How Do Flies Get Inside A House When Windows Are Closed

Flies often enter homes through open doors and windows.

But how do flies get inside a house when windows are closed?

Well, this guide will reveal the three reasons for the appearance of flies in a closed or sealed house.

You’ll find out the hidden sources of flies in a house, which are there right now, and the sneaky ways these flies use to get inside closed homes.

Plus, you’ll also learn the proven steps that pros use to eliminate these flies from their source forever.

Let’s dive in. 

How Do Flies Get In The House When Windows Are Closed?

There are three reasons for flies in a sealed house home with closed windows and doors – 

  1. The source of flies is inside your home
  2. Flies fly in through uncovered vents and unsealed cracks in your house 
  3. Some flies were hibernating inside your home

Though it looks mysterious, you’ll now find out that it isn’t. 

Let’s dive into each of the reasons.

The Source Of Flies Is Inside Your Home

The primary reason for live flies inside a closed house is that the source of flies lies inside your home.

In other words, a home with closed windows can sustain the entire life cycle of the flies.

Sounds terrible?

Well, read on. 

There are many types of flies that infest closed homes.

The most common are fungus gnats, phorid flies, drain flies, cluster flies, and house flies. 

All these flies can lay eggs inside your home.

Damp soil beds of indoor potted plants are the go-to places for fungus gnats to lay their eggs.

The larvae of fungus gnats feed on the molds and fungus that develop on the soil beds. 

After a few days, the larvae mature into flying adults. 

So, you see them in a closed house without having no clue from where they’re coming.

How do flies get inside a house when windows are closed

Fungus gnats resemble mosquitoes. But unlike mosquitoes, fungus gnats don’t bite. 

Fungus gnats can also lay eggs in the tray underneath the fridge. 

That’s why fungus gnats are one of the bugs that infest refrigerators.

Drain flies, which also show up in a closed house, will nest and breed on the gunk and slime that chokes the drains. 

They’ll lay eggs on the slime that blocks drains.

The larvae of the drain flies feed on these wastes.

When the larvae mature, adult drain flies will emerge out of the drains of bathtubs and sinks.   

Phorid and fruit flies can lay eggs in the trash bins, holding food waste and organic waste in your home and property. 

When these eggs hatch in the garbage cans, the larvae of these flies, also known as maggots, infest the trash bins.

Flies can also inhabit damp places like the leaky pipes underneath sinks in the kitchen, bathroom, and basement.

All these flies breed fast. A single female of these fly species doesn’t lay dozens of eggs.

She can lay hundreds of eggs in a few days.

For instance, a female drain fly lays up to 100 eggs in the sludge of the drains and damp wastes in your yard.

The eggs hatch within 43 hours, and the larvae turn into adults within 27 days. 

With the house flies, it’s even worse.

A single house fly can lay over 500 eggs inside your home in a three-to-four-day periods.

And the maturity period from the hatching of the eggs to the larvae turning into an adult house fly is only three days!

Now you know that if the source of these flies is inside your home, then the sudden appearance of flies in a closed house is not mysterious. 

It’s bound to happen.

Hence, it’s essential to eliminate the source of these flies. 

Taking only cosmetic actions that will target only the flies when they’re alive isn’t the solution to the fly infestation in your home.

Later in the post, you’ll find out how to get rid of flies inside your house from their source.

For now, let’s get into the second reason for flies inside the house despite closed windows and doors.

Flies Fly-In Through Uncovered Vents And Unsealed Cracks In Your Home

Let’s face it. There are enough sources of flies outside your house too.

The sources are many, from trash bins in the yard to decaying organic wastes, water holes, and damp soil beds. 

These places are the sources of flies like fungus gnats and house flies.

However, they’re also the perfect environment for biting flies like mosquitoes and biting midges to thrive.

Horseflies can also multiply at a skyrocketing speed under similar conditions in a farm or barn.

These flies are tiny. So, they can easily sneak through the unsealed gaps on the window frames and door frames.

Crevices on the walls and your home’s foundation are also entry points of flies and bugs inside your home.

Not only that. 

Vents are the go-to sources of flies to sneak inside your home.

Vents in the attic, garage, bathroom, chimneys, holes that allow utility wires, and gaps between the exhaust fans’ wings are common entry points for flies inside a home.

Flies Have Emerged Out Of Hibernation

Some flies like the phorid flies, blowflies, and fruit flies hibernate during the winter months.

They’ll hide inside the garbage piles curled up, waiting for the spring to arrive.

However, cluster flies can hibernate inside your home.

During the fall and winter months, cluster flies will sneak inside your home, looking for a warmer place to hibernate.

Most of the places they target for hibernation have minimal to no human footfalls.

So, places like the attic, storage rooms, basement, and at times, cluttered garage are their preferred places to hibernate.

Cluster flies will remain hidden in these places till spring arrives.

With the arrival of spring, cluster flies emerge out of hibernation inside the house. 

That’s why there’s a sudden appearance of these flies inside the home despite closed windows and doors.

All these cluster flies are under fatigue because they didn’t eat for months while hibernating.

They desperately try to get outside the home. In doing so, they bang themselves again and again on the window frames.

Many of these flies die in the process. 

So, you can also notice a sudden appearance of dead flies in your house near the windows during the spring and summer months. 

How To Prevent Flies From Getting Into A Closed House?

How to prevent flies from getting inside a closed house

Two things are crucial to prevent flies in a house with closed windows and doors –

  1. Eliminate flies’ sources and their habitat
  2. Block their entry points

Let’s find out how you can easily do it.

#1 – Remove Wastes From Your Home And Property

Remember, piling wastes in your home and property are prime real estate for flies to live and breed.

And if these wastes are damp, it’s even better for flies.

So, the first thing you must do is ensure no waste accumulation inside and outside your home. 

Do not let food wastes in your kitchen trash cans accumulate for days. 

These food wastes in the trash bins of your kitchen are the main culprit for drawing flies, ants, and roaches inside your home.

So, dispose of the food wastes daily. 

If there are maggots in the trash bins, pour some bleach before disposing of the trash.

Bleach kills the maggots.

After disposing of the waste from the garbage bins, always clean it.

Spray disinfectant in the trash bins to remove the smell that can draw bugs and flies.

Do the same with the wastes lying in the garbage cans of your yard too. 

Also, regularly remove the organic wastes like foliage and rotting pieces of firewood and mulch beds in your yard.

These are not just the breeding grounds for flies. 

They also draw many invasive bugs like ants, roaches, and the worst, termites.

#2 – Control The Dampness Levels Of Your Home

To control the dampness levels of your home, you’ll need to fix the water leakages both in and outside your home.

Additionally, you’ll also need to ensure that there’s no waterlogging problem in your yard or garden.

Dampness attracts flies. 

And the increase in dampness inside your home is because of water leakages.

Fix any leaky pipes in the plumbing areas of the sinks of your bathroom, kitchen, basement, and laundry rooms.

If there’s water leakage in your yard, fix it too.

Remove old tires, containers, or anything that accumulates water. Stagnant water is a breeding ground for mosquitoes. 

Also, fill up any holes that are accumulating water. 

These holes keep the soil beds of your yard and garden unnecessarily wet. 

That makes the soil beds a breeding ground for flies like gnats.

#3 – Unclog The Drains Of Your Home

Clogged drains are the source of drain flies. 

So, if the wastes are choking the drains in your bathroom, kitchen, basement, or elsewhere in your home, then clean the drains.

These wastes become the egg-laying grounds for drain flies

And choked drains are the primary reason for drain flies in your home

Not to mention that the gunk and sludge blocking the drains become a breeding ground for drain and sewer roaches.

One of the ways to clean clogged drains is to pour hot water mixed with dish soap and baking soda into the drain.

#4 – Seal The Gaps And Cracks On Your Home To Prevent Flies From Entering

The gaps and crevices on damaged window frames, door frames, and on your home’s roofs, walls, and foundation are the entry points for flies and bugs.

Flies will sneak inside your home through these gaps. 

So, it would be best to seal these gaps. And do a proper repair where it’s needed. 

Installing weather stripping on the window frames and door frames is an easy and effective way to close the gaps in these areas.

Alternatively, you can also use a silicone-based sealant to caulk these gaps. 

Silicone-based sealants are durable, and bugs can’t chew through the caulk. 

#5 – Cover The Vents In Places Like Attic, Garage, Chimney, Basement, And Bathroom

Many homeowners ignore the vents in these places.

These vents are easy and accessible entry points for flies

Bugs like kissing bugs, spiders, and wasps use these vents to intrude into human dwellings to hibernate during winters.

The worst part?

It’s a go-to point for rodents like mice, rats, and squirrels to sneak inside your home.

Either cover the vents or install screens with fine mesh on them. 

If there’s a chimney in your home, use chimney covers during the spring and summer when you’re not using the fireplace.

#6 – Spray Essential Oils To Repel Flies

Many homeowners use fly sprays to kill flies. Fair enough. It will help if you use it too.

But fly sprays don’t stop flies from entering your home.

For that, you’ll need essential oils

Essential oils like peppermint, lavender, and eucalyptus are bugs and fly repellents. 

Bugs and flies hate the smell of these essential oils.

You can prepare a mixture of any one of these oils with water and spray it in your home, attic, basement, bathroom, and kitchen. 

It’ll keep the flies away.

Outdoors, use peppermint spray on soil beds, mulch beds, woodpiles, and dense vegetation around the home’s perimeter.

That’ll also keep bugs and flies from hiding or nesting in these places.

If you want to use a spray to kill any flying bugs in your home, use a pyrethrin-based spray. 

These sprays are more effective on flies than other sprays.

Cluster flies can nest or lay eggs in the gaps of the window frames. 

Spraying pyrethrin-based sprays on the window frames will destroy the flies’ eggs and eliminate their larvae.

Fly swatters are also handy fly killers. 

But always dispose of the dead flies and clean the surface where you smashed the flies with a disinfectant.

#7 – Install Bug Zappers Outdoors In Your Yard

Flies enter homes from outdoors. And bug zappers help in eliminating the flies that try to sneak inside. 

Install a bug zapper on your patio deck or near the doorways. 

You can use fly traps to lure the flies and entrap for indoors.

Keep the fly traps in places where you notice them often. 

Places like the kitchen, bathroom, and appliances like fridges and dishwashers are ideal for keeping fly traps. 

Swarms of flies hover around these places because of their dampness.

You can also make a DIY fly trap with the help of using dish soap and apple cider vinegar. 

Mix equal apple cider vinegar and dish soap parts in a small bowl. You can also add a pinch of sugar to it.

Stir the mixture well. And cover it with a perforated piece of cloth.

Keep this fly bait or fly trap in places where you notice flies. 

The fruity smell of the apple cider vinegar will draw the flies to it. 

When the flies enter the bowl through the holes of the cover, the stickiness of the dish soap in the mixture will trap them.

Dispose of the liquid in the bowl when too many flies inside it. 


Flies inside a home with closed doors and windows aren’t a mysterious occurrence. 

There are common reasons for it which you learned in this guide.

But there’s one thing that you should always keep in mind. As long as your home has conditions that sustain flies, flies will appear in the fly season. 

So, to eliminate flies in your home, you need to remove the conditions that sustain them. 

This guide revealed how you could do it by following a 7-step process that safely and permanently eliminates flies from their source.

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