Found this on the web, it relates to Scotland, but probably applies to the UK generally.
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It is the female midge that bites. It can only lay its eggs after it has had a blood meal; which is where you and I come in. Midges start to become a problem in June and usually last through to August when their numbers diminish rapidly, before they finally disappear with the first real frost of autumn. The numbers of midges vary considerably from year to year, depending on the severity of the preceding winter, the amount of spring rainfall, and the temperature.
To avoid midges, it helps to know a little about their likes and dislikes. They like the cool indirect light of dawn and dusk, and dislike direct strong sunlight. They like damp conditions and dislike dry conditions. And they like still air and dislike anything above a fairly gentle breeze. All this tends to mean that midges are less common the middle of the day than in the mornings and evenings; that they are rarer on exposed hills than in sheltered valleys; and that the can be fond of woodland and forest areas. Finally, it is worth knowing that midges prefer dark coloured clothing to light.
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Pretty much what's already been said. :-D
Oh, I also read that the majority of swarming midges and gnats DO NOT BITE! I didn't know that, I assumed they did. I believe some varieties of midges bite, but most dont. Interesting.
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Many people believe that all midges bite, this is a common misconception. Most species of midgies are actually harmless. These "friendly" midgies belong to the Chironomidae family, and have no piercing mouthparts. Lots of harmless midges, such as the "dancing midge", are mistaken for biting midgies and are often killed by wary people.
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and....
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Biting midges tend to be especially small, and typically have a wingspan of less than 2mm across. Their small size is an advantage, as it allows them to feed undetected. Biting midges can be identified by inspecting their wings. All of them have very characteristic dark spots or blotches on their wings. The pattern of these markings can help identify which species of the Ceratopogonidae family that the midge belongs to.
Only a few of the biting midges actually feed off humans. Many of them feed off other warm-blooded creatures - such as mammals and birds. Some even feed off other insects!
Only the female midges bite - they do so to feed their eggs. The males have a different type of mouth, suitable only for feeding from vegetation.
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