Original illustration by PestControlBasics.com. Use anatomical labels above to confirm your identification.
🔍 Identification
1.5-3mm; very dark grey to black; hairy body and wings; wings held tent-like over body at rest (gives a moth-like appearance); poor, erratic flight. Found near sinks, tubs, and floor drains. The hairy wing texture distinguishes them from fruit flies under a hand lens. Flight is weak and bouncing, not the smoother flight of fruit flies.
🧬 Biology & Behavior
Drain flies breed exclusively in the biofilm inside drain pipes — not in standing water or food. The gelatinous organic biofilm coating drains is both food and habitat for larvae. Bathrooms with infrequently-used drains accumulate biofilm fastest. Adults emerge from drains continuously as long as biofilm provides breeding habitat.
⚠️ Damage & Health Risk
Psychological disturbance; nuisance. No disease transmission, no food damage. Their presence indicates drain biofilm buildup.
🔧 DIY Treatment
Enzyme drain cleaner (not bleach) applied weekly for 6-8 weeks breaks down biofilm. Test breeding drains: place tape sticky-side-down over the drain overnight — adults caught on tape confirm which drain is breeding. A stiff drain brush weekly physically removes biofilm. Bleach is ineffective — it kills surface bacteria but doesn't dissolve the physical biofilm matrix.
👷 When to Call a Pro
Rarely warranted alone.