Shore Flies and Root Aphids

📐 FIELD GUIDE ILLUSTRATION

Fungus Gnat (Bradysia spp.) identification illustration with labeled anatomical features — PestControlBasics.com

Original illustration by PestControlBasics.com. Use anatomical labels above to confirm your identification.

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PestControlBasics Editorial Team

Reviewed by Derek Giordano · Updated 2026

🔍 Identification

Shore fly (Scatella): 3-4mm; darker than fungus gnat; short antennae; white spots on wings (diagnostic); runs rapidly across surfaces rather than flying weakly. Breeds in algae on wet surfaces (irrigation lines, wet benches, algae mats), NOT in potting soil. Bti doesn't work. Root aphid: 1-2mm; soft-bodied; waxy white coating; found on roots when plant is removed from pot; aerial plant shows wilting, yellowing, and slow decline with no visible cause.

🧬 Biology & Behavior

Shore flies: Breed in algae — treatment must target algae elimination, not soil. Bti that kills fungus gnat larvae has no effect on shore fly larvae in algae. Root aphids: often confused with root mealybugs; both are underground; root aphids move and have distinct body shape; caused significant losses in cannabis, lettuce, and ornamental production.

⚠️ Damage & Health Risk

Shore fly: nuisance; potential pathogen transfer on feet. Root aphid: significant plant decline, yellowing, stunting; root system destruction; economic losses in commercial production.

🔧 DIY Treatment

Shore fly: eliminate algae with 10% bleach solution on surfaces; improve drainage and air circulation; copper-based algaecides on growing surfaces. Root aphid: imidacloprid soil drench; pyrethrin root drench; complete removal and replacement of growing media with sterilization of containers.

👷 When to Call a Pro

Commercial greenhouse: professional IPM program targeting specific organisms with correct products — misidentification causes significant product waste and crop loss.

❓ FAQ

How do I know if I have fungus gnats or shore flies?

Check the wings: shore flies have white spots on dark wings — visible with magnification. Shore flies run rapidly across surfaces; fungus gnats fly weakly. Check where adults concentrate: near wet algae-covered surfaces = shore flies; near moist soil = fungus gnats. This matters because the treatments are completely different.

What causes root aphids?

Root aphids can be introduced through soil, transplants from infested growing operations, or ants (ants farm root aphids as they do aerial aphids). In cannabis production, root aphids are an increasingly common and serious problem. Inspect roots of any transplant before adding to your growing space.

🪰 Shore Fly & Root Aphid — Misdiagnosis Guide