Gardening0 min ago
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There was an old song of the American Deep South all about the "blue-tailed fly". From the song, it's clear that such insects were a blasted nuisance, having to be continually brushed away by servants...even, in the end, resulting in the Master's death after falling from his fly-pestered horse.
I'm sure the version, such as you offer in your title, is just the somewhat cruder British version of the same idea...something constantly buzzing around.