Fighting Flies

March 23, 2015
By Debra M. Eldredge, DVM

Every spring, horse owners gear up for a major battle: fighting flies. This is a battle best fought on two fronts—first, minimizing the number of flies to begin with, and second, keeping your horse comfortable.

The two most common flies around horse barns are house flies and stable flies. House flies are nuisance flies that don’t bite, but they can spread disease and irritate your horse. Stable flies bite at the legs and flank, which really stresses horses out and causes them to stomp. Horse flies and deer flies are less common, but rank very high on the irritant scale due to their painful, persistent bites. By employing a comprehensive fly control program, you can help keep your fly problem under control.


When fighting flies, cleanliness is very important. Pick out stalls at least once a day. The farther the manure piles are located from the barn, the better. Frequent spreading helps to destroy fly larvae and dragging pastures to break up manure helps to reduce fly populations.

Flies like to reproduce in warm, wet areas with organic debris. Along with manure piles, this could include areas where old feed has built up and around water troughs. This is one reason why good drainage is so important! Always clean up any feed spills, including hay and concentrates.

Natural Fly Predators

Some horse owners prefer to use natural methods of reducing flies around their barns. One method is to encourage the nesting of birds that eat flies, like purple martins and barn swallows, two prodigious fly eaters. Barn swallows may leave small “piles” under their nests in your barn, but those are easily cleaned up as the fledglings grow.

Another type of natural fly predator is parasitic wasps. These wasps lay their eggs in fly pupae, providing a suitable environment for their developing offspring and killing the fly larvae. If you decide to try this method, you will need to supplement your normal population of predators and start very early in fly season. Flies reproduce more quickly than wasps do, so the wasps need high numbers and frequent releases. Check with your local cooperative extension to determine which species thrive in your area.

Feed-Through Fly Control

A relatively new weapon in fly control is the use of insect growth regulators (IGRs). An IGR’s mode of action is specific to insects; these products prevent the development of fly larvae by interfering with the production of chitin, a key component of the fly’s exoskeleton. Fly maggots exposed to this chemical don’t molt normally and die before they develop into winged flies.

The IGR supplements are easy to feed; simply follow the label directions. Most products can be top-dressed on feed or mixed in with your horse’s grain ration for finicky eaters. In order to help stop fly populations from becoming established, add an IGR to your horse’s regular diet before fly season gets underway. The supplement must be continued throughout fly season.

Premise Sprays

Residual premise sprays, which provide lasting fly control, can be applied to the barn and around the property. Always check for animal and human safety precautions when applying premise sprays and follow the directions exactly! Remember, premise sprays may harm beneficial insects as well as the troublemakers you want to remove.

On-Animal Topicals

Your ultimate goal is to keep flies off your horse and there are various topical options to kill and repel flies, including fly sprays, spot-ons, lotions, roll-ons, ointments and fly masks.


All fly sprays are not created equal. Some contain multiple active ingredients for quick knockdown and repellency while others offer residual control that lasts for days. Others offer more than just fly control, such as coat conditioning or sweat-resistance. Some horse owners prefer to use natural fly sprays, as they often contain natural or organic ingredients. No matter what type of fly spray you choose, experiment with different sprays to find one that works well for your horse. If you need to bathe or hose him off frequently, a sweat-resistant version is ideal. Different formulations may work better for different horses.


Pastured horses need longer lasting fly protection since they don’t get sprayed every day and are ideal candidates for the use of a spot-on fly control product. Spot-ons provide horses with long-term repellent action against a multitude of insects such as flies, mosquitoes and ticks. Again, follow the directions carefully, as some spot-ons may restrict usage for foals.


Flies are attracted to horses’ eyes for the moisture and protein. Fly activity may contribute to eye infections in horses, as well as, being an irritant. Generally, roll-ons are specifically formulated for use around your horse’s face and will repel flies. Some roll-ons can also be used inside your horse’s ears to repel gnats that feed there. Check the product label for proper usage.

Masks and Sheets

Fly masks and sheets are effective ways to keep flies off your horse and shield any eye, face or body wounds that your horse may have. Fly masks with ears may protect your horse’s ears from flies, mosquitoes and gnats, but be sure to choose a mask with an ear mesh fine enough to exclude them.

Fly Traps

Odor-free sticky tapes or traps do a good job of catching flies inside the barn. Use fly attractant traps on the perimeter of your property to draw flies way from the barn. Fly bait can be used in areas of heavy fly populations, but always follow label directions for use and take precautions to keep cats and dogs who frequent the barn safe from any poisonous baits.

The reality is that some flies will appear in your barn no matter what measures you take. But even though fly fighting is a constant battle for horse owners, with some care, planning and consistent use of fly repellent products, you can win the war!