Why Are There Lots of Flies Suddenly in My House?

Flies are scavengers that feed on dead and decaying matter. While they typically live outdoors, they might be spotted indoors occasionally when they enter a home in search of food, shelter, or water. However, when lots of flies suddenly appear in your home, it is a cause of concern because some flies spread pathogens that cause disease and other infections.

Learn more about why many flies are suddenly in your home and the steps you can take to prevent a sudden influx of flies.

Reasons Why Lots of Flies Suddenly Appear in a House

Common fly varieties include house, fruit, drain, and blue bottle flies. The species in your home depends on where you live and the prevailing environmental conditions. Several potential reasons for a sudden influx of flies are:

1. Decaying Matter

Most flies feed on organic matter. They hunt for food on countertops, trash cans, compost piles, and stagnant water. Fruit flies feed and breed on rotting or overripe fruit. Drain flies feed and breed on organic matter in your drains or pipes. So, the sudden increase of flies in your home is likely due to the presence of decomposition. If you can't see the source, it may be a dead rodent in the walls or under the floorboards.

2. Warm Temperatures

Flies thrive in warm temperatures of 75°F and higher. Their larvae can mature in 4–13 days. Keeping the indoor temperature cool can ward them off or delay larvae hatching.

3. Rapid Reproduction

Most fly species reproduce quickly. If you spot one or two flies today and don't get rid of them quickly, you might be dealing with an infestation in a few days. The average lifespan of most flies is between 15 and 30 days, depending on factors like the availability of food. Yet, female houseflies can lay as many as 500 eggs during their short adulthood; it takes only 7 to 10 days to complete the life cycle from egg to adult. So, if you spot five female flies in your kitchen, you could be dealing with over 2,000 adult flies in less than a month.

Measures to Prevent and Control Fly Infestations

If you already have a fly infestation, destroying their breeding grounds is the best way to eliminate them. Depending on the fly species, breeding grounds vary, so correctly identifying the fly species you are dealing with is helpful.

After you get rid of the flies, prevent re-infestation with these measures.

1. Keep a Clean House

Vacuum and clean all surfaces and utensils to eliminate any potential food sources. Also, regularly flush and clean plumbing pipes because they are ideal breeding sites for drain flies.

2. Eliminate Potential Breeding Grounds

Compost piles, clogged dish drains, uncovered trash cans, leftover food, and waste can quickly become breeding grounds for flies. Make sure all trash cans are covered. Empty them regularly and clean them thoroughly—inside and out. Clean and remove pet waste immediately. Also, keep pet feeding bowls clean and dry.

3. Prevent Access

Typically, flies live outdoors. However, they access your home through doors and windows. If they find a food source and a conducive environment, they can turn your house into a breeding ground. Ensure the screens are not damaged. Seal all crevices and install weather stripping around windows and doors. Use caulk or foam to seal any openings, especially where pipes come through the exterior of your home.

4. Store Food Properly

Place food in sealed containers and promptly clean any food or beverage spills. Store leftover food adequately covered and in the refrigerator. Dispose of overripe fruits and cover any trash cans. All food attracts flies, other insects, and rodents.

5. Call an Exterminator

Contact a professional if you have an infestation you cannot get rid of. Professionals can correctly identify the flies and eliminate their breeding grounds.