Carpenter ants

Asked June 28, 2017, 11:41 AM EDT

I normally believe in do the least harm, so I have never routinely attempted to wipe out ants on my property. However, having recently moved to the Pacific Northwest (Eugene, Oregon) from Colorado where the winters got to cold to have termites, and bought a house, I am concerned about carpenter ants. Our house is on a normal sized city lot, but in an area with a lot of trees. I have found carpenter ants in some wood that was left on the property, including an old railroad tie that is pretty much hollowed out, and I seem them foraging around the yard. I have been told, by pest control people of course, to try to get rid of them, but have read that wood has to be staying wet for carpenter ants to infest it. My question is should I try to eliminate them from the property, or leave them alone and trust that unless I have water damage they will stay away from the house. Is it worth it to pay a pest control company to treat the perimeter of the house, or will DIY products from the hardware store do as well. Thank you so much for any advice.

Lane County Oregon carpenter ants house pests

1 Response

I cannot improve upon this excellent answer from a WA Master Gardener expert.

Large black ants—often carpenter ants—may frequently be found throughout a house, both inside and out, as well as in surrounding areas. Color is not a reliable identifying characteristic: in the PNW there are several species of carpenter ants that vary from black, to red and black, to a light brown. Carpenter ants vary in size within each species. The most common carpenter ant infesting structures is Camponotus modoc, a black ant with red-brown legs. Carpenter ants commonly nest in standing trees (living or dead), stumps, logs, or on the forest floor. Worker ants from a large “parent” colony, found outside, will frequently move into a dwelling as a “satellite” colony. Workers, often in the thousands, appear in two different size classes: majors and minors. Major workers are the soldiers of the nest, while minor workers mostly expand the nest and collect food. Communication and travel between the colonies are maintained, and the satellite colony may contain larvae, pupae, and winged reproductives. Only parent colonies contain the functional queen, eggs, and early instar larvae. Each spring, carpenter ant nests release large numbers of winged queens. Do not be too alarmed by this phenomenon; most of the queens die before they can start new nests. The queens mate with winged males and quickly shed their wings; thus, you rarely see ants with wings. Carpenter ants do not eat wood, they only nest in it. They eat protein (dead insects) and sweets, especially aphid honeydew, collected from outdoors. Because carpenter ants can build nests in sound, dry wood as well as in wall voids, crawl spaces, and within foam and other insulation, they are capable of causing structural damage and must be taken seriously. There are several ways to detect a carpenter ant nest. You may find sawdust piles near ant entryways. The sawdust is kicked out as digging proceeds. You may observe ants trailing into or out of the dwelling, perhaps through a crack or under the siding (this, by itself, does not locate the nest, it only indicates the presence of one or more nests somewhere inside). You also may hear scraping sounds made by worker ants as they enlarge the nest inside a wall (the house must be very quiet). Finally, nests often are uncovered during remodeling/construction. In early spring, before aphids and other food is abundant, workers may forage indoors, often in kitchens. Common but overlooked passageways into a house are routing holes for telephone, TV, and electrical cables, especially if the cables pass near trees that harbor aphids. Management Control of carpenter ants is best left to competent pest management professionals. They have the experience and the tools necessary to locate nests and apply pesticide products effectively and safely. Drilling wall voids, applying materials inside, underneath and in attic spaces may not be necessary to control carpenter ants, as exterior perimeter treatment with non-repellent materials will control them. If performed during the high foraging season, pesticide is transferred among ants, ultimately eliminating the nest in the structure. When carpenter ants are seen inside during winter, it is best to vacuum them up and wait until the spring foraging season to initiate treatments. - - - - - Thank you for your inquiry. And welcome to Oregon and its different set of naturally occurring friends and enemies!

Jean Master Gardener Diagnostician (Washington, Multnomah and Clackamas Counties) Oregon State University Extension Service Volunteer Metro Master Gardeners (