Flies, Worms and Yucky Things

Fly and parasite control is an important part of horse ownership.

Horse has flies on nose
Photo by Patrick Lefebvre/Shutterstock

Things that fly, bite and bother your horse are in the air, and in the gut. Whether you board your horse or have your pony at home, now is the time to think about parasite control for horses to protect your equine friend from pesky pests like worms and flies before they cause problems.

Fly Control

Fly spraying a horse to prevent flies
Spray your horse daily and before riding to get the most out of your fly repellent. Photo by Shelley Paulson

As the weather warms, flying insects of all kinds start to emerge at the barn. You may notice your horse start to swish his tail on a calm day in the pasture or nip at his flank while you’re on a trail ride. Not only are flies annoying, but they can also irritate your horse’s skin and spread disease. Learning how to manage flies early in the season means you’ll be a pro at fly control by summer when they are even more of a menace.

The first step in effective fly control is good barn hygiene. Make sure manure is picked up in the barn aisles and stalls are cleaned daily. Also keep fresh water in your horse’s buckets. Manure and stagnant water are prime breeding grounds for bugs that bite, including mosquitoes.

Next, don’t fear the fly spray. As a horse sweats, sprays wear off, so a good routine is to spray your horse in the morning and in the evening, and before you ride. Don’t forget to re-apply if you bathe your horse.

Hold the spray about 6 inches away from your horse’s body and apply up and down his legs and under his belly and up the neck. Face application is important, too, but be careful. Many horses don’t like to be sprayed in the face, so applying spray to a clean cloth and wiping your horse’s ears and around his eyes is better, especially so spray doesn’t accidentally get in the horse’s eyes. There are also fly wipes specifically made for this. A fly sheet and fly mask may also be a solution if your horse has sensitive skin.

Preventing flies using a mask
Physical barriers like fly masks are a great way to create a no-fly zone. Photo by JFJacobsz/Shutterstock

Finally, don’t forget about the secret weapon against flying insects: a good breeze. Wind makes it impossible for flies (and mosquitoes) to land on your horse, and no landing means no biting. If your horse’s stall has a window, open it when possible. A fan in the stall or in the barn aisle can also be a huge help in preventing pests from bothering your horse (make sure to use a fan rated for farm or industrial use so the motor is sealed off from dust and there is less risk of fire).


Internal parasites, also called worms, are common in horses because immature worms (larvae) live on blades of grass and are passively eaten when a horse grazes. Larvae emerge in pastures in the spring. These larvae then develop into adult worms within the horse’s intestines.

While this sounds gross, it’s really important to realize that a small number of worms typically does not harm a healthy adult horse. However, large worm infections can cause problems, like diarrhea, weight loss and sometimes colic.
Equine parasite control can be done with one of several deworming drugs made for this purpose, but not all horses need to be treated. So how do you know if your horse needs a dewormer?

Using paste to prevent worms in a horse
Your vet can help you select a dewormer after doing a fecal egg count. Photo by Gina Cioli

In the spring, ask your vet to do a test called a fecal egg count. To do this, your vet will take a sample of your horse’s manure, mix it with a special liquid, and look at the sample under a microscope. Parasite eggs are shed in your horse’s manure, so if your horse has worms, their eggs are seen as small oval shapes under the microscope.

Don’t worry if your horse’s manure is positive for eggs; this is very common. What’s most important is the number of eggs. Your vet will count them and tell you how many she finds. If there are many eggs—typically over 200—your vet may recommend treating your horse with a dewormer.

If there are fewer eggs, this indicates a mild infection, and your horse typically won’t need treatment unless he is young or otherwise sick. Not overusing dewormers helps prevent the development of resistance by the parasite to these important drugs.

To help control worms on the farm, remove manure piles in small pastures and paddocks to prevent the spread of worm eggs. Not allowing your horse to overgraze a pasture is important, too. Grass should be kept about 3 to 4 inches tall—shorter than that and it’s time to move your horse to another field, if possible, to allow the grass to re-grow.

With a little planning and awareness, you and your horse can be worry-free from worms and flies this spring!

This article about flies, worms, and more appeared in the Spring 2020 issue of Young Rider magazine. Click here to subscribe!



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