Fungus gnats are tiny insects that feed on organic breakdown in soil, potting mix, and other container media. Their larvae eat fungi and organic materials in the soil, but they also chew roots, making them a nuisance in greenhouses, nurseries, potted plants, and interior plantscapes. Indoors, adult fungus gnats can emerge from houseplants and cause a nuisance.

When a large number of eggs hatch close together, the larvae congregate and travel in a snake-like pattern, crawling atop one another. Migrations are frequently seen crossing a sidewalk or driveway.

Body 

• Dark-winged fungus gnats (Sciaridae), sometimes known as fungus gnats (Orfelia and Bradysia species), are black, delicate-looking flies that seem like mosquitoes. The legs of adult fungus gnats are slender, and their segmented antennae are longer than their heads. 
• Their long antennae identify them from the more robust shore flies, which are also found in greenhouses but have short bristle-like antennae and are linked with algae and decomposing organic debris. 
• Female fungus gnats lay tiny yellowish-white eggs on moist soil’s surface. Legless larvae with white or translucent bodies and gleaming black heads hatch from the eggs. Larvae grow to be around 1/4 inch long when fully mature. 
• They evolve into pupae after living in the soil. 
• Pupae are white at first, but they darken as they grow older. 
• The tendency of some fungus gnat larvae to feed on plant roots and lower stem tissues is well documented. 
• These feeding habits can cause plants to become stunted or even die. Fungus gnats are regarded as serious pests that can harm both houseplants and commercial crops. 

Damage

• Adult fungus gnats don’t harm plants or bite people, therefore, their presence is mostly seen as an annoyance.
• Larvae, on the other hand, can damage roots and limit plant growth in high numbers, especially in seedlings and young plants. 
• When high populations were linked with moist, organically rich soil, significant root damage and even plant death were found in interior plantscapes and houseplants. 
• Thus, wilting houseplants could be caused by fungus gnat larvae or (more usually) other reasons for unhealthy  weak roots, rather than a lack of water. 
• Wilted plants are most commonly caused by too much or too little water, root decay fungus, and unsuitable soil conditions (e.g., inadequate drainage or waterlogging).

Migrating larvae

Dark-winged fungus gnats are occasionally seen in large numbers in turf growing in high organic soils and areas with abundant thatch, especially after wet periods. Natural areas nearby and mulched beds may be contributing to the problem. When a large number of eggs hatch close together and the maggots migrate, they may form a snake-like line crawling on top of one another. These are particularly noticeable when walking along a sidewalk or down a driveway.

How to treat fungus gnat larvae?

Management of fungus gnat larvae

• Because the fungus gnat spends the majority of its life as a larva and pupa in organic matter or soil, the most effective control strategies focus on these immature stages rather than the mobile, short-lived adults. 
• Fungus gnat problems can be reduced by using physical and cultural management techniques, such as minimising excess moisture and organic debris.
• This pest can be controlled with commercially available and naturally occurring biological control agents. Insecticides are an important control tool in some commercial plant production, but they aren’t generally suggested for fungus gnat control in and around the house.

• Fungus gnat larvae may be controlled by insect growth regulators, microbials, and other pest control agents put to the growing media. Because most pesticides have little effect on eggs or pupae, you may need to apply them again.
• Because the bacterium Bacillus thuringiensis israelensis (Gnatrol) must be consumed in order to be effective, it can be employed before fungus gnat larval numbers are high. Young larvae (1st instar) are more effective than older larvae (3rd and 4th instars). Bacillus thuringiensis israelensis should be used until fungus gnat numbers begin to diminish. It has no effect on the larvae of shore flies.
•  Apply a drench or use an irrigation system as directed on the label. It is only poisonous to larvae for 48 hours, according to reports.

Conclusion

Fungus gnats (Mycetophilidae and Sciaridae families) are a common pest of indoor plants, particularly where humidity and moisture levels are high. The harmless adults are usually initially observed flying over home plants or gathering at a neighbouring window. Adult gnats that aren’t biting can become a nuisance. The larval stage, which feeds in the soil, is the one that might harm sensitive plant roots. Adults can lay up to 300 eggs in rich, moist soils and live for about a week. During their two-week lifespan, small larvae emerge within 4-6 days and begin feasting on plant roots. Before young adults leave the soil and begin the next generation, the pupal stage lasts 3-4 days. A predaceous mite (Hypoaspis miles), the parasitic nematode Steinernema feltiae, and the rove beetle Atheta coriaria are among the biological control species available for fungus gnats. Because of the semi-aquatic environment in which they dwell, beneficial nematodes and predaceous mites employed to control fungus gnats do not appear to function as effectively against beach flies.