Fungus gnats — the pest that says you're overwatering
Fungus gnats are one of the most common indoor plant pests — small flying black insects that resemble tiny mosquitoes or fruit flies, hovering around the soil surface or near your face. Fungus gnats are a signal that the soil is staying too wet for too long, which creates the moist conditions they need to reproduce. The adult gnats do not harm the plant, but their larvae live in the soil and feed on fungi and organic matter — and in severe infestations they may also nibble on delicate root hairs.
What to look out for
- Flying insects near the soil — Tiny black flies hovering around the plant, or flying up when you move the pot or water it.
- Insects crawling on the soil surface — Before they fly, fungus gnats often run quickly across the top of the potting mix.
- Slow plant growth (rare) — In heavy infestations, larvae in the soil may damage delicate root hairs, causing slight wilting or slower growth.
Examples of fungus gnats in real homes
How to treat them
- Allow the soil to dry — Without consistent moisture the larvae cannot survive and the adults cannot lay new eggs. Push a tampon into the soil overnight to absorb excess moisture, water only once the soil has dried enough for the plant's group (see the Water guide), move the plant to bright indirect light so the soil dries faster, and use a fan — or the AC on fan mode — to keep air moving.
- Apply mosquito bits — Sprinkle Mosquito Bits over the soil surface. As you water, they gradually release BTI — a natural bacterium — which kills fungus gnat larvae in the soil.
- Water bottom-up — Instead of watering from the top, sit the nursery pot in a tray of water for about 15–20 minutes so the plant absorbs moisture from below. This keeps the top layer of soil dry — which is where gnats typically lay their eggs.
- Add a barrier — A thin layer of sand or fine decorative stones on the soil surface helps stop adult gnats reaching the moist soil to lay eggs.
- Use yellow sticky traps — Place yellow sticky traps near the affected plant to capture adult gnats and reduce their population.