Feb 2, 2012 – Home Is Where The Crud Is?
QUESTION:
I went on a fly job last fall and was informed that the home was infested with 200-300 flies for the past couple of weeks. I expected to find the usual fly - fruit fly, phorid, or drain fly. I was also informed that another company had treated the area before me. I am sure I looked in the same spots he did, which were sink drains, under the sink, washing machine lines and drains. I was unable to find any signs and inspected the rest of the house. As I came into the front room on the south-facing wall, on the outside of the electrical outlet, I spotted a couple 1/8 inch flies. I took off the outlet cover and sprayed a flushing agent behind the outlet. Within ten minutes, thirty flies came out of the outlet and died. I removed the outlets and dusted inside and behind the outlet boxes and after a week this seemed to resolve the problem. But I still have remaining questions. What organic material could they be feeding on and breeding in behind the wall? Could this be a foundation leak? Could this be an underground sewer leak? And, could they reappear in the spring due to temperature change? Feedback is much appreciated.
ANSWER:
One thing that was missing from your question was the species of fly that you discovered, and this is very important in determining the possible breeding sources or other reasons for the presence of these flies. If you had not suggested you were expecting small flies like phorids or drain flies I would have said that this sounds like a classic Cluster Fly problem. But these much larger flies don't look anything like the small, orange phorids or gray, hairy drain flies. Cluster flies are larger than house flies, have distinguishing short, curly golden hairs all over their thorax, and commonly overwinter within the walls or attics or other voids in structures. Since your first call came in the fall, and you are in the Northeast, this would be very characteristic of Cluster flies. If it turns out that these are the larger cluster flies then there isn't necessarily any sanitation problem within this home. The flies are just opportunistic and found a way into this home to spend the cold winter months.
View past Ask Mr. Pest Control questions.
I went on a fly job last fall and was informed that the home was infested with 200-300 flies for the past couple of weeks. I expected to find the usual fly - fruit fly, phorid, or drain fly. I was also informed that another company had treated the area before me. I am sure I looked in the same spots he did, which were sink drains, under the sink, washing machine lines and drains. I was unable to find any signs and inspected the rest of the house. As I came into the front room on the south-facing wall, on the outside of the electrical outlet, I spotted a couple 1/8 inch flies. I took off the outlet cover and sprayed a flushing agent behind the outlet. Within ten minutes, thirty flies came out of the outlet and died. I removed the outlets and dusted inside and behind the outlet boxes and after a week this seemed to resolve the problem. But I still have remaining questions. What organic material could they be feeding on and breeding in behind the wall? Could this be a foundation leak? Could this be an underground sewer leak? And, could they reappear in the spring due to temperature change? Feedback is much appreciated.
ANSWER:
One thing that was missing from your question was the species of fly that you discovered, and this is very important in determining the possible breeding sources or other reasons for the presence of these flies. If you had not suggested you were expecting small flies like phorids or drain flies I would have said that this sounds like a classic Cluster Fly problem. But these much larger flies don't look anything like the small, orange phorids or gray, hairy drain flies. Cluster flies are larger than house flies, have distinguishing short, curly golden hairs all over their thorax, and commonly overwinter within the walls or attics or other voids in structures. Since your first call came in the fall, and you are in the Northeast, this would be very characteristic of Cluster flies. If it turns out that these are the larger cluster flies then there isn't necessarily any sanitation problem within this home. The flies are just opportunistic and found a way into this home to spend the cold winter months.
The presence of a few cluster flies sitting on a wall inside the home also would be normal, as warmth from the home's interior could activate them, or if you had a warm spell outside it could warm them up enough to get them moving around. However, if these did turn out to be one of the small flies then proper ID is still critical to control, and finding a lot of them within a wall would be pretty unusual. Whether they are phorids, drain flies, or even vinegar flies (which would be REALLY unusual in a wall) it hints of something in there that they could be breeding in, and this would be a very wet area where organic material has built up. Both phorids and drain flies can breed in the same settings, but it is going to be a sloppy wet one. If they actually are breeding within that void then a plumbing leak would be possible. If they are only in there because they moved to that spot from some other nearby breeding site then it is also possible that plumbing under a slab or in the soil is leaking and creating a soupy situation for their larvae. A leak from the outside due to some breach in the foundation could, I suppose, also be possible, as anything that creates excessive moisture could create the proper conditions for these small flies.
But, identification is oh so important, and it still sounds more like a classic cluster fly problem. A neat tool that I think would be perfect for this and for so many other jobs, where you need to look inside a hidden void, is a remote camera on an extendable and flexible tube, and one of the major Big Box stores has had this on their shelf for a year now for only $100. You slip the tube into that void and view the scene inside on the screen that you hold in your hand. Now you may be able to see if there is any obvious sign of dampness and growth of fungus or buildup of junk. You also can see if there are any other flies hanging out in there. This seems like such a great tool for the PMP that takes away a lot of the guess work.
If these are cluster flies and you did not kill all of them, then yes, some will try to reappear once the weather warms and they need to get back out. If they are one of the small flies breeding in organic sludge, and that sludge and the cause of it are not repaired, then yes you will continue to have the flies breeding in it and appearing as the adult flies.
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