Most commonly they move from the ground to your attic for the winter when it gets cold.
Flies in attic winter.
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.
Attic flies common this winter by donald lewis department of entomology the large black pesky flies that show up in bed rooms and on window sills from late fall through early spring have been very abundant this year possibly because of the wetter than normal weather we had last summer.
One of the best tips for getting rid of attic flies is to keep them from entering the house in the first place as trying to eliminate them after they are in hibernation can be difficult.
Some species of flies such as face and cluster flies lay eggs in the cracks and crevasses of a home.
These insects are born out of earthworms if you can believe that and like to overwinter in protected areas.
Thus the common name they have of attic flies.
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 are an expected nuisance in the spring and summer but some homeowners will find themselves in the midst of an infestation in cold winter months.
By instinct they seek shelter away from the elements such as in the fall when it gets cold.
These eggs hatch throughout the winter and the little flies have nowhere to go but the home.