Fly Control for Horses

Michael W. Dryden DVM, PhD, DACVM
University Distinguished Professor
Department of Diagnostic Medicine/Pathobiology
Kansas State University

Stable Fly A number of flies will feed on and cause irritation in horses. These flies include biting midges, horse flies, deer flies, stable flies, horn flies and face flies. In addition, horse stables can have conditions conducive to house fly development which can be a problem if they migrate into residential areas.

Biting midges

Biting midges have a variety of common names such as “punkies” or “no-see-ums". These flies feed upon a variety of warm-blooded hosts including humans. Although very small in size, (usually no longer than 3 mm), these insects inflict a fierce bite, often resulting in a lesion which is more painful than that of a mosquito. They may produce insect bite hypersensitivity in horses (also known as Sweet itch, Summer eczema, & Queensland itch). The condition is characterized initially by numerous papules or wheals, tufted hair and hyperaesthesia which are followed by intense pruritus. Self-inflicted trauma causes exfoliation, exudation of serum and patchy alopecia.

Topical (sprays, spot-ons and wipes) residual synthetic pyrethroids, permethrin and resmethrin formulations (with repellent activity) can be used to control biting midges. Canine formulation of permethrin-dinotefuran (Vectra 3D) has been approved (but not marketed) for horses. 8ml/400lbs may last 3 weeks. Also helpful are:

Screened enclosures (<16 mesh)
High airflow fans
Residual insecticide (cyfluthrin, permethrin and spinosad) sprays applied to walls and ceilings inside barns.
In cases of extreme hypersensitivity blankets or “body suits” can be used.

Horse Flies and Deer Flies

Horse flies and deer flies are large and heavy bodied species that live along edges of ponds, lakes or streams.

Currently, no satisfactory chemical control has been developed for these insects. The wetland habitat that supports the larvae makes it impractical, illegal and environmentally unacceptable to treat breeding sites. Adults do not constantly rest on any surface, so residual insecticide treatments are not effective. Fogging or the use of aerosol insecticides will only knock down what is present at the time of treatment, but more flies can migrate into an area in a matter of minutes. Daily treatment with Pyrethrin (1%) or weekly treatment with synthetic pyrethroid (permethrin or resmethrin). Repeat as needed.

Box, pyramid, umbrella or canopy traps such as HORSE PAL® traps Newman Enterprises, Omro, WI, can be helpful based on horse & deer fly attraction to large dark objects.

Stable fly (Dog fly, biting housefly)

The stable fly has a slender, rigid, piercing - sucking proboscis projecting forward. Females and males feed on blood (obligate Ectoparasites) and are only on the host when feeding. They often cluster around feet and legs of livestock.

Eggs are laid on feed, decaying vegetable material, old manure, and moist hay. Flies can disperse long distances, up to 160 miles. They rest on shady surfaces such as fences, feedbunks, buildings and vegetation surrounding cattle lots after the temperature reaches 80°F. Central U.S. populations appear March – April, peak late June early July, then decrease in midsummer and then a second fall peak occurs mid-September.

Stable flies are primarily a problem in confined livestock operations, since the females lay eggs in accumulated old manure (at least two weeks old), spilled feed, compost and grass clipping piles, and wet silage.

The major development sites in a confinement livestock operation include: behind feeding aprons, under fences and gates, along and behind mounds, bedding in sick pens, along drainage areas and debris basins, around potholes (low areas), dairy calf hutches, old stack butts, in silage and haylage drainage areas, along and under feed bunks, in feed storage areas, in winter feed grounds for beef herds, and around leaky waterers.

This fly has typically been a pest of confined livestock; however it has become more of a problem in rangeland livestock where large round bales have been used. The old wet accumulated hay on the bottoms of bales is an attractive oviposition site for the flies. Also becoming a problem in suburban areas since flies will oviposit in grass compost piles.

Proper sanitation denies flies effective oviposition and development sites. Remove or contain manure; clean around feed bunks and feed aprons, under fences and gates, around water systems. In most instances, if sanitation is poor, chemical control may offer only minimal and temporary relief.

Translucent or semi-translucent plastics traps are attractive to stable flies. Alsynite traps, often called “Broce Trap,” are adhesive coated &/or insecticide treated (Olsen Products Inc. Medina, Ohio (Biting Fly Trap) & other companies) Polyethylene terephthalate such as the Bite Free Stable Fly Trap Farnam is also sold by numerous distributors for stable fly control.

Resting surfaces can be treated with residual sprays. Flies rest on the treated surfaces and absorb the insecticide. Residual insecticides should be effective for 10 days unless washed off by rain or broken down by high temperatures or bright sunlight.

Area sprays, mists or fogger applications of short acting residual knockdown insecticides. Area sprays are most efficient when fly activity is low and they are aggregated such as early morning, late evenings or during the hottest part of the day when flies are resting in shady areas. The area sprays may have to be applied two or three times a week.

Animal sprays must cover legs and underside of body where flies commonly attack and be repeated as needed. They provide limited effectiveness because flies are only on the host long enough to feed. Canine formulation of permethrin-dinotefuran (Vectra 3D) has been approved (but not marketed) for horses. 8ml/400lbs may last 3 weeks.

Stable Fly Production at pasture feeding sites can be controlled by:

Continual movement of feeder location between feedings.
Rolling hay out in different locations throughout the pasture.
Avoid rolling out poor quality or rotted hay that will not be eaten.
Grinding hay helps decrease waste.
Avoid overfeeding to prevent trampling of hay, which becomes habitat once mixed with manure.
Feeding locations should have adequate drainage to keep moisture from accumulating around the feeder.
Proper cleanup and removal of residue is necessary. Because the majority of fly production occurs in May and early June, the site must be cleaned and waste disposed of before April 15.

Housefly

The housefly is a cosmopolitan fly that serves primarily as a nuisance pest. Eggs are laid in moist, decaying organic substrates. Eggs are laid and larvae developed in fresh manure, garbage, sewage, food waste, lawn clippings, etc.

Sanitation is the “KEY” to fly control around a feedlot and is primarily manure management. House fly control in confinement operations is often fruitless without proper sanitation.

Residual sprays should be applied to resting sites such as ceilings and walls (Fenthion, Diazinon, Permethrin, Cyfluthrin, other synthetic pyrethroids, spinosad*). These sprays only help for a short time.

Insecticide impregnated material called baits kill flies when they land and feed on bait. Baits, like those listed below, attract using pheromones and sugars.

Golden Malrin® Fly Bait granular scatterbait. Muscamone® fly attractant draws flies in. Then, as they feed on the sugar-based bait the active ingredient methomyl kills flies.
QuickBayt® Bayer, Quick Draw Fly Bait, Maxforce Granular Fly Bait (aggregation pheromones, sugar and imidacloprid) – Available as granules for spreading or as dissolvable granules for spray application. Flies die within 1 –2 minutes. 4wk duration.
QuikStrike^® Fly Scatter Bait Dinotefuran & (Z)-9-Tricosene as the attractant or QuikStrike^® Fly Abatement Strip with Nithiazine & sugar.
Elector Bait® Elanco – Pheromone and Spinosad is the first active ingredient in a new class of insect-control products, the spinosyns. Unique mode of action with no known cross-resistance. Delayed mode of action that kills house flies after they have eaten and left the bait area, Can be applied as a dry bait or mixed with water to make a paste that can be painted on surfaces.

Ultraviolet light traps collect flies inside an inverted cone or kill them with an electrocuting grid.

Face Fly

Face flies look like houseflies only little larger. Adults (females mostly) feed on cattle and horse secretions: tears, saliva, nasal discharge, blood (from wounds/insects or placenta), serum.

Over-wintering adults survive in barns and homes and come out in late April to mate and disperse to pastures.

Insecticide impregnated cheekbands, nosebands or pollbands are often used to control face flies, but there is no published data to support their efficacy. Similarly, oral larvicides are controversial on face fly control in horses. While effective when used in cattle, the benefit may be quite limited as face flies do not prefer horse manure as an oviposition site.

Insecticide sprays or wipes can be applied to animals’ face (permethrin, fenvalurate, resmethrin, coumaphos) and face masks can be a very effective face fly control system for horses.

Horn Flies

Horn Flies are half the size of a house fly. They resemble the stable fly but more slender along with other subtle differences. Females lay eggs in fresh manure (less than 3 minutes post defecation; greater than 3 minutes old, it is no longer attractive). Horn flies are controlled through topical residual insecticides; permethrin, fenvalurate, resmethrin, coumaphos.