If there are many, why not call an exterminator? Also to prevent entry you can put a net on the door, from those that have a magnet and closes itself after leaving. If you talk about flies you can put a sticker on which they will stick, will It looks ugly, but still helps. Or look on the Internet for some sprays, I'm not familiar. And at home (I live in an apartment) before there were black bedbugs, and now some very tiny black bugs. I'm afraid of insects and it's awful the feeling of lying down and crawling next to you. : D
1 Cezarek0472 answered
Put on nets and nothing will come in