Fungus Gnats
Sciaridae
Soil Pests & Nematodes Low Risk 2-4 mm (adults)
📖 Description
Fungus gnats are primarily a nuisance pest for adult indoor gardeners, but their larvae can cause significant damage to seedlings and young plants by feeding on roots and root hairs. The larvae thrive in consistently moist, organic-rich soil where they feed on fungi and decaying matter, but they also damage living root tissue. Adult fungus gnats are annoying but harmless to plants. They are one of the most common indoor plant pests, especially during winter when soil stays moist longer.
⚠️ Symptoms to watch for
- Small dark flies hovering around plants or running on soil,Yellowing leaves and stunted growth in seedlings,Root damage visible when repotting,Wilting despite adequate watering,Larvae visible in soil when surface is disturbed
🩹 Treatment
- Allow top 1-2 inches of soil to dry between waterings (organic),Apply Bacillus thuringiensis israelensis (Bti) to soil (organic),Set yellow sticky traps for flying adults (organic),Drench soil with hydrogen peroxide solution (1:4 ratio) (organic),Apply beneficial nematodes (Steinernema feltiae) to soil (organic),Use pyrethrin soil drench (chemical)
🌿 Organic treatments
- Allow top 1-2 inches of soil to dry between waterings,Apply Bacillus thuringiensis israelensis (Bti) to soil,Set yellow sticky traps for flying adults,Drench soil with hydrogen peroxide solution (1:4 ratio),Apply beneficial nematodes (Steinernema feltiae) to soil
🧪 Chemical treatments
- Use pyrethrin soil drench
🛡️ Prevention
- Avoid overwatering — let soil surface dry between waterings,Use well-draining soil mixes,Ensure pots have adequate drainage holes,Top-dress soil with sand or gravel to deter egg-laying,Quarantine new plants and check soil for larvae
🪴 Affected plants
- Indoor Plants,Seedlings,Succulents,Orchids,Herbs,Geraniums
🦋 Natural predators
- Predatory Nematodes,Rove Beetles,Hypoaspis Mites
🌱 Host plants
- Indoor potted plants,Seedlings,Succulents
🔄 Lifecycle
- Females lay 100-200 eggs on moist soil surface.
- Eggs hatch in 3-6 days.
- Larvae feed on organic matter and roots for 10-14 days.
- Pupation occurs in soil for 3-7 days.
- Adults emerge, live for 7-10 days, and begin laying eggs within 24 hours.
- Multiple overlapping generations occur continuously indoors.
📅 Season
- Year-round indoors, especially Fall-Winter
🔎 Appearance
- Tiny, dark, mosquito-like flies that hover around plants and soil surface.
- Larvae are translucent white with black heads, found in the top layer of moist soil.
💥 Damage level
- Low
🔁 Reproduction rate
- Fast
🗺️ Geographic regions
- North America
- Europe
- Asia
- Australia
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