It’s nearly summer again, and with it comes warm weather, sunshine — and flies. We’ve all been fighting these winged pests for years and know what to do. But climate conditions vary every season, and different fly species can move into new areas with the changing weather. Sometimes reaching for the same old fly spray just isn’t good enough.
Reviewing your fly control strategies every year is a good idea. Here’s a brief overview of the species that might be out there and what you can do to protect your horses from them.
Fly species, habits and habitats
The first step in stopping flies is to identify the offenders—many look very similar, but often the different pest species can be identified by their unique behaviors and habitats. And they are best controlled by strategies that target their lifestyles. Here are the flies most likely to be bothering your horses:
• Stable flies look like house–flies, but they inflict painful bites, most often on a horse’s legs, but also on the belly, face and neck. They can be found around livestock practically anywhere in the country, but they will reach their peak in warmer climates, especially in hotter, wetter weather. Stable flies prefer bright sunny areas and tend not to enter dark enclosures.
• Horseflies and deerflies inflict painful bites that bleed. Deerflies tend to attack the head and neck, smaller horseflies bite on the legs, and the larger ones feed on the horse’s back. These types of flies lay their eggs in moist soil or vegetation near ponds, marshes and other bodies of water and are most commonly found in or within a few miles of forests or wetlands. However, some may travel as far as 30 miles in search of blood meals. Horsefly and deerfly species prefer bright sunlight on hot, still days.
• Houseflies do not bite, but they congregate near open wounds and secretions, such as tears or mucus. They breed in moist, decaying vegetable matter, including garbage, hay and grass clippings as well as manure. Houseflies prefer dark, interior spaces.
• Blackflies inflict painful bites, usually on sparsely haired areas, such as the ears and genitals. Although they can be found as far south as Florida, blackflies are notorious pests up north. They are most abundant in forested areas with slow-moving waterways, such as streams, lakes or canals, in which they lay their eggs. They feed primarily on bright, sunny days and prefer not to fly into dark enclosures.
• Horn flies tend to congregate on the horse’s belly, where a single fly may bite multiple times before flying off. On cooler days, they may also feed on the neck, shoulders and back. Horn flies are normally found near cattle, and they lay their eggs only in fresh cow manure, but they will affect horses in shared or adjoining pastures.
• Face flies do not bite, but they congregate on the face to feed on saliva, tears and mucus. Face flies prefer cattle, and breed only in cow manure, but they will also land on horses pastured within a quarter mile. They are most active in the spring and summer but not in hot, dry weather.
• Culicoides (biting midges, biting gnats, no-see-ums) attack different parts of the horse, depending on the species, but the more common ones tend to bite at the tail head, ears, mane, withers and rump; others go for the belly. Although the individual flies are tiny, they form dense swarms that inflict many bites at once. These flies breed in wet places, such as slow, still streams, marshes and rotting vegetation, and are most active just after sunset.
• Mosquitoes will bite anywhere on the body. Most abundant in warm, wet weather, mosquitoes breed in stagnant water, and their populations spike near marshes, ponds and any chronically wet ground, especially after flooding. Smaller puddles, such as those that form in abandoned tires or blocked rain gutters, can also serve as breeding reservoirs. Mosquitoes are most active in low-light conditions, such as in shady woods or at dawn or dusk.
Reduce, repel and eliminate
Chemical controls include insecticides and repellents. Fly sprays are common, and many brands are available, but most contain similar active ingredients.
• Insecticidal/repellent sprays usually contain pyrethrin, a natural compound derived from a type of chrysanthemum, or a pyrethroid, usually permethrin, a similar synthetic compound. These formulations deter flies from landing and kill the ones that do bite. These work against many smaller biting flies, including mosquitoes, houseflies, stable flies, deerflies and gnats.
Repellents, which are often marketed as “all natural” alternatives to the insecticides, contain strong-smelling oils, such as citronella, cedar or tea tree. They do not kill flies but instead discourage them from landing by masking the odor of the horse. Both insecticides and repellents are available in lotions, gels, roll-ons and wet wipes as well as sprays; these are useful for applications around the face as well as touchups along the trail, but they are best used as complements to the sprays, rather than replacements.
• Spot-applied permethrin products are an alternative to sprays. Like flea-control products for cats and dogs, these are applied via drops at key points on a horse’s body.
• Repellents can also be found in products like fly collars and leg bands—which, not unlike flea collars for dogs, are worn on the horse’s body and deter flies from landing nearby.
Horse clothing can also physically block flies from landing on the horse.
• Fly sheets are lightweight coverings for the horse’s torso, and many come with extra appendages, to extend coverage over the tail, belly and neck, where culicoides tend to attack. Light-colored fly sheets provide an extra deterrent to horse- and deer flies, which track victims by sight and are attracted to large, dark objects. Also available are quarter sheets, which cover a horse’s rump and flanks while under saddle.
• Fly boots, mesh coverings for the lower legs, can guard against stable flies and other insects that alight there.
• Fly masks are see-through mesh shields that cover the eyes to ward off face flies and houseflies attracted to tears; some come with ear nets, coverings for the ears, which are useful if blackflies are a nuisance. Others come with fringed extensions that fall down over the nostrils to deter flies from landing there. In addition, some fly masks are designed for use with bridles to protect the face.
• Ear nets, designed for use with a bridle, are crocheted cotton coverings that keep flies off of the ears and poll; many of these have a tasseled front edge that lies above the eyes for further deterrence.
• Out in the pasture, make sure horses have a well-shaded run-in shed that offers refuge from flies that like sunlight. For extra protection, hang long panels of burlap or netting over the doorway, impregnated with fly spray. These will brush off and repel any flies on a horse’s coat as he pushes his way through the doorway—just be sure to train the horse to understand that he can get through what might look like an impenetrable barrier. In addition, stabling horses during peak insect activity periods may also help—turn them out at night if daylight fliers, like blackflies, are prevalent. Horses sensitive to culicoides do better if stabled at dusk.
Leave them no place to go
• Inside the barn, automatic misting systems release fine sprays at regular intervals from nozzles in the ceiling.
• Fans placed strategically to keep the air moving in the aisles and stalls can also deter flies: Smaller insects like houseflies and gnats prefer to fly in still air, and the breeze also disperses the carbon dioxide a horse exhales, which can attract some flies.
• Very fine, well-sealed screens in the windows will keep out mosquitoes and gnats.
• A variety of traps are available, baited with food, pheromones or other attractants designed to appeal to different types of flies. House- and stable flies are attracted to scent lures, such as sugar or manure. Horseflies are attracted to dark colors, so a large black ball is sometimes used to lure them into a chamber they can’t escape. Fly sticks and tapes lure house- and stable flies onto sticky surfaces that entrap them.
• Bug zappers are blue-light devices that electrocute flies drawn into an electric grid; two drawbacks are that they must be placed where they cannot be knocked down by animals, and they can also attract and kill beneficial insects.
Close the breeding grounds
• Remove manure from stalls and paddocks daily. Stable- and housefly eggs, which are laid in manure, hatch after 10 to 21 days, so an ideal control practice would be to get the manure off the property each week.
• Release beneficial predators. These tiny wasps or nematodes can be purchased from farm and garden suppliers. When sprinkled on manure or other breeding areas, they hatch and parasitize immature flies to reduce the number that reach adulthood. Feed-through fly control products, added to each horse’s feed, pass harmlessly through his system but then kill any insect larvae hatched in the manure.
• Compost manure. This process generates enough heat to kill any eggs.
• Spread manure over fields. Just make sure the layer is thin enough that it dries quickly in the sun. Avoid spreading manure in pastures where horses are actively grazing, and keep it away from muddy, high-traffic areas that tend to remain wet.
• Remove wet bedding as diligently as you do the manure. Stable flies are highly attracted to the smell of horse urine. It also helps to spread hydrated lime, also called “slack lime” or agri-cultural lime, on wet spots on stall floors.
• Eliminate stagnant water where flies breed. Fill in potholes, clean clogged gutters, repair leaking plumbing and pick up unused items, such as flower pots, old tires and toys, that can collect rain. Rinse and refill water buckets each day, and remove fallen leaves and other debris from troughs.
• Add goldfish to troughs to devour mosquito larvae.
Controlling flies around the farm may seem like a Sisyphean task—no matter how much you do, there will always be more. But keeping up with these basic chores will go a long way toward reducing their numbers. Your horses will thank you for it.