Drain flies (family Psychodidae), also known as moth flies and sewer gnats, are—I hate to say—kinda cute. They're all little and fuzzy, and they've got those big ol' Dumbo wings. What's not to love? Well, for starters, if you've seen one, there's a really good chance that a couple hundred of his close relatives are either very nearby or they will be soon. But before you freak out, make sure that the little puddin' you're looking at is actually a drain fly (see left). They are very commonly mistaken for fruit flies. Both are small, hang out in groups, and, in general, piss people off.
The drain fly did not get it's name by accident. No, siree. Drain flies, when they are in the house, most commonly lay their eggs (10–200 of them) in the organic matter (e.g., hair, grease, food, sludge, etc.) that builds up in your drain pipes. When the eggs hatch (after two days or less), the drain fly larvae live in and eat that organic matter for somewhere between 9 and 15 days before emerging as adults. Adult drain flies are most active in the evening. During the day they spend most of their time hanging out on walls and other flat surfaces, which makes it easy to kill drain flies. The adults, if left unsquished, usually live for around two weeks. But don't be fooled into thinking the problem is gone just because the adults have died off or you've killed them. If measures aren't taken to get rid of drain fly larvae and drain fly breeding grounds, you will never be rid of them.
How to Kill Drain Flies in the Drain
First, figure out where they're coming from. This is usually pretty easy. If you've ever seen a drain fly's sad, jerky attempts at flying, you'll know it's not their greatest skill. With this in mind, if you see one, there's a good chance that they're coming from the nearest drain. To find out for sure, grab a piece of tape, lay it sticky side down covering about ¾ of the drain in question, and continue checking it for the next few days. If they are coming from that drain, there should be flies stuck to the tape.
Remove their breeding grounds. First, if you use one, remove and clean the hair catcher. Then grab a pipe brush and a plumbing snake from the hardware store and get to work. Your main goal is to get rid of all the ick that the drain flies might lay eggs in. Use the pipe brush to do what you can to clean the sides of the pipe off. Then use the snake to pull out any clumps of hair or other nastiness that you can get to. Take your time and do a good job. Also, expect to get dirty. It's a gross job.
Pick your favorite drain cleaner. It will be very difficult for you, even with the snake, to get all of the organic matter out of your pipes. So get yourself to the store and grab a jug or two of your favorite drain cleaner. This should get most of the rest of the gunk out of your pipes. Follow the instructions on the packaging carefully and allow the stuff to work for the maximum amount of time. Don't be afraid to do it a couple of times.
It's time to do some plunging. I know it sounds like overkill, but you need to do everything you can to get every last bit of organic matter out of the drain. Before doing this, though, run lots and lots of water down the drain to make damn sure you've flushed down all of the drain cleaner. When plunging, things splatter, and you don't want to get splattered with any caustic chemicals. So run some water and start plunging. Do it for several minutes. When you're done plunging, fill the largest pot you have with water, boil it, and dump it down the drain. Don't burn yourself.
Do some basic maintenance to avoid recurrence. The most important thing you can do is to clean your drains at least once a month. I know it sounds tedious, but you should really do it. Also, if you have a garbage disposal, run it briefly every day. Take your garbage out on a regular basis and keep the can clean. Keep the kitchen clean, too. Don't risk leaving food on plates for long periods of time. Check the water trays under house plants and drain them after watering plants. Patch holes in window screens, and don't leave the doors open. Re-grout tiles in the shower and on the floor. Keep the caulking around the drain clean, as they like to lay eggs there, too. Make sure there isn't any wet lint under the washer. Phew.Further Drain Fly Control
Luckily, drain flies don't bite. They actually pose very little threat at all. There's much speculation that because of where drain flies hang out, they carry all sorts of bacteria and harbor disease. However, there's very little evidence to back this up (I know, seems improbable). What there is evidence for is that if you have a large drain fly infestation, you are at risk of developing bronchial asthma from breathing in dust and body parts from dead drain flies. It's pretty unlikely but possible. Mostly, they're just annoying little pains the ass. Not just inside the house, either. You will probably want to be getting rid of drain flies in the outdoors too. Look around for any decaying matter or standing water. Start with the gutters; drain flies love clogged gutters. They're also pretty big fans of bird baths, outdoor ponds, old tires filled with water, and compost piles. Also, make sure your air conditioner is draining properly.
If you're simply looking for how to get rid of drain flies using pesticides, well, too bad. However, there are a number of products made specifically for controlling drain flies by destroying their breeding grounds. DF 5000 Drain Gel is a super thick gel that's designed to be poured down drains. It uses bacteria cultures and enzymes to break down that lovely organic stuff that drain flies like so much. Drain Gel uses bacillus spores and works the same way. Similarly, Invade Bio Drain Gel uses microbes and citrus oil. Invade Hot Spot is a spray foam that also uses microbes and citrus oil and is good for floor drains and around drain pipes. If you're looking for something to kill the adult drain flies before you start working, Invader HPX (active ingredient propoxur) is worth looking into.
