I was tired of catching flies the old fashioned way, and after some googling i found that you can put a lid on a mason jar and have a fly catcher. Now, i don't have mason jars, but i have a ton of these olvarit (baby food) jars, and found a salt shaker mod for it here on thingiverse https://www.thingiverse.com/thing:1792266
After some modding of the file, i now have an olvarit fly trap.

And ohyeah, you can actually close it again using the original lid with the flycatcher inside.

2 files;

vliegenval.stl - original
vliegenval-v2.stl - the hole is a bit lager in diameter, allows for bigger flies to pass through