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Watch for carpenter ants this spring

Jeffrey Hahn, Extension Entomologist

Typical carpenter ant.  They are identified by having a one
segmented node and an evenly round thorax when viewed in
profile.  Photo credit: Jeff Hahn, U of MN Extension
Carpenter ants are the most important ant pests found in Minnesota. They can be a problem when they nest in homes and other structures. Because nests are in wood and other hidden areas, it is challenging to know where they are located. Finding the nest and treating it is the best control for carpenter ants.

Always verify that you have carpenter ants. While, people often think of carpenter ants as “big, black ants” (which they are, up to almost ½ inch long), some carpenter ant species are red and black and are smaller, only 3/16th inch long. Some species of field ants, a nuisance species, are black and a similar size to carpenter ants.

Finding carpenter ants in your home in the spring can mean that a nest is present, especially when persistent numbers are found. If you find a swarm of winged carpenter ants indoors, that is a sign of an indoor nest. However, if you find just a few carpenter ant queens (winged or wingless) in your home, they probably just wandered into your home accidentally and no nest is actually present.

A wingless carpenter ant queen.  Finding one or two in your
home (like the author did) is not an indication of a nest
although she is looking to start a nest.  Photo credit:  Jeff
Hahn, Univ. of  Minnesota Extension
If you are having problems with carpenter ants in your home, it is very challenging to eliminate them yourself. For control to be effective, it is necessary to deliver insecticide into the nest to kill the queen and the workers. Killing the foraging workers you see does not impact the nest.

Baits can be effective for some ant problems. However, the ant baits available to residents are not sufficiently attractive or effective to successfully eliminate a carpenter ant nest.

The best control for carpenter ants is to contact a licensed pest management service to treat the nest. An inspection is important to find the foraging trails and if possible the nest(s).

There are several options for treating the nest. Many technicians use a non-repellant residual insecticide, such as Termidor, sprayed around the building’s exterior. The carpenter ants pick up the residue and take it back it to the nest where it gets spread through colony, ultimately eliminating it.

Technicians may also set out baits to control carpenter ants. They have access to a variety of baits and have the experience to use them. It is not unusual for technicians to use more than one bait to be successful. Remember that baits take time so be patient and allow carpenter ants to take enough back to control the nest.

Carpenter ants tunnel and nest in wood.  Control them to
prevent damage to your home.  Photo credit: Jeff Hahn,
Univ. of MN Extension
If the exact location of the nest is discovered, it can be treated directly with a dust. This may require drilling into walls or injecting dust through outlets.

Once treatment has been applied, a technician needs to evaluate how successful the initial control was and whether any additional steps are needed.

However, treating the entire house multiple times on a scheduled basis is considered excessive and less effective. Treatment should be targeted and as specific as possible.

For additional information, see Carpenter ants.
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