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Which Insect is Causing Your Horse’s Sweet Itch?

September 20, 2022 5 min read

Which Insect is Causing Your Horse’s Sweet Itch?

If your horse has insect bite hypersensitivity, also known as sweet itch, it’s easy to feel desperate for a solution. In your hunt for sweet itch remedies, you may want to investigate which insect your horse is allergic to. 

While it’s not an exact science, there are ways you can attempt to figure out which insect your horse could be reacting to. Allergy testing is the most common go-to, however these panels can come back with multiple positives that will be impossible to avoid, i.e. dust, trees, hay. Multiple positives can be confusing and overwhelming and not give you or your vet a good starting point to manage your horse’s sweet itch. 

Understanding which insect your horse is allergic to has many benefits. For example, if you learn your horse’s sweet itch is being caused by gnats (which is most common), you can use fans in your horse’s stall to interrupt these weak fliers. Or, if you learn your horse is allergic to mosquitos, you can keep your horse inside from dusk to dawn when mosquitoes are most active. 

Learning which insect is causing the reaction is the hard part. The following are a few different ways you can attempt to discover which insect your horse is allergic to. 

Observe Your Local Environment

Different insects require different environments to survive. Some must have access to running water in order to breed, while others prefer standing water sources. Even what they eat varies based on species. By analyzing your local environment, you can ascertain which insect your barn may be hosting. Plus, if you understand how your local habitat is impacting the insect population at the barn, you can take steps to reduce or change the makeup of that population.

Culicoides spp are the most commonly thought of culprits of insect bite hypersensitivity. Colloquially called gnats or no-see-ums, these small insects prefer to live in areas where there’s standing water, decaying vegetation, and manure. Unfortunately, most horse farms have plenty of these three things, between manure piles, grass clippings and old hay, and water troughs. 

Black flies must have access to running water in order to breed, but in terms of what they eat… unfortunately that is in plentiful supply on most horse farms. Female black flies must have a blood meal in order to breed, which is why our horses are so bothered by these pests. 

Stable flies are accurately named as they must have access to decaying bedding and manure in order to survive. As all equestrians know, horse farms have both of these in bulk. 

Unfortunately, like almost every method, this is not an exact science. There is some overlap of the preferred habitats between species. For example, both deerflies and horse flies must have access to vegetation and water. But if you combine this tactic with others, you can still narrow down which insects are most common in your local habitat. 

Who Lives Nearby?

If you’re not located near any running water sources and you’ve taken care to manage your manure, you may be frustrated to find you’re still dealing with a healthy population of nuisance insects on your farm. This may be because of your neighbors. 

Many insects are attracted to particular species of livestock. For example, horn flies are attracted to cows and cow manure, in particular. House flies, who prefer poultry manure, may be more prevalent near chicken farms. 

It’s also important to look at the stable management practices of your neighbors. No matter how well you manage your manure and work to control your fly population, if your neighbors are practicing bad stable management, you will have a never-ending battle on your hands. 

When looking at the local farms in your area, don’t just consider those that live right next door. Biting insects can travel much further than you may realize. For example, most species of mosquito can travel between one and three milesHorn flies from cow farms can be an even bigger problem, as they can travel up to 10 miles in their search for cows. However, once horn flies find a cow farm, they tend to stay within a few miles of their preferred targets. 

By looking at your neighbors you may be able to ascertain the population of the insects on your farm. This can help you discover which insect is most likely causing your horse’s allergic reaction. For example, horn flies can cause sweet itch, so if you live within a few miles of a cow farm, chances are high that horn flies could be causing your horse’s insect bite hypersensitivity. 

Analyze the Location of Sweet Itch Lesions

Did you know that the location of your horse’s lesions can tell you which insect caused them? Certain species of insect prefer to bite or only have access to a few areas of your horse’s body. By analyzing where the highest concentration of bites are, you can figure out which insect is most likely to cause your horse’s sweet itch. 

Culicoides spp typically bite near the mane and tail and along the abdomen and belly, but will also attack the ears, especially on horses whose ear hair has been clipped. Black flies are less particular and bite all along the face, ears, abdomen, groin, forelegs, and thighs. Horn flies prefer to bite the very center of the belly, at the navel. Mosquitoes, on the other hand, bite along the sides of the horse. 

Adjust Your Horse’s Turnout Schedule

Did you know that the time of day your horse is bit can tell you a lot about which insect your horse is allergic to? Unfortunately, discovering which time of day your horse is bit can be complicated. One bite from a midge can have an impact lasting twelve hours. Just because you come to the barn in the evening and see new lumps does not mean that the lumps happened that evening. 

Instead, consider your horse’s schedule. What time of day are they outside? Are they on night turnout or day turnout? Do they live outside 24/7?

Mosquitoes and midges are most active at dusk and dawn and in the period of time right after sunset. Black flies are out and about in the morning and evening, while stable flies, horn flies, deerflies, and horse flies are most active during the day. 

Look at your horse’s turnout schedule and see where it overlaps with the feeding schedule of flies and other biting insects. Try adjusting your horse’s turnout schedule to see if this helps to alleviate symptoms. 

Spend Time With Your Horse

As a last resort, spend some time in the pasture with your horse. Notice what bugs are around you and what insects are surrounding your horse. Do you see flies or smaller insects, like mosquitoes or gnats?

If you’re unable to discover the root of their sweet itch from just one session hanging out with your horse in the pasture, change to a different time of day. You may be surprised to see a big change in your horse’s reaction to the insects at dusk versus in the afternoon. 

If you’re very lucky, you may be able to see the entire process from start to finish. For example, a bug may bite your horse and a few moments later, you’ll notice a lump.  

Sweet Itch: Frustrating for Horse & Owner

Insect bite hypersensitivity is a frustrating condition to manage. It’s hard to watch your horse suffer and not know the root cause of the problem. Owners of competition horses will be at a loss for sweet itch remedies as most contain prohibited substances, like steroids. 

Zarasyl is a new product on the market that is steroid and antibiotic-free, making it competition safe for all horse sports. Filled with non-toxic and non-irritating ingredients, this easy-to-apply cream helps to nourish your horse’s skin from the inside out. 

Click here to learn more about the science behind Zarasyl. 

Click here to learn more about insect bite hypersensitivity.