Because houseflies only live a maximum of 2 months, most die by the time winter weather rolls around. Some flies in the pupal stage survive through the winter.
Before the start of winter, many flies lay eggs. The eggs hatch into larvae, which are known as maggots. The maggots will survive in food or feces until they grow large enough to wrap themselves in a cocoon-type structure where they can then ride out cold temperatures. Flies are cold-blooded and so the larvae that mature into adult flies during cold weather fly more slowly than those that can warm up in the sun.