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Information about Fungus Gnats

Sonia Nair Mar 23, 2019
Fungus gnats are small insects with a very short lifespan, but their larvae can be a threat to your plants.
Gnats are those small flying insects that resemble mosquitoes in looks, but the former are smaller in size. These insects have a short lifespan of around two to four weeks. However, within this time, they may prove harmful for your plants. Apart from that, flying gnats can be a nuisance inside the house.

Houseplants and Fungus Gnats

So fungus gnats are insects that can damage houseplants. The name is derived from their love for fungi. These insects are found to feed on fungi, organic material in the soil, and the young roots of plants. They can be equally harmful to indoor and outdoor plants.
In fact, the larvae of fungus gnats are responsible for feeding on the young roots and seedlings of plants. The adult insects are often found to fly around, and are considered a nuisance, rather than a pest. While flying fungus gnats in the garden or near houseplants is a sign of their presence, you may also notice yellowing and wilting of leaves.
Such symptoms are caused by the gnat larvae that feed on the young roots of the plants, thereby depriving them of sufficient nutrition. These gnats may also act as vectors of plant diseases, as they fly from one plant to another. Before starting with control measures, you must confirm that the problem is actually caused by fungal gnats.

Physical Features

These insects have a grayish black body color. Fungal gnats are similar to mosquitoes in size, but are smaller with a length of around two to five millimeters. They are delicate-looking insects with gray colored wings, that sport Y-shaped markings.
The wings are almost translucent. The antennae and the legs are long and slender. They feed on fungi, plant waste, and organic materials in the soil. Fungus gnats love moist soil, in which eggs are laid by the females.


They have a short lifespan, which consists of four stages - eggs, larvae, pupa, and adult insects. The eggs are laid as strings on the superficial layers of the medium, which is mostly moist soil or peat moss. The eggs hatch within four to six days, and the emerging fungus gnat larvae have cream-colored bodies with black head capsules.
Their body length can be around five millimeters. They feed on the root hair of plants and seedlings, for around two weeks. After that, they pupate and within four to six days, adults emerge.
These insects are poor fliers, but most of them are females, and this explains their rising population. The adults live for around seven to ten days only. So their lifespan is very short, and may range between two to four weeks.

Control Measures

As they can cause damage to plants, and nuisance in the house, fungus gnats have to be controlled as soon as you notice them. It has been observed that over watering is a common cause for fungus gnat infestation, as these pests love moist soil. Certain potting mediums, like peat moss attract these insects.
It has also been noted that soil with old compost may become a breeding ground for these insects, as they feed on the decaying organic matter. If you opt for organic measures, you may use a type of bacteria called Bacillus thuringiensis var. israelensis, which is used for biological control of fungus gnat larvae.
Even parasitic nematodes and predatory mites are found to be effective in controlling these pests. You may also use yellow sticky traps for trapping adult gnats.
In short, getting rid of fungus gnats is not a tough task, as you can get the necessary materials from the local nursery or garden store. You may also seek the help of a horticulturist for some guidance. However, prevention is always better to avoid infestation. This can be done by avoiding over watering and by controlling fungal infections of the plants.