If you've noticed tiny moth-like flies around your shower drain, the good news is that they won't bite and don't carry disease. The better news is that a thorough cleaning and a few simple steps can eliminate these tiny intruders.
What are drain flies?
Drain flies, or moth flies, resemble tiny moths. They're between 1/16 and 1/5 of an inch long and have moth-like wings and tiny hairs that give them a fuzzy look. They don't fly far or gracefully, and feed on organic material that builds up in sink and shower drains. The small white or grayish worms in an infested drain are drain fly larvae.
Locating a Drain Fly Infestation
The first step to evicting drain flies is identifying the source. Because the flies can establish a breeding ground in a sink, shower, or toilet, you'll want to either determine their exact home base or treat your entire bathroom.
To find out whether drain flies have made themselves at home in a particular drain, coat the inside of a margarine or other lightweight plastic container with petroleum jelly and leave it over the drain at least overnight. If that's where the flies are coming from, you'll find them stuck in the petroleum jelly.
Eliminating Drain Flies
Open the drain and remove the drain trap.
Thoroughly scrub inside the drain down to bare metal with wire brush.
Flush the drain with bleach and boiling water
Scrub and replace the drain trap and drain cover.
You can substitute commercial drain cleaning preparations for bleach, but cleaning out the organic deposits in your shower drain is an essential step. No amount of flushing with any preparation will eliminate the flies without removing their breeding spot.
After your shower drain is thoroughly cleaned, adult flies can be eliminated with insect-killing spray. If you prefer not to use this, the adults will die in about 20 days, and if you've succeeded in eliminating the decaying matter in the drain, no new flies will appear.