Fungus Gnat Larvae: How To Kill Them Off Quickly

Ed Wike
Written by
Last update:

Fungus Gnat Overview

Fungus gnats are small black flies that typically infest soil mediums and plugs that are kept moist. They will lay their eggs in moist, damp soil, so they are often found in soil that is watered excessively or that has been kept in a saucer of water for a long time. You can also root your plant directly in the soil you intend to grow it in, which creates less of a risk for fungus gnat infestations. They will lay their eggs in the soil and their larvae will feed on the root hairs, as well as the soil surrounding the root system.

The most noticeable sign of an infestation is a fungus gnat larvae, called a maggot. It is long and thin, white or tan colored, and small enough to get through soil, which can make spotting the white maggot a difficult task. Before the larvae appear, the fungus gnat fly whines and buzzes around one area of the plant. When you see the white maggots, it is too late and the mother has already laid her eggs. Fungus gnats typically spend three weeks as a larva, so keep an eye out for the adults as well. The most effective control for the female adult is to cover the area with a fine layer of diatomaceous earth, which will dehydrate the female flies when they come into contact with it and cause them to die.

Types of Fungus Gnat Larvae

Not all fungus Gnats are pests. Many types are aquatic and are actually beneficial to the underwater environment. Fungus Gnats are found in moist soils, compost piles, among well-watered plants, as well as in mushrooms, other decaying organic material, and even in water. Fungus Gnats are usually transparent or yellowish and have a grayish-brown to black head. The larvae have a feathery gill-like breathing apparatus. Many types of adult fungus Gnats are capable of flying. These larvae live in the water and slow-moving areas of your aquarium, and they aren’t usually seen. If they are in the aquarium, the gnats will most likely be in anaerobic places where they can thrive.

One of the most common fungus Gnat species seen in aquariums is Dicranopalpus ramosus which has been known to survive to adulthood in aquarium conditions using mainly the nitrate and nitrite as its source of food. Dicranopalpus ramosus will feed on fecal matter and other waste in the aquarium.

Life Cycle Of Fungus Gnats

Fungus gnats start their lives as eggs in the soil of houseplants and potted plants that are kept indoors. In fact, fungal gnat eggs are microscopic, but you should be able to see the adults quite clearly as they fly around. The females will lay up to 100 eggs on the soil of houseplants and they will hatch into larvae very quickly, in just a few days. Within the larval stage, the larvae will feed on fungi and decaying organic material in the soil. After a little under a week, the larvae will turn into pupae and the pupae will eventually hatch into adult flies.

If you look closely you may notice a whitish web around the pot of your houseplant. That's a fungus gnat nursery. The larvae live there and they grow there, burrowing in the soil and eating the fungi that are living there. The soil of houseplants should be damp, but never soggy or standing in water. So, you need to check the moisture levels of your houseplants regularly.

Common Habitats For Fungus Gnat Larvae

If you had fungus gnat larvae last year, you will likely see them again this year. A lot of clients contact us after the first sign of infestation, and that is just too late.

After 3-4 generations last year, we probably have a climate here in the South, where we can expect hundreds of generations per year in hot, wet summers, and low generations in cool summers. If you have breeding occurring in decaying organic matter, these insects will be a problem.

They like to infest houseplant soils and potting mixes. They are also found around the edge of fish tanks, and in bathtubs they are attracted to the residue of soap and other cleaning chemicals, which they use to build their egg sacs. So when you go to bed at night, you can see the larvae skimming across the water, around the top of your bathtub.

So, find your soil, your potting mix, your fish tank and your bathtub. Those are your breeding grounds for fungus gnat larvae, and they are usually breeding in it, no matter what you do … after dark.

What Do Fungus Gnat Larvae Eat?

Fungus gnats are the larvae of a small fly (one to two millimeters long) which appears as a greenish black fly as an adult. These flies are attracted to moist soil, compost and decaying organic material with high levels of sugar and carbohydrates. They can also be found in moss. Since fungus gnat larvae gravitate towards rotting or decaying plant matter, potting soil, mulch, and compost, they have an affinity for gardeners and their gardens.

One way to attract fungus gnats is to use untreated sawdust in your garden.

Fungus gnat larvae eat decaying or guanoed soil. They will eat fungi, bacteria, and decaying matter. The larvae eat soil as their primary source of food. They will however also eat other organic wastes, such as proteins (reptile droppings are favorites), mucus, decaying plant material, and fungi. A wide variety of plant material and products will attract gnats and their larvae.

These are some of the things that attract fungus gnats:

  • Using peat or peat moss in your garden (or container) soil mix
  • Using untreated sawdust for mulch or for under container growing mediums
  • Composting based on manure, moss, hay, or composted materials

When Fungus Gnats Strike

Fungus gnats are quite annoying when they are present in significant numbers. Because they are small, you might not be aware of them until you see small white larvae, wet spots on the surface of your soil, or emerging fungus gnat adults around your plant pots.

Fungus gnats like to live in dry, dark places, so they typically like to host around house plants, ferns, and other popular house plants. Fungus gnat adults can fly, so be on the lookout for swarms of gnats hovering around your house plant pots.

You can prevent fungus gnat colonization by keeping your verdant plants as healthy as possible. As we mentioned, fungus gnats like to pop up in dry, dark places, so make sure that your house plants have sufficient drainage and that they aren’t left in the dark.

If your house plants are too large and well-established to simply uproot, you can use pesticides to kill off fungus gnat larvae, adults, and eggs.

How To Get Rid Of Fungus Gnat Larvae

(Without Using Pesticides)

The adult fungus gnats are not a problem to have. They don’t bite and they don’t make a bunch of noise. Their presence can be tolerated and they don’t tend to damage plants. In fact, some of these harmless gnats are attracted to houseplants and to fungus growing on plants. Often, their bites are worse than their presence … but you may not realize you have fungus gnats, until you do. But once you have them, you will thank yourself for killing the larvae.

Fungus gnat larvae are tiny maggots that are white. They are easy to miss but they are mean eating machines. They can quickly devour any weakened plants or existing fungus. Often, your plants will look wilted to the touch and you may see little piles of the white larvae as you lightly stick your finger into your plant potting soil.

When you realize what the problem is, don’t panic. It is easy to get rid of fungus gnat larvae.

Remove the larvae manually:

It’s a good idea to have some hand-held narrow pointed tweezers lying around. They come in handy for removing other gnat infestations and for plucking weeds.

Organic Fungus Gnat Control

Fungus Gnats fast facts: Fungus gnats are attracted to fungus-heavy soil in potted plants and houseplants. Heavy feeding, like a monthly application of a high phosphorus fertilizer, can do the same thing on indoor and outdoor plants.

The larvae feed on fungi and the mycelium of fungi.

The larvae feed on fungi and the mycelium of fungi. Adults feed on nectar.

Fungus Gnats are winged insects with long legs, they have flat, elongated, mosquito-like bodies, they easily hover and feed on the surface of leaves.

They can only fly short distances, but they are attracted to lights.

The best way to get rid of the adult fungus gnats and end the life cycle is a non-pesticide solution.

How to Kill Fungus Gnats

The best way to get rid of the adult fungus gnats and end the life cycle is a non-pesticide solution.

Clean Up and Keep Clean:

Fungus gnats are attracted to the things that provide food, for this reason, you need to keep your living space clean as much as possible.

Remove any dead or diseased plant material and dispose of it. Clean up any spills of strong smelling liquids such as bleach, drain liquids from potted plants.


Environmental Fungus Gnat Control

Fungus gnats are impossible to overlook because the larvae are so tiny they look like pollen coming out of the soil. It is only when they turn into adult gnats that you notice them and they create more of a mini epidemic in your home.

Adult fungus gnats are actually harmless and they do not bite or feed on humans or animals. When they come out, you will notice them flying over your plants or you may see them flying around your house or office kitchen. However, their larvae are the real pests. They can quickly destroy your plants and fungus gnats preferably feed on the roots of the plants.

Preventing Fungus Gnats

(FGs) From Invading Your Houseplants

Fungus gnats are among the smallest of house pests, and that’s what makes them so hard to monitor. Once they get a start in your home, it’s hard to stop them from thriving and multiplying. There are several ways you can prevent fungus gnats in the first place:

  • If you have recently repotted your potted plants, mist the soil surface with an insecticidal soap spray. This will kill off the larvae before they’re able to reproduce.
  • If you have indoor plants, especially if they are potted, keep them away from the base of outdoor trees, or plant deciduous trees to create a visual barrier.
  • If you land in an infested potting soil, discard it.
  • Make sure that your potting soil isn’t too wet. Fungus gnats breed in moist soil.
  • They thrive in dark, warm environments, so brighten up your houseplants’ surroundings with indirect light, and ensure there’s adequate airflow in your home.
  • Place your potting soil in the freezer before repotting.
  • Cover your houseplants with a fine mesh material to keep out their young nymphs.