Bry.Rip Plant Guide
Fungus Gnats — photo 1
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Fungus Gnats 🐛

Minor Pest also: soil gnats, dark-winged fungus gnats

Affects these houseplants: African VioletAlocasia PollyAloe VeraAnthuriumBaby Rubber PlantBird's Nest FernBoston FernCebu Blue PothosChinese EvergreenChinese Money PlantChristmas CactusDieffenbachiaHeartleaf PhilodendronJade PlantLucky BambooMarble Queen PothosMoney TreeMonstera AdansoniiNeon PothosNerve PlantPhalaenopsis OrchidPhilodendron BirkinPhilodendron BrasilPhilodendron MicansPolka Dot PlantPothosPrayer PlantRattlesnake PlantSatin PothosSpider PlantString of PearlsStromanthe TriostarSyngoniumZZ Plant

Family Sciaridae (dark-winged fungus gnats)

At a glance

  • Looks like: Tiny (2–4 mm) black flies drifting around the soil and lower leaves
  • Tell-tale sign: A puff of little flies when you water or disturb the pot
  • Severity: Nuisance — mostly harmless to healthy plants; a symptom of overwatering

How to identify

Small, dark, mosquito-like flies that hang around the soil surface and scatter when disturbed (unlike fruit flies, which orbit fruit and the kitchen). The harmless-looking adults aren’t the issue — it’s the larvae in the top inch of soil, thin translucent maggots with black heads that feed on fungus, organic matter, and occasionally fine roots in consistently moist potting mix.

Damage

Adults are a nuisance only. Larvae can nibble seedling and fine roots in heavy infestations, but on established plants they’re mostly a sign that the soil is staying too wet.

Treatment (least-toxic first)

Following Integrated Pest Management:

  1. Let the soil dry out: The single most effective fix — allow the top 1–2 inches to dry between waterings. This kills larvae and breaks the cycle. See Watering & Root Health.
  2. Trap the adults: Yellow sticky traps flat on the soil catch egg-laying adults and let you monitor numbers.
  3. Treat the larvae: A BTI drench (Bacillus thuringiensis israelensis — “mosquito bits” steeped in water) targets larvae and is safe for plants/pets. A top dressing of sand or fine gravel also blocks egg-laying.
  4. Bottom-water for a while so the surface stays dry.

Prevention

Don’t overwater. Use fresh, well-draining mix; avoid leaving standing water in saucers. Bottom-water plants prone to gnats.

Affects (in this guide)

Pothos and any plant kept in chronically moist soil — it’s a watering issue more than a plant-specific pest.

Sources