Fungus gnats are small black flies that resemble mosquitoes. They feed on fungus and rotting organic plant matter in potting soil. Though they don't bite or sting humans, they can damage and kill plants. Fungus gnats' offspring are white-bodied larvae with black heads that you may find in your potting soil. Left untreated, the larvae may attack the roots and stems of your plants if there's no fungal food. Left untreated, fungus gnats will spread from plant to plant in your home. Learn how to kill fungus gnats.
Purchase an 18-watt Insectalite Fly Trap to kill fungus gnats (see link in Resources). This trap uses ultraviolet light and pheromones to attract these pests.
Use a pyrethrin spray or aerosol to knock down and kill fungus gnats. Make sure the label states the product is for "gnats." One example of a product you can use is Garden Safe All Natural Houseplant & Garden Insect Killer (see link in Resources).
Use yellow sticky traps to monitor and kill fungus gnats in your home. You can lay these non-toxic traps across potting soil. Or, you can hang them up to catch even more pests besides fungus gnats. One example of a yellow sticky trap can be found at planetnatural.com (see link in Resources). Or, you can make your own (see link in Resources).
If you use only sterile potting soil, you shouldn't have a problem with fungus gnats.
Read and follow the directions on products to achieve the best results, and use them safely too. Fungus gnats breed in moist potting soil. Avoid overwatering your house plants to help keep their populations down. Allow the soil to become dry before you rewater.