Fly Bites

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Also Known As

Insect bites, Stings


Equine diseases carried by flies and the discomfort caused by hordes of these pesky flying insects make control of the fly population and the prevention of fly bites an important part of every horse owner's daily routine during much of the year.

Depending on the season, these flying insects can make a horse's life miserable as they bite, suck blood, and feed on secretions around the eyes and other tender parts of the horse's body and limbs. A wise horse owner makes use of many tools, not only to keep the biting insect population down, but also to protect horses from extreme discomfort, and the infections and diseases related to fly bites.

Before taking preventative measures, it is necessary to know which insects are in the environment around your horse and the best ways to deal with these various fly populations.

Horseflies, deerflies, stable flies and horn flies are the most common flying insects that attack horses, and they come in a variety of shapes, colors and sizes. When they bite to ingest blood, the bites are not only painful, but they open the way for screwworm attacks and infection.

Blood-sucking gnats such as the black fly (buffalo gnat) and "no-see-ums" are very irritating to horses and cause head-tossing, ear-twitching and incessant biting or rubbing. Bites from gnats ooze serum and form scabs or blisters. Black flies secrete a toxin capable of causing cardiac and respiratory depression.

Non-biting flies include the housefly, bot fly, and face fly. Although they do not "bite," they cause great discomfort by feeding on secretions from the eyes, nose, and mouth. These species carry diseases including equine infectious anemia, anthrax, contagious conjunctivitis and eyeworms.

The bites of the stable fly produce skin lumps that are called external parasitic nodules. The nodules become worse when rubbed.

Blowflies and screw worm flies lay their eggs in open wounds with the navel stump of the newborn being a favored site. The eggs develop into maggots that lead to irritation and infection.

Flies pass through four stages of development: egg, larva or maggot, pupa, and adult, and the best forms of prevention and control take these four stages into consideration.


  • Allergic dermatitis/skin eruptions and lesions
  • Mechanical dermatitis causing inflammation, abrasions, scabbing, scarring, nodules, ulcerations and hair loss
  • Surface parasites evidenced by eggs, maggots, hatched larva
  • Fungal diseases
  • Bacterial and viral diseases


Most flies live out their life cycles in manure piles, compost heaps, stagnant water, feed bins, garbage, and environments that are wet, unclean, and left for long periods of time without clean-up control.

Since many kinds of flies are a natural part of the environment, taking preventative steps to keep them out of stalls, barns, pastures and other places where horses live, exercise, and work will remove the main cause of fly bites.


Minimizing the fly population by getting rid of or covering up their favorite breeding environments is the best prevention of fly bites. Removing manure daily and keeping it dry by spreading it will eliminate a major source.

Covering manure piles and compost with plastic and cleaning up spilled hay, grain and trash is also very helpful. Commercial pelleted and mineral block feed additives such as Rabon, Endrol, and Equitrol are said to safely pass through the horse's system and kill larvae in fresh manure.

Eliminating stagnant pools, scrubbing out feed bins and buckets, and keeping feed bags and bins closed will keep flies from feeding from these sources. Trash should be kept covered and as far away as possible from barns and stalls. When setting up horse facilities, care should be taken to stay away from wet, low-lying areas.

Fly traps, fly paper, and other commercial fly bait/capturing devices may be used to cut down on fly populations. In addition, an automatic misting system in the barn/stall areas and an on-going chemical warfare campaign making use of pyrethrins and resmethrins which are toxic to many insects, but considered safe for warm-blooded animals can be very effective.

Insect repellants formulated for equine use are a good addition to the supply kit and can be used whenever needed to keep the horse from being bitten.

Residual insecticide surface sprays provide long-term results. Labels should be studied to determine the product's effectiveness and safety.

No insecticide should be used on horses unless they are specifically recommended for that purpose. Many of these products should not be inhaled, ingested, or allowed to make contact with skin and eyes, so care must be taken when using insecticides.

Topical insecticides containing pyrethrins and permethrins can be applied according to label instructions as necessary to control flies and external parasites. Some topical insecticides can be wiped or sprayed on the areas where flies tend to congregate. A light spray to the shoulders, neck and withers is often sufficient, but application to the lower body and legs can also help prevent fly bites.

Stabling horses before sunset can also be helpful since many biting insects are most active in the evening. The use of face masks and light coverings to protect the body of the horse can be effective.

Controlling where flies can land by means of sheets, face masks, and leg wraps will help keep flies off horses, especially around the sensitive eye, ear and nose areas can be helpful also. A coating of petroleum jelly applied to the skin is also a good protectorant


The most important aspects of fly bite treatment are stopping the horse from itching and preventing secondary infections. Topical steroids, systemic steroids, or a combination of both have been effective in long acting itch relief. Since steroid use can lead to side effects, a veterinarian should prescribe the correct dosage and kind of steroid to be used.

Secondary infections may be bacterial, fungal or parasitic. If affected areas ooze discharge or have a bad odor, it is likely that a bacterial infection has occurred. When bites result in open wounds, good wound care should be observed by cleaning the wound to remove any discharge and then applying a topical ointment or spray. In some cases, systemic antibiotics may be prescribed to combat infection.

Fungal infections may be more difficult to recognize and sometimes a culture for fungus may need to be performed. This is especially important if a horse is not improving with typical treatments. Depending on the type of fungal infection, the veterinarian can prescribe the proper treatment.

In cases of internal parasitic infection as a result of fly bites, a veterinarian will need to determine the organism involved and the best treatment to eradicate it from the horse's system.

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EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.