Fungus gnats like any other harmful insects can destroy your houseplants.
These very tiny and dark-colored flies are approximately two to five millimeters long and thrive in damp places.
The average lifespan of this fly is only one week to 10 days.
However, females can produce a maximum of 200 eggs.
Maggots devour plant roots and other fungi in the compost.
These grow fast in a span of two to three weeks.
While fungus gnats do not affect the plant's growth, these can cause a lot of irritation.
Hence, it is important to learn how to deal with these insects.
Here are some suggestions that can help you control or prevent gnat infestation:

• See to it that your soil conditioner is completely dry between watering schedules.
  These insects love humid conditions so avoid excessive watering.
  This will help control the growth of fungus gnats in ordinary conditions.
  
• Put an additional layer of sand above the compost.
  This should be done right after the process of re-potting.
  These flies will find it hard to go through the sand so adults cannot get inside the compost and the young gnats will not break out from the soil.
  It works with certain plants but not with others.
  This technique is more effective for plant pots with sunken drain holes.
  If the apertures are hollow, the gnats will not be able to go in and out easily.
  
• Try to water plants from the base.
  You can place water on the tray or inserted a hose into the fertilizer while placing a cap at the top of the hose.
  Pour water and replace the cover afterwards so the insects cannot move freely while the compost remains dry.
  
• Cheap adhesive fly traps are also effective.
  You can buy these traps in grocery outlets.
  Place some of these gummy insect catchers near your plants.
  Adult gnats are attracted by the yellow color and fly straight to the paper.
  Nevertheless, this can only be a temporary solution since it cannot stop gnats from laying additional eggs.
  
• Spray your houseplants with neem oil.
  This is vegetable oil obtained from the evergreen tree which is often used for herbal medicines and organic farming.
  A lot of plant growers use this oil and believe in its fast effects.
  Some of them combine a mild solution of water and neem oil and spray the plants.
  However, there are people who say that makes the compost damp which in turn attracts more insects especially fungus gnats.