Greetings from Australia, summer here is insane with flies so I use the following and it works a treat, 20 drops of lavender and eucalyptus oil mixed with 1 cup warm water, I spray it around the windows and doors and on all flyscreens once a week smells great and the flies can’t stand it
The flys are leaving HORMONES. Scrub like crazy with a stiff broom and a siding safe cleanser, rinse well. Good luck.
They may be cluster flies. In that case, use a repellant to make them find some other digs. You can also hang up a Ziploc bag filled with water. https://www.backyardchickens.com/threads/flies-and-the-proper-way-to-deal-with-them-in-masses.663356/
If they get inside the house https://www.thespruce.com/cluster-fly-description-2656663
Or you could try a fly trap. http://forums2.gardenweb.com/discussions/1433333/fly-control-outside-the-house
Check to make sure there is nothing attracting them like something dead, or pet feces. Then eliminate that source of food.
Thank you!!!!
Greetings from Australia, summer here is insane with flies so I use the following and it works a treat, 20 drops of lavender and eucalyptus oil mixed with 1 cup warm water, I spray it around the windows and doors and on all flyscreens once a week smells great and the flies can’t stand it