Lots Of Dead Flies In House Suddenly? Here’s Why It Should Alarm You

This guide reveals the reasons for the sudden sightings of lots of dead flies in your house. 

You’ll find out why you see these dead flies in places like your basement, window sills, bathroom, and even returning after vacation. 

Plus, you’ll also learn what species of these flies are and how you can stop seeing these flies from entering your home in the future.

And a lot more! Keep reading to know it all. 

What Are These Dead Flies In Your House?

The dead flies that you see in your house are the cluster flies. You’ll find out later in the post how they enter homes.

For now, let’s find out more about them and if they bring any risks.

What Are Cluster Flies? And How Different They’re From The House Flies?

Cluster Fly

Cluster flies, also known as attic flies, are dark grayish with a striped abdomen. These flies can grow up to 10 mm in length, and their average lifespan is two years.

On a casual look, cluster flies resemble house flies.

However, there’s quite a difference in the appearances of cluster flies and house flies.

The first is cluster flies are bigger than house flies. They’re also darker than the house flies.

The second, easily visible, is bristles of yellowish hair on their thorax.

While at rest, the wings of cluster flies are more one-over-the-other than the house flies. The house flies’ wings look more spread out when they’re at rest than the cluster flies’ wings.

How Do Cluster Flies Get In The House?

Cluster flies enter homes during the late fall to overwinter. They’ll fly inside your home through open doors, vents, chimneys, and windows.

Cluster flies are also efficient crawlers. So, they’ll also crawl inside your home through the thin gaps and cracks on the window sills, door frames, doorways, and walls.

On entering, they’ll look for cluttered warm places in your home to hide and overwinter.

That’s the time when cluster flies will hide in the attic, basement, storage room and may even sneak inside the gaps and cracks of the wall. 

They’ll spend the entire winter in your home, hiding and waiting for the spring months to arrive.

Reason For Dead Cluster Flies In Your Home During The Spring And Summer

Dead Flies In House

When spring arrives, cluster flies come out of hibernation.

So, you’ll notice sudden appearance of flies inside your home even if your home had closed windows and doors.

But they’re starving and weak. 

Looking for food, the flies want to get out of your home.

They’ll repeatedly bang themselves on the window screens and the vents and ducts of your home’s attic and basement.

The result? The cluster flies die. Repeated efforts over time to get out depletes their last remaining body fat, and they die out of exhaustion.

That’s the reason you see piles of dead flies near window sills bathroom, near the ducts and vents in the attic. 

Where Do Cluster Flies Come From?

Cluster flies are not typical household pests like house flies. They’re outdoor flies that feed on the nectar of flowers and earthworms’ larvae. 

The only reason they sneak inside homes is to overwinter. 

That’s why homes near fertile lands, barns, or homes with lush gardens can be overwintering places for cluster flies.

Do Cluster Flies Spread Diseases?

The best part is that cluster flies don’t spread diseases as houseflies do. Cluster flies don’t sit on wastes, rotting carcasses, or feces like the house flies.

Cluster flies also don’t have any interest in your food. 

So, these cluster flies are clean, and they don’t carry any bacteria like the house flies carry and transmit to your food.

You can confuse them with horse flies (horse flies bite), especially when you live in a barn and have livestock. 

Do Cluster Flies Bite Or Sting?

Cluster flies don’t bite. They don’t sting either. 

In the spring and summer months, cluster flies appear suddenly out of nowhere. 

This sudden appearance and the constant buzzing of cluster flies inside the home is a total nuisance.

So, to prevent it from happening, you need to take steps beforehand to ensure that you don’t have the cluster fly problem the following spring.

But before that, let’s find out why the sudden appearance of cluster flies in your home should concern you. 

Why Should Dead Cluster Flies In Your Home Make You Worry A Bit?

Dead Cluster Fly

If cluster flies can sneak inside your home to overwinter, that means other bugs can too.

Many biting bugs and flies can sneak inside your home to spend their winters. 

Wasps are one of them. There’s also a sudden appearance of wasps in the home from nowhere for the same reasons as cluster flies.

Wasps can also make nests in your home if they can get inside. That can cause a spike of wasps in your home within a span of a few months.

Another biting bug is the kissing bug. It’s dangerous and can leave some nasty bites on your face.

The worst part? Kissing bugs can even hide near your bed in your bedroom. 

Stink bugs too sneak inside homes to overwinter. 

And when all these bugs enter homes, they attract their predators, the spider.

Spiders enter homes in the summer months to escape the sweltering heat outdoors. 

However, the presence of their prey inside your home can draw spiders in the winter months too.

So, if you’ve got cluster flies in your home, then there’s a big chance that other bugs can also use your house for hiding and breeding. 

What to do about it? Well, you’ll need to take steps that prevent cluster flies from sneaking inside your home. 

How To Prevent Cluster Flies From Entering Your Home?

You can follow these five steps to get rid of cluster flies in your home and prevent them from coming back.

For best results, start doing these steps in late fall.

#1 – Seal The Gaps And Cracks On Your Home’s Walls, Doors, And Window Sills

Cluster flies, and bugs like wasps, kissing bugs, and stink bugs, exploit cracks and gaps on the home’s walls, doors, and window frames to enter your home.

If there are any gaps, seal them. Use a silicone-based sealant to do the job as the sealant is sturdy, and bugs can’t chew through them.

#2 – Install Window Screens With Fine Mesh

Window screens with fine mesh come in handy to stop flies from flying inside your home. These screens don’t stop the airflow either.

So, install these screens on your home’s windows if you can. You can also install them on the ducts and vents of your attic, basement, and HVACs. 

These vents are prime entry points for lots of bugs, flies, and rodents like rats, mice, and squirrels.

#3 – Treat Your Outdoors For Cluster Flies

The source of cluster flies is outdoors. So, sealing your home won’t necessarily ensure that these flies won’t enter your home.

Hence, it’s essential that you treat your outdoor areas like yard or garden.

But do not use pesticides. It’ll kill the cluster flies. Cluster flies are natural pollinators, and killing them is not a good idea.

You can repel them without toxic pesticides or chemicals. And you’ve loads of options for doing that.

One of them is using peppermint spray on your garden and plants. The pungent smell of peppermint keeps a lot of bugs and flies away. 

And it’s safe for plants and humans too.

You can also spray peppermint spray on the exterior walls. The smell of peppermint will stop the cluster flies from sitting on the wall.

A mixture of white vinegar and water is also a good option. The acidic smell of vinegar is repugnant to many pests, flies, and bugs.

However, vinegar is acidic. And overusing it can affect the soil’s health.

Also, white vinegar emits an acidic pungent smell that can be discomforting if you don’t like it.

#4 – Hang Sticky Fly Traps

Sticky fly traps near the windows, doorways, and vents are also a great way to stop not just cluster flies but also many other flying bugs and pests.

If you want to make a DIY trap, keep sweetened water in a bowl and cover it with a perforated lid.

The lid holes should be big enough to allow the flies to sneak inside the bowl.

The sweet water will attract any flies hidden inside your home. Once they sneak inside the bowl through the holes, they’ll fail to get out. 

Dispose of the water with flies in it. 

This trick also works in trapping tiny flying bugs, like gnats and drain flies, in your home.

#5 – Keep A Bug Zapper Outdoors

Bug zappers help reduce the flies and, to an extent, eliminate the chances of flies and mosquitoes in your home.

Keep one of them on your patio deck or the terrace. The bug zappers draw the flies, and when the flies land on it, it electrocutes them. 

We do not recommend using any insecticide sprays indoors to eliminate cluster flies. You don’t need it.

What To Do With Dead Cluster Flies In Your Home?

Use a vacuum cleaner on the dead cluster flies to remove them. Check all the tight gaps and corners near where you found the dead cluster flies.

Chances are some of them lying inside those gaps. 

Pull your furniture and check at the rear side. Also, if there’s a carpet, then check underneath the carpet too.

Also, check your attic, the storage room, and the basement for any cluster flies, living or dead. 

If you find any, get rid of them using a vacuum cleaner. 

Ensure that you don’t leave any dead cluster flies in your home. In the spring and summer months, ants and roaches are active.

Dead cluster flies will attract them.

Dead Flies In Home During Winter

During the winter months, the dead flies you see in your home are not cluster flies. Cluster flies hide and hibernate during the winter.

The dead flies in the winter are house flies. These flies might drop off from a dead animal like a rodent hidden in the gaps of the walls of your home.


During the spring and summer months, the dead flies in your home are cluster flies. These flies sneaked inside you during the winter to hibernate.

Cluster flies suddenly appear inside your home when they’re out of hibernation during the spring months. Failing to get out of the house causes them to die.

In this guide, you’ve learned the five preventive steps to keep cluster flies away from your home.

There are also reasons why the sightings of cluster flies can point you towards a bigger bug problem that may be lurking inside your home.