Horse Flies Suddenly Appear In Homes: 3 Reasons Revealed

Are you under a sudden invasion of horseflies in your house?

If yes, then this guide will take you deep into why horse flies suddenly appear. 

You’ll also find out the best practical ways to get rid of horseflies in your home and property.

Keep reading. 

Horse Flies Identification

Horse Flies Suddenly Appear

Size – from ½ an inch to 1 inch in length

Color – ranging from dark brown to black.

Wings – Large transparent wings with intricate vein pattern. Wings have a slightly tinted or smoky appearance.

Eyes – The most prominent feature in a horse fly is their large eyes. Eyes are large, prominent, with iridescent green or purple color. The eyes occupy a significant portion of the head.

Mouthpart – A horse fly has sharp scissor-like mouthpart, which is also known as mandibles. It uses its mouth to lacerate the skin to draw blood.

Horseflies have a pair of antennae. But they’re very small. You can barely notice the antennae when they’re stationary.

Despite looking like house flies, horse flies are not delicate. They look strong and sturdy and a tad bigger than the common house fly.

It’s the female horse fly that bite humans and animals to feed on blood. The females need regular bloodmeals for egg development. 

The male horse fly doesn’t bite. It feeds on the flower nectar and pollen.

Female horseflies can track a human or animal by detecting the carbon dioxide it emits. Body movements of their prey are also one of the cues that the horseflies can detect. 

Horseflies got their name from their habit of biting horses in barns and stables. But they horseflies can bite any mammal, including humans

Horsefly Season – When They’re Most Active

Horseflies are active during the warmer months of the year, starting from late spring. 

Horsefly activity peak when temperatures and humidity are as per their liking. So, the peak activity period of horseflies can also depend on the environmental patterns and geographical location.

The most common areas where horseflies activity is bothersome is in rural areas where there’s a lot of decaying manure, hay, and livestock. 

Horseflies Habitats And Life Cycle

Horseflies need water to complete their lifecycle. So, they will primarily nest near water bodies or in the areas which are damp and have a lot of organic wastes.

Female horseflies will lay eggs on the damp areas near water bodies such as lakes, rivers, wetlands, swimming pools, and ponds.

These are also egg-laying grounds for other biting flies like mosquitoes, biting midges, and for nuisance flies like fungus gnats and bottle flies.

The horsefly eggs hatch within 1-5 days after being laid. The hatching period depends on the temperature and humidity.

When the eggs hatch, horse fly maggots or larvae appear. These are tiny legless creamy white worms.

The horse fly maggots will feed on little insects, earthworms, and even on tiny frogs in their habitat.

After a few weeks of feeding, the larvae turn into pupae before emerging as an adult horsefly. 

So, the entire life cycle of horseflies can be on your property if there are conditions that support the horse fly infestation. 

Why Are Horse Flies In The House All Of A Sudden?

Horseflies appearing suddenly in the house is a cause of concern. You’re at risk of painful horse fly bites. These biting flies can also hide in the house in places like attic.

Horseflies are primarily outdoor flies. They mostly bite during the day outdoors.

But horse flies can infiltrate your home too. Here’s why –

Open Doors And Windows

The most common way that flies and crawling bugs can enter the house is through open doors and windows. 

Attracted By Light

Horseflies are attracted to light. So, they’ll fly inside the house through the open doors and windows to reach the glowing light bulb.


The water that air conditioners discharge has ammonia in it. The smell of ammonia attracts horse flies into the house.

Fertilizers contain ammonia too. So, if you’ve been overfertilizing your soil or there are racks of fertilizers in your property, then they’ll attract horse flies. 

Nearby Breeding Sites

The most ignored reason for the sudden appearance of horseflies in the house is that there’s a breeding site near the house.

There might be decaying organic wastes, livestock shelter, or a water body near the house which are causing a sudden appearance of horse flies in the warmer months of the year.

Infested Livestock Or Pet

Another reason for horseflies in the house is the pets or livestock bringing the horseflies home.

Horseflies will latch onto animals and will remain on them as long as they’re feeding on their blood.

When these animals come home, they bring horseflies.

How To Stop Horse Flies From Entering The House?

Closing the entry points and getting rid of the horse flies and their habitat are keys to prevent horseflies from entering the house.

Here’s how you can do it.

Find The Sources Of Horseflies

If horseflies have suddenly appeared in your home, then it’s a clear sign that there’s a horsefly habitat nearby.

Those habitats are mostly damp areas like wet soil beds or decaying organic matter near water bodies.

The places where you keep your livestock can also be the breeding ground of horseflies.

If you’re living in a barn or farm, then chances are high that they’re breeding on things like manure and animal waste piles.

If there’s an infestation, then you’ll notice grubs crawling on these places.

Use Horsefly Killer Sprays

There’s no other option but to use chemical insecticide sprays and IGR (Insect growth regulator) to kill horse flies on your property.

Mix 4 tablespoons of insecticide with 4 ml of IGR in one gallon of water. Stir the mixture well. And pour the mixture in a spray bottle.

Use the spray on the breeding grounds of horseflies and in the places where you’ve noticed horsefly activity. 

Also, use the spray on the outer section of the windows and doors.

Do not use the spray inside the house to get rid of horseflies. We’ll come back to it in a minute.

It’s essential to use IGR with the insecticide spray. The IGR gets into the system of the horsefly larvae and prevents them from growing into adult flies.

Use A Horsefly Repellant Spray On Your Livestock

If you’ve horses or other livestock, then it’s essential to protect them from horseflies. 

Horseflies will attack your livestock. And too many horseflies can be lethal for the animals.

So, use horsefly repellant spray on your animals to protect them from horseflies. Apply it only on the skin. Don’t use the spray on the eyes and nose of the animals. 

Install Window Screens With Fine Mesh

Window screens with fine mesh keep flies and other insects from invading the house. These screens have dense holes that flies can’t crawl or fly through.

Install these screens on the windows and on the vents of the attic. It’ll also prevent hibernating flies like cluster flies from invading the house.

Seal Cracks And Gaps On The Windows

It’s not only from the open windows, but also from the cracks on the windowsills and frames horseflies enter homes.

Seal those cracks with a silicon-based sealant. 

Remove Excessive Vegetation Around The Pool

If there’s a swimming pool on your property, then it can attract horseflies. The reflecting light from the water draws flies like horseflies and deer flies to homes. 

Plus, the vegetation around the pool and damp soil beds become the breeding grounds for these flies.

So, remove the excessive vegetation around the pool. And ensure that the soil bed around the pool is not damp. 

You can keep your pool covered while you’re not using it. It will prevent the flies from picking up the light.

Use A Pyrethrin-Based Spray On Horseflies Inside The House

Pyrethrin-based sprays fly killers. If horse flies have invaded your home, then use the spray on the flies to kill them.

Inspect areas like attic and basement for horseflies. Some flies can sneak inside these areas and hide. If you find any flies in these areas, then use the spray to eliminate them. 

Hang Fly Traps Near Windows And Doors

Fly traps are life savers when it comes to preventing biting and stinging flies like horseflies, deer flies, and wasps from entering the house.

The easiest way to do it is to hang disposable fly traps near windows and doors.

Activate the fly trap by breaking in the seal. Pour water into it and keep it near the windows.

Keep the fly traps in places where you’ve noticed horseflies coming through. So, you may want multiple fly traps. 

Maintain Cleanliness And Follow Proper Garbage Disposal

Not letting decaying organic wastes accumulate on your property and effectively disposing animal wastes are keys to horse fly prevention. 

Ensure that you follow the waste disposal protocols and you’re maintaining cleanliness in your property, especially in barns and stables. 

How To Protect Yourself From Horse Fly Bites

Horse fly bites are intensely painful. Swelling can occur on the bite wound and it severely itches after the bites.

Some people can also get allergic reactions like fever after the bites. However, horse fly bites don’t cause any diseases.

To protect yourself from horse fly bites, wear DEET based skin-friendly insect repellants. Also wear full sleeved shirts and pants while outdoors.

Horseflies Vs Deer Flies

Deer Fly
Deer Fly

Both horseflies and deer flies share the same habitat. They also have the same color. So, distinguishing between them can be difficult.

You’ll need to notice the wings and size of these flies to distinguish between them. 

Deer flies are smaller than horse flies. The size of deer flies varies between ½ and ¼ inches (6 mm to 12 mm), whereas the horse flies can be an inch long. 

Horseflies have veiny wings that appear transparent or slightly opaque.

In contrast, deer flies have dark bands or spots on their wings, setting them apart from horse flies. 


Horseflies suddenly appear in the house if there are active breeding sites near the house. 

These flies will fly through the windows in the house and will bite. 

The best way to prevent that from happening is by removing their sources and blocking their entry by installing window screens and traps. 

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