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Carpenter Ants
- Carpenter ants are potentially the most damaging structural insect pest in temperate climates -
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Summary: Carpenter ants are large, powerful ants that can destroy wood and other building materials. They replace termites as the most important structural pests in many temperate climates.
Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)
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Carpenter ant identification
 Most ants are small and nest underground, only rarely becoming anything more than a nuisance. Carpenter ants (see photo right), on the other hand, are large ants that nest above ground in cavities such as tree stumps and sometimes in the walls, subfloors or roofs of our houses where they can cause damage.
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Winged (left) and wingless (right) carpenter ants
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How do carpenter ant colonies start?
Carpenter ant colonies are started by a queen (above, left). Mated queens generally fly during late spring and locate a suitable cavity in which to begin laying eggs. She can use almost any protected cavity such as inside a wall, under floor insulation or outside in a tree stump. The cavity is not always associated with wood since carpenter ants do not necessarily need wood for survival (again, unlike termites). As an example, rigid foam insulation is frequently damaged by these ants.
In the eastern US ant damage is often associated with moisture because colonies tend to start where wood has been moisture-damaged but this is not necessarily the case in the western US where colonies and damage can occur in very dry situations.
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How do carpenter ant colonies grow?
Once the first brood of female worker ants is produced the queen stays within the nest. Worker ants leave the nest to forage for food and water. Carpenter ants are opportunistic predators and scavengers taking a wide variety of foods. This behavior of moving between nest and foraging grounds, combined with their large size, makes thee ants relatively easy to detect during routine inspections. You'll see ants "trailing", moving in line (more or less), between the structure and outdoors.
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As the colony grows worker ants excavate and enlarge the original cavity. It is this "colony expansion" activity that causes damage to building materials. Colonies can continue to grow over many years and may split into several "satellite colonies" when the original colony grows too large.
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Do-It-Yourself carpenter ant control
Standard treatments to control carpenter ants involve creating a barrier of insecticide that foraging ants must cross in order to forage for food and water. New insecticides like Termidor Insecticide can be used for a perimeter spray that avoids drilling wall voids. Carpenter ant baits are a new addition to the control arsenal. Baits can be used in areas where conventional insecticides can not, or should not, be used. Click on the links above for details about DIY control of carpenter ants.
Questions from homeowners
Take a look at this page where I've compiled a few of the most common questions and answers I get about these structrual pests.
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