Les Mouches Plats

Until May 2012, I had no idea that there was such a thing as Mouches Plats.  Anne and I (or rather our horses, Gigi and Flurry) encountered them when we were in the Morvan region, on the last stage of Le Big Trek.  We found it difficult to find information about them at the time, but I have since learned quite a bit.  Unfortunately, they are here in Provence and I regularly pick a few off each of the Boys.

This post might help others identify and deal with them – I believe they are becoming fairly common in Devon and the New Forest, and I’m guessing that with this year’s warm summer, they may spread further afield.


Their Latin name is Hippobosca Equina, but the French just call them Les Mouches Plats – Flat Flies.  Their English name is Horse Keds, or Horse Louse Flies.  (Apparently there are also Sheep Keds.   Yech.  I wouldn’t fancy hunting them down on a sheep.)  They survive by sucking blood, not only on horses, but on cattle, goats and probably deer as well.

They look like they are wingless, like lice, but they do have wings.  Their flight appears to be weak – when flicked off, they half-fall, half-fly to the ground – but they are more than capable of of picking themselves up and flying straight back up onto the horse again.

They land anywhere on a horse and cling on to the hair.  From there, they scuttle and fly in short hops along the horse’s body until they get to the back end, where they disappear between the hind legs and under the tail.  I’ve seen them land on my horse’s neck when out trekking.  Aero is particularly sensitive to them (no surprise there, the big wuss) and starts twitching his skin frantically when one lands to try to shake it off.   Flurry isn’t too bothered by them until they make their way to to his nether regions and then he starts swishing his tail and stamping.

They must tickle like hell as they crawl around on the bare skin under the dock and between the hind legs.  It’s no wonder the horses swish their tails like crazy trying to dislodge them, but once they’ve landed, they cling on tight and they’re very hard to shift.

They feed by biting the bare skin and sucking blood under the tail, between the hind legs, or around the sheaths of gelding and the udders of mares.

When present in large numbers, they can cause anaemia, but to be honest they cause so much discomfort to the horses that I hunt them down and kill them on sight.

They are not deterred by fly sprays, either chemical ones or natural ones.

Apparently a coating of oil or Sudocreme (zinc & castor oil) under the horse’s tail stops them from getting a grip once they arrive there, but you’ll need to put it ALL OVER the area between the hind legs – around the sheath/udder, right up high between the thighs and all the way down between the ass cheeks.  Then if the horse sweats up a lot, this will rub off so you may still have to be track down and remove some fliers after a ride.

Alexandrine has a technique to catch them which involves duct tape.  She wipes the piece of tape (sticky side out) between the horse’s um… “cheeks” and the flies stick to it.  Then she rolls it up and crushes them.

Me, I hunt them down singly.  They invariably fly away if I bring my hand down on them from above.  I’ve found that the best approach is to sweep my hand towards them over the horses skin and grab them quickly from the side or to pursue them into the dark regions between the horse’s hind legs.  It’s a good job my boys trust me… and a compelling reason to desensitise any horse to being groped “back there!”

Finally, here’s the story of my first encounter with them in the form of some shameless self-promotion – an extract from my book, Through the Ears of an Irish Cob, which recounts the full story of Le Big Trek (I hope it’ll be ready for publication in the early autumn).  Anne and I were at our final base in the Morvan region, staying at Camping du Lac at St Agnan, which was owned by an English couple called Andrew and Moira.  We’d been there a couple of days and were just getting ready to head off one morning…

As I was walking towards Flurry from behind, he swished his tail and something caught my eye.  It looked like he had droppings caked under his tail, squished in along his butt crack – possibly a sign of diarrhoea, definitely not a good thing.   I lifted his tail for a closer look and recoiled in horror.  What had looked like a couple of lumps of horse poop was actually a seething mass of flies, clustered together between the cheeks of his bum.  As soon as I lifted his tail, they scattered in all directions, some of them flying weakly in a series of small hops to land further down his legs and some of them scuttling along like crabs to settle around his anus or to disappear into the crevice between his hind legs.

“Jesus!” I exclaimed.  “Look at these!”

Anne came over for a look and was equally repulsed by the loathsome little creatures.  Neither of us had ever seen anything like them before – they were about the size of a small house-fly, but were flat, like a tick, with a body shape very much like a louse.  Anne checked under Gigi’s tail, but for some reason she didn’t have any – Flurry seemed to be much more attractive to these little creepy-crawlies.

I brushed off as many as I could, but as fast as I flicked them off, they hopped and flew back up his legs again.  I managed to catch one or two and tried to crush them, but they seemed like ticks – hard-bodied and impervious to finger pressure.

“We’re going to have to figure out what these are,” I said, frustrated at their persistence.  “They can’t be good, I guess they’re laying eggs around his bum (I was wrong).  We’ll have to find out how to get rid of them.”

There wasn’t anything we could do about them at the time, so we carried on tacking up and I put the dogs in the jeep once more, gave the keys to Andrew and we set off to clock up the morning’s quota of kilometres….

Some internet research later taught us that the flies were called Horse Louse flies and were not found in Ireland, but we struggled to find a way to get rid of them.  A few days later, Le Big Trek completed, we arrived at a posh riding stables in Dijon, where we were to meet the truck which was taking our beloved horses home…

“Let’s clean up the horses so they don’t look like a pair of mucky old carthorses,” I suggested. 

We set to work and groomed the two horses thoroughly.  To my disgust, I found that Flurry had a full complement of the icky louse-flies in his nether regions and when Anne investigated Gigi, she found that she had them, too.

“Shit, what if we’re responsible for introducing these things into Ireland?” I groaned.  “We have to get rid of them all.”

They were evasive little beggars.  Try to come at them directly and they half-fly, half-hop a short distance and then scuttle into the dark crevices between the horse’s hind legs, hiding around the udder on mares and the sheath on geldings as well as right up in the tight crack where their thighs meet.  When I did manage to catch one, as soon as I placed it on the ground to stomp on it, it flew straight back up under Flurry’s tail again. After a few attempts, I worked out a method of sweeping my hand across his skin to catch them before they took flight.  Then, clutching them tightly between my fingers – ignoring their insectile wriggling – I placed them under my toe and started applying pressure through my boot before I even opened my fingers. 

I was doing pretty well and Anne was encouraged by my success rate, so she started hunting them down on Gigi, too.  We spent a gruesome hour crawling around underneath our horses’ hind legs, shining a torch up into their nether regions, fishing for horrid little squirming flies right up in the dark, warm crack between their hind legs, all the while worried that someone would come in and ask us what the hell were we doing.  Finally, we stopped, certain that we’d got them all.  The concrete floor all around us was dotted with little splats of blood where we had squashed them, and Flurry and Gigi certainly looked a lot happier without their passengers.

The best way to kill them is not as described as above – it’s too easy for them to escape.  Loosen your grip even slightly and they’re gone.  The best way is to ehhh… well… rip their heads off.  It’s fairly terminal.

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