Skip to content Skip to navigation menu


A number of insects can cause damage and irritation to horses. These insects include biting flies, nuisance flies, lice, and bots. Occasionally other arthropods such as mites and ticks may cause problems.

Biting Flies

Several types of biting flies bother horses. These include mosquitoes, black flies, deer flies, horse flies and stable flies. Of these pests, the stable fly is probably the most important biting fly pest during the summer.

Stable Flies

Both male and female stable flies feed on blood. They are persistent feeders that cause significant irritation to the host animals. Adults are approximately 1/3 inch long and resemble house flies. Females stable flies deposit clusters of up to 50 off-white coloured eggs at a time. A single female can lay up to a thousand eggs during her lifetime. Stable fly larvae have a typical maggot shape and are similar to those of the house fly. There are three larval stages. The last stage larva is about 2/5 inch long and is a cream/white color.  After the third stage larva finishes feeding, it shortens, hardens and darkens in color. 

Stable flies will feed on blood from practically any warm blooded animal including horses, humans, pets and other livestock. Peaks of feeding activity commonly occur during the early morning and again in the late afternoon. Stable flies prefer feeding on lower parts of the horse such as the legs and belly. Both male and female flies feed on blood; the female requires blood meals to produce viable eggs. Eggs are deposited into a variety of decaying animal and plant wastes but are rarely found in fresh manure. Larval development requires 11 to 21 days, depending on environmental conditions. Mature larvae then crawl to drier areas to pupate.

Stable flies are active during the summertime and are one of the most important pests of horses and livestock. Stable flies prefer to feed outdoors and rarely are found feeding or resting indoors. These flies are strong fliers and dispersion from one livestock facility to the next is common. They remain active into October. However, larval development slows as autumn temperatures decrease. At temperatures near freezing, larvae can survive but continue to develop slowly in habitats such as manure where fermentation generates heat.

Horse and Deer Flies        

Horse and deer flies are large biting flies which can inflict painful bites on horses and humans. Several species may become abundant enough to constitute a problem for grazing horses, particularly animals near stream or low wet areas. Further, because the bite is painful, horses may become restless and unmanageable when they attempt to ward of attacks by these flies. Immature larval horse flies are aquatic or semi-aquatic and the last stage lava overwinters. Life cycles are long, most species have only one generation per year and some species may have a two year life cycle. Only female flies feed on blood. Control is difficult; individual animal treatment using repellents or insecticidal sprays may reduce fly bates. 

Black Flies

Black flies are small, long, humped-backed biting flies which can produce large populations in the spring and early summer, particularly in pasture areas along streams. The immature stages are found in flowing water. Pupation occurs under water and the adults float to the surface, ready for flight, feeding and mating. Adult feeding on horses and other animals can pose serious animal health problems and the irritation caused by black fly bites can make horses unmanageable. Anemia may occur in the vertebrae host as a consequence of black fly feeding on its blood when the black fly population is high. Bites may cause severe reactions such as toxemia and anaphylactic shock; these reactions can result in death. Control is difficult, species which feed in the ears of horses can be controlled using insecticidal applications or by using petroleum jelly in the interior of the horses ear. When possible at-risk horses should be stabled during the day and pastured at night. Black flies only feed during daylight hours and do not usually enter stable areas. Area sprays or general topical applications of insecticides are not very effective. 

Biting Gnats

Biting gnats can be a serious pest to horses. Blood loss and irritation associated with the feeding of these very small, blood feeding flies can be very significant. Direct treatment of horses with wipes or sprays containing insecticides or repellents may provide relief for the horses.

Horn Flies

The horn fly is normally a pest of grazing cattle. However, when cattle and horses are pastured together this fly will also feed on horses. Horn flies are about half the size of stable flies. The horn fly usually remains on the host animal almost continually, both day and night. Females lay eggs on fresh cattle droppings. Control of horn flies on cattle using established treatment methods such as self-treating devices provides the best approach to this problem if horses are pastured with the cattle. Sprays or wipes can be used successfully on horses.

Stable Fly Management

A sound sanitation program is of paramount importance to fly control. Control of stable flies in stables usually incorporates several methods. These methods also apply for the house fly. Chemical control directed at larval and adult stages of both insects is usually required periodically during the fly season.

Sanitation around stable

The basic aim of a sanitation program is to reduce or eliminate larval development sites on the yard. A number of areas require attention because of the varied habitats suitable for larval development of these flies. Manure management is essential in limiting fly production. Timely spreading of manure promotes drying and prevents larvae from developing. Even small areas, where manure mixes with straw, are ideal breeding sites for large numbers of both stable and house flies. Wet areas where manure, mud and plant debris accumulate also form ideal breeding habitats for these fly species. Improvement of the drainage systems around stables can eliminate these fly reproduction sites and make chemical control efforts much more successful.

Chemical control

A variety of chemical control techniques are available to the horse owner. Generally, control of adult flies using residual insecticides as surface treatments and knock-down sprays to kill existing adult flies are the most effective techniques. In stables a combination of residual and space sprays is used, often on an alternative schedule. Treatments applied directly to horses are not as effective for control of stable or house flies as residual surface treatments. In practice, both techniques are usually needed. It is important to always follow the label recommendation for rate and frequency of any pesticide treatment.

Direct animal applications of sprays and dusts may be used in some situations to protect animals. Products used for direct animal application usually have short residual activity and this type of application is labor intensive.