Aphids vs Fungus Gnats: How to Tell Them Apart

Aphids and fungus gnats are different insects with different habits. Aphids are soft-bodied plant-sap feeders that often cluster on new growth and leave sticky honeydew. Fungus gnats are tiny, mosquito-like flies whose larvae live in moist potting mix or other damp organic matter. Identifying which you have decides the fix.

Side-by-side identification

	Aphids	Fungus gnats
Where you see them	On stems and leaf undersides; often in groups	Adults flying near soil, windows, or lamps; larvae in moist media
Body	Pear-shaped; cornicles (tiny tubes) at the rear of many species	Slender, dark, long legs; adults look mosquito-like
Signs	Honeydew, sooty mold, curled or distorted leaves, cast skins	Adults rising from wet pots; larvae in damp soil
Main harm	Sap feeding; virus transmission on some crops	Mostly nuisance indoors; larvae feed on fungi/organic matter and may nick fine roots

Sources: UC IPM — Aphids; Maryland Extension — Fungus Gnats; UC IPM — Fungus Gnats; household ID: Maryland Extension ID guide.

Fungus gnat control (brief)

Let potting mix dry between waterings as the plant allows; empty saucers.

Use yellow sticky cards to monitor adults.
If needed, use a Bti (Bacillus thuringiensis israelensis) product labeled for fungus gnats in soil.
Check drains if you have no plants—see fungus gnats with no plants.
Do not assume outdoor-only products or unlabeled sprays are appropriate indoors—see does Sevin kill fungus gnats and spinosad for fungus gnats.

Aphid control (brief)

Hose or wipe aphids off sturdy plants; prune heavily infested shoots.
Protect natural enemies; manage ants that farm honeydew.
If needed, use insecticidal soap or horticultural oil labeled for the plant and pest—thorough coverage matters; avoid drought-stressed plants and extreme heat.
Skip broad “spray everything” lists that ignore labels.

Source: UC IPM — Aphids.