Finding tiny black fungus gnats buzzing around your house can be annoying and worrying. An infestation of these pests indicates excess moisture allowing fungi to grow somewhere in the home. Understanding what attracts them, locating the source, and taking action is key to getting rid of them.
In this article we’ll explore what causes fungus gnat infestations indoors, how to find and eliminate breeding sites, and effective methods to get rid of these nuisance flies.
What Attracts Fungus Gnats Indoors
Fungus gnats are drawn to damp areas where fungi and mold grows. An infestation implies there is a moisture issue within the home. Some common causes include:
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Overwatered Houseplants – The most typical culprit is houseplants with soil that is too wet, Gnats lay eggs in the moist organic matter Frequency 1
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Leaky Pipes and Plumbing – Leaks under sinks or appliances and condensation promote fungus growth. Gnats are attracted to lay eggs. Frequency: 1
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Wet Basements or Crawlspaces – Standing water, leaks, high humidity, and poor ventilation lead to fungal growth. Frequency: 1
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Malfunctioning Appliances – Leaky dishwashers, washing machines, and HVAC systems often create damp conditions gnats feed on Frequency 1
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Roof and Plumbing Leaks – Any water intrusion from damaged roofing, pipes, or siding can nurture fungi. Frequency: 1
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Wet Window Sills and Baseboards – Condensation on windows and cold surfaces allows gnats to thrive, Frequency 1
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Organic Debris – Piles of leaves, mulch, and rotting wood outdoors near the home’s foundation are breeding grounds. Frequency: 1
Finding and fixing these moisture issues is key to eliminating an infestation at its source.
How to Find the Breeding Site
Determining where fungus gnats are originating from is an important first step. Here are some tips to locate their breeding site(s):
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Inspect Houseplants – Check soil of potted plants for excess moisture and gnat larvae in top layers. Isolate and treat infested plants. Frequency: 1
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Monitor for Leaks – Scan along baseboards, under appliances, around plumbing, and in the basement for any moisture or condensation. Frequency: 1
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Check Window Sills and Cold Surfaces – Look for signs of moisture accumulation and associated fungal growth. Frequency: 1
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Monitor Organic Outdoors Debris – Ensure piles of leaves, compost, wood, etc. are not too close to the home’s foundation. Frequency: 1
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Use Potato Slices – Place raw potato slices on the soil of suspected houseplants. Larvae emerging on the potato indicate infestation. Discard slices after each check. Frequency: 1
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Follow Flying Gnats – Pay attention to what areas flying adults are congregating around to narrow down the source. Frequency: 1
Once potential sources are identified, take corrective action to eliminate excess moisture supporting the gnats.
How to Eliminate a Fungus Gnat Infestation
A multi-pronged approach works best to fully clear a fungus gnat infestation indoors:
Fix Underlying Moisture Problems
- Repair plumbing and appliance leaks. Frequency: 1
- Improve ventilation in humid areas. Frequency: 1
- Address standing water in the basement. Frequency: 1
- Remove piles of organic debris near the home outdoors. Frequency: 1
- Ensure proper drainage away from the foundation. Frequency: 1
Adjust Houseplant Care
- Allow soil to dry out completely between waterings. Frequency: 1
- Remove excess organic matter in potting mix. Frequency: 1
- Apply sand layer over soil to dry out surface. Frequency: 1
- Repot plants in fresh, sterile mix if heavily infested. Frequency: 1
Use Traps and Killers
- Set out yellow sticky traps and apple cider vinegar traps. Frequency: 2
- Apply a thin layer of diatomaceous earth on dry soil. Frequency: 1
- Spray plants lightly with insecticidal soap or neem oil. Frequency: 2
- Release predatory insects like nematodes or Hypoaspis miles mites. Frequency: 2
Consider Professional Pest Control
- For severe infestations, professional exterminators have access to stronger chemical treatments like insect growth regulators. Fumigation isn’t common or recommended for fungus gnats. Frequency: 1
With persistence eliminating excess moisture and employing targeted organic and chemical treatments, even severe fungus gnat infestations in a home can be eradicated. Don’t allow an infestation to persist – take action to remove these nuisance flies and prevent future occurrences.
Effective Indoor Traps and Treatments
Using traps and targeted treatments for both larvae and adults works well to manage fungus gnat populations:
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Sticky Traps – Yellow sticky traps or tape placed near infested plants or damp areas snare flying adults. Frequency: 1
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Apple Cider Vinegar – A dish of apple cider vinegar with soap added lures and drowns adults. Frequency: 1
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Diatomaceous Earth – This abrasive dust kills larvae when applied to dry soil and crawling adults. Avoid plant leaves. Frequency: 1
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Insecticidal Soap – Insecticidal soap sprayed on plants kills adults on contact and deters egg-laying. Rinse residue off plant leaves after application. Frequency: 1
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Neem Oil – Neem oil lightly misted on plants acts as a repellent to adults and prevents larvae from establishing in soil. Test first for sensitivity. Frequency: 1
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Nematodes – These beneficial microscopic worms kill fungus gnat larvae when watered into the soil. Safe for plants. Frequency: 1
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Predatory Mites – Releasing Hypoaspis miles mites in soil preys on larvae. They help control populations naturally. Frequency: 1
Using traps continuously along with repeated applications of organic treatments will help shrink both adult and larval populations until fungus gnats are eliminated.
Preventing Future Infestations
Once an infestation is cleared, here are some tips to help prevent indoor fungus gnats from returning:
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Allow potted plant soil to dry out between waterings. Only water when the top inches become dry. Frequency: 1
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Provide proper drainage holes in containers and remove excess water in drip trays. Frequency: 1
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Avoid potting mixes with heavy compost which stays too moist. Use a fast-draining commercial mix. Frequency: 1
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Inspect new plants closely and isolate them before introducing indoors. Treat as needed. Frequency: 1
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Fix any plumbing or appliance leaks promptly. Monitor for wet spots. Frequency: 1
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Improve ventilation in humid, low-air circulation areas of the home. Frequency: 1
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Keep window sills, baseboards, and cold surfaces free of condensation. Insulate if needed. Frequency: 1
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Remove organic debris near the home’s foundation like piles of leaves or mulch. Frequency: 1
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Continue using preventive yellow sticky traps and treatments like diatomaceous earth or nematodes. Frequency: 2
With good moisture control and vigilance, fungus gnat infestations in the home can be avoided in the future. But quick action at the first sign of flying gnats is key to preventing major infestations.
Controlling moisture that allows fungi and mold to grow indoors is vital for preventing fungus gnat infestations. Through vigilance and integrated pest management, these nuisance flies can be cleared from a home and kept away for good. Don’t tolerate an infestation – take prompt action!
Chamomile Tea & Cinnamon
Chamomile and cinnamon are powerful natural fungicides, which kill off the gnats’ primary food source, therefore making the soil inhospitable.
Brew a litre of strong chamomile tea with boiling water, allow it to cool and mix the tea with 4 parts water. Use tea mix to water plants as usual.
Sprinkle cinnamon all over the surface of the soil for a fungicidal double whammy.
Repeat for 3 weeks, or until gnats are gone
Within days the chamomile/cinnamon dousing had dramatically reduced the gnat populations, however, over the next few weeks it couldn’t quite kill off the remaining population.
Drying Out Soil
Many infestations happen as a result of overwatering plants. By waiting longer between watering sessions, theoretically you can make your plant soil dry and inhospitable to gnats.
Turn up around 2cms of soil in the plant. This exposes the larvae and eggs and helps dry out the soil more quickly.
Wait until the soil is dry to a depth of about an inch and a half before watering again.
It did reduce the number of larvae wriggling about underneath the soil, but it didn’t come close to eliminating the problem completely.
Because many plants can’t be chronically under-watered for a long time, it means that once you resume normal watering, the gnats will just multiply again.
Gnats are drawn to apple cider vinegar, which makes it the perfect bait in this handy trap.
Fill a wide brimmed jar or bowl with apple cider vinegar, cider or beer
Add a drop or two of washing up liquid to get rid of surface tension
Cover the rim with cling film and pierce with a fork a number of times
The gnats will now crawl through the small holes in the cling film, but will be unable to escape and will drown in the vinegar
The main limitation of this method is that it only kills adult gnats, and therefore doesn’t do anything to kill the hundreds of larvae and eggs which still remain in the soil.
That said, it did kill a fair deal of adult gnats, meaning that the breeding population of gnats was heavily curtailed and it therefore reduced overall numbers.
Gnat larvae love raw potato, which makes potato slices a cheap way to measure how heavy the infestation is and get rid of some larvae in the process.
Slice or dice a potato into inch wide blocks
Bury potato pieces just beneath the soil surface
Wait 4-8 hours and then pull out the chunks. If the infestation is heavy, the potato will be literally crawling with larvae.
Throw away the potato to get rid of all the larvae cling-ons
Each potato slice can only get rid of dozens of larvae at a time. Since adult gnats can lay 200-300 eggs at a time, getting rid of a heavy infestation with potato slices alone would be impossible.
However, as a way to measure gnat population size and see if your other methods are working, it is fantastic.
How To Stop Fungus Gnats From Breeding & Spreading Indoors (4 Easy Steps)
FAQ
Why is my house infested with fungus gnats?
Fungus gnats usually get into homes by flying inside or from infested plants brought inside the house. Fungus gnats are also attracted to damp soil, so make sure you properly store potting soil before and during use.
Will Lysol spray kill fungus gnats?
Lysol Disinfectant Spray. The gnats that live and breed around your houseplants can be easily killed by Lysol or a store-brand disinfectant spray. Spray directly into the dirt and work it in and around the top soil, I use a fork. That’s it. Pretty simple and works like a charm every time.
How to get rid of fungus gnats at home?
Sand on the Soil Surface
I came across a suggestion that applying a shallow layer of coarse sand to the surface of your houseplants could get rid of fungus gnats. By turning that top layer of soil into a fast-draining desert with no organic matter, the bugs would lose their habitat and die off.
Can fungus gnats infest humans?
Adult fungus gnats are primarily a nuisance. They can enter buildings as flying adults and develop indoors through all life stages. They do not bite people or animals and, in the United States, are not known to carry human pathogens.
Where do fungus gnats lay eggs in the house?
Indoors, fungus gnats tend to have overlapping generations where eggs, larva, pupae and adults are all present at the same time. Fungus gnat females lay up to 200 eggs (in clusters) in cracks and crevices on the surface of the moist soil of potted plants.
Do fungus gnats mean I have mold?
If you have mold and a gnat issue it likely means your soil is too moist. Bottom water less frequently to really help with this.