Drain Flies

Signs You Have Drain Flies

What homeowners spot first

1. Tiny gray moth-shaped flies sitting on walls near a sink, tub, or shower
2. Flies hovering or hopping out of a floor drain when you walk past
3. A few flies in the basement laundry sink or utility drain even when nothing is running
4. Steady presence in a bathroom that's wiped down daily but still produces flies
5. Flies caught on a strip of tape laid sticky-side-down over a suspect drain overnight

Drain fly larvae live in the gelatinous biofilm that builds up on the inside of pipes, P-traps, and floor drains. Females lay 30 to 100 eggs at a time in that gunk, and the full lifecycle runs about 8 to 24 days, which is why a few flies can turn into a steady cloud over a week or two. Adults don't bite, don't transmit disease, and rarely travel more than a few feet from where they hatched.

Drain fly control starts with finding the breeding drain, which is almost always biofilm built up inside a pipe or P-trap. We use enzymatic drain foams that cling to the pipe walls and break down the gunk, mechanical brushing when a drain is badly fouled, and an insect growth regulator in the trap to stop the next cycle. Surface sprays alone never solve the problem because the larvae are sitting safely below the water line. New customers start service for $49, and a quarterly plan at $119 keeps the rest of the home covered too.

Why do I have drain flies if my drains aren't clogged?

Drain flies breed in the biofilm on pipe walls, not in standing water, so a drain that flows fine can still grow them. The gunk sits above the water line on the inside of the pipe where you can't see it. In our experience across Boise and Meridian homes, the worst breeding drains are usually basement floor drains and rarely-used guest-bath showers, not the kitchen sink most people suspect.

Will bleach kill drain flies?

Not reliably. Bleach kills a few adults and skims the surface gunk, but it slides past the biofilm too quickly to reach the larvae living inside it. Enzymatic drain foams that expand and cling to the pipe wall for 30 to 60 minutes work much better. If you've already tried bleach twice with no luck, that's the usual sign you need a foam treatment in the right drain.

How do I find which drain is the source?

Lay a strip of clear tape sticky-side-down over each suspect drain at night, leaving a small gap for airflow. By morning the breeding drain will have flies stuck to it and the others won't. Check every drain in the house including basement floor drains, laundry-room utility drains, and second-bathroom showers, since those are the spots most Boise homeowners forget. If you'd rather skip the detective work, call us at (208) 297-7947 and we'll find and treat the source on the first visit.