Where have all the flies gone?!!

Found a windowsill full of the tiniest fruit flies a couple of weeks ago. Had to use the hoover to get rid. Can only assume something had flew in during the hot weather and set up camp. All sorted now.

Question though, why does the blue bottle insist on flying in squares right under 'big light'?
 
I don't notice them because I use Jungle spray because we have ponds and rivers through and on our course & have horseflies which are nasty buggers so I always spay. My dog loves chasing flies in the house but I must admit it's not as often a spectacle as it used to be.
 
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