Sewer Fly Larvae: What They Are and Why You're Seeing Them Sewer fly larvae are the worm-like, legless offspring of drain flies (family Psychodidae) — small, fuzzy, moth-like insects that breed inside the organic slime coating your pipes and drains. If you've spotted tiny pale wrigglers near a drain, here's what you need to know at a glance: Feature Detail Size 4 to 10 mm long Appearance Translucent/pale, legless, dark stripe on back Where found Shower drains, sink P-traps, t