Haven't seen a bluebottle for many years, they used to be very common before we had a fridge. They would hurtle themselves at the mesh of the meat safe, horrid things
I can have my patio doors and windows open anytime I want and no flies can get in at all. I have magnetic nets and they are brilliant and not expensive. Best things I ever bought.
They are brilliant barry. I got black ones because that's all I could find at the time. But my daughter recently got me a packet of white patio ones she found in bargain bucket in either Homebase or B&Q for £3.99.
You do have to check the patio ones have snapped shut behind you. I only ever have the one door open but that's enough for me. It doesn't take a fly long to whizz in if it gets the chance. Hate the things.