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Fungus Gnats: Where Do These Little Flying Bugs Come From?

Updated on August 2, 2017
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Thoughthole has more than 8 years of hands-on experience in the horticultural maintenance industry and shares many tricks of the trade.

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What Are These Tiny, Annoying, Relentless Flies and Where Are They Coming From?

Fungus gnats are tiny flying insects often mistaken for fruit flies. A fungus gnat is much smaller than a fruit fly and has a tiny black body (while fruit flies are commonly tan and have very visible bodies). Most people notice that they have fungus gnats because the tiny flies will often try to fly into a person's nose, mouth, or eyes, as they are attracted to moisture. This trait causes them to be commonly reported as "those little, annoying, flying bugs." They can be especially irritating to someone who sits at a desk near the origination of the infestation. Fungus gnats feed on moist, decaying, organic material. Although they are found in house plants, they do not live on the plant itself, but in the soil or in dead leaves.

The flying winged gnats are the adults that lay eggs in soil where conditions are moist and there is decaying matter to feed upon. The eggs of the gnats hatch in the soil, and the larva live and feed on fungal material found there. When the larva grow into adults, they fly out in search of new locations to procreate and feed.

What's the Difference Between a Fungus Gnat and a Fruit Fly?

Fungus Gnat
Fruit Fly
smaller than a fruit fly
small
tiny black body
brown or tan colored
attracted to moisture and decaying organic material
attracted to fruits and vegetables
feed on moist, decaying organic material found in houseplants' soil
feed mainly on produce

How to Get Rid of Fungus Gnats

Step One: In order to get rid of them, you must first identify where they are coming from. This is usually fairly simple. Tap on the pots of any houseplants in the area where they seem to swarm. If there are gnats, they will begin to fly up out of the plant, and bingo, there is your point of origin.

Step Two: Once you have identified their source, it's time to figure out what they are eating. Look for the following food sources:

  • Overly moist soil and standing water in containers or pot liners.
  • Dead leaves, leaf husks, or any other organic debris on top of the soil's surface or down inside pots and liners.
  • Soil that contains organic material like wood chips.
  • Old dirty liners with fungal residue.

Step Three: After the food source has been discovered, it simply must be removed. If the fungus gnats have no food source, they can no longer live an reproduce.

  • For an over-watered plant, you must begin drying out the soil. Over-watered plants get root rot, and rotten roots are a perfect food source for fungus gnats, not to mention over watering will eventually kill most houseplants.
  • If there are dead leaves or any other kind of debris in the soil or inside liners or containers, it must be removed.
  • Organic material inside the soil is the most difficult issue to correct. The easiest solution is to discard the plant. If you are fairly handy you may try re-potting the plant in proper indoor potting soil, but for this to be successful most of the old soil must be shaken away from the plant's root system.
  • If a liner with built-up residue and fungus is discovered, wash it thoroughly or get a new one.
  • If you have exhausted all of the above measures and the gnats are not gone, there are soil additives on the market that kill the fungus gnat larva, but this is only recommended if all other attempts have failed.
  • You can also purchase gnat traps. Like flypaper, these are yellow sticky tabs. You place them in a plant and they catch the adults that fly up out of the pot. If you find a sticky trap covered in gnat carcasses, it will be clear that you have found the infested plant.

Dead leaves are what the gnats may be feeding on.
Dead leaves are what the gnats may be feeding on. | Source
Optimum clean soil surface free of organic decaying material.
Optimum clean soil surface free of organic decaying material. | Source

How to Prevent a Fungus Gnat Infestation

  • Water your houseplants with water only.
  • Give plants the proper amount of water and allow them to dry out between waterings.
  • Keep your plants clean. Remove dead leaves, stems, debris, etc.
  • Always use indoor potting soil for indoor plants. Do not add compost or wood chips to the soil.
  • Avoid purchasing any plants that have evidence of fungus gnats.

Goodbye Gnats

Following these simple tips and keeping your plants properly watered will work wonders for keeping your home or workspace free of obnoxious little fungus gnats. There is no need to throw away all your houseplants! All you need is a little know-how.

Got Gnats?

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    • thoughthole profile image
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      thoughthole 3 weeks ago from Utah

      That sounds like quite an unpleasant discovery Karen B.

      The scope of my expertise in this area is limited to indoor situations, and I live on the other side of the country in a very different climate from that of NJ, so I would likely not be the best person to answer your questions. This may be a subject in which a general pest control expert could provide insightful information.

      I would imagine that the recent storm systems hitting the East coast have given rise to all manner of pests that flourish in moist conditions, fungus gnats included.

      Sorry I could not be of more help.

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      karen b. 3 weeks ago

      I was quite disturbed upon finding a writhing slimy mass of small "worms" on my concrete driveway yesterday...grossed me out and have never seen anything like it before. I sprayed it with raid a few times until I saw no more signs of life. Went online and found out this was a fungus gnat larvae train. Much to my horror, there was another train this morning on my concrete porch not far from the train yesterday...sprayed it, also. They appear to be coming from my lawn. I'm in New Jersey and it was a rather soggy summer. Is this event unusual where I live? Should I be concerned?

    • thoughthole profile image
      Author

      thoughthole 5 weeks ago from Utah

      Sandy & Casey,

      While my expertise with gnats is in respect to indoor plants, I am confident fungus gnats will only be present if they have some decomposing moist material to feed on. The key is to find the food source, and get rid of it. Fungus gnats are often more prevalent during seasons of greater precipitation, namely spring & fall for much of the US. It is possible they may be originating outside, if this is the case it may be a bit more difficult to isolate a specific source. Outside or in look for moist wood, bark, roots, dead leaves etc. If the source remains elusive it may be an indicator of something out of the ordinary going on in or around the home causing structural decay, perhaps a water leak.

      Good Luck!

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      Casey 5 weeks ago

      I don't have indoor plants and when I got out of the shower the little bugs were all over the bathroom and in the window. I went to my kitchen and there all over the lights?? What do I do?

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      Sandy 5 weeks ago

      I believe I have fungus gnats. Everything here sounds right except I don't have indoor plants. I do have a little aquarium. Could that be it and if it could how do I fix this?

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      Gwen 8 weeks ago

      Someone gave me a house plant, instead of flower, for the passing of a loved one. This article was very helpful.