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Sweet Itch, Biting Midges and Horses
- Control the allergy and use repellents -
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Summary: Sweet itch is an allergic skin condition in horses caused by the bite of a tiny midge. Horses with severe reaction to these bites should be treated for the allergy. Other, less sensitive horses, can be protected with fly repellents alone.
Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)
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 Sweet itch is a skin condition in horses caused by the bites of a tiny (2-3 mm) midge in the family Ceratopogonidae. These flies are called biting midges, gnats, "sand flies", no-see-ums and punkies. The skin ailment is the result of an allergic reaction to the bites of the midge.
Horses vary in their response to bites -- some react strongly with open, weeping sores while others hardly react at all. The sores are caused by constant rubbing and biting to relieve the itch. These same flies also bite people producing intensely itchy lesions as well.
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These tiny biting midges (flies) are nearly invisible to the unaided eye.
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Biting midges develop in wet, marshy or swampy soil but even a small spring can produce large numbers of these flies. The larvae are aquatic or semi-aquatic. Midge infestations tend to be very "spotty" across fields, high in some areas while absent from others. Short of draining the ground it is nearly impossible to eliminate midges. Instead it is best to use repellents to protect horses from bites.
common misnomers: "sand flies", true sand flies belong to the family Psychodidae; "gnats", this term is generally used for another family of flies; however, among horse owners biting midges are frequently called "gnats". Sweet itch is also known as Queensland itch, kasen (Japan), dhobie itch (Phillippines) and summer itch.
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Using repellents for sweet itch
The best defense is to treat horses with a midge or "fly" repellent to prevent bites. You should also move horses, if possible, away from pastures of known midge infestation. There are allergy treatments for the allergic reaction itself -- check with your vet.
There are three choices for treating horses with fly repellent -- sprays, wipes and "spot-on" applications. The spot-on treatments are similar to the new flea control medications used for dogs and cats. Sprays are probably more convenient to use but some horses won't allow you to get near them with a spray bottle. Wipes or spot-on applications may be your best bet in these cases. Click in the table below for product information.
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Midge repellents for horses
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spray
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wipes
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spot-on
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Follow package instructions carefully in terms of how often you should re-treat.
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