You are sitting on your sofa, perhaps enjoying a cup of tea, when a tiny black speck zig-zags across your vision. You swat it away, thinking it’s a one-off. Then you see another. And another. Soon, every time you water your houseplants, a small cloud of these annoying flies rises from the soil.
If this sounds familiar, you are dealing with fungus gnats. At Bath Pest Controllers, we see this issue constantly, especially in homes where indoor gardening is a hobby. While they might seem like a small annoyance, a few gnats can quickly turn into a massive infestation that is hard to manage without the right plan.
In this guide, we will walk you through how to get rid of fungus gnats, why they chose your home, and the best ways to stop them from coming back.
What Are Fungus Gnats?
Before you can figure out how to kill fungus gnats, you have to know what you are looking at. These are small, delicate flies that belong to the families Sciaridae, Diadocidiidae, and others. They are dark in colour, usually black or very dark grey, and they have long legs that make them look a bit like tiny mosquitoes.
Unlike many other pests, these flies aren’t interested in your food. They are interested in the moisture and organic matter in your plant pots. The adults live for about a week, but in that time, a single female can lay hundreds of fungus gnat eggs in the top layer of moist soil.
Do Fungus Gnats Bite?
This is one of the most frequent questions our team gets during a call-out. People see these flies buzzing around their faces and worry about their family or pets.
The short answer is: No. Do fungus gnats bite? They do not. They don’t have the mouthparts to bite humans or animals, and they don’t feed on blood. They are mostly a “nuisance pest,” meaning they won’t make you sick, but they will certainly drive you crazy by flying into your face or landing in your drinks.
However, while they don’t bite you, their larvae can “bite” the roots of your plants. If the population in the soil gets too big, the larvae will stop eating fungus and start munching on the tender root hairs of your houseplants. This can stunt a plant’s growth or, in severe cases, kill it.
Fungus Gnats vs Fruit Flies: Spotting the Difference
Many homeowners get these two confused. It’s an easy mistake to make since they are both small and fly around the house. However, treating them requires different methods, so identification is a big deal.
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Fungus Gnats: These stay very close to your plants. They are attracted to light and moisture. Their flight is clumsy and zig-zaggy. They look like tiny mosquitoes with long legs.
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Fruit Flies: These are usually found in the kitchen. They are attracted to overripe fruit, sugary spills, and drains. They are typically tan or light brown with distinct red eyes.
If you find that your problem is actually in the kitchen near the bin, you might want to read our specific guide on how to get rid of fruit flies for more targeted advice.
Why Are There Fungus Gnats in My House?
If you have fungus gnats in house areas, it usually comes down to one thing: moisture. These pests are almost always brought in through new bags of potting soil or new plants from a nursery. Once they are inside, they look for a damp place to start their family.
We find that overwatering is the biggest reason an infestation stays alive. If the top inch of your soil is always wet, it provides the perfect nursery for their eggs. They also love high humidity and poor air circulation. In Bath, where older homes can sometimes hold onto moisture, this becomes a very common problem.
The Life Cycle: Fungus Gnat Eggs and Larvae
To stop the cycle, you have to understand the stages.
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The Egg: Laid in the top 1 to 2 inches of moist soil. They hatch in just a few days.
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The Larva: This is the “worm” stage. They are translucent with black heads. They live in the soil and eat fungus. This is the stage where most of the damage happens to your plants.
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The Pupa: They go into a resting stage in the soil before emerging as adults.
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The Adult: These are the flies you see buzzing around. Their only job is to find a mate and lay more eggs.
When people ask us how to get rid of fungus gnats, we tell them they have to attack the larvae in the soil, not just the flies in the air.
How to Kill Fungus Gnats: Step-by-Step
If you want to handle this yourself, there are a few professional-grade tricks you can use.
1. Let the Soil Dry Out
This is the simplest fungus gnat control method. Since the eggs and larvae need moisture to survive, letting the top two inches of soil dry out completely can kill off a large portion of the population. If you stop watering for a bit longer than usual, you make the soil a hostile place for them.
2. Use a Fungus Gnat Trap
You can buy yellow sticky traps at most garden centres. These traps are coated with a sticky glue that attracts the adults. The yellow colour mimics a healthy leaf, and once the flies land, they are stuck. While this won’t kill the larvae, it stops the adults from laying more eggs.
3. Mosquito Bits for Fungus Gnats
Many professionals recommend mosquito bits for fungus gnats. These “bits” contain a natural bacteria called Bacillus thuringiensis israelensis (BTI). BTI is a biological control that specifically targets the larvae of gnats and mosquitoes but is safe for people, pets, and the plants themselves. You can soak the bits in water and then use that water to “feed” your plants. The larvae eat the BTI and die within a day or two.
4. Nematodes for Fungus Gnats
Another great biological option is using nematodes for fungus gnats. These are microscopic roundworms that you mix with water and pour into the soil. They are natural predators that hunt down and eat the gnat larvae. We often suggest this for people who want a completely organic solution.
Professional Fungus Gnat Treatment
Sometimes, the infestation is too far gone for DIY methods. If you have hundreds of plants or the gnats have moved into the wall cavities or damp crawl spaces, you need professional fungus gnat treatment.
At Bath Pest Controllers, we don’t just look at the plants. We look at the whole building. We check for leaky pipes, damp insulation, or clogged drains that might be acting as breeding grounds. We use professional-grade treatments that are much stronger than what you find in a shop, but we always prioritize safety for your home. You can see more about our approach on our common household insects page.
Managing Fungus Gnats in Soil
If you find fungus gnats in soil, you might be tempted to just throw the plant away. Don’t do that yet! You can “re-pot” the plant by removing as much of the old soil as possible, washing the roots gently, and putting it into fresh, dry soil.
Another trick is to put a half-inch layer of sand or decorative gravel on top of the soil. The adults find it very hard to crawl through sand to lay their eggs, and the larvae have a hard time emerging through it. This creates a physical barrier that breaks the life cycle.
Summary of Control Methods
| Method | Targets | Effectiveness |
| Sticky Traps | Adults | High (for monitoring) |
| Drying Soil | Eggs/Larvae | Medium |
| Mosquito Bits | Larvae | Very High |
| Nematodes | Larvae | Very High |
| Sand Barrier | Adults/Larvae | Medium |
Why Professional Help is Best
We know that some people enjoy the challenge of DIY pest control. But for a lot of our clients, they just want the problem gone immediately. Fungus gnats are small, but they are hardy. If you miss even one damp corner, the whole cycle starts again in two weeks.
When we come to your home, we bring years of experience and specialized tools. We can identify the exact species and apply the right treatment so you don’t waste money on products that don’t work. If you are struggling with any kind of fly or bug, check out our other insect control services for a permanent fix.
Preventing a Future Outbreak
Once your home is clear, you want to keep it that way.
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Inspect new plants: Before you bring a plant home, check the soil for any movement.
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Clean your pots: If you are reusing a pot, wash it with hot soapy water first.
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Watering schedule: Use a moisture meter to make sure you aren’t overwatering.
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Quarantine: Keep new plants in a separate room for two weeks to make sure they aren’t carrying any hidden guests.
If you follow these steps, you can enjoy your indoor garden without the frustration of tiny black flies ruining your peace.
No. While they are both small and fly, drain flies have fuzzy, moth-like wings and live in the sludge inside your drains. Fungus gnats have longer, mosquito-like bodies and live in soil.
They can, but only if they find another source of moist organic matter. This could be a leaky pipe under a sink, a damp basement, or even a dirty bin. However, 90% of the time, they are tied to houseplants.
Vinegar is great for fruit flies, but it doesn't work very well for fungus gnats. Fungus gnats are more attracted to the colour yellow than the smell of vinegar. For them, sticky traps are a much better choice
They are active during the day, but they are highly attracted to light. If you have a lamp on at night, you might see them congregating around the bulb or on your TV screen.
Because of their life cycle, it usually takes about 2 to 3 weeks to completely clear an infestation. You have to wait for the eggs currently in the soil to hatch and be treated.
Cinnamon is a natural fungicide. It can help kill the fungus that the larvae eat, which might slow them down, but it usually isn't enough to kill off a large infestation on its own. It is better used as a preventive measure.