Fungus Gnats: Where Do These Little Flying Bugs Come From
What Are These Tiny and Annoying Black Flies?
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). Gnats are also attracted to decaying organic material, wheres fruit flies only feed on produce. These bugs 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. They can eat away at the roots of your plants and cause them to yellow or die. When the larva grows into an adult, it flies out in search of new locations to procreate and feed.
Most people notice that they have fungus gnats in their home because these tiny bugs 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.
Where Do Gnats Come From and What Are They Attracted to?
- Moisture: They love to live and breed in the moist soil of overwatered house plants, in containers or pot liners, or around areas with standing water, such as sinks, open bottles of beverages, etc. 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.
- Decaying organic matter: Fungus gnats feed on moist, decaying, organic material, such as dead leaves, leaf husks, fungus, or any other organic debris on top of the soil's surface or down inside the pots and liners. They are also attracted to soil that contains organic material, like wood chips, peat moss, or compost, which is also why you may find them in compost bins or trash cans with decaying material.
- Light source: They typically swarm around windows, lamps, and other light fixtures.
- Carbon dioxide: Like most flies, fungus gnats love CO2, which is why they like to hover around your mouth and nose.
What's the Difference Between a Fungus Gnat and a Fruit Fly?
smaller than a fruit fly
tiny black body
brown or tan body
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
Use the following methods to catch and kill fungus gnats that are present in your home. Use a combination of methods and do it repeatedly for at least 4 weeks.
Dry Out the Soil
For an over-watered plant, you must begin drying out the soil. Overwatered plants get root rot, and rotten roots are a perfect food source for fungus gnats. As a side note, overwatering will eventually kill most houseplants, so please don't do it.
Remove Dead Leaves
If there are dead leaves or any other kind of debris in the soil or inside the liners or containers, it must be removed. Dead, decaying material is a food source for gnats.
Massacre With Steel Wool
This method works like a charm. Place a thin layer of steel wool on top of the soil of your potted plants. Any larvae trying to fly out will literally get shred to pieces, and adults flying in to lay their eggs will also die. Leave the wool in for at least 4 weeks to ensure that all generations of larvae are exterminated as they try to fly out. It's a simple yet magical technique.
Remove the Top Layer of Soil
Once you believe all the larvae are dead, remove the top part of the soil. This is to ensure that any eggs remaining will be removed. Replace this top half with sand. Sand drains well and dries quickly.
Drown Them in Vinegar or Beer
Place jars filled halfway with apple cider vinegar or beer near the source of origin. Screw on the lids and poke holes in them large enough for the gnats to enter. If you don't want to ruin your lids, you can cover with plastic wrap and poke holes in it. The gnats will enter to drink the vinegar or beer and drown. Do this repeatedly until you see fewer and fewer gnats in the jars.
Use Potato Slices to Control Larvae
Cut slices of potato up and place them on the surface of your potting soil. Fungus gnat larvae will swarm onto these tater slices after about four hours, and you can then dispose of them. Do this repeatedly until all the larvae are gone.
Kill Larvae With 3% Hydrogen Peroxide
Allow your soil to dry before watering your plant with a mixture of 1 part hydrogen peroxide and 3 parts water. You must dilute the hydrogen peroxide and only use the 3% hydrogen peroxide you find at the drugstore and nothing higher.
Control Larvae With Food-Grade Diatomaceous Earth
DE is natural and non-toxic, but it contains microscopic shards of silica that can rip larvae apart as they crawl through it. Mix some into the top layer soil (this is where gnats lay their eggs). If your repotting or planting something new, mix DE into the potting soil for prevention.
Purchase Products Containing BTI
These products, such as BTI Mosquito Bits, contain the bacteria Bacillus thuringiensis var. israelensis, which kills the larvae of many insects, including fungus gnats. Mix into your soil and larvae will be wiped out instantly.
Catch Flying Gnats With Yellow Sticky Traps
Like flypaper, these yellow sticky tabs catch gnats so you can discard of them. Just place the stick traps horizontally on top of the plant soil, and they will catch the adults that fly up out of the pot. Discard the sticky trap once it is covered in gnat carcasses, and continue using new traps until you see fewer gnats.
Discard or Repot the Plant
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 repotting 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.
Get a New Liner
If a liner with built-up residue and fungus is discovered, wash it thoroughly or get a new one.
The Fungus Gnat Life Cycle
It takes about 17 days for gnats to mature from egg to full-grown flying adults. They then live a week before they die. Use a combination of methods and do it repeatedly for at least 4 weeks to ensure that at least two generations of gnat larvae cannot fully form into adults, therefore killing off their population.
How to Prevent a Fungus Gnat Infestation
- Don't Overwater Your Plants: 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.
- Use Sand: Fill the top of your pot with 1/2 inch of sand. Water drains quickly in sand, keeping the top layer dry, and thus preventing gnats from laying their eggs.
- Use Indoor Potting Soil: Always use indoor potting soil for indoor plants. Do not add compost or wood chips to the soil.
- Don't Use Compost, Peat Moss, or Mulch: These materials retain moisture and contain decaying material that fungus gnats are attracted to. Don't using potting mixes containing these materials and replace the potting soil with indoor soil if necessary.
- Consider Using Perlite or Vermiculite: Both of these materials improve aeration while retaining moisture. Like diatomaceous earth, they are sharp, so they present an unwelcoming environment to fungus gnats. Ask your local nursery which material you should use for your plants as perlite dries out too quickly for water-loving plants and vermiculite holds too much water for plants that need well-drained soil.
- Check Plants For Infestation Before Buying: Avoid purchasing any plants that have evidence of fungus 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.
Questions & Answers
We're in an office with minimal plants and fungus gnats are all over. Where could they come from? Are they dangerous?
Fungus Gnats are not dangerous; they are however incredibly irritating. It does not take much to produce a substantial Fungus Gnat population. If the plants in your office have been inspected for organic material like dead leaves and bark, standing water causing root rot, or any other moist rotting material in the soil surface or in the liner and the source cannot be located it would be good to check garbage disposals, look for leaks or spills in kitchens, garbage can, etc to see if they may be the cause of the issue.
Are these bugs also attracted to light? I thought we had fleas. Keep finding little black bugs appearing to hop however they also fly, we don't have any bites, and they are mostly near my house plants, and also I am finding them in the bathtub and bathroom sink. I want them gone.
I have not noticed Fungus Gnats to be attracted to light. Moisture/humidity is the big draw for them, so they are commonly found around sink drains, and human faces in addition to houseplants.
Mine are larger than fruit flies and I can't find them in plants, are they really fungus gnats?
If the insects in your home are larger than Fruit Flies, and there is no sign of plant infestation, then you must have an issue that is not due to Fungus Gnats. It may be best to consult a pest control specialist to identify the offending bug in your home, & treat it accordingly.
We are in an office/warehouse. There are no plants, but we have had a few leaks from the roof. could it be from there the fungus gnats are coming from?
If there is a persistent condition of moist material like wood, soil, leaves, paper, etc. associated with the roof leak, that could very well be the place your gnats originated.