Check out this massive fly

This weekend The Ranger discovered that the biggest fly in the UK was much bigger than he’d previously thought. Yes, we heard you wanted to see a picture of a simply gigantic horsefly. So here it is.

Tabanus sudeticus (c) Cat James


This is Tabanus sudeticus, sometimes called the dark giant horsefly. It seems, oddly enough, that this impressive insect has not really got a commonly-accepted English name. It’s referred to in one place as the “dark behemothic horsefly”: a charmingly descriptive name, albeit a little cumbersome. Yes, it’s sitting on my finger and no it didn’t bite me. They can be up to 25mm long (that’s one inch) and 50mm across the wings – a massive fly and the largest dipteran in Europe (I think it was bigger! Having measured the Ranger’s finger, the fly could’ve been at least 30mm – The Cat). Horseflies are big, fast-flying creatures, and they will bite any big mammal, including humans. The bite is very painful, and as horseflies cut the skin when they bite (rather than pierce it), horsefly bites can take a long time to heal, and can cause infection. Unlike insects which surreptitiously puncture the skin with needle-like organs, horse flies have mandibles like tiny serrated scimitars, which they use to rip and slice flesh apart. So I’m quite glad my new friend didn’t take a nibble out of me. Given the size of it, it might have left me rather drained and anaemic.


I was walking in a wet meadow in West Hampshire, where the thick, lush vegetation was buzzing with life. Swallows swooped overhead, and we were admiring the bee-flys that seemed to be almost swarming around us. Suddenly, my companion Cat shuddered to a halt having nearly trodden on what she at first thought to be a moth. It turned out to be the biggest fly we had ever seen. It was soon captive in a jamjar and being admired safely through glass. In the video above a 5p coin is in the jar for scale.

Tabanus sudeticus (c) Cat James


Adult horse flies feed on nectar and sometimes pollen, and the female flies drink a blood meal before laying eggs. Males don’t drink blood – so which is this character? The key is in the eyes. Like many big-eyed dipterans, the males have holoptic eyes which meet in the middle, whereas the females have a bar separating the two big eyes. Clearly, in the picture you can see that this one is a female. Mmm. Good job she wasn’t hungry. After a bit of cooing and gawping; we decided to let the captive free, as she seemed to be getting a little irritated by her imprisonment. It shook itself, cleaned itself for a moment, and flew off with a noise that sounded more like the low drone of a stag beetle or moth than the buzz of a fly. We’ll report the sighting to the Hants fly recorder in due course as the species is not very widely distributed. One would imagine that any sightings would be quite often noted, as the things are so spectacular. Anyway, we didn’t have a saddle that would fit it, otherwise we might have tried to ride it home.

56 thoughts on “Check out this massive fly”

  1. Had one of those gym bunny horseflies in the house today. Weโ€™re at Hengistbury head, Bmth. Last seen flying off carrying next doorโ€™s Yorky

  2. Took some photos a couple of hours ago of one that had landed on my wife’s car, getting on for an inch long. Have noticed a couple in the area in the last day or two, one dipping down to a pond en route in a direct line.

    This is urban Hedge End (near Southampton) and a sliver of remnant habitat running through it known as Wildern Nature Park.

  3. In the hundreds on the estate I work on in Cornwall, I’ve also been massacred by the big buggers this year. An awesome insect to say the least.

    1. We have seen a number of them this year here in Maryland’s Eastern Shore region of USA. They fly around aggressively as we get out of our pool. About an inch long. Hadn’t noticed so many in past years.

  4. A beast of a fly, I live in Swansea and one of these creatures seems to be hanging around my house quiet frequently. Caught it trying to get into my car through a partially opened window, I prodded it and it flew off sounding like a WW2 Bomber.

  5. Had two of these in our garden today. One sat and watched me for a while from a vantage point on a large cardboard box, and flew off when I confronted it. The second flew I and out of our garden room, checking out the inhabitants as it did. Scary flies, but probably not as dangerous as they look. I’m in Brockenhurst.

  6. Found one today. On a common was walking and heard a buzzing noise making me take a closer look and I saw this. Mid wales, Powys.

  7. Had one of these bruts on my house wall today…never seen anything like it before..and will be quite happy not to see it again..!!!…north Pembrokeshire .

  8. One good thing has come out of this wet spell, it has suppressed the giant dark horsefly biting the hell out of my pigs this year.

  9. Wow, I came across one of these earlier today, after never having heard of such a thing. I live in Cornwall and am well used to horse-flies, but this was a monster at a full inch long – hence, I googled it! Thank you for explaining about it.

  10. One of these monsters was on my windscreen. I too thought it was a kind of hornet. Couldn’t believe how big it was. Sat there as cool as you like whilst doing 40mph. Eventually I pulled over took a picture (sent it to our local science society to have them identify it) then turned on the wipers. I wasn’t going near it. Thanks for telling us what it was. I’m in Bournemouth by the way.

  11. You’re probably sick of getting replies to this post, but thanks for helping me identify it. Just found one in my garden. Unfortunately my papillon got there first and ripped its wing off. My dad says his neighbour in Northwest Wales once told him it was called “Bob the Driver”.(And something he cannot remember in Welsh!)

  12. Our son was bitten by one of these in Brittany last weekend. It got him on the forehead and within an hour one side of his face had swollen up, closing his eye completely. Even with various medicines the other eye followed the next day. It has taken a week to go down and he as been told to stay on the tabs for another week. Beware.

  13. We seem to be inundated with these things. First saw them a few years ago hassling the cattle. This year they seem to be everywhere along the banks of the fields. Monsters. They have been too fast to get decent photos, but I will keep trying. We are in Pembrokeshire. Thanks for helping identifying this beast, we thought they were some species of hornet going by the noise they make.

  14. Just found one of these stunned by the side of the road in Greenock but it was really huge with a body well over an inch in length (no doubt at all it was over 3cm, nearer 3.5cm). I admit i had no idea what it was, picked it up by the wing in put it into the grass at the side of the road as i thought it a member of the hoverfly family. I’ll not be doing that again.

  15. We have just caught one in our conservatory in Stirling (Scotland). Last year we had 5. Glad to have at last found out what they are!

  16. just seen a few of these beasts on the isle of arran. Knew it was unusual due to its size (approx 35mm long) but ive never seen a horse try to buck to get a fly off before! the bite must have hurt as the horse bolted across the field. since i first seen it they are daily hassling the 2 horses in the field next to our holiday house. im going to have nightmares now. your meant to get big scary biting insects in australia and africa, not arran!

    1. Be very careful around them, they land ever so gently and you don’t feel them until it’s too late, I have now had an antibiotic injection because of the swelling on my arm, which is still most painful – happy holiday!

  17. I have been trying to catch one of these giant horse flies for over four years …. the length of time they have been driving my horses mad. We live within Dartmoor National Park in Devon, UK. None of my horsey friends believed me regarding the size. I think they thought I was nuts. I have caught one at last! They are usually too fast and make the horses bolt. Yesterday was cold and wet and a female (one inch long) was sitting on my horse’s rump. She (the fly) should have gone to Specsavers because I got her into a jam jar. She is now in my kitchen waiting to have her photographs taken.

    1. I have a couple of horses (in South Devon) and have noticed how these clever flies will always try to land on their rump – the one place they can’t really get at! The fly is so huge I can see it clearly from across the field as it hovers above the horse’s rumps (as they run around trying to get away). They are a danger when riding because the horses hear them coming like a biplane and are beside themselves with fear. There only ever seems to be one at a time and I have wondered if they have territories?

  18. Several of these have been sighted in Dumfriesshire recently. Those I saw were around 3cm long. Didn’t know what they were, so thanks for the info.

    1. As they don’t have a common name I think they should be called “the dark invader” because that is how it feels, got bitten by one yesterday, the top of my arm has a 9mm swelling that feels more like a burn with the centre beginning to gather.

  19. We have had several strikes on our young horses over the last week (mid July). Just sighted 3 together – two on a horses fly rug (12cm apart), the other ‘buzzing’ around.

  20. We have them all the time in the summer months, in fact I have seen so many I can’t count, they are so loud you can hear them before you see them, and they are pretty fast too. Usually near horses and water, the horses go pretty crazy when they land on them due to there terrific bite, often when a horse is bitten it requires a vet visit as depending on the area of the body bitten, there can be quite substantial swelling. Luckily I have never been bitten myself …. Anyone wanting to see them I would recommend visiting the new forest, find a horse and water, and at the moment JULY seems productive for viewings, lol must be breeding season for those blood loving females I guess! A lot of people assume they are hornets as they are large and stripped but they are grey, not yellow, and far more aggressive than the poor old hornet!

  21. A large one of these giant horseflies, well over an inch long, attached itself to my veranda door last night. It had quite a foreboding presence as it peered through the glass at me. Fairly unusual in urban Glasgow I would have thought.

  22. We found on of these in the poltunnel yesterday. Managed to get some brilliamt close-up phots whilst it was munching on a sugar lump. We are near Aberystwyth.

  23. Just hard one trapped in our hallway – scared the life out of us! Managed to catch in a cup and let it go – just hope it doesn’t come back!

  24. iv never seen one of these alive but i did once see the remains of one pushed to the outside of a house spiders web in my home once. Hoping to see one alive but don’t know how common they are down here in Plymouth lol

  25. I have just seen one of these feeding on my pig in sunny Devon. It was 2.5cm long and it has ripped a hole in the pigs side. I have ridden horses for thirty five years and have never seen one of these proportions, to be honest I don’t want to see one again.

  26. Just had one on the front window of the house , seemed to be half asleep. We managed to measure it using a steel ruler from the inside of the glass and I can confirm it was 33mm from head to tail.though it’s fore legs stretched out much more another good 10mm infront of the head .Llanberis North wales..

  27. I believe that I was bitten by one of these in Les Montagnes Noires near Carcassonne in France about 3 weeks ago. During the day I had swatted any number of little grey horseflies which had decided I was the perfect lunch and was then bitten on the calf by a monster. She was swatted as well, but not before she had started feeding. For the next 4 days my calf was badly swollen and extremenly uncomfortable. I recommend not being too friendly to the critters – it may be interesting to see them, but they aren’t nice to know !

  28. On holiday in Kinsale County Cork a couple of weeks ago my fiance and I had to rapidly exit a shop when we saw the biggest horsefly I have ever seen buzzing in the window. I examined it from the safe exterior of the shop. Body width was a little over a cm and I estimate the length as approx 2-3cm. Much MUCH larger and bulkier than the common grey horseflies that lazily attack you on sunny walks near livestock. I am so glad I did not meet this particular beast in the great wide open. ๐Ÿ™‚

  29. Thanks!

    Your site has been a help in confirming ID of one which came into our lounge yesterday and frightened both of us so much it was swatted! I’m glad it was not a Hoverfly, as I’d have hated had we killed one of those, but having been bitten by a similar Horsefly in the past, I have no great regrets this time.

    (I have several photos of ‘her’! More than covered a 2p piece. How do I contact the West Hants fly recorder, please?)

    The Ranger responds: Glad we could help! Hants recorders here.

  30. I’d never come across one of these before, but having found one on my drive two days ago and researching what the species it was, my daughter and partner also found one while out walking the dog last night. We live in rural mid Wales where there are no records, (until I get mine in later!) both specimens were laid on the tarmac, but in locations 5 miles apart. Would anyone know if this is normal behaviour?

  31. ye gods, this is the fly that has been making my poor horses’ life a misery. they seem to hunt in packs and the horses are terrified of them.

    Have you come across a New Forest Crab fly – now they are really nasty too.

  32. I had one of these in the house today. Quite scary – I thought it was a hornet at first. I managed to set it free before my cat got a second breakfast. I am in Southampton.

  33. I once saw a fly so big it blotted out the sun.

    It was sitting on my nose at the time so possibly perspective had something to do with it.

  34. This fly species is getting bigger and bigger with each comment posting. I saw one that was 9 cm. Any advance on 9? ๐Ÿ˜‰

  35. 6-8cm? I have heard of fishermans’ tales, but never entomologists’ tales. If it was that big, you have enormous brake cables. They don’t comne much longer than 2.5cm, even in the Highlands.

  36. Excellent pictures above, I took one recently of a gigantic specimen, albeit through a window of a camper van, in the highlands of Scotland. It landed on the hood of my dark coloured jacket which was drying off in the sun over the saddle of my bike. In the foreground is the brake cable of the bike to give some scale. I measured the area of the hood that the horsefly is sitting on after it flew away, and yes it measured SIX – EIGHT cm!!!! The length of my forefinger!

    The Ranger responds: That’s the beastie alright. 8cm? That’s gotta be a record!

  37. Found one of these on the front door step of our house in West Wales. It was huge. As an engineer i’m quite good at estimating size and this thing was easily 40mm long. Took a photo of it against a

  38. Just last night, we had one of these in our bathroom. The window had been open all day and it was walking along the sill.

    We’re in Cumbria on the south coast 2 miles from the sea. It was gigantic, quite an impressive thing. I have spent hours trying to identify it and am very chuffed to have come across thing page! Finally! Great site!

  39. I’ve just seen one of these in my rural Dumfriesshire garden…the first I ever saw…thought it was a kind of large wasp first then looked again and searched for it on the net. Think it was a male,about 30mm long. I am quite used to a large variety of unusual bugs and biting insects here being on the fringe of forest and grazing land.

  40. So glad I didn’t handle the one that I just ducked to avoid that flew into the shed 10 minutes ago and then caught in a container and took a couple of pics of. A beast at about 2.5cm long. Thanks for your research – hope I never see one again! From sunny Devon ๐Ÿ˜€

  41. What a brute – looking at the map I’m pleased to see that they don’t menace Kent, but I can see a dot in Devon where I was bitten a few years ago – memorably painful!

  42. Wow.

    The eyes are really huge and you can see the opalescence due to their multifacetedness. My natural philosopher interests would have been completely overwhelmed by my running away instincts.

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