I came home late tonight after fireworks and went to secure the windows for the night only to find both the interior and exterior of the coop covered in mosquitoes. I know the black flies can kill the chickens and I assume the mosquitoes could do the same along with the other diseases they carry. I looked up old posts and didn't really find a concrete answer besides screen. To cover all openings with screen would take a while - I have vents along the entire roof line and eaves of a 12 foot coop and I'm not a climber! I also let them free range so the doors are almost always open. I read lots of suggestions but I'm looking for things that have actually worked besides the obvious of covering all openings with screen.