You may have noticed tiny, black, fly-like creatures that like to hover around your houseplants. They can be very annoying and might have you concerned. Luckily, these fungus gnats do not typically harm the plants and can be easily taken care of with a few preventive measures and Harris Potted Plant Insect Traps.
Identification
Fungus gnats are small flies that are about ⅛ inch long. They are attracted to potted plants because of the moist soil and decaying plant material. Once they have found a place with plenty of moisture, they will lay their eggs in the soil. When the larvae hatch, they feed on fungi in the soil, which is how they get their name. Fungus gnat larvae are about ¼ inch long with an elongated whitish body and shiny black head. Occasionally they will eat the rotting roots of the plant, but they seldom do damage. Fungus gnats are often confused for fruit flies, but these two household pests are usually found in different areas. Fungus gnats will stay near house plants, while fruit flies will be around decaying fruits and vegetables.

Fungus Gnat by user B. Schoenmakers at waarneming.nl, a source of nature observations in the Netherlands. CC BY (https://creativecommons.org/licenses/by/3.0)
Fungus Gnat Control
Fungus gnats can enter homes on plants, in potting soil that has been infested, or through open doors and windows. Fungus gnats thrive on excess moisture in the soil of your potted plants, so it is very important to avoid overwatering. To do this, make sure that you allow your plants to dry out a bit before watering again. You don’t want them to be so dry that the plants are wilted, but you definitely do not want the soil to be wet still. It is also important that your soil and containers have good drainage. Along with these watering tips, you can also try the following to prevent fungus gnats:
- Use a sterile potting soil when planting or re-potting your plants. It is very tempting to reuse potting soil, but if there are eggs or larvae already in the soil, you will exacerbate the problem.
- Use soil covers like gravel, sand, or moss on the top of your potting soil. This will help prevent the gnats from laying eggs there.
- If you currently have fungus gnat problems, replace the top one inch of the soil with new, sterile soil.
- Store opened potting soil in a sealed container so that it does not become infested.
- Check any plants that you buy or move inside to ensure that there are no eggs or larvae in the soil.
- Use sticky traps in your potted plants. These will catch the adults and reduce the amount of eggs in your soil. Check the traps often and replace them when needed.
For more help with flies, check out How to Use Harris Potted Plant Insect Traps and Flies: The Ultimate Guide.
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