If you board your horse or have neighbors that don’t practice good manure management, you must resort to other control methods, such as fly bags, traps, and wearable gear.

“Fly bags have a purpose, but they aren’t a (total) control,” Machtinger says. “Fly bags only trap houseflies and might also trap beneficial insects. Plus, people often don’t use them correctly; they hang them out until they are so full that they are creating an opportunity where flies can breed.”

Replace fly bags at least weekly. “Placement is also important,” she adds. “Have fly bags in a warm area where they intercept (flies coming from other) livestock properties or in locations lacking manure management.”

There are no effective traps for horn and face flies, because they only rest on the animal. “(These flies) are going for mucosal secretions on the eyes, mouth, and nose of a horse,” says Machtinger. The only way to manage them is with on-horse management—mechanical barriers such as masks, sheets, and fly boots—or repellents.

“Masks, sheets, and fly boots (are) physical exclusion devices used to create a layer between horse and fly that are also useful for many other types of pests (such as mosquitoes or midges), so there’s more bang for the buck,” she says. Machtinger’s personal recommendation is to use zebra-striped fly sheets and masks, because scientists are learning a zebra’s stripes might confuse and repel flies. “(This) gives extra protection against horseflies and stable flies—and pretty much all flies.”

She cautions, however, that other horses might spook at pasturemates wearing zebra-striped fly sheets when you first introduce them.

When fitting a fly sheet (see sidebar for tips), you can choose from many varieties and fits. “You want a fly sheet with good airflow,” says Machtinger. Fly sheets designed to protect from biting midges, which can cause the reaction referred to as sweet itch, are more snug and protect the horse better from these pests.

Olds says fly wraps also work well for controlling stable flies. These cover lower legs, which is the fly’s preferred area for feeding. “During fly season farriers will notice a lot of cracked hooves from stomping,” she says. “Horse caregivers often underestimate the problem; flies feed once and go off to rest, so every fly that you see is a new one. When I talk with horse owners, I explain how a lot of studies show that (any kind of) constant chronic stress makes your immune system stressed, leaving an individual susceptible to other stress factors. Eventually something has to give.”

Manufacturers are also developing gear treated with insect repellent. The pyrethrin binds to fibers in the cloth, making it safe even around cats (pyrethrins are toxic to cats), and it doesn’t wash off. “You cannot treat horse gear yourself,” says Machtinger. “But if you have a fly sheet that you love and you want to have it treated, there are companies that do this.” Bonus: Treated fly sheets also repel mosquitoes, and they might even work to repel ticks, she adds.

Lastly, fans can serve as additional mechanical control options, particularly against midges, which are weak flyers.