Fly by day, rest at night

Much like a human with a normal routine, houseflies are only active during the daytime hours.

Picture from Paqwak

During the overnight hours, houseflies find peace while resting at the corners of rooms, ceiling hangings, cellars, and barns, where they can survive the coldest winters by hibernation.  When spring arrives adult flies are seen only a few days after the first thaw.