Question - how many seconds does it take for a fly to come into your house when you have opened the window or back door ?
Are they just lining up and waiting ?
I have long suspected that the b*ggers do ~ I think they hide just round the corner of the window where you can't see 'em.
Nice to know I am not alone in my suspicions.
See also wasps in Autumn and those hooooge bumble bees that can never find their own way back out.