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Protecting Your Horse This Spring from Flies and Worms, Oh My!

Photo by Kwadrat/Shutterstock

Tiny creatures certainly have the ability to make our lives, as well as the lives of our horses, miserable. While we can never completely eliminate pests such as flies and parasites, we can do a lot to keep them at bay—especially when the weather starts getting warmer in the spring and we plan our spring horse care strategies. Let’s look more in-depth into the pests that plague our horses and what we can do to manage or eliminate them.

Pesky Flies



The flies that most horse owners deal with are the big four: stable flies, face flies, bot flies and horse flies. The best way to reduce the number of flies that annoy your horse is to make it hard for them to reproduce. Implementing fly-control methods in the spring will pay off come summer when fly populations are at their highest.

Face flies feed on the moisture around a horse’s eyes and nose. Photo by Anjajuli/Shutterstock

Knowing where these flies start their lives will help you put a stop to their reproductive cycle.

STABLE FLIES: These nasty greyish-black flies have a painful bite that they inflict on horses, most often on the legs. They lay their eggs in rotting vegetation, dirty bedding, manure and areas of urine.

FACE FLIES: These small, dark flies don’t bite, but instead feed on the moisture in the corners of a horse’s eyes, on the moist part of the horse’s nose and on open wounds. They lay their eggs in manure.

BOT FLIES: Unlike most other flies, bot flies do not bite or feed on the outside of the horse. Instead, they lay their eggs on the horse’s legs, shoulders or mouth with the intention of the horse swallowing the eggs.

Once inside the horse, the eggs hatch and the larvae burrow into the horse’s stomach, where they do damage for several months before passing out through the manure and continuing their life cycle.

HORSE FLIES: You can’t miss one of these flies when it lands on your horse. Horse flies are large with a black body and a white head. They prefer to leave their painful bite on the withers or rump and will easily draw blood.

Their breeding place of choice is damp soil near irrigation ditches, lakes and rivers.

Bot flies lay their eggs on the horse’s coat where they are likely to be ingested. If not removed, they can damage the horse internally. Photo by Dusty Perin

Getting Fly-Free

Given the reality of how these pests live their lives, what can you do to minimize the number of flies that harass your horse? Plenty!

Here’s how to reduce pests at the barn.

MANAGE MANURE: It’s obvious that with the exception of the horse fly, the most common flies to bother horses spend their entire lives in the stable environment. Stable flies, face flies and bot flies all need manure to reproduce, with the stable fly also branching out into dirty bedding.

This is why frequent stall cleaning and manure removal is key when it comes to keeping flies to a minimum. Picking up and disposing of manure and soiled bedding every day is a must if you want to make your barn inhospitable to flies.

PHYSICAL PROTECTION: You can keep your property clean, but you don’t have much control over how your neighbors manage their manure. If you’re boarding your horse, you’ll discover that large numbers of horses make it a lot harder to control fly populations.

To provide physical protection, a fly mask keeps face flies out of your horse’s eyes. A fly sheet for your horse’s body and fly wraps for his legs will keep even more insects off your horse. Photo by Rob Kemp/Shutterstock

In both of these situations, you’ll need to provide your horse with physical protection from flies. Start by using a fly mask to keep face flies out of your horse’s eyes. A fly sheet for your horse’s body and fly wraps for his legs will keep insects from being able to reach his skin.

SPRAYS AND TRAPS: Repellent in the form of fly sprays, wipes and mists can also help keep flies off your horse. You can apply fly repellents topically to your horse daily or install an automatic misting system in your barn that will provide a dose of repellent at regular intervals.

Fly traps can also be helpful because they capture flies that are buzzing around, stopping them from annoying your horse and reproducing in your horse’s manure and bedding.

BIOLOGICAL CONTROLS: A natural way to help control fly populations is with beneficial insects that feed on fly larvae, killing the maggots before they turn into flies. These tiny wasps don’t bother horses, but they will dine on developing flies.

You can buy these fly parasites through mail-order services, placing them outside in your stabling area when they arrive each month. You’ll need to start adding fly parasites to your stable soon in order to head off the fly explosion that starts in the spring.

If using spray-on fly repellent, you will need to re-apply thouroughly every day. Photo by Clix/Shawn Hamilton

FEED-THROUGH FLY CONTROL: Equine feed supplements designed to keep fly eggs from hatching in manure can be helpful in keeping fly populations under control. These products work by disrupting the fly’s development cycle in the manure with the use of an insect growth regulator (IGR). The IGR passes through the horse’s system into the manure, where it prevents the fly from developing. Feed-through fly control works best if all horses on the property are given the product on a daily basis.

Spring Horse Care Against Internal Parasites

The other common creepy crawlies that can make life difficult for horses and their owners are worms. A handful of these internal parasites are a real nuisance and are prevalent among domestic equines. These pests enter the horse’s body through the mouth and complete their life cycle in manure. Infected horses can become very sick if worms are allowed to go unchecked.

The most common worms to affect horses are strongyles (large and small), roundworms, pinworms and tapeworms.

LARGE STRONGYLES: Large strongyles are only a half-inch long, but they can wreak havoc on a horse’s intestines. They can cause colic, as well as blood vessel and organ damage.

SMALL STRONGYLES: Small strongyles burrow into the intestines of the horse and cause damage to delicate tissues. They are very common in horses and can result in colic, diarrhea and weight loss.

ROUNDWORMS: These nasty worms can grow up to a foot in length. They live in the horse’s digestive tract and cause colic and poor condition. They are most common in young horses less than a year old. Older horses usually develop an immunity to roundworms.

PINWORMS: Pinworms are about 2 inches long and live in the horse’s rectum, where they may cause irritation and discharge. Horses infected with pinworms often rub their tails against fences and trees.

TAPEWORMS: You can help get rid of the worms in your horse’s body by using a dewormer every few months. These products are available in tack and feed stores, but should be given under the guidance of your veterinarian, because some worms are developing resistance to the most common dewormers. Your vet can help you rotate the different types of wormers to help prevent this.

Fecal testing under your vet’s guidance will help you choose the most targeted dewormer to use in light of increasing drug-resistance among internal parasites. Photo by Sari Oneal/Shutterstock

Fecal egg testing involves having your horse’s manure tested every few months for parasite eggs. This technique is becoming the preferred method by many veterinarians for parasite control.

Because the weather is getting warm, spring is a great time to start your spring horse care strategies against parasites, as well as flies. A number of mail-order laboratories provide this service, which requires you to send a small manure sample for testing. The resulting fecal egg count helps determine if your horse has worms, and which species, so you can effectively treat the infection with an over-the-counter dewormer.

You can do a lot to help prevent worms from taking hold of your horse by maintaining good manure control at your stable. Pick up manure and soiled bedding frequently, and keep water troughs and feeders clean.

Starting good stable hygiene in your spring horse care plan is the best way to keep both flies and parasites under control throughout the year. Your horse will thank you for it.

This article on spring horse care on preventing parasites and flies appeared in the March 2020 issue of Horse Illustrated magazine. Click here to subscribe!

Further Reading on Spring Horse Care

Audrey Pavia

Audrey Pavia is a freelance writer and the author of Horses for Dummies. She lives in Norco, Calif., with her two registered Spanish Mustangs, Milagro and Rio.

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