Problems & Solutions, April 2000

Q. I have had several complaints from customers about large flies being found throughout their houses. This is the first time we have experienced this. What could they be? (T.S., Pa.)

A. The first step is to establish what type of flies these are — my first thought is cluster flies. These flies will overwinter in a structure and come out during the winter when we have a few warm days. This winter has caused many of these complaints. The second possibility is that this is another overwintering fly, the black blowfly, which can overwinter in structures in the Northeast. These flies are bigger then cluster flies but are responding to the same stimulus as the cluster fly — warm temperatures. The presence of blowflies does not mean that there is a source of breeding in the structure. At this time of the year their presence is most likely due to overwintering.

Control should incorporate light traps. For cluster flies, place the light traps in attics where the flies are likely harboring. Applications of aerosols or dust into voids around windows and walls can affect those possibly harboring in these voids. Applications of residual pesticides around windows and eaves can reduce the number of flies next year. For cluster flies, it is important to do this application in late summer. Caulking and sealing opening around doors and windows can also reduce the possibility of the flies entering the structure.

Q. A customer has wasps emerging from inside a structure. They do not appear to be Polistes (paper wasps) but look similar. They are brown with yellow markings, particularly a circle or ring around the abdomen. Any thoughts? (N.I., N.Y.)

A.. After discussing this with the PCO, I felt that the wasp was a Polistes — one that isn’t very common in his area. But after I received a sample of the wasp, I determined that these are potter wasps. The bodies are more robust then Polistes and the markings the PCO described on the phone are typical for this species of potter wasp.

Generally the reason this wasp becomes active in the winter is because it is overwintering in the structure. However, the PCO said that the customer has been using a wood stove in the area where these wasps seem to be coming from. Here, it’s not the warm winter that caused the insects to become active — it is the heat from the wood stove. You should look around the stove’s vent pipe, especially from the outside, for the small clay "pots" these wasps make. They are not a threat to people as they very seldom sting. They will most likely die once they emerge from the harborage. Caulking openings around the pipe will most likely stop the problem from occurring next year.

Q. We have treated an old structure for termites several times throughout the past several years. The foundation is constructed of fieldstone and we are concerned about using termiticide because the well is close to the foundation. Any advice? (A.V., Md.)

A. This is typical for these types of structures. I believe you have a couple of options left and perhaps one, or both, will stop the activity in the structure.

Upon investigating the foundation wall where the latest activity has been seen, we found that the wall was 2 feet thick. This offers major obstacles, let alone that it is a field stonewall. Drilling into the wall and injecting under low pressure, allowing the termiticide to percolate through the wall, is one option. The other is using a foam machine to try to get termiticide into as many nooks and crannies as you can. If you have used the latter successfully in other treatments, this should be no exception.

Also, since the wall has been exposed from above in the remodeling that is taking place, you can inject liquid from the top, perhaps allowing for better gravity flows into the wall. Make sure you have a man on the inside of the foundation wall on the basement side to look for termiticide leaks.

Next, dig down to the footer on the exterior side of the wall, treat the soil and replace it. This is going to take a lot of work because the soil is heavy soil and the depth to the footer is about 4 feet.

The other option is to install above-ground bait stations on the basement side where you found termite activity. I would place as many baits as possible to get the bait into that group of foraging termites. Remember to replace bait stations as they are consumed, which in this case means visiting the property at least every three weeks. You could also install in-ground stations because there seems to be a lot of activity around the structure. You could get hits with these stations and reduce the foraging populations significantly, if not entirely.