Bye, Bye Flies!

Controlling the fly population at any barn is an annual battle. And with new fly-born diseases, it's more critical than ever.

With summer just around the bend, equestrians thrill to the warm, sunny days, a welcome reprieve from winter’s blustery cold. But we all understand the mixed blessing, too: That rising mercury signals the start of fly season. Battling these bugs is an annual war that, let’s face it, we’ll never win. No matter how many anti-fly weapons you use, you’ll never kill every last one of the pests. But, with a good strategy of attack and defense, you can dramatically reduce the fly population at your facility, making life more comfortable (and healthier) for both horses and humans.

Know Your Enemy

Sure, flies are annoying, but more importantly, they can be dangerous. Wes Watson, PhD, an assistant professor of entomology and an extension specialist at North Carolina State University, researches control strategies for pest management in livestock systems, including equine operations. He breaks horse-attacking flies into three groups and explains the inherent hazards of each:

  • Nuisance flies, including house flies and face flies: Mechanical vectors of several pathogens and parasites; face flies can also damage the conjunctiva of the eye.
  • Biting flies, including stable flies and horse flies: Take bloodmeals from the horse several times a day; bites are painful and often on the horse’s lower legs, which can make the horse stomp and become difficult to handle. Horse flies are known vectors of Equine Infectious Anemia.
  • Myiasis-producing flies, including bot flies: Myiasis refers to the invasion of the organs and tissues of the horse by the fly larva. For example, bot fly eggs and larvae are ingested by the horse, then complete development while attached to tissues in the horse’s digestive tract. (The mature larva is excreted in the droppings to pupate on the ground and emerge as an adult.)

The house fly and stable fly tend to create the most problems around the barn, says Watson. That’s largely because they thrive in an environment rich in organic matter (manure, bedding, spoiled feed) and moisture (urine). The females of each species can lay about 200 eggs during their 10- to 14-day lifespan, and development (from egg to larvae to pupae to adult) takes as little as 10 to 14 days (with house flies developing faster than stable flies). You can see why fly populations explode so rapidly and why your best and first line of attack is to eliminate fly breeding grounds. In other words, clean up!

Attack the Home Front

You know that proper sanitation includes removing manure, soiled bedding and spilled feed from the barn. “But,” says Watson, “it’s also important to consider what happens to that material after it leaves the barn.”

If you stockpile waste near the barn, he explains, you provide an ideal breeding site for flies. Instead, immediately spread the manure and bedding (i.e., on open areas away from the barn). This helps manure dry faster, thereby reducing its appeal as a fly breeding site. Composting is another option. Heat in the compost pile kills flies before they develop and the composting process leaves you with a material similar to organic soils, he says.

Extend your manure management strategies to pastures as well, by regularly removing manure. Alternatively, if you live in a hot, sunny climate, you can harrow the field to break up manure, again so it will dry faster, thus providing a less hospitable environment for flies.

Food for Thought

Feed-through worming products offer another way to reduce fly numbers. Found in mineral blocks and feed additives (such as Farnam’s Equitrol), larvacides such as Rabon are ingested by the horse, but pass through without being digested. They then kill insect larvae in the horse’s manure. Watson believes feed-through fly controls are effective when used properly and sees little evidence to justify concerns that insects may develop resistance to them.

Set the Trap

Using the above methods, you can make a dramatic impact on the number of flies born on your farm. But you probably won’t eliminate every potential breeding site, and even if you did, you’ll still have flies. Afterall, not every bug around your barn was born there. Your next step is to control the flies that do make it to adulthood and choose your property as a homesite. Fly traps provide an effective, often economical way to do that.

Non-insecticidal traps, says Watson, range from time-tested sticky strips (a.k.a., fly tape) to jug traps. Traps often contain attractants, such as the fly sex-pheromone muscalure, to draw the flies inside, where they drown. (Watson notes that this pheromone attracts house flies, but not stable flies.)

Carolyn Dulai, a horse owner in Haslett, Michigan, says she’s found rotten meat to be a more potent attractant, but you must be prepared for the stench. Watson adds that meat-based traps will attract numerous fly species, many of which are not considered a problem for horses.

Some traps are designed to be disposed of when full; otherwise they may be emptied, then “recharged” with more attractant. Dulai notes that you should bury dead flies at least one foot underground and that you should experiment with height and location to find the most effective placement for the trap.

Pesticide-based traps use an attractant to entice flies to feed on toxic bait, such as nithiazine or methomyl, explains Watson. You can also purchase the bait alone and use it in your own homemade jug trap: Cut four holes into the sides of a milk jug, says Watson, place an ounce of methomyl bait inside, then suspend the trap from a wire. Make sure traps are out of your horses’ reach.

Watson notes that horse flies require some special ingenuity, since they’re attracted to equine bodies, not spoiled food, etc. He recommends two commercially available traps specifically for this species, adding that, “Using these traps for one year, we have removed over 5,000 horse flies from two 10-acre horse pastures.”

EPPS Traps consist of black fabric panels and two trays of soapy water. The fly believes the trap is a horse, attempts to land and falls into the soapy water where it drowns. The trap is most effective when positioned in the flyway between fly resting sites and the horses, says Watson. Finding the right location may take some experimentation.

The Horse Pal trap consists of a pyramid atop four legs, with an inverted funnel and kill jar at the top. A large black ball suspended just below the pyramid attracts the flies, which become trapped in the pyramid and kill jar.

Recruit Allies

Predators are another effective and natural way to reduce the fly population, such as a parasitoid wasp.

Parasitoid wasps (a.k.a., “fly parasites”) actually do their work before flies ever see adulthood. The tiny insects lay their eggs in the fly pupal case, effectively killing the fly before it hatches, says Watson. Smaller than a stinging wasp, parasitoid wasps won’t bother humans or other animals. On the other hand, these wasps can be harmed by insecticides, which shouldn’t­ be sprayed on barns or stalls if you’re using these helpful bugs.

Ideally, says Watson, you’ll release them at a rate of 10,000 wasps for every five horses, every two weeks, in order to keep up with the fly population. (He notes that costs vary, but generally run about $13 per 10,000 wasps.) Watson also says you should use a species of wasp adapted to your region, so make sure the supplier knows where your facility is.

Barns naturally attract birds and many birds enjoy snacking on flies. With both bats and birds, your only concern is making sure to clean up their droppings; otherwise, you simply have one more fly attractant on the ground.

Target the Survivors

Using a combination of any or all of the above strategies, you should notice a marked decrease in the fly population at your barn. However, there are bound to be survivors, and if their numbers are enough to hassle your horse, fly repellents are the next logical step.

You can use repellents on a barn-wide basis. One method, says Watson, is to manually spray stalls and aisleways with a repellent (most commonly a pyrethrin-based product), removing horses from the barn first. (If you’re using fly parasites in your pest management program, wait three to four days after spraying before releasing them.) Alternatively, you can install an overhead spray system that automatically mists the barn at timed intervals throughout the day.

While these systems can certainly be effective, Watson cautions that overuse can lead to problems. “I have seen systems timed to apply insecticide seven times each day,” he notes. “Similar systems were a popular means of fly control in poultry production years ago. Within two to three years of installation, most were ineffective because of insecticide resistance.” He believes that “useful and effective insecticides should be conserved for when we really need them.” Overuse may also have health ramifications for your horse, so you’ll need to keep a close eye out for warning signs such as fever, lethargy and loss of appetite.

You should also realize that automated spray systems do require some maintenance—occasional draining and cleaning. And, according to some users, costs can run to about $300 per year just for the repellent, not including the system itself.

Of course, nearly everyone who owns horses also uses repellent products designed to be applied directly to the horse. From traditional wipes and sprays to roll-ons, foams and gels, from standard chemical-based products to natural varieties and homemade concoctions, your choices here are huge and diverse. Opinions on what works and what doesn’t are just as varied. The bottom line, says Watson, is that “Repellents are an effective short-term remedy for flies on an individual horse basis, when used as the label directs.” As for the chemical vs. natural debate, he only cautions that many of the natural products have not been as rigorously evaluated.

Add Some Armor

When your horses are turned out, an overhead spray system is beside the point. And, as we all know, repellents applied to the horse will wear off—usually sooner, rather than later. One last line of defense, then, is to protect your horse with anti-fly apparel. Primarily, this means mesh blankets, masks and leg wraps that act as barriers against bugs while allowing air to circulate.

Watson acknowledges that these products can provide some relief. However, he adds, it’s important that the “clothing” fit appropriately. For example, if a fly mask is loose, flies will still be able to crawl underneath and attack the horse. You should also realize that your horse’s entire body won’t be covered, even if he wears a blanket, mask and leg wraps. Blankets, for instance, keep flies off the horse’s back and sides, but often leave the belly exposed. Similarly, leg wraps end at the knee and hock, leaving the upper limb unprotected.

Fly bands and fly collars are another type of “wearable repellent” for horses. Again, the main drawback is that these products repel flies only on a limited area of the horse’s body.

You Have the Tools

When all is said and done, perhaps the entire battle of the flies boils down to this: Flies have one primary weapon—an amazing reproductive capability. We, on the other hand, have a world of anti-fly weaponry at our disposal. With a little experimentation and effort, you should be able to combine these tools into an effective management strategy, keeping flies to a minimum and enjoying those sunny days to the fullest.

Allies in Fly Control

Most fly control products—including traps, feed-through products, barn-wide and individual-horse repellents and anti-fly apparel—can be purchased at your local tack shop or farm supply store. For information on other fly control strategies, try these sources:

  • Your county or state Cooperative Extension Service (information on manure management, parasitoid wasps, general fly control and integrated pest management).
  • National Integrated Pest Management Network (information on integrated pest management as well as contact information for state IPM coordinators;
  • California Environmental Protection Agency, Department of Pesticide Regulation, Environmental Monitoring and Pest Management Branch (information on parasitoid wasps):; 916-324-4100 [Editor’s note: There are numerous commercial suppliers of fly parasites; they are easy to locate using an Internet search engine.]
  • Organization for Bat Conservation, 517-339-5200,






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