IPM for carpenter ants


April 27, 2023

Photo: ©Gene White

Photo: ©Gene White

While carpenter ants can be beneficial in nature by helping to break down dead wood, they can also cause damage to homes and structures if they establish a nest indoors. Also, carpenter ants can certainly nest in fences and decks, especially if they are made of wood that is damp, decaying, or has other structural weaknesses. Carpenter ants prefer to nest in wood that is softened by moisture or decay, which makes it easier for them to excavate tunnels and create a nest. It’s important to take steps to prevent carpenter ant infestations and to address any infestations promptly to avoid the potential damage that can weaken the structure and compromise its integrity, which can be dangerous and costly to repair.

Carpenter ants can play an important role in the ecosystem by controlling pest populations and breaking down dead wood. Their predatory behavior can help keep other insect populations in check, which can ultimately benefit the environment and human health. Their important role in breaking down dead wood in nature helps to recycle nutrients and promote the growth of new plants. As they tunnel through dead and decaying wood, they break it down into smaller pieces, which can then be further decomposed by fungi and bacteria. This process helps to release nutrients that are trapped in the dead wood, making them available for other organisms to use. Without ants and other decomposers, dead wood would accumulate and take much longer to break down, which could lead to a buildup of organic matter and a decrease in soil fertility.

However, it’s important to keep in mind that their beneficial behavior in nature does not outweigh the potential damage they can cause if they establish a nest indoors or in structures like fences and decks. Carpenter ants can also be a nuisance to humans, as they may pinch if provoked. In addition, they can contaminate food sources if they are foraging in kitchens or other areas where food is stored or prepared, which can pose a health risk.

The integrated pest management (IPM) method to properly deal with carpenter ants will vary depending on the location and severity of the infestation.

For the preventive treatment of outdoor nests, applying a perimeter treatment at the exterior of the structure is recommended to deal with any ants passing through the foundation walls. For curative treatment of indoor nests, locating and treating the nest using appropriate pesticides is essential.

A comprehensive inspection should be conducted to determine the location of the nest and the extent of the infestation. This information is essential for selecting the most effective treatment method. Additionally, it’s important to identify and address any underlying conditions that may be contributing to the infestation, such as moisture problems or damaged wood, to prevent future infestations. This may require a partnership between the client and a licensed pest management professional (PMP) who has experience in identifying and treating carpenter ant infestations. Besides the thorough inspection, the PMP should the customer the following questions:

  1. Have you had carpenter ants before? If the structure was treated for carpenter ants in the past, there is a chance that the nest was missed or a new colony has moved in due to lack of competition.
  2. Have you noticed any visible ant trails inside the building? Carpenter ants often create visible trails that they use to travel between their nests and food sources. If your customer notices any visible ant trails inside the building, it may be a sign of an indoor nest.
  3. Have you noticed any strange odors or moisture issues inside the building? Carpenter ants are attracted to moist wood and may be more likely to nest in areas with moisture problems. If your customer has noticed any unusual odors or moisture issues inside the building, it may be a sign of a carpenter’s ant nest.
  4. Have you noticed any structural damage to the wood inside the building? Carpenter ants can cause damage to wood structures if they are nesting inside. If your customer notices any structural damage to the wood inside the building, it may be a sign of carpenter ant activity.
  5. Have you seen carpenter ants carrying pupae or larvae into the building? This indicates that there is a nest inside.
  6. Have you seen lots of carpenter ants in areas with no food or water? This can be a sign that they are coming from an indoor nest and not just foraging for food.
  7. Have you seen carpenter ants with wings inside the building during late winter or early spring? This could indicate that there is a mature nest inside the building that is producing winged reproductives.

By asking these questions, you can get a better idea of whether carpenter ants are nesting inside the building or just foraging for food. If it appears that there is an indoor nest, it is important to take action to eliminate the nest and prevent further damage to the structure. Once the inspection is complete, the following treatment options may be considered:

  1. Exterior treatment with non-repellent insecticides is a common method of preventing carpenter ant infestations in wooded areas or areas near parks. These insecticides can be applied around the perimeter of the building, creating a barrier that carpenter ants cannot detect or avoid. This can prevent carpenter ants from entering the building in search of food or a nesting site.
  2. If an indoor nest is suspected, the next step would be to locate and treat the nest with an appropriate insecticide. Dust, foams, and liquid insecticides can be used for this purpose, depending on the location and extent of the infestation. Both baits and liquid insecticides can be effective in treating carpenter ants, but the choice of treatment will depend on the location and extent of the infestation, as well as safety considerations.
    1. Baits work by attracting ants to a poisoned food source, which they carry back to the nest, effectively eliminating the entire colony. Baits can be effective if properly applied along foraging trails, and they are generally safer than liquid insecticides because they have lower toxicity to humans and pets. However, baits can be slower than liquid insecticides in achieving control, and they may not be effective if the ants are not actively foraging.
    2. Liquid insecticides, on the other hand, can be applied directly to ant trails and entryways to kill foraging ants and prevent them from entering the building. They can also be used to treat indoor nests or outdoor nesting sites. However, liquid insecticides can have higher toxicity and require a careful application to avoid exposure to humans and pets.
    3. In some cases, a combination of bait and liquid insecticides may be used to achieve quicker control while minimizing risks. It is important to follow label instructions and safety precautions when applying any type of insecticide.
  3. Wood replacement: If there is significant damage to wood structures, it may be necessary to replace the damaged wood.
  4. Follow-up: Follow-up inspections and treatments may be necessary to ensure that the infestation has been completely eliminated.

In conclusion, It’s important to note that prompt action is necessary to prevent damage to structures and reduce health hazards when dealing with carpenter ant infestations. The questions that you can ask the customer are also helpful in identifying the location of the nest(s) and the extent of the infestation. The treatment options, such as non-repellent insecticides for exterior treatment and baits and liquid insecticides for indoor treatment, are effective methods for controlling carpenter ant infestations. Follow-up inspections and treatments are also important to ensure that the infestation has been completely eliminated.

Useful References

Hansen, L. D. and A. L. Antonelli. 2005.  Carpenter ants: Their biology and control. WSU Coop. Ext. Bull. 0818. 6p.

Akre, R.D. and A.L. Antonelli. 1992. Identification and Habits of Key Ant Pests of Washington (Workers and Winged Reproductives) WSU CES. EB 0671.

Bolton B. Bolton’s Catalogue and Synopsis version: 1 January 2012. [2012-01-10T00:00:00+02:00]; 2012

Hansen, L. D. and R. D., Akre. 1985. Biology of carpenter ants in Washington State (Hymenoptera: Formicidae: Camponotus). Melanderia 43: 1–62.

Hansen, L. D. and J. H. Klotz. 2005. Carpenter ants of the United States and Canada. Cornell University Press. Ithaca, New York. 204 p


About the Author

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Dr. Mohammed El Damir, BCE, is technical and training director of Adam’s Pest Control, Medina, Minn.

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