How Do Flies Get Inside A House When Windows Are Closed

Open doors and windows are the entry points for many bugs and flies.

But there are instances you come across buzzing flies in a house that you shut and close before leaving for a vacation or business trip.

So, how does that happen?

This guide will reveal how flies get inside a house when windows are closed.

Plus, there are seven steps that you can take right now to prevent flies from showing up in a closed house. 

Keep reading.

Here’s How Flies Get Inside A Closed House

How do flies get inside a house when windows are closed

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

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

Let’s dive into each of the reasons to know more.

The Flies Are Nesting Inside Your Home

It’s pretty common for the source of pests to be inside your home.

These pests will hide inside your home, establish their colonies, breed, and increase their numbers without invading outside intervention.

With flies and with many household insects, it’s no different.

The source of flies can be right there in your home if your home provides them the condition to live and breed.

Choked drains of your kitchen sink, bathroom sink, soil beds of indoor potted plants, stored food, fruits, and vegetables, and places like the attic and basement are the places where flies can lay eggs.

On top of that, flies multiply very fast. 

For example, a female house fly can lay 500 eggs in three-five days. 

And from the hatching of larvae to maturing into an adult fly takes only three days! 

So, with such a short maturity span in their life cycle, your home can have a fly infestation within a week. 

But house flies are only a type of fly that can live inside your home.

Flies like fungus gnats, cluster flies, and drain flies can also hide and nest inside your home.

Fungus gnats will lay their eggs on the damp soils of potted plants. 

The larvae from the eggs will feed on the molds and fungus that develop onto the moist soil.

And within a few days, the larvae will mature into adults, causing a nuisance in your home and making you wonder about their source.

The adult fungus gnats feed on decaying organic wastes. So, the food wastes in your kitchen trash bin are their go-to source of nutrition. 

The food droppings and stains on electrical appliances are also their foods. 

That causes flies like drain flies and fungus gnats to enter appliances like fridges, dishwashers, and coffee makers.

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

Flies don’t need open windows and doors to fly inside your home.

Many flies are efficient crawlers too.

So, the tiny gaps and holes on window sills, walls, the home’s foundation, and the door frames are the entry points for flies and bugs.

Vents in the attic, bathroom, and the tiny gaps around the utility lines pathways are the points that flies can crawl through. 

Flies Have Emerged Out Of Hibernation

When the fall season ends, many bugs and fly species look for a place to hibernate. 

And your home is one of the places that they target. It’s because your house provides them the warmth they need in the winters to survive.

The places they choose to hibernate inside your home are the areas that are cluttered, receive less to no light, and have fewer human footfalls.

So, places like the attic, storage rooms, basement, and the clutter in the garage can be the flies’ hibernating locations.

And when spring arrives, these hiding flies come out of hibernation. That leads to a sudden fly problem in your home despite no open windows or doors.

Many homeowners notice it when they come back to their closed home after months and see flies buzzing inside the house!

The flies that come out of hibernation are starving and exhausted. And they try their best to get out. 

So, while looking for any opening to get out, many of these flies die.

That’s one of the reasons you may see dead flies in your house out of nowhere.

Cluster flies are one fly species that lie around dead inside the house in the spring, especially when they are hibernating in the winter months.

How To Prevent Flies From Getting Into A Closed House?

How to prevent flies from getting inside a closed house

You’ll now find seven easy steps to prevent flies and bugs, like kissing bugs and stinking bugs that hibernate inside houses.

Follow these steps before leaving your home for extended periods in the fall and winter.

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.

Flies lay eggs on the trash in the garbage cans. Not disposing of the wastes will lead to the formation of maggots, which are the larvae from the flies’ eggs.

So, after disposing of the trash, clean the garbage cans with bleach or white vinegar. Both kill maggots and disinfect the garbage cans.

Also, regularly remove the organic wastes like foliage, 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 termites.

Remove pet feces in your yard and regularly change the litter in the litter box. Flies sit on animal droppings and the pathogens in the excreta sticks with their legs and wings.

Flies will transfer these pathogens to your food when they sit on it. Consuming those foods can be disastrous for your health.

Also, flies like gnats and fruit flies can also lay eggs in a cat litter box.

That makes the cat litter box as one of the hidden sources of fly infestation.

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.

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.

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. 

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.

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.

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 despite closed doors and windows.. 

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 prevents flies from hiding in your home.