Why You Have So Many Flies (And What To Do About Them All)

by | Flies, Insects

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Are flies suddenly swarming your home or yard and becoming a serious problem?

A lot of flies mean there’s a fly infestation in your house or area where at least 1 female fly laid a batch of eggs that hatched and grew into flies. In warm, wet weather eggs can produce adult flies within a week. Young females can lay hundreds more eggs, and the infestation keeps getting worse.

If you have a fly infestation, you will see many fly eggs, maggots (worm-like larvae), and/or adult flies. If you can’t see them, you’ll often hear flies buzzing around your property or in your house. Knowing if you have flies that breed indoors or outdoors and how to find the fly nest will go a long way in helping you minimize or get rid of your fly problem.

In this article you’ll find out:

  • Which flies breed in houses
  • Which flies breed outside
  • How to find a fly infestation

Flies that breed in houses

If flies are breeding in your house, you will notice a lot of flies over a long period of time as each generation lays eggs that produce more flies that lay eggs, and so the cycle continues. To get rid of such an infestation, you’ll need to find the source of the problem and break the breeding cycle.

If you have a lot of flies in the house but their numbers vary – sometimes there are a lot and other times none – flies might be coming in for food or shelter before dying off or leaving, and they are probably not laying eggs in your home. You should focus on finding the breeding area outside if this is the case.

Small flies are more likely to breed and live in a house. When indoors, they usually lay their eggs in trash cans, in the kitchen, in the attic, or in the garage. Small flies that commonly breed in houses are cluster flies, drain flies, fruit flies, fungus gnats, and phorid flies.

Small flies breed in houses when there is a moist, dark place to lay eggs and food for the maggots to eat when they hatch from the eggs. But small flies also breed outdoors and might just be in your house to eat or stay warm.

If you want to stop flies from coming into your house, click here to find out how flies get inside and how to stop them.

Large flies tend to breed in houses when there’s a dead animal in a wall or in the roof of the house. Once the animal carcass is removed or fully decayed, these flies leave the house because they prefer to lay eggs and breed outdoors.  

Flies that breed outside

Photo of a swarm of black flies on the ground
Large flies choose to breed outside rather than in a house.

All flies can breed outside but larger flies are more likely to choose to breed outdoors than small flies when given the choice. Some big flies that like to breed outside are blow flies, flesh flies, and house flies.

If you see many of these flies inside your house, you might have a dead animal or rotting matter where they are laying eggs. But the problem could be temporary and the flies are inside to eat food or enjoy a better climate than what they get outside, and they aren’t there to stay.

How to find a fly infestation

Here are a few simple steps to follow to find a fly infestation:

1.     Identify the type of fly infestation you have

If you have a lot of flies, knowing what kind of fly they are will help you know where to look for the nest or breeding area and to identify what is attracting the flies to your house or yard.

Below is a series of pictures to help you identify flies that commonly infest people’s properties. Catch one of the flies and compare it to these pictures to decide what fly you have a problem with.

All the pictures are clickable links – click on one that looks most like the fly you caught for more information on that type of fly.

Blow flies

Photo of a blow fly with labels to identify a blow fly

Drain flies

Photo of a drain fly with labels to identify a drain fly or moth fly

Fruit flies

Photo of a fruit fly with labels to identify a fruit fly

Fungus gnats

Photo of a fungus gnat with labels to identify a fungus gnat fly

Horse flies

Photo of a horse fly with labels to identify a horse fly

House flies

Photo of a house fly with labels to identify a house fly

2.     Look for the flies in their favorite places

Female flies lay eggs where there is food for maggots to eat. When fly eggs hatch, worm-like maggots emerge and need to eat to grow and turn into adult flies. Fly maggots typically eat moist, decaying things like feces, rubbish, dead animals, compost, or dead plants. But their diet depends on the type of fly and so this will affect where they lay eggs.

Now that you’ve identified the type of fly infestation you have, use the table below to find out where to look for the flies’ eggs and adult resting areas.

Type Of FlyWhere To Look For These Flies
Blow FliesLook for blow fly eggs:
– On a dead animal
– In the wound of a living animal
– In animal feces
– In garbage
– In rotting grass clippings
– In neglected compost piles
– In the eyes, nose, or ears of a healthy animal  

Look for blow flies:
– Near garbage, especially if there are meat scraps
– Near newly dead animals, such as a squirrel that has died in a wall, attic, or crawl space
– By broken sewer pipes
– In cat litter trays and animal feces
Drain FliesLook for drain flies in:
– Standing stagnant water
– Sewers and septic tanks
– Clogged gutters
– Drain pans under refrigerators
– Bottom of garbage cans
– Bathrooms and humid basements, near kitchen sinks and garbage disposal units, and in drains
– Under cracked tiles
– Areas where air conditioning units drain
– Sliding glass door tracks
Fruit FliesLook for fruit fly eggs:
– Fruit flies with red eyes lay eggs in rotting fruits, trash cans, and garbage disposals
– Fruit flies with dark eyes (brown or black) lay eggs in dirty mops, damp rags and sponges, near drains and urinals, and in empty cans or bottles  

Look for fruit flies:
– In overripe or rotting fruits and vegetables
– At the bottom of trash cans
– In recycling bins
– Near spills or loose lids on vinegars, wines, beers
– By floor drains
– In any rotting material
– On wet rags, sponges, and mops
Fungus GnatsLook for fungus gnat eggs:
– On soil
– In rotting wood
– On animal waste
– In overwatered pot plants  

Look for fungus gnats:
– On soil, especially the soil in pot plants
– Walking over plants
– Wherever there’s decomposing material
– In bathrooms, laundry rooms, and crawl spaces
Horse FliesLook for horse fly eggs:
– On rocks and plants near water  

Look for horse flies:
– Near horses, livestock, and other large animals
– Close to water, wet areas, and swimming pools 
House Flies – Indoors, house flies are usually found by windows, on walls, in or near trash cans, by pet food, in garages
– Outdoors, look for house flies near garbage bins, in long grass, by compost piles, and wherever there is animal feces

3.     Take steps to get rid of those specific flies

If you want to get rid of your fly infestation, it’s best to take steps that will kill and prevent that kind of fly. There’s no one size fits all when it comes to killing fly pests.

Simply click on the type of fly infesting your home or yard in the list below and you will be taken to a list of recommended methods and products that you can use to get rid of the fly infestation.

How to get rid of:

I'm Monique. I love gardening and spending time in my backyard growing things. Here's where I share what I know about backyard pests and what to do about them, so you can enjoy your yard too.

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Monique loves gardening and spending time in her backyard, where she grows flowers, succulents, herbs, fruits, and vegetables.

Monique spends a lot of time researching how to protect her backyard from harmful pests and trying to attract beneficial insects and animals.

She shares everything that she learns and tests here at Backyard Pests.


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