Imagine not having screens on the windows and letting every single bug in the nearby area take up residence inside and being okay with it cuz "it's only a few months out of the year".
It's just available in my local hardware store, just measure your window and buy the correct size. It was like 20 euros.
It has velcro strips that attack to the frame of the window with clue or something and the screen has the other end of those velcro straps so you can take it off for winter.
There were solid frame ones too but I like this so I can roll it up for winter and it was cheapest.