Summary: The presence of Phorid flies, also known as humpback flies, can indicate that a serious plumbling issue exists. Sometimes, excavation is required to remove contaminated matter under a floor slab caused by a broken pipe.
I often get messages from people who discover small flies in their bathrooms or kitchens. Their notes usually refer to these flies as œdrain flies, but that moniker is a general description of any fly that appears to live near or in drains. The fact is, there is no such specific fly known as the drain fly. There are drain moths which resemble miniature moths with fringed wings, but no drain flies. There are lots of flies that breed in drains like fruit flies, and Phorid flies, but no drain flies.
So, here's the deal. That little fly you have in your bathroom may be telling you that you have a plumbing leak. That's right! A plumbing leak, which we all knows equates to big dollar repair bills. However, before you jump on the phone to call in a plumber, first on the hit list of things to do is collect a few of the flies and have them identified by an expert.
The definition of an œexpert is someone who has the ability to accurately identify the insect. You will need to do some sleuthing to be sure you have the right person. Safest method is to take the bug to your local natural history museum and ask if they have a staff entomologist. That person will give you the Latin name of the bug, its origins and how to breed them. Way too much information, but at least you will know the identification is right. Lots of so-called pest control professionals say they can identify insects, but often get it wrong. Ask them to show you a photo of your bug as proof. If they cannot do that, say a polite œThank you and keep searching. If you live in a city with a good sized university they may have an entomology or biology department head that can provide the identification.
Why all the fuss about identification? It's because certain types of bugs breed in certain types of environments. Not all flying insects like the same surroundings, so knowing your insect will tell you exactly where it may be breeding. No need to replace batteries if the bulb is burned out. Get it?
Okay! Let's say your bug has now been identified as a Phorid fly, also known as a humpback fly. That information tells you that you have a fly that primarily breeds in and feeds on moist decaying organic matter. That narrows it down. If the problem is in the kitchen you could find the breeding spots in any areas where you have fermenting foods, dirty garbage containers, in the opening to the disposal or even in slimy drains. A bigger problem is when you have broken floor tiles or bad grout and dirty mop water has leaked in between and under tiles. Bigger still is when there has been a break in a drain line, especially if that drain line goes into and under the slab. Now we are talking serious repair bills.
The Phorid fly resembles a fruit fly, but lacks the red eye color. These flies measure about 1/8 inch in length and have a humpbacked shape thorax. That's the middle section of the insect. Head, thorax and abdomen. The Phorid is a reproduction champion with females capable of laying forty eggs in twelve hours. Their entire live cycle is only about 25 days, so you can see how a population goes from zero to zillions in a very short time.
One good way of telling if you have Phorid flies is that they run rapidly across surfaces, zig-zagging, rather than immediately flying when disturbed. Most flies instantly take off, but the Phorid fly does this little dance.
Control includes cleaning drain pipes and other surfaces that are dirty. It might help to use a drain snake to dig out clots of hair and other yummy gunk in drains. Do not pour bleach down the drain. Bleach is a sanitizer, not a pesticide. Save your money. You can clean drain lines with a round brush and some liquid detergent.
If these flies have established themselves under tile you need to seriously consider lifting the tiles to dry the sub-surface. Sometimes you might get lucky just by using a dehumidifier or fan to eliminate the moisture. If the problem is a result of a broken pipe under the slab, you really need to think about breaking through the slab and removing the moisture laden soil. Some pest control companies may suggest treating through the slab using a pesticide foam. Give it a try. It is certainly cheaper than excavating. If it works, you are ahead by a few thousand bucks. If it doesn't, at least you tried. Do not try to treat under the slab with liquid pesticides. The mixture will be made up mostly of water and you certainly do not want to put more moisture down. That's like adding fuel to the fire. Foam is mostly air and it won't greatly affect the moisture level.
Now, if you discover you have dancing flies, you'll know what you need to do.