Q Can the sudden appearance of dozens of large black, hairy flies in the house have anything to do with exterminating a flying squirrel in the attic? We have window screens in good repair and doors are kept closed.

A You are describing a type of blow fly. These are the iridescent green or blue (sometimes black) flies that are common around garbage or dead animals.

The most likely reason you find them in your house is that an animal or bird became trapped in the building -- maybe in a chimney or wall void -- and died. The carcass would attract blow flies, which lay eggs in decaying matter. Maggots hatch from the eggs, feed on the dead animal and develop into adult flies. And those are likely the flies that are trapped in your house.

The flies will go away after the carcass is consumed. Depending on the size of the animal, this generally takes a couple of weeks.

Unless you can remove the dead animal, which will solve your fly problem, you will have to wait until the blow flies have finished their job.

This may or may not have anything to do with the flying squirrel in your attic. An animal could have entered after the exterminator did the job, or perhaps babies were left after the mother was killed and removed. When hiring an exterminator, homeowners should request humane removal of pests if possible. Specify that you'd prefer trapping to poisoning and don't want babies left to die.

Includes information from the University of Minnesota Extension Service

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