Fungus gnats

Occurrence: Fungus gnats (Sciaridae) are small flies that infest soil, mulch, compost, etc. where plant materials decompose.

FoodTheir larvae feed primarily on fungi and organic materials in the soil, but can also gnaw on roots, which can make them a problem among indoor plants (including plants in greenhouses).

CombatAlthough the adult mosquitoes can be annoying, it is the larvae that are the real pests. The adult mosquitoes can be controlled with glue traps, while the larvae must be controlled by regulating water and soil conditions and possibly using biological agents.

We recommend the following remedies to combat fungus gnats:


Fighting mourning mosquitoes

Most of a fungus gnat's life is spent in the larval and pupal stages, in soil or organic materials. Therefore, to get rid of the fungus gnat, you need to control it in these immature stages rather than targeting the adult mosquitoes (which can move around and only live for a short time).

In practice, you should try to reduce soil moisture and remove or reduce the amount of organic matter in the soil. In addition, you can use commercial pesticides.

In addition, we recommend the following remedies to combat fungus gnats:


Monitoring the mosquitoes

Keeping an eye on your plants is usually enough to determine whether or not the fungus gnats are a problem. When present, adult mosquitoes can be seen in the following locations:

  • On and around plants (also in the soil)
  • In windows and window sills
  • On walls
  • In the air (flying)

In addition, you will also see larvae in the soil around infested plants.


Glue traps

There are special glue traps for fungus gnatswhich can be used indoors and in greenhouses. The traps are effective because they actively control the fungus gnats while allowing you to easily monitor the extent of the problem (the more fungus gnats in the traps, the bigger the problem). The traps are placed on sticks in the plant soil.

You can also cut a potato in half and place the cut side (not the peel side) into the soil; the larvae will start feeding on the potato if they are present. The halved potatoes can also be used to lure the larvae of the fungus gnat away from the plant roots. After the potatoes have been in the ground for a few days, discard them and replace them with fresh potato pieces.

You can buy recommended glue traps here.


Biological control

There are 3 biological agents that can be used to control fungus gnats:

  • Nematodes (in the family Stone enema)
  • Predatory mites (in the family Hypoaspis)
  • BTi (Bacillus thuringiensis ssp. israelensis such as Gnatrol®SC)

The latter product is primarily used in horticulture, plantations, agriculture, etc.


Water and soil

Fungus gnats thrive in moist soil full of plant debris and fungi. To avoid fungus gnats, avoid overwatering your plants and ensure they are well-drained. Proper drainage can be ensured in several ways; make sure there is proper drainage in the plant container, use a layer of pebbles as drainage, mix sand or pebbles into the soil, etc.

Between waterings, you should also allow the soil surface to dry. All excess water should be removed and make sure there are no blockages in the drainage. Also check for leaks.

Compost, garden waste, plant-based fertilizers, topsoil and other types of soil where plants decompose are also among the preferred breeding grounds of the fungus gnat.

Therefore, if you have problems with fungus gnats, avoid using these types of soil for your plants. Once you have infested plants, don't move them around, as this will allow the fungus gnats to spread to other plants. However, heavily infested plants can be discarded.

In the summer months, you can also sun treat the soil in the following ways:

  • Moisten the soil and fill it in a plastic bag (e.g. a black or transparent garbage bag)
  • Close the bag and place it slightly above the ground (e.g. on a pallet)
  • The soil in the bag should be evenly distributed and a maximum of 20 cm deep
  • Leave the bag in a sunny area for 4-6 weeks

The method described above controls not only fungus gnats, but also weeds and other soil pests. Sun-treated soil should be stored above the soil surface to avoid infestation before use.


How do you spot mourning mosquitoes?

Because adult black flies are attracted to light, they are often noticed around windows indoors. However, unlike more active insects such as houseflies (Musca domestica), fungus gnats are relatively weak fliers that don't usually move around much indoors. In the home, they often stay near potted plants and run around in the plants, their soil, fallen leaves, etc.

Females lay small eggs in soil or plant debris. The larvae have shiny black heads and a long, clear or whitish, legless body. They feed on topsoil, leaf mold, grass clippings, compost, root hairs and fungi. If the environment is very humid and there are enough larvae, they can leave slime trails that look like snail trails.


Damage to plants

Adult fungus gnats do not harm plants or bite humans or animals; their presence is more of an annoyance or minor nuisance.

The larvae, on the other hand, can - when there are enough of them - damage the roots of plants, which can both inhibit their growth and make them susceptible to disease. This is especially true for sprouts and young plants. If the soil is moist and contains enough nutrients, plants can even die in some cases.

When a plant withers - despite adequate watering - it's usually a sign of unhealthy roots. This phenomenon can be caused by the larvae of fungus gnats gnawing on the roots, but in many cases the cause is different (such as rotting roots, fungus in the roots, inappropriate soil conditions, etc.)

The most severe root damage usually occurs on indoor plants. Although the caterpillars also attack plants outdoors, the damage is usually not as extensive.


Description of the mourning mosquito

As mentioned above, it is especially the species Orfelia and Bradysiareferred to when talking about mourning mosquitoes.

These species are dark and fragile-looking compared to, for example, the black and white species. mosquitoes. They are 1 - 7 mm long (usually around 3 mm) and have clear, light gray or dark wings (although in some species the females have no wings). The body is slender and dark with long legs. Their antennae are divided into 8 - 16 segments.

Adult mourning gnats are very similar in appearance to mayflies (Ephydridae), which also live in greenhouses where plant material decomposes in the soil. However, waterflies differ from fungus gnats in that they have shorter antennae and are generally more robust.


The larvae of the fungus gnat

The larvae grow up to 1 cm long. They are whitish or clear in color with black heads. The larvae live in the upper layers of soil where food is most easily accessible.

You can watch a video with mourning mosquito larvae below:

The life cycle of the mourning mosquito

Fungus gnats develop over 4 stages:

  • Eggs
  • Larva
  • Doll
  • Adult

The eggs are laid in moist, organic environments such as potted plants or greenhouse soil. At 24°C, the eggs hatch after about 3 days. The larval stage consists of 4 sub-stages. The larvae feed on the soil in which they hatch and develop into pupae after about 10 days. Approximately 4 days later, the adults emerge from their pupae.

A generation of fungus gnats can develop in about 17 days. The development time is highly dependent on temperature; the warmer it is, the faster the development. The number of generations therefore also depends on the temperature, but indoors there will usually always be several generations per year.



Fungus gnats are a range of species in the family Sciaridae. Fungus gnats are not actual mosquitoes because they belong to the family Culicidae - but the mourning gnats and mosquitoes both belong to the two-winged (Diptera).

So far, around 1700 species have been identified worldwide, of which over 600 originate from Europe. However, it is estimated that there are around 20,000 species in total, with the majority being unidentified species in tropical climates.

In Europe, there are several species that are considered pests, but it is mainly the species Orfelia and Bradysiareferred to when talking about mourning mosquitoes.



Fungus gnats are found all over the world - even in the most extreme climates such as Antarctic islands and mountains over 4000 meters above sea level. In deserts, they burrow into the sand at extremely high temperatures. Some species live exclusively in caves. However, the vast majority of species live in forests, swamps and moist meadows where they live in foliage.

Moist soil with decomposing plant materials is their preferred environment; and this is also why they thrive in flower pots, greenhouses and the like.

They spread with the wind and by drifting in the water - for example, on dead wood. In addition, they are also transported around by humans in topsoil and the like.


We recommend the following remedies to combat fungus gnats: