Mel, just a suggestion for you.
Every summer we are really plagued by flies especially when the farmers are muck spreading, the darned house gets full of them.
We hang up fly papers which get snided in the pests in no time.
Trouble is, fly papers are horrible to put up and even worse to take down - so sticky, plus they look horrendous.
I bought some stickers that look like a Daisy flower and put them in the windows at the top, because that's where they seem to congregate.
They are coated with insecticide and any fly that walks over the flower (which are said to attract bugs) soon ends up on it's back and dies, usually in the window ledge.
I was a bit concerned about using them at first, just in case a bee or ladybird crawled over the flowers, because I would hate to kill any of those.
Luckily, bees and ladybirds don't come into the house much - too many outdoor garden flowers to attract them.
The stickers do work and last for quite a while, but getting them off the window when you no longer want them there can be a bugbear (sorry! couldn't help that! )
I scratch ours off with soapy water and wire pan scourer.
Might help you out a bit.