Culicoides (a/k/a buffalo gnats, humpies) are small biting flies that are mostly active at night. They are usually found close to a water source, especially running water. They are aggressive biters that feed in specific areas on the equine body. The areas commonly affected are the ears, belly, and topline, especially the mane and tail base.

Culicoide hypersensitivity refers to an allergic reaction that is seen in a fairly high percentage of horses that are bitten by these gnats. Horses that suffer from allergy to these bites become intensely itchy. They aggressively rub and scratch the affected areas. The hairs become rubbed out, the skin becomes thickened, inflamed, red, crusted and scaly. In severe cases, the affected areas may bleed from the trauma induced by scratching.

Diagnosis is fairly easy and is determined by hair loss in these typical locations, along with the presence of these biting midges.

Treatment involves recognition of the cause and management to reduce exposure. Management changes are the most important part of treatment. This includes reducing exposure to the biting flies by stabling at night, using fans to keep air movement in the barn, and the use of topical insect repellents. Sheets and masks may be helpful.

Steroids and antihistamines are recommended in more severe cases to reduce itchiness and irritation.