Tiny flies appearing around bathroom sinks, tubs, or shower drains can be frustrating. Many Indiana homeowners notice them suddenly, often after humid weather, plumbing changes, or seasonal shifts. These insects rarely signal serious danger, yet their persistence can create concern about sanitation, plumbing health, or household hygiene.
Understanding why they appear requires looking at indoor moisture, regional climate patterns, plumbing design, and insect biology. Once you understand what causes these flies, controlling them becomes much easier.
What Those Tiny Bathroom Flies Usually Are
Drain Flies Are the Most Common Cause
In most Indiana homes, the small flies seen hovering around bathroom sinks, tubs, or shower drains are drain flies, often called moth flies or sewer flies. These insects are tiny, usually gray, tan, or light brown, with fuzzy wings that give them a soft mothlike appearance. They tend to rest on bathroom walls, mirrors, tile surfaces, or fixtures where moisture is present, often remaining still for long periods before fluttering short distances.
Drain flies breed inside the slimy organic layer that gradually forms along the interior surfaces of plumbing pipes. This layer develops from everyday household residue including soap scum, toothpaste particles, skin cells, hair, bacteria, and cosmetic products. Over time, these materials combine with moisture to create a biofilm that provides both food and protection for developing larvae. Because this process happens slowly and out of sight, homeowners often do not realize it is occurring until adult flies begin appearing…