Question
QUESTION: We have had a 4 mth old problem with drain flies, which began in Sept. We have cleaned all drain traps and are applying a drain gel each night. We even had the city flush our sewer drain at the curb. However, in the AM we find many dead ones around the downstairs sink and 3-4 flying in the house. What else can we do? I feel so frustrated and it does not help knowing they carry disease.

ANSWER: Maunie,

Fortunately drain flies do not carry any diseases, there's a related fly that does but this one does not occur in the US (see http://www.livingwithbugs.com/drain_fly.html for a picture and life history of drain flies). Drain flies are only a nuisance and pose no health threat whatsoever. Have you had your flies identified? There's two similar-looking flies that often occur in homes in large numbers, fungus gnats and drain flies. If you have cleaned out the drains thoroughly it may be fungus gnats that's the problem. Usually when the drains are cleaned drain flies will go away. Fungus gnats develop in soil so are often associated with potted houseplants, especially plants the are frequently watered (see http://www.livingwithbugs.com/fungus_gnat.html for a drawing of a fungus gnat). Do you have potted houseplants near where you are finding the flies?

Post a follow up and I'll help you figure this out.

Jack DeAngelis
http://www.livingwithbugs.com



---------- FOLLOW-UP ----------

QUESTION: I questioned our county extension service re. drain flies. I was told that if they have a black body, they most likely are drain flies. As far as the gnats, the only plants I have are a cactus, ivy, fushia and mother in laws tongue. So far, I have not seen any flies around them. The flies seem to like to hang around the bathroom and kitchen. I have enclosed containers for all my cereal, cookies, etc. In addition, I was my dish scrubbers nightly in the  dish washer. I clean the toaster tray as well.
I also use the drain packets for disposals sold at Home Depot.What else can I do? I know there is probably something I have not thought of. Oh, yes,My husband really cleaned our sump pump but they don't seem to come from there, but then there is a lot to know about these little buggers.
Any more info would be appreciated, and thank you for getting back to me
so quickly.

Answer
Fungus gnats also have a black body but your description of where you find the flies does sound like drain flies, unless you have houseplants in these rooms. Neither fly will infest cereals, etc., so no concern there. Try this - when you are not using the sinks place wet rags over the drain and in the overflow to seal them. If this reduces the number of flies you see you'll know for sure that this is where they are coming from. Likewise, if you can move the houseplants to a room that can be closed that might tell you something as well. I'm still not convinced these are drain flies. Post a follow up.

Jack DeAngelis
http://www.livingwithbugs.com