These are not the same as the blue bottles that buzz hard against the windows in the warmer weather or the house flies and smaller flies that are active in summer too.
Flies in attic room.
Apply insecticide to the outside of your attic to prevent flies from coming in.
Do this in the summer or early fall at the latest.
These flies are known as cluster flies a name that describes their habit of clustering in large numbers inside attics cluster flies do not reproduce indoors and home owners bothered by these pests do not need to fear the flies are hatching from a dead animal or other unpleasant material within the attic or walls.
Once the flies are dead it is important to clean the area thoroughly so that other bugs such as roaches do not move in to eat the dead flies.
Cluster or attic flies are the genus pollenia in the blowfly family calliphoridae.
Unlike more familiar blow flies such as the bluebottle genus phormia they do not present a health hazard because they do not lay eggs in human food.
Spray as best you can around your roof chimney eves ventilation holes etc.
Bug bombs that release poison throughout a room can be used to kill the flies in an attic or crawlspace.
Flies that gather in roofs around windows and on walls inside in the autumn and winter are called cluster flies also known as attic flies.