How To Identify and Get Rid of Fungus Gnats From Indoor Plants (Prevention)

What Are Fungus Gnats?

The ramifications of having an infestation of larvae from Fungus Gnats can be either a mere nuisance that can be tolerated or cause for concern for the continued well-being of your houseplant. Considering their size and lifespans, it would be safe to assume that they shouldn’t pose much of a threat, but they can if not dealt with.

Fungus Gnats are tiny at sizes of 2-8 mm long and are often mistaken for Mosquitos, with a lifespan totaling 25 days. Their lifecycle starts when females lay between 100-200 micro eggs in the moist, warm soil in a plant pot.

It takes 3-6 days for them to hatch and when they do they feast on the roots of the plants hungrily.

They also eat any type of organic decaying matter and fungi as they prepare themselves for the next stage.¹

For 15 days they will be rooting around in the soil, feeding and growing out of sight before cocooning themselves in silk to emerge as adults at the end of that time period. If the temperature is to the liking of the females, it is possible another generation could be laid that could mature to adulthood even quicker, which can lead to an infestation.

They then survive for about 8 days and by that time the next adult generation is ready to take their place to continue the circle of life.

This generational overlapping occurs quite frequently in this species every year and the best way to stop it them to prevent them from settling down in the first place.

What Attracts Fungus Gnats and Where Do Fungus Gnats Come From?

Sciaroidea is the name of the superfamily that these little pests derive from. Under that large umbrella, there are about 20 families.

The Sciaridae, Diadocidiidae, Ditomyiidae, Keroplatidae, Bolitophilidae, and Mycetophilidae, are just a few of them that like to dine on parts of houseplants.

Within all these extended families are about 15,000 species, most of them gnats, some of them flies. They are all classified as being in the sub-order of Nematocera, which includes close relatives such as mosquitos, crane flies, black flies, and midges.

And this loose grouping of these flying insects, some termed as flies, others midges, some mosquitoes, and gnats, sometimes makes it difficult to differentiate exactly which family they belong to.

Knowing what attracts Fungus Gnats and where they come from will give you an idea on how to prevent them from infesting your houseplants.

Just from the brief descriptions below it is plain to see that they have a lot in common, but also a lot that sets them apart.

Because of these veined wings, it has also come to be known as the dark-winged Fungus Gnat. If any gnat is found wandering over the base or over the leaves of your houseplant, it is probably one of these.

They are translucent and have a predatory side to them that is surprising for a creature that moves so slowly. But it has a secret weapon.

Fungi are their main source of food but as they slither about they emit a slimy, clear fluid that is slightly acidic. As smaller invertebrates come into contact with this secretion, they slowly die and are eaten.

If none are available the larvae will turn to cannibalism and consume the pupa close at hand. For them, it’s survival by any means necessary.

Some of their species have a bioluminescence capability to light the way of prey into their deadly embrace, and in Australia and New Zealand they are sometimes called ‘Glowworms’.

But worse still, they can carry other diseases that can prove fatal. As soon as they are detected, they need to go.

Irrespective of whether these delicate-looking gnats pose a health hazard to your plants or are just a nuisance, the last thing anyone needs is to have hundreds of them infesting the soil beneath your fragrant houseplant.³

If the adults cannot be identified for what they are or go unnoticed, sometimes the slimy trails of the larvae can be spotted and give them away.

(Image: Katja Schulz¹⁰)

A quick trick to double-check if they are present under the surface of the soil is to feed them. They won’t be able to resist a free nibble if you place a few slices of potatoes into the soil.

If they are hiding within the soil, after a few days they will be drawn towards the free food and will have gathered beneath the slices.

Now that they are completely exposed, a suitable treatment can be applied or you can just pick up the slimy slitherers. Yuck.

How To Get Rid of Fungus Gnats From Indoor Plants (How To Prevent Fungus Gnats)

Stopping a host of Fungus Gnats from buzzing into your home through an open window is nigh on impossible, they are that small. They migrate from the great outdoors and set up nests in damp soil that attracts them from outside, and lay hundreds of eggs.

There are a few steps that can be taken that may not stop them from curiously strolling around your indoor plants and considering whether to set up a new colony that is easy to maintain.

Here are some of the steps on how to prevent Fungus Gnats from infesting your houseplants:

1. Ensure the container has sufficient drainage to prevent the soil from becoming waterlogged.
2. Eliminate any pools of standing water.
3. Allow the surface of the soil to dry out. If too wet, it will act like an invitation and the gnats will be immediately drawn to it.
4. Discard unused organic material from compost or fertilizers.
5. Plant low maintenance plants indoors that require very little watering.
6. Place a layer of sand, some pebbles, or indoor mulch on the topsoil to deter their presence and absorb any excess moisture.

It is at this larvae stage that the most damage can be done to them, and when they are at their most vulnerable.

How To Kill Fungus Gnats (How To Get Rid of Fungus Gnats)

There are some very effective methods of eliminating Fungus Gnats when detected at the larvae stage.

First, clear away any traces of decaying or decomposing organic matter that can be their food supply, and reduce the lighting. Gnats are attracted to bright lights and this will prevent any more of them from sneaking into your home while your back’s turned.

Dispose of any stagnant pools of water regardless of how small, inside and outside the house.

(Image: Katja Schulz¹²)

The use of insecticides and pesticides are two forms of Fungus Gnats treatments that are highly effective.

Diflubenzuron is an insecticide that has been approved on an international level for the control of Fungus Gnats and their larvae, with just a single application potent enough to kill an entire host of larvae infesting the soil in an indoor or outdoor setting.

It is non-toxic to humans or pets, but the effect on the larvae is dramatic, triggering them in the early development stage, and it is safe to use near plants.

This insecticide will not kill off the adult gnats, but with the larvae gone, and the soil cleaned up, they will either die off quickly or move on.

Another solution is to apply a naturally occurring bacteria to the soil called Bacillus thuringiensis israelensis (BTI).⁴

This bacteria has become a key ingredient in dozens of biological products that are all effective in the treatment of Fungus Gnats, both in residential environments as well as in commercial premises such as greenhouses.

Fungus Gnats Hydrogen Peroxide (Fungus Gnat Larvae)

To remove any doubt that all the larvae have been destroyed, hydrogen peroxide will ensure that they won’t survive.

It is actually a naturally occurring compound but is often manufactured to improve its versatility.

To use, mix with 4 parts water and pour over the soil, drenching it. Quite a lot needs to be poured in to infect every single larvae in the pot.

It will kill them on contact, and those who somehow manage to avoid getting wet from the solution will find that the acidity of the soil has increased to such a level that they will still be killed off, just a fraction slower.

This treatment can be undertaken on an annual basis to remain pest free.

After they have disappeared, apply an organic fertilizer to prevent potential damage to the soil from any loss of beneficial bacteria.

This is an important step after treating the soil to ensure the continued health of plants like a beautiful Pink Princess Philodendron or a precious bonsai Smoke Tree cared for indoors.

How To Set a Fungus Gnat Trap and How To Get Rid of Fungus Gnats in Houseplants

There are several effective methods to eliminate the larvae of Fungus Gnats, but what about the adult gnats themselves?

It can be pointless destroying the nest of larvae if the female adults are consistently going to be laying a fresh batch. Just like their offspring, they have got to go.

The trick, according to experts, is not to spend every waking moment waving them away, but attracting them into a trap of your own making.

Make a concoction with a tablespoon of apple cider vinegar as the base, add dish soap, and a tablespoon of sugar then fill a bowl with room-temperature water. The adults will be drawn in – and trapped.

Sticky tape is also an easy trap to make from household items, but a yellow card or paper has to be used as, for some reason, gnats are attracted to the color yellow.

(Image: Ich¹¹)

Either coat it in a sticky substance or double-sided tape that will hold them fast when they stroll in to investigate.

These are just a couple of simple homemade gnat killers that are easy and quick to put together. Others can be purchased from hardware stores or nurseries that are organic, lethal, and safe for indoor use.⁸

Any of these can be placed near houseplants at the first suspicion that the larvae are present, or even as a precautionary method if you’ve had a previous infestation.

Fungus Gnats vs Fruit Flies

Telling the difference between Fungus Gnats vs Fruit Flies can prove helpful, especially when you want to get rid of them. What might work on one, may not work on the other.

So how to tell them apart and how to deal with them invading your comfy living space?

They are both the same size, give or take a millimeter but let’s have a closer look at them both, and compare them head to head.

• Head size and shape: The head of a Fungus Gnat is small and pea-shaped with very long antennae.
  Fruits Flies have much broader and bigger heads and shorter antennae.
• Body shape: The bodies of gnats are long and much slender. Fruit Flies have bodies that are shorter and stouter.
• Legs: Fungus Gnats have very long legs while Fruit Flies legs are shorter.
• And the eyes have it: The eyes of Fungus Gnats are tiny, virtually invisible.
  The eyes of Fruit Flies are large and positioned on the side of the head. Those are one of its outstanding features and are unmissable
• Nesting and feeding: Where they set up home is a firm identifier, larvae of gnats get laid in the soil of plants.
  Larvae from Fruit Flies are laid in rotting fruit and houseplants have no lure for them at all.

Plants That Don’t Need Sun (Fungus Gnats Prevention)

Preventing adult gnats from being attracted to your houseplants can boil down to plant selection.

Some plants require a lot of attention which generally means daily sun exposure requirements, pruning needs, and watering. A lot of watering.

(Image: John Tann¹³)

There is a range of indoor plants that are fine being neglected, shoved into a dimly lit corner, and only getting a drop of water every few weeks. When a plant is that hardy and does not need watering every other day, then that will reduce the risks of infestation from the larvae of Fungus Gnats.

Here are 10 plants that don’t need sun or water:

The Chinese Money Plant is often mistaken for the Money Tree but they are from different families, the Chinese Plant belongs to the Pilea peperomioides, and the money tree to Pachira aquatica.

Money Tree care involves more water than its namesake, requiring a deluge poured into the container until it flows out of the drainage holes at the bottom. With that much water, there is a risk that the undesirable Fungus Gnats may be attracted to lay eggs in the soil.

So, when choosing a money houseplant, make sure it is the right one.

If, after choosing the correct drought-tolerant plants and taking care not to over water them, an infestation still comes to pass, knowing exactly how to identify and get rid of Fungus Gnats from indoor plants (prevention is even better), will help in eliminating these pests from your plants quickly – and permanently.

Frequently Asked Questions About Fungus Gnats