Biting Midges, "No-See-Ums" & Sweet Itch In Horses

-- Use insect repellents and head nets to avoid bites --

Summary: Biting midges, or no-see-ums, are tiny flies in the family Ceratopogonidae. Like black flies and mosquitoes, biting midges can cause intensely itchy skin lesions and an allergic reaction. Insect repellents and head nets offer the best protection. Sweet itch (summer itch) is an allergic skin condition in horses caused by the bite of these flies.

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Jack DeAngelis, ext. entomologist (ret.) revised: 11/2018

Biting midge identification

Biting midges are tiny (0.6-1.5 mm) flies in the family Ceratopogonidae. These flies are variously called biting midges, biting gnats, "sandflies", no-see-ums, Scottish midges, highland midges, and punkies**. The midges are nearly invisible to the unaided eye and can pass through normal window screens and even some mosquito netting. When under attack by these flies people often say something like "I'm getting bit but I can't see what's biting me!". While there are many non-biting midges, or gnats, these are the only midges that bite. At rest biting midges fold their wings across their back like scissors. The wings may be spotted and somewhat hairy.

biting midge adults

These tiny biting midges (flies) are nearly invisible to the unaided eye.

**True sand flies belong to the family Psychodidae; the term "gnats", 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 (Philippines) and summer itch.

Biting midges develop in damp, highly organic soils

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 (fresh water) or semi-aquatic and midge populations tend to be highest near poorly drained or constantly wet soil.

Biting midge populations can be very "spotty" across fields, high in some wet areas while low or absent in drier spots. Biting midges are also poor fliers so are not able to move far from their breeding habitat. Often just moving to higher, drier ground will makes things better. However, short of draining the wet ground it is nearly impossible to eliminate midges. Instead it is best to avoid problem areas or use insect repellents and head nets to protect both people and horses from bites.

Using insect repellents & head nets

Insect repellents are the best defense against these biting flies when midge numbers are fairly low. Repellents containing DEET or picaridin will give the longest-lasting protection while midge-proof head nets should be used if midge numbers are high. With head nets be sure to wear a wide-brimmed hat so as to keep the netting away from your face and neck. Repellents can be applied to clothing but keep in mind that DEET can damage plastic. Also, keep in mind that repellents don't really repel midges, instead they make you invisible to these little buggers. This is why in a swarming situation repellents alone don't work well. Finally, the new "personal foggers" such as ThermaCELL (tm) can also be effective against biting midges and mosquitoes.

Sweet itch in horses

Sweet Itch is a skin condition in horses caused by the bites of biting midges. 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. You should move horses, if possible, away from pastures of known midge infestation. There are also very effective allergy treatments for the allergic reaction itself so check with your vet. Horses can also be protected against biting midge with repellents.

Insect repellents for horses (DoMyOwn.com)

Under attack by biting midges!

What does it look like to be caught in a swarm of biting midges? Simon Booth, a well-known UK landscape photographer, was caught in a swarm of biting midges while filming in Scotland. Fortunately for us he filmed the encounter and posted it on YouTube. Watch as his reaction turns from mild annoyance to near panic. This truly is an example of an artist suffering for his art!

This swarm was so intense that only a good head net combined with the wide-brimmed hat and an insect repellent would have been completely effective in this situation.

Supplies

Professional-level pest control supplies are generally not available in home and garden stores but can be found at DoMyOwn, our affiliate.

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