No, fungus gnats do not kill your houseplants. These pests are a nuisance because they fly around the house but rarely destroy your plants. Sometimes, if the infestation is heavy, they may cause root damage but in most cases, fungus gnats will only eat rotting roots.
Fungus gnats adults have a lifecycle of about a week. They lay up to 300 eggs in rich, moist soils and within 4 to 6 days, tiny larvae emerge. They begin feeding on fungi, plant roots, or organic compost during their 2 week period.
Inspect your plants thoroughly before purchasing for any signs of insect pests. Carefully turn up soil near the base of the plant looking for the glossy, clear larvae. Do not buy any plant that has any signs of these gnats.
It is easy to kill gnats in the soil using organic solutions that will not harm your plants or pets and is not toxic to your house environment. Go ahead, choose your favorite solutions, and eliminate these fungus gnats for good!