Our garage adjoins our house and is full of flies after I have swept and tried to clean! We have French doors and one side stays open a lot. We live in the country and are going in and out a lot. Also, grub worms are constantly on the concrete floor of the garage. By the way, we do not keep vehicles in our garage. Would appreciate any home remedies you have to offer for getting rid of these pests!
Getting Rid of Flies and Grub Worms
Houseflies can be a real problem in the country. Make sure there's no refuse close to the house which can draw them. Grub worms are different problem. They're usually found in the soil, because that's where they live and feed. Perhaps you have a number of those, and they're migrating into your garage. This article offers some solutions that might help: https://www.gardeningknowhow.com/plant-problems/pests/insects/get-rid-of-grub-worms.htm
Have you seen those new screens that hang loose, but have a weighted magnetic strip at the bottom so they close tight after you walk through? That might be a solution for your french doors.