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Equine Health Resource

Biting Midge or Black Fly Infestation

Synonyms: Buffalo Gnats, No-See-Ums

This diagnosis refers to biting midges bothering or biting horses. It does not refer to the hypersensitivity known as Culicoides Hypersensitivity or Sweet Itch. Horses can be bitten and bothered by these insects without acquiring the allergic syndrome.

These tiny insects are blood suckers, and are mostly active at night. They tend to bite horses along the top-line or along the belly, depending upon insect species. In male horses, the sheath is often affected, resulting in irritation to and swelling of the sheath. Close investigation reveals tiny blood spots, small scabs, or the feeding insects themselves. The ears are another favorite target. Feeding flies cause bleeding and intense irritation on the inner surfaces of the ears.

These insects are more common near standing or running water, and in many areas are only a problem during relatively short periods of the year.

Diagnosis requires presence of and identification of the insects near or in the affected area.

Treatment is insecticide ointments and sprays to repel the insects, and anti-inflammatory creams to ease inflammation.


  • What management changes can I make to reduce insect annoyance to my horses?
  • How can the irritation be treated to provide relief?

    Good facilities management to decrease the population of biting midges including the use of fans, screens, fly repellants, fly masks and sheets. Keep horse in protected stalls during times of high fly activity which, in many cases, is nighttime.

    Helpful Outside ResourcesCredible Equine Health Information on the Internet

    Author: Doug Thal DVM Dipl. ABVP


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