Insect Pests of Horses

• Biting Flies
  • Stable Flies
  • Horse and Deer Flies
  • Black Flies
  • Biting Gnats
  • Horn Flies
• Nuisance Flies
  • House Flies
  • Face Flies

• Mosquitos
• Lice
• Ticks and Mites
  • Ticks
  • Mites
• Horse Bots
• Blister Beetles
• Chemical Controls for Insect Pests of Horses

Larvae: Stable fly larvae have a typical maggot shape and are similar to the house fly. There are three larval stages. The last stage larva is about 2/5 inch long and is a cream white color.

Pupae: After the third stage larva completes feeding, it shortens, hardens and darkens in color. The chestnut brown pupa is 1/4 inch long. Stable fly pupae are very similar in appearance to house fly pupae and are difficult to distinguish since, in their natural habitat, they are usually mixed with house fly pupae.

Stable Fly Life History and Habits
Stable flies will feed on blood from practically any warm blooded animal including horses, humans, pets and other livestock. During periods of high stable fly activity, humans can be severely annoyed; this insect has been called "the biting house fly." Individual flies may feed more than once per day (Scholl and Peterson, 1985). 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 hosts such as the legs and belly of horses and cattle. 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. Fly larvae develop in excrement mixed with straw, soil, silage or grain (Guyer and King, 1956; Meyer and Peterson, 1983) but are also found in wet straw, hay, grass clippings, other post-harvest refuse, and poorly managed compost piles. Large round hay or straw bales, where contacted by moist soil, may also serve as a larval development site. Larval development requires 11 to 21 days, depending on environmental conditions. Mature larvae then crawl to drier areas to pupate. The pupal period varies from six to 26 days depending on temperature. The entire life cycle from egg to adult is generally completed in three to six weeks.

Stable flies are active during the summertime in the north central plains 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 piled silage or manure where fermentation generates heat (Scholl et al., 1981).

Stable Fly Management
A sound sanitation program is of paramount importance to fly control; all other types of control are doomed to failure without this important first step. Control of stable flies in barnyards, stables or corral areas usually involves 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 or corral. The basic aim of a sanitation program is to reduce or eliminate larval development sites on the farmstead. 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. Modifications of the drainage around corrals to reduce excess moisture can eliminate these fly production 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 most barnyard situations, a combination of residual and space sprays is used, often on an alternating 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 usually are needed. These and other methods of more limited usefulness are discussed below. ALWAYS FOLLOW THE LABEL RECOMMENDATIONS FOR RATE AND FREQUENCY OF ANY PESTICIDE TREATMENT.

Applications of residual insecticides to premises are frequently used to control both house and stable flies. Longer residual insecticides provide control for an extended period when sprayed onto sites where the adult flies congregate. Sides of buildings, inside and outside surfaces of stalls and fences may be potential day or night resting sites for these flies. Observation of your own barnyard situation will quickly tell you the favored resting sites for flies. Flies contact the insecticide when they land on the treated surfaces.

Knock-down sprays are effective in killing adult flies present at the time of application. The chemicals used for these applications are usually short residual insecticides having a quick knock-down and high contact toxicity. Several types of spray or fogging apparatus may be used for these applications. Wind velocities should be low at the time of application and the droplet or particle size should be small (50-75 microns) to ensure drift through the corral area. This method requires less time for application but has the disadvantage that it will only kill flies present at application and thus provides short-term relief.

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

Other methods of fly control such as baits, electric grids and traps may have some limited use for house fly control but are ineffective for the blood feeding stable fly. Baits may be used effectively for house fly control in enclosed areas. Fly papers, cords and strips may also help alleviate fly problems in these areas. Such methods are usually ineffective in open areas.

Control of immature flies (larvae) is sometimes possible. Usually, the best approach is to remove the potential source of fly production with sanitation practices. When this is not possible, a larvicide can kill the developing flies. A larvicidal insecticide may be applied directly to places where eggs are laid and larvae develop.

Biological control has potential for controlling barnyard fly problems (Morgan, 1980; Peterson and Meyer, 1983; Peterson et al., 1983). A number of parasites and predators of both house and stable flies exist that help to reduce fly numbers. Some of these natural parasites are available commercially but to date research has not demonstrated cost-effective fly control.

Figure 1.
Adult stable fly
or dog fly.