They suck blood like mosquitoes, they intentionally search for humans, fly around and wait for a convenient moment. Maybe we are talking about different kind of flies. So we cover windows with an insect screen (net) in summer.
Yeah, those I kill without mercy wherever I see them. And they don't sting like mosquitoes, they bite and suck.
(Sometimes I am with hippi people who don't kill flies etc. - so they are annoyed by them, but don't know what to do besides complaining, so when I then do the killing, they don't really object)
This is extra large size fly, we have these insects, but they usually live in the countryside and hunt for cows. Normal size fly is this https://en.wikipedia.org/wiki/Muscidae
You might go to countryside or forest to enjoy nature but instead your blood will be enjoyed by plentiful selection of insects of all sizes ranging from tiny Simuliidae to large Tabanidae.