Do Fungus Gnats Bite? Debunking the Common Myth

Fungus gnats are tiny, black flies often found around indoor plants and windows. These small insects can be a nuisance in homes, but many people wonder if they actually pose a threat or if they bite humans.

The good news is that adult fungus gnats do not bite people or damage plants. Instead, their larvae feed on fungi in moist soil, particularly in potted plants containing organic matter. Overwatering plants can contribute to the growth of fungi, attracting more gnats. So, while they might be annoying, they are typically harmless to both plants and humans.

However, when present in large numbers, fungus gnat larvae can potentially damage roots and stunt plant growth, especially in seedlings and young plants. Thus, it is important to monitor plant care to minimize the risk of a fungus gnat infestation.

Identification and Appearance

Fungus Gnats Vs Fruit Flies

Fungus gnats and fruit flies are often mistaken for each other due to their similarities in size and appearance. However, they belong to different families, with fungus gnats belonging to the Sciaridae family. Some key differences between them are:

  • Fungus gnats are attracted to moist soil and decaying plant matter, while fruit flies are attracted to ripe and fermenting fruits.
  • Fungus gnats have a darker color and a more delicate appearance compared to the more robust and often lighter-colored fruit flies.
Characteristic Fungus Gnats Fruit Flies
Family Sciaridae Drosophilidae
Attraction Moist soil, fungi Fruits
Typical Color Dark Light brownish
Appearance Delicate Robust

Size and Physical Features

Fungus gnats are tiny insects, typically measuring between 1/16 to 1/8 inch in length. They have a dark color, slender legs, and segmented antennae that are longer than their heads (^source^). Their delicate, mosquito-like appearance makes them easy to distinguish from fruit flies.

Some key physical features of fungus gnats include:

  • Tiny body size, ranging from 1/16 to 1/8 inch long
  • Dark color, often black or brown
  • Slender legs
  • Long, segmented antennae
  • Delicate, mosquito-like appearance

It’s worth mentioning that fungus gnats typically don’t bite and are considered more of a nuisance than a threat to humans. However, their presence may indicate overly moist soil or decaying plant matter, which could be detrimental to your plants.

Life Cycle of Fungus Gnats

Egg

Fungus gnat eggs are oval, shiny, white, semi-transparent, and extremely small. They can be found in small groups (10+) or singly on surface soil or host plants. The eggs take approximately four to six days to hatch. Some key features of fungus gnat eggs include:

  • Oval and shiny
  • White and semi-transparent
  • Found on surface soil or host plants
  • Hatch within 4-6 days

Larva

Larval fungus gnats, also known as white worms with a shiny black head, feed on fungi in moist soil. They need these conditions to survive and can cause damage to roots and stunt plant growth, particularly in seedlings and young plants. Larvae’s characteristics:

  • Small white worms
  • Shiny black head
  • Found in moist soil
  • Can damage plant roots

Pupa

The pupal stage is a transitional period between the larva and adult fungus gnat. During this stage, the gnat is not actively feeding or causing damage. Pupal characteristics:

  • Inactive stage
  • No active feeding

Adult

Adult fungus gnats do not damage plants or bite people and are primarily considered a nuisance. Fungus gnats are tiny, black flies commonly seen around lamps and windows. They contribute to the breeding process by laying eggs in moist soil. Adult fungus gnat features:

  • Tiny, black flies
  • Do not bite or damage plants
  • Lay eggs in moist soil

In summary, fungus gnats go through a life cycle involving eggs, larvae, pupae, and adults. Their presence can be a nuisance, and their larvae are capable of damaging plant roots in the right conditions.

Infestation and Damage

Indoor Plants

Fungus gnats are small flying insects that infest indoor plants. They lay eggs in moist soil, and the larvae feed on plant roots and organic matter. Commonly found in greenhouses, they can affect a wide variety of plants such as Bradysia coprophila and B. impatiens.

Root Hairs Damage

The larvae of fungus gnats cause damage by feeding on root hairs, resulting in:

  • Stunted plant growth
  • Weak and fragile roots
  • Reduced nutrient uptake

Yellowing and Nutrient Deficiency

Infested plants often suffer from:

  1. Yellowing leaves
  2. Nutrient deficiency
  3. Slow growth

As the root system weakens, nutrient uptake becomes inefficient, leading to visible symptoms in leaves.

Damping Off and Root Rot

Infestation with fungus gnats can also lead to damping off and root rot in plants. These conditions, often caused by the soil-borne fungus Pythium, are associated with:

  • Mushy, darkened roots
  • Collapsing seedlings
  • Wilting plants
Infestation Signs Infested Plant Effects
Larvae in soil Root hairs damage
Adult gnats flying around Yellowing, nutrient deficiency
Poor plant growth Damping off, root rot

Following these guidelines ensures information is conveyed effectively while keeping the content short and adopting a friendly tone of voice.

Prevention and Control

Allow Soil to Dry Between Waterings

To prevent fungus gnats, let the soil dry between waterings. This reduces larvae survival rate and discourages gnats from laying eggs. For example, water your houseplants only when the top inch of soil is dry.

Use Well-Draining Potting Mix and Avoid Overwatering

Using well-draining potting soil helps avoid overwatering, which contributes to fungus growth. Ensure that excess water drains from potted plants, reducing the damp conditions that attract fungus gnats.

Pros of well-draining potting mix:

  • Reduces chances of overwatering
  • Prevents formation of damp conditions, discouraging gnats

Cons of well-draining potting mix:

  • May require more frequent waterings

Repotting and Sand Barrier

Repotting plants with fresh soil eliminates larvae and eggs, while creating a sand barrier on the soil surface adds an extra layer of protection. A 1-inch layer of sand prevents gnats from laying new eggs and accessing plant roots.

Gnat Traps and Yellow Sticky Cards

Using gnat traps and yellow sticky cards helps in managing adult fungus gnats. Place traps near infected plants to capture adult gnats and stop them from laying eggs.

Treatment Methods

Apple Cider Vinegar and Liquid Dish Soap Trap

One simple, non-toxic method for fungus gnat control is the apple cider vinegar and liquid dish soap trap. Just follow these steps:

  1. Mix a small amount of apple cider vinegar with a drop of liquid dish soap
  2. Pour the mixture into a shallow container
  3. Place the container near your plants

Fungus gnats will be attracted to the scent and become trapped in the mixture. Remember to replace the solution as needed.

Sticky Traps

Using sticky traps is another effective method for capturing adult fungus gnats. Place the traps near your plants and replace them when full.

Pros:

  • Non-toxic
  • Easy to use

Cons:

  • Only targets adult gnats

Insecticides and Biological Control

In some cases, chemical control may be necessary. Consider using Bti (Bacillus thuringiensis subspecies israelensis) or Steinernema feltiae nematodes to control larvae, as they are more eco-friendly options. However, if you must use an insecticide, opt for pyrethrins or a pyrethroid-based product.

Consulting a Pest Control Professional

If all else fails and you’re still struggling with a fungus gnat infestation, consider consulting a pest control professional. They can assess your situation and provide effective solutions.

Method Pros Cons
Apple Cider Vinegar & Dish Soap Trap Non-toxic Requires frequent monitoring
Sticky Traps Non-toxic Only targets adult gnats
Insecticides & Biological Control Targets larvae Chemicals may be harmful
Pest Control Professional Expert knowledge Can be costly

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 – Fungus Gnat Larvae

 

mass of larvae
Location: suburbs of New York City
September 23, 2011 10:04 am
Hi,
What are these? Photo attached
Thanks
Signature: Jane

Fungus Gnat Larvae aggregation

Hi Jane,
You have an aggregation of Fungus Gnat Larvae.  According to BugGuide, they migrate when there is a population explosion. 

Fungus Gnat Larvae

 

Letter 2 – Fly from Tennessee likely Dark Winged Fungus Gnat

 

Subject: Flying insect
Location: Hendersonville, TN
May 11, 2013 10:20 am
Hello,
I live in Hendersonville TN and recently painted the front of my home. In the past couple of days I have noticed hundreds of these bugs on the house, or flying around near the gutters. Can you please tell me what they are, and how to get rid of them. Are they termites?
Thanks
Signature: Greg Sisk

What's That Fly???
What’s That Fly???

Hi Greg,
We are uncertain how to classify this Fly.  We thought it resembled a March Fly, and that would explain the large numbers, but the antennae are wrong for typical March Flies.  Perhaps one of our readers can provide an identification.  We have also requested assistance from Eric Eaton.

Eric Eaton Responds:
Reminds me most of a dark-winged fungus gnat, family Sciaridae, but could be a gall midge, too….
Eric

Letter 3 – Dark Winged Fungus Gnat

 

Subject:  Black wings with yellow wody
Geographic location of the bug:  Middle Tennessee
Date: 09/08/2019
Time: 07:21 PM EDT
Your letter to the bugman:  These are all over my porch , theye are bigger than a knat but smaller that a fly
How you want your letter signed:  Peggy plant

Dark Winged Fungus Gnat

Dear Peggy,
We are so sorry because this has been on the back burner for nearly a week because we thought this was a March Fly but we were never able to find a match in that family.  This is a Dark Winged Fungus Gnat in the family Sciaridae based on this BugGuide image.  According to BugGuide:  “Often found in flowerpots. In moist and shadowy areas up to 70% of all Diptera species can be Sciaridae.”

Dark Winged Fungus Gnat

Letter 4 – Fungus Gnat

 

black flying bugs
(great!) website and don’t see anything that matches what we have here – Every year about this time (Columbia, SC) we get these black flying bugs – they come in for a week or so and then go away. They don’t bite, don’t really seem to do much of anything except occasionally fly around. I think they are harmless but I’d like to know what they (or their larvae) eat so I know if my trees are in danger. It’s mostly just a little un-nerving to see hundreds of them on your wall (they seem to like the coolness of the brick) – looks kind of amityville horror-esque. I’m sending three photos – one looking down on them, one is a side view (so you can see the yellow abdomin – in this photo they almost look like lightning bugs but they definitely are not), and one is a shot of the wall – all those black spots are these bugs.
Thanks for any help you can provide.
Kim

Hi Kim,
We wanted to be sure exactly what type of gnat you are being visited by, so we checked with expert Eric Eaton. Here is what he has to say: “Ok, these are indeed gnats, dark-winged fungus gnats to be exact, family Sciaridae. I don’t know much about the outdoor varieties, but understand they can be overwhelmingly abundant at times. Adults do not bite, may not even feed at all. Eric”

Letter 5 – Fungus Gnat

 

We’re in Fungus Gnat Hell
Thu, Jan 22, 2009 at 9:13 PM
Is this some sort of Fungus Gnat? They act like a cross between a mosquito and a small fly. About the size of a mosquito, with long wings. But in flight much slower than any mosquito or fly (that is, I can swat one). They appear to have invaded us after an extended warm spell here in San Diego. They don’t seem to bite, and appear generally harmless, but worry that they’re a danger to the outdoor plants or citrus trees. My kids are freaking out b/c they think they are mosquitoes, lying in wait to torment them and suck their blood while they slumber…
Kel
Coastal San Diego

Fungus Gnat
Fungus Gnat

Dear Kel,
In our estimation, you are correct that this is a Dark Winged Fungus Gnat in the family Sciaridae.  Charles Hogue, in his book Insects of the Los Angeles Basin, identifies a Root Gnat in this family, Bradysia impatiens, that also looks like your specimen.  Hogue writes:  “This is the tiny black gnat that flits in your face while you are watching television and that always seems to get stuck in fresh paint.  The larva lives in decaying plant material, such as compost, peat, and sphagnum;  it also commonly infests the roots and stems of various herbaceous plants.  The insect may develop in the media used for potted plants, which explains its mysterious appearance indoors.”

Fungus Gnat
Fungus Gnat

Letter 6 – Fungus Gnat Larvae

 

small larve
Location: Randleman,NC
May 30, 2011 7:56 am
ifound this crawling accross my sidewalk one morning and it was unusual i have never seen anything like these before not knowing what they were i sprayed them with ant spray since we have a common problem around here with termites. the next morning same scenario in the pics you would see the dead ones from the day before. please help me identify the bugs in these pics. Thank You
Signature: IZZY

Fungus Gnat Larvae

Hi IZZY,
This is an aggregation of Fungus Gnat Larvae from the family Sciaridae.  We have profiled this phenomenon numerous times in the past on our website.  BugGuide provides this information:  “Sometimes abundant enough to form a crawling mass of several inches across and several feet long, similar to armyworm migrations. (2).  They feed on fungi in decaying plant matter (they often show up in potted plants that have been overwatered). [comment by Chris Borkent]  They can be pests in green houses.”

Letter 7 – Fungus Gnat Larvae

 

Subject: Parade of insects in slime?
Location: Hillsboro, Virginia
July 8, 2016 8:47 am
I saw this streak of ‘slime’ on my sidewalk yesterday, about 1/2″ wide and 8″ long which was moving slowly as if flowing forward. It was composed of tiny whitish oblong insects, maybe smaller than a grain of rice which were moving forward in unison in this ‘matrix of ooze’
Photo shows streak of slime on sidewalk. The colors are about the same. I took a short movie of the movement but the file is too large to send.
Hope you can help.
Signature: Sandy

Fungus Gnat Larvae
Fungus Gnat Larvae

Dear Sandy,
These are Fungus Gnat Larvae in the family Sciaridae.  According to BugGuide:  “Sometimes abundant enough to form a crawling mass of several inches across and several feet long, similar to armyworm migrations. Can be pests in greenhouses and in commercially grown mushrooms.”

Oh my GOSH!!!!  Thank you so much for the quick answer.  I will use you again.  How very interesting.  I will search for more about them.
Thank you thank you.
Sandy

Authors

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  • 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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7 thoughts on “Do Fungus Gnats Bite? Debunking the Common Myth”

  1. I would very much like to use an image of a snake of fungus gnat larvae posted by Jane, in a children’s educational book I am producing called ‘Wow! Wildlife Animal Camouflage’ for Rosen. The print run will just be 1,000, and the size of the image would just be a small inset picture. Do you own copyright? If you do, could we use the image? Or could you possibly give me a contact email of the person who does (i.e. Jane?) I will put a credit inside the book, and could pay a small fee.
    All the best,
    Alix Wood

    Reply
    • Hi Alix,
      What’s That Bug? does not own the copyright to photographs submitted to our site, but we reserve the right to publish photos and letters to our website and to other What’s That Bug? authorized publications. We fully support educational books. Smaller publications, which are basically labors of love fall, are of special interest to us. We will allow you to use the image in your book. Please credit Jane and What’s That Bug? and should Jane ever respond to this posting and comment, you can work out the payment details with her.

      Reply
  2. Wow, I have been looking for this for some time. I just returned from a trip to Peru where I swa this strange cluster. My wife was not impressed adn would not fork over the camera! But this pic is exactly what I saw. Thanks

    Reply
  3. Here in rural central Virginia we are seeing several masses of these crossing our large blacktop parking area. As they move over the rough surface the mass looses members as it migrates across the blacktop. Those that are left behind appear to die within an hour or so. Since they are crossing an area of some 30 feet, a good number of them do not make it across.

    Ants that run across them so far have shown little interest in either the live ones or the dead.

    Reply
  4. Here in rural central Virginia we are seeing several masses of these crossing our large blacktop parking area. As they move over the rough surface the mass looses members as it migrates across the blacktop. Those that are left behind appear to die within an hour or so. Since they are crossing an area of some 30 feet, a good number of them do not make it across.

    Ants that run across them so far have shown little interest in either the live ones or the dead.

    Reply
  5. I stepped on one of these this morning and it either stung or bit my foot. We’re in North Texas. I’m very curious to know what it is.

    Reply

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