Fungus gnats (Sciaridae), also known as sciarid flies, are small black flies often found around houseplants and potted plants in humid environments. Although the adult flies are not directly harmful, their larvae can cause significant damage by feeding on the roots of plants. Fortunately, you can naturally control fungus gnats using nematodes.

What attracts fungus gnats?

Fungus gnats aren't particularly picky when it comes to their preferred environment. They are mainly attracted to humid conditions and organic material in potting soil. Wet soil is the ideal place for these small flies to lay their eggs, and that's where the problem begins. The larvae that hatch from the eggs feed on dead roots and other organic waste in the soil. This makes the soil a paradise for fungus gnats, allowing them to reproduce quickly. It is therefore important to keep a close eye on what is happening in your potting soil, so you don't give the sciarid fly a chance to establish itself! Therefore, also check the potting soil when you have bought new houseplants.

Fungus gnats can be active indoors all year round, but you'll often see an increase in autumn and winter. Why? During these seasons, you bring your plants indoors, where they often remain in moist potting soil for longer. Indoor humidity is usually higher, which is the perfect climate for fungus gnats to establish themselves. The good news is that with proper care, you can significantly reduce the chance of an infestation. By taking good care of your plants, you not only ensure healthy growth but also keep fungus gnats at bay!

How do I know if I have fungus gnats?

Do you notice small, black flies around your houseplants? Then you may have fungus gnats. These critters are often confused with fruit flies, but they primarily stay near moist potting soil. A clear indication is that fungus gnat larvae feed on roots in the soil, which can cause your plants to wilt or not grow properly. Do you see small white larvae with black heads in the potting soil? Then it's highly likely that fungus gnats are the culprits.

Fungus gnats are primarily harmful in their larval stage. The larvae feed on the roots of young plants, which can lead to weakened or dying plants. These are the most common signs of a fungus gnat infestation:

• Presence of gnats: Small black gnats hovering around the base of plants or above the potting soil, especially in humid environments such as greenhouses and indoor spaces.
• Root damage: Fungus gnat larvae feed on the fine roots of plants, resulting in wilting and poor growth of young plants.
• Poorly growing or wilting plants: Due to root damage, plants may wilt, fail to grow properly, or in severe cases, die.

Indirect damage and additional risks

The damage caused by fungus gnat larvae to the roots weakens the plant, making it more susceptible to other pests and diseases. Young seedlings and cuttings are particularly at risk from root damage, which can severely impede plant growth.

The most effective way to control fungus gnats is to use nematodes against fungus gnats. Nematodes, such as Steinernema feltiae, are natural enemies of fungus gnat larvae and penetrate them to kill them from the inside out. For optimal control, use yellow sticky traps, which are very effective for catching adult fungus gnats so they can no longer lay eggs. In combination with the nematodes against the fungus gnat larvae, you will be rid of your pest within a few weeks.

The advantages of this biological control method are:

• Environmentally friendly: Nematodes specifically target fungus gnat larvae and do not affect other beneficial organisms.
• Effective and sustainable: Under the right conditions, nematodes can significantly reduce the fungus gnat larval population, without the need for chemical pesticides.
• Safe for humans and animals: Nematodes are completely safe for children, pets, and other animals, making them ideal for use in indoor and outdoor environments.
• Easy to order: Order nematodes online today and have them delivered tomorrow!

Small black flies in the house

Do you suddenly see small black flies in your house hovering around your houseplants, especially when you water or move the pot? In many cases, these are fungus gnats. They don't appear out of nowhere, but from the potting soil. In moist soil, adult flies lay their eggs, after which larvae live in the top layer of the soil. These larvae mainly feed on rotting material, but with many larvae or vulnerable plants, they can also damage young roots. As a result, a plant may sometimes lag in growth or become limp faster, while you might think that extra water helps.

The problem often worsens due to overwatering, overly dense potting soil, or poor air circulation around the roots. The flies themselves are mainly annoying, but the real cause is underground. Therefore, simply catching the adult flies is usually not enough. You are treating the symptom, while the larvae continue and new flies constantly emerge.

Biological control is usually the safest and most sustainable route indoors, as you don't have to use chemical agents in your home and you directly tackle the source. For practical implementation, using nematodes is a natural way to reduce larvae in the potting soil and thus break the cycle.

What is a fungus gnat?

What exactly is a fungus gnat? In practice, the fungus gnat is the adult form you see around plants and windows, and it is often lumped together with the term "mourning fly." They are small, dark-colored gnat-like flies with slender legs and a somewhat slow, fluttering flight. They prefer to be near moist potting soil, as that is where they reproduce. You often see them on the rim of the pot, on the soil itself, or on the window as they are attracted to light.

The damage primarily occurs because the cycle takes place in the soil. Adult specimens live briefly and are mainly annoying, but they do lay eggs. From these eggs hatch larvae that live in the top layer of the potting soil. With a small infestation, you mainly notice flies, but with a larger infestation, larvae can feed on root hairs. This can cause extra stress, especially for cuttings, young plants, and plants that are already somewhat weaker.

For lasting results, it is therefore important not only to tackle the visible flies but also the larvae in the soil. That is where the cause lies, and that is where you break the cycle. A biological approach with nematodes specifically targets these larvae and helps stop the cycle without aggressive chemicals in the home.

Fungus gnat nematodes

Fungus gnat nematodes are a biological way to control fungus gnats. Nematodes are microscopic and naturally live in the soil. When you distribute them with water over the potting soil, they actively move through the moist soil. They search for fungus gnat larvae, penetrate them, and eliminate them. As a result, a larva can no longer develop into a new adult fly, and the pressure of the pest gradually subsides.

The big advantage of this approach is that you don't have to spray chemical agents in your living room. You target the larvae, precisely where the problem originates, while your plant itself remains unaffected. The adult flies you still see may continue to fly around during the initial period because they have already emerged from the soil. This is normal. You will mainly notice the difference when no new generation emerges.

Moisture is important for proper functioning. Nematodes need a moist environment to move around, so the potting soil should not be bone dry. At the same time, it helps to better regulate your watering afterward, so you don't constantly create the perfect nursery for new eggs. This way, you tackle the cause and prevent yourself from having to start over and over again.

Fungus gnats in potting soil

Fungus gnats in potting soil are so persistent because potting soil provides exactly what they need: moisture, organic material, and a sheltered place to lay eggs. Especially the top few centimeters of the soil are important. If this layer often stays wet, an ideal environment for eggs and larvae is created. You then see small flies on and around the pot, but the largest mass is invisibly in the soil. This is also why it sometimes seems as if the problem keeps returning out of nowhere, even if you catch many flies.

Overwatering is the most common accelerator. Not because one extra watering immediately causes an infestation, but because constantly wet potting soil keeps the cycle going. Poor ventilation also plays a role. In a dense decorative pot or a corner without airflow, the top layer dries more slowly, giving larvae ideal conditions for longer. New potting soil can also already contain eggs, especially if a bag has been warm and moist for a long time. We therefore recommend treating new houseplants with nematodes.

Biological control against fungus gnats primarily helps by tackling the larvae and thus breaking the cycle. As soon as the larvae disappear, the influx of new flies stops, and it becomes calm around your plants again. Combine this with smarter watering, so that the top layer can dry out in between, and you won't constantly be mopping with the tap running.

Where do fungus gnats come from if you've never had them before? Usually, they simply come in from outside. This can be through a new houseplant, through contaminated potting soil, or because adult gnats fly in from outside when a window is open. A single gnat flying in is not a disaster, but as soon as moist potting soil is available, the cycle can begin. Adult fungus gnats lay eggs in the top layer of the soil. Larvae hatch from these eggs, feed in the soil, and then pupate, creating a new generation. In a warm house, this can happen faster than you expect.

Indoors, fungus gnats are particularly active because conditions are stable. No cold nights, often regular watering, and pots of soil that rarely dry out completely. As a result, a small introduction can quietly build up into a visible infestation. You often only notice it when you suddenly see a cloud of gnats flying up when watering, or when they are hovering around the window.

You prevent recurrence by combining two things: eliminating the ideal conditions and tackling the larvae in the soil. Catching only adult gnats is often not enough, because the next generation is already ready. A biological approach with nematodes works precisely on that point, interrupting the cycle and preventing it from starting over and over again.

Nematodes against fungus gnats

Nematodes against fungus gnats work for the same reason as with other fungus gnats: the real problem is in the potting soil, with the larvae. The adult fungus gnats you see around your plant are mainly a sign that a next generation is building up underground. Nematodes are microscopically small soil inhabitants that you introduce into the potting soil with water. There, they move through the moist soil and actively search for larvae. As soon as they find a larva, they penetrate and eliminate it. As a result, the larva can no longer develop into a new gnat, and the infestation subsides without you having to stress your plant with aggressive agents.

The great thing about this approach is that your plant itself is not involved in the control. You don't damage leaves, you don't change the soil with chemicals, and you work very targeted. This also makes it an environmentally friendly method, especially indoors where you prefer not to use sprays. You often don't see complete silence overnight, because adult specimens that are already flying around may remain visible for a while. You notice the difference when there is no new growth and the number of gnats clearly decreases each day.

For good effectiveness, it is important that the potting soil is moist enough, otherwise nematodes cannot move properly. After that, it helps to keep your watering a bit stricter, so that the top layer does not remain continuously wet. This way you tackle the source and make the environment less attractive for a next round.

What are fungus gnats?

What are fungus gnats exactly, and are they the same insects as small dark gnats? In practice, these words are often used interchangeably, but people don't always mean the same thing. Fungus gnats are usually the small, dark flies you see near houseplants, because they are attracted to moist potting soil. They flutter somewhat slowly and like to sit on the soil or against the window. The word "rouwvliegen" (mourning flies) is sometimes used as a general term, but can also refer to other small flies that are mainly attracted to moisture and rotting material.

The difference mainly lies in behavior and habitat. The typical houseplant variety likes wet soil and plant pots, because eggs are laid there and larvae develop. If you mainly see flies when you touch the potting soil or water, then chances are you are dealing with that cycle. If you see small flies around fruit or waste, it could be something else. Still, the confusion is logical, because they are all small black flies that quickly become annoying indoors.

Because the infestation around houseplants usually comes from the soil, it is smart to focus there. You only truly prevent new fungus gnats when you tackle the larvae and at the same time make the soil less attractive by better managing watering. Biological control of fungus gnats helps precisely with this, because you interrupt the cycle without chemical agents.

Steinernema feltiae against fungus gnats

Steinernema feltiae against fungus gnats is a widely used biological method to tackle the infestation at its source. These nematodes are so small you can't see them, but they are active in the potting soil. As soon as you spread them over the soil with water, they move into the moist top layer where fungus gnat larvae live. They specifically search for these larvae, penetrate them, and eliminate them. This is exactly what you need, because adult fungus gnats are mainly a consequence of what happens in the potting soil.

The convenient thing about this approach is that you don't have to guess or spray in your living space. You work in the soil, where the cycle begins. This stops reproduction before new gnats continuously emerge from the soil. You may still see gnats in the initial period, as adult fungus gnats already flying around complete their natural lifespan. This is not unusual. The real gain lies in the absence of new growth, which leads to a clear reduction in activity around your plants over time.

This biological control is safe for plants, humans, and pets when you follow the usage instructions. It is also an approach that fits a sustainable way of plant care, as you do not unnecessarily disturb the ecosystem in the pot.