Why Are There So Many Flies on My Window? Discover the Key Factors Attracting Them

Have you ever walked by your window and noticed an abundance of flies gathered on the sill? It’s a common household issue that leaves many people wondering why these critters seem to be drawn to this specific location. Understanding the reason behind this phenomenon can help you better address the problem and keep your home fly-free.

One of the main culprits for attracting flies, especially house flies, to your window is light. These insects are naturally attracted to light sources and will gravitate towards windows, as they appear like an escape route to the outdoors. Additionally, windows can provide warmth which entices them further.

Another factor to consider is the presence of food and moisture sources close to the windows. Flies are always in search of sustenance, so if your windows are near a trash can, food prep area, or even houseplants, they might be attracted by these sources. Keep your surroundings clean and free of any food remnants to minimize their presence.

Why Flies Are Attracted to Windows

In this section, we will discuss the reasons why flies are often found on windows. We will cover the following aspects:

Light Attraction

Flies are attracted to windows because they are drawn to light sources. This is particularly true during daytime hours when sunlight is shining through your windows.

  • Flies use light to navigate and find food sources
  • They perceive light coming through windows as a way to escape

Reflected Images

Another reason for flies being attracted to windows is the presence of reflected images on the glass.

  • Windows can reflect vegetation, other insects, or even food sources, which can trick flies into thinking there’s something of interest on the surface
  • Reflections of light off glass or other surfaces can also be attractive to flies

Transparency Aspect

Lastly, the transparency of windows can be confusing to flies.

  • Flies may not be able to perceive the glass as a solid barrier
  • They might try to fly through it, thinking it’s an open space

In summary, flies are attracted to windows mainly due to light attraction, reflected images, and their inability to perceive the transparency of glass. By understanding these factors, you can take steps to reduce the number of flies gathering on your windows.

Life Cycle of a Fly


Flies breed in various environments, such as decaying organic matter, food waste, and in some cases, animal feces. Their breeding habits depend on the species, but most tend to lay their eggs in moist and warm locations where their larvae can easily find food upon hatching. For example, house flies often lay eggs in garbage or animal waste.

Egg Laying

Female flies lay their eggs in clusters containing hundreds of eggs at a time. Depending on the species, they can lay up to several thousand eggs in their lifetime. They choose their egg-laying sites carefully, often selecting areas that provide shelter and a food source for their offspring. Here are a few common egg-laying sites for different types of flies:

  • House flies: garbage, decaying organic matter, food waste, and animal feces
  • Fruit flies: overripe or rotting fruits and vegetables
  • Cluster flies: cracks and crevices in the soil, where their primary food source – earthworms – can be found

Hatching and Growth

Fly eggs hatch into larvae, also known as maggots, within a short period – generally 12 to 24 hours after being laid. They grow and develop in this stage by feeding on their surrounding environment. As they mature, they go through a series of molting processes, shedding their skin to accommodate their growing bodies. Finally, maggots will find a protected spot to pupate before emerging as a fully developed adult fly.

In summary, the life cycle of a fly progresses as follows:

  1. Egg: Laid in clusters suitable for larval growth and development
  2. Larva: Feeds on its environment and grows through several molting stages
  3. Pupa: Transforms into a pupa to metamorphose into an adult fly
  4. Adult: Emerges from its pupal case and begins seeking a mate to repeat the cycle

Understanding the life cycle and habits of flies can help you recognize potential breeding sites around your home and take appropriate measures to remove or prevent fly infestations.

Types of Common Flies

House Flies

House flies are the most common flies found in and around homes. They are about 1/4 inch long and have a dull gray color. These flies have unique mouthparts that allow them to sponge up liquids, so they cannot bite. They can spread various diseases and are considered a nuisance due to their flying and buzzing habits1.

Cluster Flies

Cluster flies are another type of common flies found in homes. They measure about 3/8 inches long and have a dark gray, non-metallic appearance. They often show up indoors around windows or lamps during fall, spring, or winter, and are generally sluggish fliers 2. These flies can become active on warm sunny days or when indoor temperatures rise, but they don’t transmit diseases like house flies.

Fruit Flies

Fruit flies, also known as vinegar flies, are among the smallest flies found in homes, with a length of 2.0-2.5 mm. They are typically light brown, and the most common species have bright red eyes. Fruit flies’ larvae feed on yeasts and can often be found near overripe fruit 3. Although not a significant health risk, they can still be a nuisance in your home.

Black Flies

Black flies haven’t been mentioned in the provided search results. However, based on general knowledge, they are known as biting flies and can be found in different environments, usually near water sources. Black flies can be a nuisance due to their painful bites, which can cause itching and swelling.

Fly Type Size Color Habit Health Risk
House Flies 1/4 inch Dull gray Buzzing, flying Yes
Cluster Flies 3/8 inch Dark gray Sluggish flying No
Fruit Flies 2.0-2.5 mm Light brown Near overripe fruit Low
Black Flies Varies Black Biting, near water Varies

By identifying the type of fly in your home, you can better understand their habits and take appropriate measures to control and prevent infestations.

Health Risks and Diseases Caused by Flies

Pathogens Transfer

Flies can carry a large number of harmful pathogens that can pose significant risks to your health. They are attracted to feces, excrement, and garbage, earning them the nickname “filth flies.”

  • Flies pick up pathogens from contaminated surfaces and transfer them to food or other surfaces when they land.
  • Common pathogens carried by flies include bacteria, fungi, viruses, and parasites.
  • These pathogens can cause diseases like diarrhea and dysentery.

For example, houseflies and blowflies may carry hundreds of different species of bacteria, and their disease-carrying potential increases in places with large human populations 1.

Diseases from Infestations

Fly infestations not only increase the risk of pathogen transfer but may also lead to specific diseases.

  • Houseflies (Musca domestica) are mechanical vectors for several human pathogens, increasing the risk of diseases like dysentery, diarrhea, and typhoid fever.
  • Blowflies, also known as bottle flies, can occasionally cause myiasis, a rare condition where fly larvae infest living tissue, usually in open wounds, causing pain and discomfort.
  • Fruit flies (Drosophila), while less harmful than houseflies, can still spread pathogens and contaminate food.

To minimize these health risks, it’s essential to practice good sanitation and manage the fly population in and around your home. Look for potential breeding areas and clean up any food or waste materials that may attract flies.

Remember to keep your window screens secure and use fly traps or insecticides when necessary to protect yourself and your family from the potential dangers posed by flies.

How to Prevent Flies from Coming Inside

Cleaning Methods

To keep flies away, maintain a clean home. For example, regularly wipe down surfaces and vacuum floors. Flies are attracted to food residues, so wash dishes promptly and clean up any spills.

  • Wipe down surfaces
  • Vacuum floors
  • Wash dishes
  • Clean up spills

Sealing Gaps and Cracks

Inspect your home for gaps and cracks in walls, windows, or doors. Seal them to prevent flies from entering. For instance, you can use caulk or weatherstripping.

Here’s a comparison table of sealing materials:

Material Pros Cons
Caulk Flexible, paintable Curing time needed
Weatherstripping Easy to install, durable Limited applicability

Proper Garbage Disposal

Proper garbage disposal is crucial in keeping flies away. Always use a garbage can with a tight-fitting lid. Regularly empty and clean the trash can to eliminate odors and residues that attract flies.

  • Use tight-fitting lids
  • Empty trash cans regularly
  • Clean trash cans to remove odors

By following these simple tips, you can effectively prevent flies from coming inside your home.

Effective Fly Control Methods

Commercial Fly Traps

There are various types of commercial fly traps available to help you get rid of flies. Some examples include:

  • Sticky traps: Capture flies using a sticky surface.
  • UV light traps: Attract flies using ultraviolet light and then zap them.


  • Easy to use
  • Low-cost options available


  • Not suitable for large-scale infestations
  • May need regular replacement

Insecticides and Pesticides

Using insecticides and pesticides can be an effective way to control flies. Make sure to read the labels carefully and follow the instructions for your safety and the environment.


  • Effective for larger infestations
  • Wide range available for different fly species


  • Can be harmful to beneficial insects and the environment
  • May need repeated applications

Comparison table:

Method Pros Cons
Commercial Trap Easy to use, Low-cost options Not for large infestations, Needs replacement
Insecticides Effective for large infestations, Wide range Harmful to environment, Repeated applications

Professional Pest Control

If you have a large infestation or difficulty getting rid of flies, consider contacting a professional exterminator. They can assess your situation and recommend an appropriate treatment plan.


  • Expertise in handling large infestations
  • Can recommend customized solutions


  • Can be expensive
  • May involve chemicals and pesticides

Remember to maintain cleanliness and manage any potential breeding sites for flies. By implementing these fly control methods, you can keep your window and home fly-free.

Natural Fly Deterrents and Home Remedies

Essential Oils

Essential oils can help to repel flies naturally. Some popular options include lavender, lemongrass, and eucalyptus oil.

To use essential oils as a fly deterrent, simply mix a few drops with water in a spray bottle. Lightly mist surfaces where flies tend to gather, such as windows or countertops. Remember to reapply periodically throughout the day.

Sweetened Water Traps

Sweetened water traps are an easy and effective DIY solution to attract and reduce the number of flies in your home. Here’s a simple method to create a sweetened water trap:

  • Fill a container with a mixture of water, sugar, and a few drops of dish soap.
  • Cover the container with plastic wrap and secure it with a rubber band.
  • Poke several small holes in the plastic wrap for flies to enter.

Flies will be attracted to the sweet scent, enter the container, and eventually drown in the soapy water.

DIY Fly Traps

Making your own fly traps can be a cost-effective way to reduce the number of flies in your home. Here are two popular DIY fly trap options:

1. Paper Cone Trap:

  • Find a jar or container with a wide opening.
  • Create a paper cone with a small hole at the bottom.
  • Fill the container with a bait, such as fruit or vinegar.
  • Place the cone inside the container with the narrow end pointing down.

Flies will be attracted to the bait and enter the container through the cone but will be unable to escape.

2. Sticky Fly Trap:

  • Cut strips of paper or use adhesive tape.
  • Coat the strips with a sticky substance, such as corn syrup or honey.
  • Hang the strips near areas with a high fly concentration.

Flies will be attracted to the sticky substance and become trapped.

Fly Traps Pros Cons
Essential Oils Natural, pleasant scent Requires reapplication
Sweetened Water Easy to make, effective Can be messy
DIY Fly Traps Cost-effective Requires some assembly

By using these natural fly deterrents and home remedies, you can help reduce the number of flies in your home and keep those pesky insects away from your windows.


In conclusion, dealing with flies around your window can be quite an inconvenience. To prevent and control the presence of these unwanted guests, consider implementing the following methods:

  • Regular cleaning: Keep your home clean, especially around windows. Dispose of any food waste and clear potential breeding sites, such as stagnant water.
  • Proper waste disposal: Store your garbage in closed containers and dispose of it regularly to minimize attracting flies.
  • Use screens: Install window screens to keep flies from entering your home. Remember to repair damaged screens promptly.
  • Citronella: Natural repellents, like citronella essential oil, can be useful in deterring flies. Place a few drops on your window sills or use a candle with citronella oil.

By following these simple yet effective steps, you can better control and prevent flies from invading your window areas. With diligence and consistency, you can maintain a fly-free environment in your home.


  1. House Flies – Penn State Extension 2

  2. Cluster Flies – University of Maryland Extension

  3. Flies in the Home – 5.502 – Extension

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Window Fly


Large ant/wasplike bug with transparent section of abdomen
Location:  Cambridge, MA
September 12, 2010 4:50 pm
We found this bug in our apartment in Cambridge, MA, a couple of days ago. Behaviorally, it was very attracted to light, much like a fly, but is shaped very strangely for a fly. The body is about 3/4 inch long. Once we got a good look, we also noticed that the top section of the insects’ abdomen is completely transparent! Very strange!
Any idea what this could be?
Signature:  Adena

Black Soldier Fly, AKA Window Fly

Hi Adena,
Though BugGuide refers the common name Window Fly for members of the family Scenopinidae, Charles Hogue in his book Insects of the Los Angeles Basin calls the Black Soldier Fly,
Hermetia illucens, a Window Fly because of the clear areas in the abdomen.  According to BugGuide it is a:  “Large soldier fly, all black with bright white tarsi. Underneath, first abdominal segment has clear areas. Wings have purplish sheen. Likely a wasp mimic, it buzzes loudly. In particular, it appears to mimic the Pipe-organ mud dauber…“.

Letter 2 – Possibly Window Fly Maggot


Strange caterpillar like bug in bottom of trash can
I have a trash can in my back yard that I had stored old bags of dog food. I went to empty it out tonight and the bottom of it was filled with this strange bug I have never seen. It looked like there were small ticks crawling all around them too! Pictures are included. Can you identify this for me?

Hi Greg,
Your photos are rather poor quality, so it is impossible to be certain. I am convinced you have some type of maggot. It looks like a Window Fly, Hermetia illucens, Maggot. This is a large black fly that resembles a wasp. According to Hogue: “The larva is robust, tapered in outline, and somewhat flattened, with a tough brown leathery skin covered with numerous short bristles. It is terrestrial and breeds in various organic substances, commonly decaying fruits and vegetables. In urban areas, the larva occurs in garden soil, in piles of compost and ground mulch, and near garbage pails that have been placed on soil.”

As we were responding to Greg, he emailed us back this note:
Garden Soldier fly larvae
I found the type of craeture it was I asked about. It is the garden soldier fly larvae. I have had a tick problem recenly and treated the yard for them. I think that they may have migrated to that small area too. Thanks anyway.
Greg L.

Hi Greg,
The Window Fly is a member of the Soldier Fly family Stratiomyidae.

Letter 3 – Window Fly


Hermetia fly?
Location:  Redding, California, United States, North America
October 2, 2010 6:18 pm
Hey, my roommate caught this fly and I can’t figure out what it is. Short anennae, maybe 3 segments. The hindtibia are half white and half black, and the foretarsus, midtarsus, and hindtarsus are all white. Interestingly, there only appears to be 4 abdominal sternites, the first of which, appearing where the 1st and 2nd usually would be, is transparent/white. The rest of the body, including the wings, is black, or very nearly so, excepting the halters, which are a cotton candy/bread-mold blue. It looks very similar to certain wasps that live in this area, and often opens it’s wings to a position similar to bees or waspsso I thought it might be in the family Hermetia, but I haven’t been able to find a picture that matches this fly. Do you have any idea what it is?
Signature:  Collegiate ameture

Window Fly

Dear Collegiate ameture,
You are absolutely correct.  Your fly is a Black Soldier Fly,
Hermetia illucens, though we prefer the name Window Fly, a name not recognized on BugGuide.  We use the name Window Fly which was reported by Charles Hogue in his excellent book, Insects of the Los Angeles Basin, and the name refers to the transparent “windows” on the abdomen that you describe.  BugGuide uses Window Fly for an entirely different family.

Letter 4 – Window Fly


Subject: Window Fly So Cal 10/14/12
Location: Northwest San Fernando Valley
October 14, 2012 11:20 pm
The kids called me in from the wood shop to ID this bug visitor to the kitchen window. They suspected that it wasn’t a hornet, but wanted confirmation before continuing work on dinner.
I went straight to ’74 Hogue Insects of the LA Basin and there he (or she) was.
Real pleased to see this cool guy for the first time in a lifetime in the Los Angeles neighborhood.
Had to pull the window slider from its’ track to escort him out, but he flew away, apparently no worse for the detour.
The photo’s not National G quality, but the ”windows” are pretty easy to see.
Signature: Watson Fambly

Window Fly

Dear JW,
We are happy to hear that you keep a copy of Insects of the Los Angeles Basin handy for quick identifications.  It is truly a wonderful volume and a must for all Los Angeles residents interested in the lower beasts.  Anyone with a compost pile is likely to encounter Window Flies or Black Soldier Flies as the larvae are common compost denizens.  The abdominal “windows” are quite evident in your photo.

Letter 5 – Window Fly Carnage


Subject: strange fly looks like wasp in flight
Location: north east Alabama
July 27, 2013 12:02 am
recently had home invaded by this strange fly,has black and clear body with white socks on legs no stinger but looks much like a wasp when in flight.
Signature: dan

Window Fly "Invasion" ends in Carnage
Window Fly “Invasion” ends in Carnage

Dear Dan,
These are Black Soldier Flies, Hermetia illucens, also known as Window Flies because of the clear spaces in the abdomen which causes them to resemble stinging Thread Waist Wasps, which might be a defense mechanism for this benign and harmless species.  Do you have a nearby compost pile?  The larvae of Black Soldier Flies are beneficial in the compost pile.  You can read more about Black Soldier Flies on BugGuide.

Letter 6 – Window Fly Larva


larva from compost
these guys are in my compost heap. Are they good, should I be worried?
Joseph Morabito
Wildomar Cal
Picture was taken late Nov 2005

Hi Joseph,
This looks like a Window Fly Larva, Hermetia illucens. These are large flies that look like black wasps. The larvae feeds on decaying fruits and vegetables and is often found in compost heaps. It is thought that it might prey on more pestiferous maggots. They are benign.


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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4 thoughts on “Why Are There So Many Flies on My Window? Discover the Key Factors Attracting Them”

  1. This looks very much like what I found behind my dresser the other day! I’m near Toronto Ontario.

    Is this the only thing that looks like this? If so heart attack over if it’s just some fly larvae.

    My fiance really wants to know what we found and the one we caught unfortunately wasn’t a live specimen and deteriorated.

  2. This looks very much like what I found behind my dresser the other day! I’m near Toronto Ontario.

    Is this the only thing that looks like this? If so heart attack over if it’s just some fly larvae.

    My fiance really wants to know what we found and the one we caught unfortunately wasn’t a live specimen and deteriorated.

  3. I found a lot in my garage I didn’t know what they were but it’s a lot of black flies in there too they all are dead on the floor are they dangerous I’m located in Georgia


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