Gnats in the Home

It is a world out there just FILLED with bugs, and the casual visitor to this world of bugs and pest bugs is not expected to know and understand each kind that may enter their home, or be seen in their garden. That’s the purpose of these pages on BugInfo – to help you recognize some of the ones you see more often than others, and to decide whether or not some action is needed on your part. So often the critters are just wayward bugs that accidentally found their way inside, and should be gently ushered back out. Often they are highly beneficial bugs that pose no danger to you or your home, but instead offer some benefit by their existence, and definitely should be left outside where they belong.

Very often, though, people and bugs do clash, as our homes provide many opportunities for pesky bugs to cause us problems, even if it is just a nuisance level. Some of those nuisance bugs can even be a SIGN to you that some other kind of problem exists in your home, perhaps a sanitation concern that you would like to address anyhow. A few of the tiny flies that we will call “gnats”, for the purpose of this article, fall into this group, and we are going to talk about two of them – fungus gnats and drain flies. These are both flies, with several species in each basic grouping, and their common names are given to them for good reason. Fungus gnats seek out damp places where tiny bits of mildew or mold may grow, and drain flies look for places where there is a buildup of wet goo, for this is the material their larvae will feed on. In a home there can be many opportunities for these flies, telling you by their presence that some dampness exists that needs to be addressed.

The Fungus Gnats:

Fungus gnats are some of our tiniest flies, with thin, dark bodies that end in a point and a pair of tiny, clear wings. They have no ability to bite or otherwise harm us, but if the conditions are just right for them their numbers can grow to very high levels. As nearly all flies do these gnats undergo a life cycle that begins with eggs deposited by the adult flies. Since the larvae will feed on mildew and fungi of some sort the adult flies look for the damp conditions that will grow this food resource. The eggs hatch to the larval stage and the larvae progress through several stages, feeding on the fungus around them. Finally they change to the pupa stage and then emerge as new adult flies. The life cycle can be a rapid one for these small insects. When everything is perfect – plenty of food, a warm setting – the complete cycle from egg to adult fly can happen in less than 2 weeks, so a rapid buildup of gnats can occur quickly.

Inside the home a common place to find perfect conditions for fungus gnats will be house plants, more specifically the soils these plants grow in. We have a tendency to love our plants too much, and commonly over-water our plants, keeping the soil wet continually. The soils usually are high in organic matter, and this combination of moisture and organic matter is a perfect invitation for fungi to grow. It does not necessarily have to be a big mushroom growing up out of the soil, as the gnat larvae are tiny, and will find the minute bits of fungus growth within that medium. Allowing the soils in these pots to dry out on a regular basis is not only a good way to prevent the growth of fungi and fungus gnats, but it may also be better for the plants themselves. Their roots need to “breathe”, and one way we stress or even kill our plants is by keeping their roots immersed constantly in water.

There may be other possibilities indoors as well, such as areas beneath or around leaking plumbing, perhaps under the kitchen sink or, worse, within walls where pipes and fittings may have begun to leak. It could be carpets or other flooring below windows that are leaking rainwater inside, catch pans under the fridge, mildew growing on or below a window sill that has condensation dripping down off the window continually in the winter. Just think of all the places in your home where water can be, and these all offer the possibility that the water may be escaping onto surfaces and growing the fungi needed by fungus gnats. The control, obviously, is to eliminate that water problem, for it definitely is a “problem” that needs to be corrected.

If you believe the gnats are coming from some hidden locations, such as wall voids, you may want to contract with a licensed termite company to do a home inspection. They are trained to look for the problems caused by excessive moisture conditions, for this also can be a means for wood decay fungi to begin growing, or to attract certain kinds of insects that may damage the wood, such as termites or carpenter ants. If you have a crawl space beneath the home it is common for the soil there to remain damp all the time, again creating the conditions that favor either fungus gnats or possibly decay fungi. A home should be dry, and the presence of a lot of fungus gnats indoors may be telling you that moisture problems are there. These flies could also be coming from the outside, for damp conditions around the exterior also are perfect for their breeding. The adult flies are attracted to lights and may simply be entering each time a door is opened, but if they are indoors it is worth investigating.

One very strange phenomenon that happens only rarely, but perhaps you would be the one to stumble upon it, is a mass migration of the larvae of fungus gnats. This may happen when some area of the soil is just perfect for the development of large numbers of the fungus gnat larvae, and some stimulus then causes them to migrate out in a massive stream of hundreds or thousands of larvae, all moving along like a tiny river. It is thought this could coincide with the larvae reaching their mature stage and needing to find a drier area to pupate, but the exact reason is not known. When this is seen the larvae are sometimes referred to, incorrectly, as “army worms”, because of this uniform march. However, true armyworms are moth larvae that feed on plants, and are unrelated to these fly larvae.

The Drain Flies:

Our second gnat is the drain fly, also called a “moth” fly because it may resemble a tiny, gray, hairy moth. We can recognize them as flies, though, by the single pair of wings, whereas moths have 2 pairs of wings and look very different. The drain flies are usually no larger than about 1/8 inch long, with their thorax and wings covered with gray hairs. They fly in sort of a zig-zag motion and often then just PLOP down onto a wall or door. They may be found commonly in bathrooms, as this is where a lot of moisture exists that may attract them. When they are sitting on a surface they hold their wings flat over their abdomen.

Unlike the fungus gnats, which manage to breed in simply damp conditions, the drain flies need a much larger buildup of material, and over time our sink, floor, or bathtub drains can provide this micro-habitat for them. As hair and many other things get washed into sinks there eventually will be an accumulation that could even become a complete plug in that drain. This area remains continually wet, with organic buildup coating the sides of the pipes below the sink, and drain flies look at this as just heavenly. Their presence in a room such as the bathroom is a sign to you that some cleaning is necessary, and that is really how the control of drain flies will be accomplished.

For control of these gnats and most other nuisance flies we cannot focus on controlling the adult fly. Of course, if you simply have a few big flies buzzing around in the kitchen because someone left the back door open, a fly swatter is the perfect control device. But, for flies that we believe may be breeding within the structure itself our control MUST focus on controlling the larvae, by eliminating the conditions that allow them to live there. Simply swatting or spraying to kill the adult flies may give us temporary relief and satisfaction, but they will quickly be replaced by new flies coming from that larval habitat. For fungus gnats and drain flies there is no reason to set off bug “bombs” in the home, and very little reason to use other kinds of aerosol foggers to spray in the air. You need to take that careful walk through the home and find out where the flies are coming from, and then fix the problem that must be there.

Drain flies are controlled by cleaning the drains or other areas of organic buildup, and professional pest management companies have a wonderful arsenal of products that do this very effectively. These are not harsh and dangerous drain cleaners, but are products that use bacterial or enzymatic action to actually EAT the organic buildup and allow it to be washed away. It may take a few days to a week, but the result is far friendlier to the environment and to your family than the use of caustic cleaners. A service that provides retreatment of the drains in the structure on a regular interval can keep things clean and flowing, and keep insects from looking at your home as their home too.

One theme you will find in nearly every BugInfo article, where we address a pest concern, is that pesticides may not always be the answer, and rarely are the ONLY answer to the problem. Your goal is living without pests in the home is to find that long-term answer, and that will happen only when you change the conditions that brought that pest there in the first place. If we want to apply a name to this we would call it “integrated” pest management, in which you address the reasons for the pest presence first, fix those reasons so they no longer occur, and then use pesticides as needed to eliminate pests that still linger there. Pesticides are very useful tools that can be used effectively and without risk to you, your family, or your pets. However, they are best left in the hands of those who have training in their use, and these are the licensed professionals. You can look for a pest management professional in your immediate area by going to the “Find a Pest Management Company” heading on BugInfo.