The most common fly on horses is the stable fly. This bloodsucking fly looks like a house fly – it’s the same size and coloration – and has even been called the “biting house fly.” But, of course, house flies can’t bite. If you look closely, you’ll see the mouthpart projecting from the front of the stable fly’s head, looking like a bayonet. Imagine the pain inflicted when the stable fly jabs your horse with that device. No wonder the poor animal tries to get away from them.

Stable fly photo by Nancy C. Hinkle, PhD

Because stable flies feed on blood and only on blood, they spend a lot of time in close proximity to horses (they also feed on cattle). Stable flies prefer to feed on the legs, so you may notice the horse stomping, kicking, swishing its tail, licking at its legs, trying to dislodge stable flies and alleviate the discomfort.

So how can you protect your horse from stable flies? You can’t. There is no repellent that will deter them. Stable flies don’t spend enough time on the animal to pick up a lethal dose of insecticide. Plus, when insecticide is applied to the horse’s legs, tall grass quickly rubs it off. While the insecticides available for use on horses are not very effective against stable flies, every little bit helps. So spray down your horse’s legs with whatever works best for you when you head out on a trail ride, just don’t be surprised when you still see stable flies.

Because stable flies do not develop in manure, feed-through products are not effective against them. Feed-throughs are useful only against house fly maggots. Stable flies are bloodsuckers, so bait traps don’t work for them. The most useful traps for stable flies are constructed with adhesive on vanes so that stable flies are attracted to them and stick to the glue. Of course, placement is critical in order for the traps to intercept the flies before they get to the horses, but the trap must be placed outside the reach of mischievous horses that are determined to inspect the traps (or maul them).

There are many more biting flies that attack horses – horse flies, deer flies, black flies, biting midges, etc. – and perhaps we’ll address them in future articles. Meanwhile, the stable flies are already out and tormenting our horses, so do what you can to protect our equine friends.

But go back in time. Why don’t we prevent stable flies? We know stable fly larvae (maggots) develop mainly in rotting hay and wet decomposing straw. Got any of that in the neighborhood? Spraying insecticide on the hay ring will not kill maggots; the organic material binds the insecticide and the moisture dilutes it, so the insecticide will never get down to the maggots. Instead, let’s get rid of the habitat so stable flies can’t live on our property. The damp hay and straw need to be hauled off – far off. Or we can dry it out so it can’t support maggots. The sun on a hot day can dry it out (of course, any subsequent rain can make it a maggot nursery again), but it must be spread very thin so that it dries all the way, not just creating a dry thatch on top. And stable flies can fly over a mile looking for a horse to bite, so rotting hay needs to be transported far enough that the adult flies won’t find their way back.

I know, I know, prevention is so much more work than just spraying something. But if you had found a surefire product to protect your horse from stable flies, you wouldn’t be reading this.

Dr. Nancy Hinkle, UGA Entomologist + Ashley Best, Newton County Extension Coordinator

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