repeatedly ram the windshield. Had one that circled back three feet away, and dove straight in at me. And did so eight times. Their determination is scary.

  9. Jacques Hausser
    Posted June 18, 2020 at 2:57 pm | Permalink

    Interesting to see the spiracles (respiratory apertures on each segment) appearing between the dorsal (tergites) and ventral (tectites) plates as the abdomen is progressively inflated by the blood.
    The respiratory network of trachea is itself visible by transparency.

  10. Posted June 18, 2020 at 3:09 pm | Permalink

    And you wonder why your readership has taken a dive! 😉

    • GBJames
      Posted June 18, 2020 at 3:11 pm | Permalink

      If he puts up a video of a tick chewing on someone, I’m outa here! 😉

    • Posted June 18, 2020 at 4:20 pm | Permalink

      Hardy, har har; so funny I forgot to laugh!

      • Posted June 18, 2020 at 5:15 pm | Permalink

        “har, har”

        Looks like you did laugh after all. Actually, I am trying to pass your horsefly video through an online image stabilization process. If it works, it’ll make it even more repellent.

        • rickflick
          Posted June 18, 2020 at 9:10 pm | Permalink

          Ya, the shake is a bit annoying. Where is this online stabilizer? I have one in my Vegas editor.

          • Posted June 18, 2020 at 10:39 pm | Permalink

            Actually, I’ve tried a couple of online image stabilizers and they all failed. You get what you pay for I guess. I installed a free app called “4K Video Downloader 4.12” on my Windows PC in order to capture the video from YouTube. I think they have it for other platforms. I’ve never done that before but it worked well. You just cut and past the YT link into the app and it does the rest. Perhaps your Vegas editor is the way to go. I’m not in the habit of doing video work and didn’t want to go the the trouble of paying for it. Plus, we’d have to have permission from its author to do much more with it.

            • rickflick
              Posted June 18, 2020 at 10:50 pm | Permalink

              I downloaded the video and stabilized a few segments. It looks slightly better, but since it’s a very tight image, the whole thing moves, insect and background. Thus, the stabilizer struggled. Slight improvement.

              • Posted June 19, 2020 at 9:29 am | Permalink

                Yes, I suspect that the stabilization algorithm has to decide between shake and legitimate pan and is not optimized for such big shakes. Perhaps a more sophisticated de-shake algorithm would allow such things to be adjusted. Max jiggle for this one.

  11. Muffy Ferro
    Posted June 18, 2020 at 3:41 pm | Permalink


  12. Dragon
    Posted June 18, 2020 at 3:51 pm | Permalink


  13. jezgrove
    Posted June 18, 2020 at 4:03 pm | Permalink

    I should probably insert my “When I See an Elephant Fly” joke here. ..

  14. Jenny Haniver
    Posted June 18, 2020 at 5:18 pm | Permalink

    But Grandmother, what big beautiful eyes you have.

    • merilee
      Posted June 18, 2020 at 5:19 pm | Permalink


  15. Posted June 18, 2020 at 5:27 pm | Permalink

    I don’t know if one of those ever succeeded at feeding on me, but I sure get harassed a lot by them. But deer fly bites are often painless and so I don’t know when one of the little %#%*$$#@^_% is tapping into me.

  16. Paul Clapham
    Posted June 18, 2020 at 5:46 pm | Permalink

    Also posting from the wilds of Canada:

    Their feeding style makes it easy to get rid of them. You hold out your hand until the horsefly lands on it. Then you wait while it gets out its knife and fork (as in the video) and when it’s set to eat, you slap it hard with your other hand.

    This causes it to fall to the ground. But it’s not dead yet! These are tough flies. You have to follow up by grinding the fly into the dirt with your hiking boot.

    We worked on this technique one summer at an Alpine Club hut in the Rockies. After killing 15 horseflies the regional population was significantly diminished.

    • cicely berglund
      Posted June 18, 2020 at 6:12 pm | Permalink

      Waiting for one to securely attach simply invites more to land! You have no idea!
      I am at least half a K from any known horse.
      Maybe they go after bears and coyotes and racoons. Squirrels?, ground hogs? Plus they follow cars- likely attracted to the heat— tho’ maybe those are deer flies.

  17. Laurance
    Posted June 18, 2020 at 6:36 pm | Permalink

    So how did I escape being bitten? Back in the mid ’80’s I lived on a farmette in Newfield, NY, just a few miles south of Ithaca. The neighbor pastured his mules and/or his horse behind my house. Lots of insects there, and lots of horseflies. But I never got bitten.
    Times have changed and locations have changed. Now I’m ten miles north of Penn State and there just aren’t that many bugs any more. On the farmette I had flypaper put up, nasty stuff, full of flies. But here and now I have hardly any bugs at all. I do believe the mules and horse drew flies, but I’ve also noticed that I no longer get all those bugs splatted on the windshield. Climate change, species going extinct, bugs are dying off.

    Very few fireflies/lightning bugs any more, either. When I was a kid back in the ’40’s and ’50’s we’d see no end of pretty fireflies on a summer night. Not any more.

    • Diana MacPherson
      Posted June 18, 2020 at 8:02 pm | Permalink

      Pesticides. I find spray for corn quite dead;y to wildlife.

  18. max blancke
    Posted June 18, 2020 at 8:28 pm | Permalink

    Horrors. Just horrors.

  19. Posted June 18, 2020 at 8:45 pm | Permalink

    This is the stuff of nightmares. When I see one, I will kill it.

  20. Steven Hill
    Posted June 18, 2020 at 9:05 pm | Permalink

    I listed to a discussion on BBC radio some while back about how medical researchers are using nature’s evolution of the mosquito mandibles/stylets (I don’t remember which species) to improve tools for drawing blood, making injections etc. with less pain.

    Back in 2005, Peter Forbes published a book “The geckos’s foot” about how “Scientists are taking a leaf from Nature’s Book.” An interesting read. It is still available.

  21. rickflick
    Posted June 18, 2020 at 9:41 pm | Permalink

    The kids back in the day used to think it was fun to let the fly fill with blood, then smack it and leave a nice big red splatter. 😃

    • Diana MacPherson
      Posted June 19, 2020 at 10:02 am | Permalink

      With mosquitos you pinch the area they are drinking from so that you fill the mosquito up with blood too quickly & they explode.

      • rickflick
        Posted June 19, 2020 at 10:08 am | Permalink

        That’s something I never tried.

  22. Posted June 18, 2020 at 11:17 pm | Permalink

    THAT is some nasty-assed fly porn. If I were a teacher I’d make my students watch it just to freak them out. 🙂
    Man. I think we used to have them in Australia but I’ve never seen one in NYC. Like Republicans – we just don’t let them in here!

  23. Hempenstein
    Posted June 19, 2020 at 7:53 am | Permalink

    What are the stylets composed of? Chitin, or some sort of calcified material?

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