Outhouse, Acadia National Park, Maine (C) D FriedmanFly & Flying Insect Removal from Buildings
Suggestions for getting rid of pesky flies or most other flying insects inside buildings

  • FLIES, REMOVE or REPEL - CONTENTS: methods for removing or repelling flies, ladybugs, cluster flies & other flying insect pests from buildings; when to call a pest control operator; home remedies & expert advice on getting flies out of buildings of various types from homes to outhouses & privies.
  • POST a QUESTION or READ FAQs about how to get rid of fly problems in homes, outhouses & other buildings

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Flies & flying insect pests in buildings:

Hhlude fly control remedies from expert sources as well as from inventors & readers.

Some of these steps to get rid of flying insects indoors work for just about any species of flying insect that is attracted to light, odors, bug traps while others focus on specific insects (flies, mosquitoes, ladybugs). We include citations of expert sources & research on the fly problem at & around buildings, both residential & farm buildings.

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Fly control in & around buildings; flying insect control & removal in buildings, outhouses, out-buildings, farm buildings

Categories of fly control in & around buildings

Flies on an attic floor, Pelham NY (C) Daniel FriedmanControl: fly & insect control refers includes these subtopics:[1]

Photo at left: cluster flies in an attic wall and on the attic floor in a Pelham NY home.

[Click to enlarge any image]

Insecticides used for fly control ar typically described in these categories

Watch out: selection and application of any pesticide, spray, bait, and even some insect traps should be performed by an expert, trained & licensed where requested. Misapplication of pesticides, insecticides, sprays, fogs, traps, baits may be unsafe and can present serious health risks for humans or other animals in and around buildings.

Reader Question: too many flies at the Outhouse or Latrine

My outhouse is producing allot of flies inside this summer and i was wondering why and how to get rid of them. It has been a dry summer in ontario and i thought maybe the pit was producing more flies because of the dryness.what should i do? - Devon 9/2/12

Reply: suggestions for fly control at outhouses, latrines, privies

Fly Removal Suggestion: Electric Fly Ejector Gets Flying Bugs out of Buildings

Cathedral ceiling roof vent fan used as bug ejector by the editor (C) Daniel Friedman

How to combine a vent fan and a simple light bulb to blow flies, moths, mosquitoes or other flying insects out of a building.

Cervenka & Hahn (2008) and other expert sources confirm that flies are drawn to light and recommend that approach to attracting them to an area for removal by vacuuming. We took this idea further with a fly ejector mechanism that has worked well where there is a sudden and aggravating surge of indoor flying insects.

If your building already has a through-wall kitchen exhaust fan or a cathedral ceiling - roof exhaust or vent fan (below left), try clipping an incandescent light bulb as close as you can get to the center of the exhaust fan opening (we found that a 60 Watt bulb right at the edge of the fan opening worked wonderfully - Ed.).

In the photo at left that brown wood rectangle is a removable hatch that gives direct access to a roof ventilation fan. Simply remove the hatch cover, clip a light to a hatch turnbuckle or to the hatch opening trim and turn on the fan to blow irritating flies & moths outside.

At below left we show a solar-operated roof exhaust fan that could be used also as a bug or fly ejector. A whole house exhaust fan can also blow indoor bugs outside, but is a bit dramatic and may not be something you want to run in all weather conditions & temperatures.

Temporarily, even a box fan in a window along with a light bulb can produce quick and wonderful results (below right).

Solar operated roof exhaust vent fan can work to blow bugs outside if a light bulb is used (C) Daniel Friedman Box fan used as a bug ejector (C) Daniel Friedman

With other lights in the building area off and the exhaust fan running, turn on the light bulb next to the exhaust fan opening. You'll find (as we did) that most flying insects are attracted to the light and are promptly sucked (or blown) outside. Larger insects such as moths and house flies produce a satisfying ping sound as they bounce off of the outdoor exhaust fan cover. - Editor.

Fly Killing Without Sprays or Pesticides

If a household or business has a problem with flies, try suspending a light bulb, preferably incandescent, over a pan of soapy water and leaving only that light on at night. In my experience, the pan with have collected the flies by morning. - E.B. [reader] 11/29/2013. Dr. E.B. is a physicist interested in, among other things, fly control in buildings.

Cluster Flies in Buildings

Flies on an attic floor, Pelham NY (C) Daniel Friedman

Cluster flies are a nuisance in buildings that can be prevented by sealing their points of entry into buildings. But in our experience such sealing is especially difficult on many older homes and in attics with various ventilation openings in soffits, eaves, and at ridges. Experts recommend vacuuming up cluster flies, attracting them with a light to make clean-up easier.

Photo at left [click to enlarge]: cluster flies, ladybugs and wasps all contend for interment space on the attic floor of this home in the northeastern U.S.

Use of an indoor spray insecticide labeled for indoor flying insects is acceptable, though we warn that some people such as those with allergies or asthma can be troubled by the common indoor insecticide ingredient of pyrethrins.

Significantly, Cervenka & Hahn point out that use of insecticide on cluster flies on a building exterior is rather irrelevant: when you see them alive they are trying to move away from the building, and treatment does not reduce the next fall's fly population.

Cluster flies (Pollenia rudis) are named for their habit of overwintering in large clusters within the attics or upper walls of homes and buildings. They are black and a little larger than house flies, from 3/8- to 1/2-inch long, with short, yellow hairs on the thorax. Their wings overlap when at rest.

Cluster flies are unique because they are parasites of earthworms. In summer they lay eggs in cracks in the soil, and maggots enter earthworm hosts through the body wall. There are two or three generations of flies produced each year. In August and September, the final generation of flies seeks shelter for the winter in homes and buildings. Piles of dead cluster flies are often discovered in late spring when returning to northern vacation homes unoccupied during months when the flies emerge.

... Control of [cluster] flies seen in spring on the building exterior is not necessary because they are trying to move away from the structure. Killing these flies has little, if any, influence on the number of flies seen inside homes. Treatment in spring also will not reduce fly populations next fall. - Cervenka & Hahn (2008)

How to Keep Lady Bugs - Asian Lady Beetles & Cluster Flies out of Residential Buildings

Perforated soffit vents (C) D Friedman Ladybugs - Asian lady beetles in Two Harbors MN 2015 (C) Daniel Friedman

At above left is a typical perforated vinyl soffit covering panel through which one reader reports insect pests are entering: it's possible they are actually finding a different entry point than through those round perforations. At above right are Asian lady beetles (ladybugs or Harmonia axyridis) snuggled away in an apple picked by the author [DF] in Two Harbors MN in the fall of 2015.

[Click to enlarge any image]

Reader Question: need small perforation soffit vent coverings or screens to keep out Asian Lady Beetles & Cluster Flies

7 Nov 2015 Anonymous said:
The recommendations for continuous louver-style aluminum soffit vents and the "older, uglier aluminum ridge vents" ignores the real problem of insect entry. I have observed easy movement through these vents of Asian lady beetles and cluster flies prevalent in my area. I am now faced with retrofitting or replacing these vents with ones using finer mesh screening, but there are no commercially available ones that I can find. I share your negative view of the "popular plastic mesh type ridge vent" because it allows much more limited air flow, especially if the installer mashes it down flat, as I have sometimes seen. Do you have any specific suggestions for vents that allow air flow but keep these invasive insects out?

This question appeared originally at ROOF VENTILATION FAQs as part of a discussion beginning at ROOF VENT SOFFIT + RIDGE NEEDED.


Thanks for that interesting feedback: I've not heard of nor come across insect invasion through the soffit vent openings myself but I don't argue with first-hand experience.

Measurement shows size of soffit vent perforation openings (C) Daniel Friedman

The perforated soffit panels I've seen have openings just a few mm across and may be small enough to keep your lady beetles and flies out. But experts (cited) say that “Gaps of 1/8" or less will permit entry of lady beetles and other insects.” As you can see in the photo just above, the size of typical round perforation openings in a modern vinyl soffit vent strip or vent covering is 3mm or a bit under 1/8". Tiny insects can, if they have reason to do so, enter a building soffit or attic through these openings, while larger insects such as flies or wasps will be kept out.

Some older soffit vent covering panels such as aluminum units whose openings were made by stamping small rectangular slot-type perforations have openings that are still larger.

As you are considering installing different soffit vent coverings I’d suggest a simpler approach: remove enough panels to lay flat copper screening material inside the soffits to keep the Ladies and cluster flies out of the soffits. If you hold down the screening mechanically or with caulk at its edges or simply by laying a few furring strips on its upper surface that ought to keep bugs out. You’re also reducing the air intake flow rate so be sure your soffit panels are continuous rather than intermittent.

These insects (both ladybugs and cluster flies) are not considered harmful to humans (with a possible modest exception by Yarbrough 1999) but both are ranked as a nuisance pest, and both of these insects can leave a stain on surfaces if you try to sweep up their bodies. That's why vacuuming them up is a better cleanup method. None of the sources we reviewed preferred use of insecticides to mechanical exclusion of insects and all included warnings about both the limited durability of insect sprays as barriers as well as warnings that misapplication of pesticides (such as spraying into a wall cavity) may be unsafe for the building occupants.


Size of Ladybugs - Asian Lady Beetles - and Cluster FLies

Asian Lady Beetles ( Harmonia axyridis (Pallas) what many call "lady bugs") are about 4 x 7 mm in size. (about 1/4" in length). They are harmless to humans but can create a bit of a mess inside. Best advice is to vacuum up the dead insects and keep them out of the building by sealing cracks and openings through which they enter.

Cluster flies (Pollenia rudis), also commonly called "attic flies" as adults are a bit larger, measuring 8-10 mm in length. I'm surprised that you are finding them entering through your perforated soffit intake vent openings.

How to Keep Asian Lady Beetles & Cluster Flies Out of Soffit Vents: caulk, seal or screen openings

The experts at every source we reviewed recommend as first choice that you keep these insects out of your building by "mechanical exclusion" - that means screening or sealing small openings through which they are entering. None of the sources mentioned these insects entering through typical (modern) vinyl or aluminum soffit vent covering panel perforations (though it might be possible) and all of them point to entry points at cracks and gaps around windows, siding, utility pipes or wires, and underneath fascia boards or at window openings.

For both of these insects, before replacing soffit coverings themselves, I'd be sure to check to see if they are actually entering elsewhere - at a spot that is easier to seal off than it will be to take on the task of replacing or screening all of your soffit vents.

Seal the ladybug entry openings as well as cluster fly openings or gaps in late spring or summer - before these Asian Lady Beetles or cluster flies begin their hunt for a winter home. Both of these insects start looking for a passage into buildings in the fall. Close large openings with screening and small openings with caulk or exterior-rated foam.

U. Kentucky department of entomology has a nice article on Asian Lady Beetles and what attracts these harmless insects to buildings - cited just below.


… Asian lady beetles are attracted to illuminated surfaces. They tend to congregate on the sunnier, southwest sides of buildings illuminated by afternoon sun. Homes or buildings shaded from afternoon sun are less likely to attract beetles. House color or type of construction (concrete, brick, wood/vinyl siding) is less of a factor for attraction than surface contrast.

Contrasting light-dark features tend to attract the beetles -- dark shutters on a light background, light shutters on a dark background, windows edged with light-colored trim, gutters and downspouts on contrasting siding, etc. Once the beetles alight on buildings, they seek out crevices and protected places to spend the winter. - U.K. Entomology website, retrieved 7 Nov 2015, original source:

Research Citations on Asian Lady Beetle Infestation & Control at Buildings

Research Citations on Fly & Cluster Fly Control in & Around Farm Buildings

Kitchen exhaust fan also ejects bugs (C) Daniel Friedman


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