The adults can easily fly or jump from one plant to the next, laying eggs wherever they find moist soil. Adult gnats will lay eggs in the soil, and the larvae (tiny white worms that are barely visible to the naked eye) will feed on roots and other organic matter in the soil. The short answer is no, fungus gnats will not kill your houseplants. Fungus gnats look similar to fruit flies, and I have seen many people mistaken a fungus gnat problem with fruit flies. A fungus gnat infestation can come from anywhere. I also noticed very similar dark silvery bugs in the soil of my outdoor planter. Store unused potting soil in a sealed container. Pour or spray an organic insecticidal soap or a soapy water mix (I use Dr. Bronner’s Baby-mild Liquid Soap) or neem oil mixture into the top of the soil to kill gnats in potted plants. document.write('