Thin White Bugs in Potting Soil

Written by tracy hodge
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Thin White Bugs in Potting Soil
Fungus gnats gravitate toward light and are often seen swarming around windows. (Thomas Northcut/Lifesize/Getty Images)

You may be dismayed to find thin, white bugs living in the potting soil of your beloved indoor plants. These bugs are the larvae of fungus gnats, which typically live in soil and feed on organic matter. While fungus gnats do not sting or bite, they are often a nuisance because they frequently swarm when indoor plants are bumped or moved.

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Fungus gnats are also commonly referred to as darkwinged fungus gnats. The adult form of these fly-like insects are members of the Bradysia genus and live in the soil of indoor plants. Fungus gnat larvae are thin, white wormlike pests that are often visible in the top layer of potting soil. Fungus gnat larvae thrive in very wet soil, making them a common pest when plants are routinely being overwatered. Fungus gnat larvae mature rapidly and transform to their adult form within three weeks.


Fungus gnats living in indoor plants often feed on the roots of the plant, causing brown scars to form on plant roots. The roots of infested plants may also have a chewed appearance and the root hairs may be entirely consumed. Adult fungus gnats have a very short lifespan, only living approximately seven to 10 days. During this time, adult fungus gnats place eggs in the soil of indoor plants. When these eggs hatch, the white larvae feed on host plants. Fungus gnats often become a nuisance because they multiply rapidly. Each female fungus gnat places up to 300 eggs in several batches and the eggs typically hatch within six days. When infested houseplants are disturbed, adult fungus gnats swarm for several minutes before resting back onto the host plant.


Using sterile potting soil will prevent fungus gnat infestations in your houseplant. Avoid overwatering your plant, as this promotes fungus gnat development. Many plant owners continue watering their houseplants during the winter, with the same amount of water required in the hot, summer months. This results in excessive moisture in the potting soil, a condition that attracts fungus gnats. Repot your plants every so often, placing fresh soil in the pot. If you place your houseplants outdoors, always inspect them thoroughly for fungus gnats before bringing the plant back indoors. Quarantine and inspect any new plants for insects for seven to 10 days before bringing them into your home.


Hanging yellow sticky traps over your indoor plants may help capture adult fungus gnats. Insecticides are available at your local garden centre for fungus gnat control. Sprays available for flying insects may help eliminate fungus gnats indoors. Repeat the application if necessary for continued control. Strong insecticidal sprays with the active ingredient BT or Bacillus thuringiensis are often effective in eliminating fungus gnats, as well.

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