Carpenter Ants in the Winter

Finding carpenter ants indoors in the winter is an indication that they are nesting somewhere within the walls or floors of the structure. Ants found in the summer are often invaders wandering in from outdoors, but since carpenter ants, like all insects, are cold blooded, ants active in the winter must be originating from a warmed source. Even if the air temperature is very cold, heat from the sun or the furnace may warm house walls and stir dormant ants to activity.

The critical factor in carpenter ant control remains treating the nesting area. Locating the nest site is very rarely easy, but it is essential for control.

I agree there are times it may be impossible to locate the nest, but I think it is possible more often than many people assume. The most likely sources of carpenter ants are still: window and door frames and sills, shower and tub enclosure walls, and kitchen and bath plumbing walls.

Carpenter ants do not always have to have moisture and wood decay for nesting. While it is true most nests and most damage will be in decayed wood, nests may be in sound timbers or even in dry cracks and joints between structural elements or in existing cavities such as hollow doors.

One of the goals of IPM and one of the reasons we encourage carpenter control by direct nest treatment is to limit the amount of pesticide applied. Special injector applicators are available to pest control operators, but homeowners can use drilled holes and crack and crevice treatment to reduce pesticide use and exposure. Dust insecticides provide better control of carpenter ants, IF they are applied as a thin even coating into nesting and traveling areas. Homeowner sprays can be effective but great effort is needed to place the insecticide where it will do the most good. This is one pest for which professional treatment may be worth the extra expense.

However, when you shop for carpenter ant treatment you should be aware of two "sales pitches." First, I do not agree with the sales pitch that it will take a year of monthly treatments to get rid of carpenter ants. If migration from outdoors is a problem you might need retreatment, but to routinely prescribe monthly treatment, I think, is more insecticide exposure than is necessary.

The second variable among companies involves the method of application. Some companies want to systematically drill every wall void and inject an insecticide dust without any knowledge of where the nest is located. Personally, I find very little reason to follow this treatment approach. It appears that in Midwest homes where most walls are insulated with fiberglass batting or blown-in cellulose, a randomly placed application of dust into the wall void has little, if any, chance of moving much beyond the end of the applicator tip. High pressure dust applicators such as aerosols are likely to only blow a hole in the insulation with no further pesticide movement. If a wall is properly filled with insulation, the insecticide dust injected through the sheetrock or paneling will not cover the intended target, the wood of the studs and lower plate. Drill and dust treatments of every wall void increases the amount of pesticide used and greatly increases the cost to the consumer with little chance of enhanced success. Therefore, I do not, as a rule, favor the practice of treating every wall void, especially if walls are insulated.

An alternative to the through-the-wall void treatment is for the PCO to apply the dust with a power duster through existing openings such as around wall outlets, switch plates and pipe flanges. Research at Washington State University indicated the dust would drift along the utility lines such as electrical wires, conduits and plumbing lines, and coat the upper surfaces on which carpenter ants are known to walk. This type of dust treatment would be much more effective than treating a small spot within wall insulation.

None of the baits available at this time appear to be effective against carpenter ants. Certainly, the "sweet" liquid ant baits and feeding stations available to homeowners do not control carpenter ants according to the numerous "field observations" reported by dissatisfied homeowners. More effective and efficient baits that utilize the emerging understanding of ant nesting habits and foraging behavior are being developed and will be available within several years.

This article originally appeared in the March 24, 1993 issue, pp. , 1993 issue, pp. 26-27.


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