Why do you get houseflies in the house?

Answer 1

[1] House flies like moisture, organic matter, and warmth. They get into houses, by way of cracks and improperly fitted openings such as doors, screens, and windows. [2] They're particularly attracted to waste containers that hold kitchen scraps. These containers may not be tightly lidded, and may not be emptied daily into an outside container. So they're a choice environment for laying eggs. When the eggs hatch, the resulting larvae have a ready food supply. Under the best conditions, the time from egg to adult fly can be seven days.