Camponotus modoc is the most common carpenter ant found in structures in western Washington.
Shown at left: Dorsal view of the adult stages of the carpenter ant:
Bottom left--Minor worker
Bottom middle--Intermediate worker
Bottom right--Major worker.
Do You Have Carpenter Ants?
The presence of a few foraging ants in the home, or 1 or 2 winged queens during swarming times does not mean you have an infestation. These foragers may merely be scout ants seeking food or nesting sites or queens that have flown in an open door.
Foraging ants have been seen entering homes along telephone wires or along branches touching the roof or even from ground trails that come under a door. In such cases, the house may be a nesting area.
If ants are coming in, there may be a nest outside the house and eventually they may establish satellite colonies in some part of the structure. Be certain they are carpenter ants and not moisture ants, termites or yellowjackets.
Evidence of Infestation
Dr. Hansen's research showed that some common elements accompanied infestations. Although other types of structures were attacked, most infestations were in houses with these characteristics:
Most nests of C. modoc which could be found were associated with (in order of frequency):
Nests have been found in:
Carpenter ants typically have a parent colony in outside nesting areas, such as live or dead trees, stumps, logs or decorative landscape wood.
When the colony grows larger and needs room to expand or the old nest becomes less suitable, they expand to form satellite colonies. these satellite colonies are placed in nearby structures presumably because the heated, protective structures are more conducive for the older stages.
The parent colony contains the queen, young larvae and workers, while the satellite contains the mature larvae, pupae, workers, and/or winged reproductives.
The ants move back and forth from parent nest to satellite nest to feeding areas (in nearby evergreen trees and shrubs such as Douglas fir, true fir and cedar). Sometimes they can be seen carrying mature larvae (white and grub-like) or pupae (papery cocoons).
In this study, houses had from 1-3 colonies, (average = 1.3).
If the parent nest is not found, it can reestablish satellite colonies after the pesticides have become inactive or establish new colonies in untreated areas of the house.
If several nests are found, it is important to determine if they are from the same colony (therefore one parent nest) or 2 or more different colonies (therefore several parent nests). Place 2 ants, one from each trail or nest, in a jar:
Ants move along definite trails by following a chemical scent or visual clues. These trails can be above ground or subterranean and are actually constructed by cutting away vegetation, removing pebbles, excavating soil and even by covering open trails with a roof of needles from nearby trees. Trails can vary in width from 1/8" to 3/8".
The ants from a colony will follow the same path each year even if grass has grown in it. They will clear the old trail.
Ants follow natural contours. They will cross lawns and flower beds but often prefer the cover afforded by moving along the edges of things.
Again ants prefer natural, easy and protected routes:
Do not disturb any trails until you locate the nests. The ants will just get sneaky and reroute the trail which may take much longer to locate.
Ants will generally be going to and from:
Banded ants or ants with insects will be going from feeding grounds to parent (or satellite) nests. The young growing larvae and queen need the most food, so more ants will take food toward the parent colony, with fewer moving toward the satellite. Ants carrying larvae or pupae (papery cocoons) are moving from the parent to satellite colony.
Activity, therefore ease in following a trail, is greatest after sunset (roughly between 10 p.m. to 2 a.m.). A red light disturbs ants less than white light.
Trails may be difficult to locate since they may disappear under boards, sidewalks or go underground.
You have time. Keep watching for clues as you work in your yard or house. Don't get trigger happy and spray the trail, or you will have to start over if you want to find the nest.
Carpenter ants cannot eat solid food. They have a very long, exceptionally thin esophagus (food pipe) that prevents them from eating solid food.
Finding both the parent colony in the surrounding landscape and the satellite colony (or colonies) in the structure is crucial to successful control of carpenter ants.
Many pest control operators feel they can drill and inject the entire house faster and at less cost to the homeowner than it would take to locate and treat the nest areas. Others feel they can starve out the ants by spraying only the perimeter (attic, crawl space, and foundations) at monthly intervals for a year.
However, the National Pest Control Operator's Association since 1962 has recommended and still recommends that an effort be made to locate and treat the nest areas. The Washington State Pest Control Association also recommends "careful inspection" and that "a professional attempt be made to penetrate and treat potential nesting sites." From Dr. Hansen's research, it is evident that long term success will be greater if the parent colony also is located and destroyed.
Carpenter ant infestations usually involve a parent colony and one or more satellite colonies. The parent colony which houses the queen, workers, and brood requires a moist area and is usually located outside the structure unless a severe moisture problem exists within the building. Satellite colonies house workers, mature broods and may also contain winged forms. These colonies are often found within structures.
The most effective means of control begins with the location of the main colony and the satellite colonies. Clues in the location of nesting sites include extruded sawdust, foraging trails, and the presence of foraging ants.
Colonies within the structure should be controlled by a direct application of a pesticide. Boric acid dust, bendiocarb (Ficam) 1% dust, cyfluthrin, cypermethrin, bifenthrin, propoxur (Baygon) 0.5% in aerosol spray containers all are registered materials. Nests in wall voids often can be accessed through plumbing or electrical wiring. Electrical plates can be removed and an insecticide applied into the wall void along the outside edge of the electrical box. Ants follow wiring and plumbing routes through the structure. If the colony is inaccessible for direct treatment, a 1/8 inch drill bit can be used to make small holes in the walls so an insecticide applicator wand can be inserted for application of the insecticide. Dust formulations are effective against all Hymenoptera because the dust adheres to the hairy surfaces of their bodies. As they clean themselves and feed other ants and larvae, the insecticide is spread throughout the colony. This formulation is effective as long as it does not become wet, so it is used primarily in wall voids.
A perimeter spray of the structure should also be made during the season of carpenter ant activity from April through September. This will disrupt foraging trails and help to prevent re-entry from parent colonies nesting outside the structure. The exterior perimeter spray should include application against the foundation, under the edges of siding, around window and door frames, and on carpenter ant trails. In structures with a crawl space, the inside of the foundation and sill plates should also be sprayed. Cyfluthrin (Tempo), deltamethrin, bifenthrin, permethrin, cypermethrin (Demon) are all registered materials. The synthetic pyrethroids, cyfluthrin and cypermetherin, have a long residual (2-3 seasons) if placed in areas not exposed to direct sunlight and rainfall such as under the edges of siding and on the inside of foundations and on sill plates in crawl spaces.
Perimeter sprays may be recommended when the parent colony cannot be located or controlled. Examples would include structures built in forested areas where trails in natural areas are difficult to follow, in urban areas where the parent colony is located in the heartwood of a living tree, or when the parent colony is located in wood buried during construction or in landscaping. the frequency of application is dependent upon the choice of insecticides and the concentration. For materials with a shorted residual, application may be needed several times during the season. This can be reduced to an annual application or longer with the synthetic pyrethroids.
Exercise caution in handling all pesticides and be sure to read the label for both cautionary statements and use procedures.
It may take some long-term observation to find the nest sites. DO NOT DISTURB any ant activity you can see until you have located the nests and are ready to initiate control measures. Disturbing their activity will cause the ants to develop new routes which may take you longer to find.
You may wish to listen to Dial Extension tapes on Carpenter Ants. They are
available to Washington State callers at (206) 296-3425 or toll free during
business hours at 1-800-325-6165 and ask for extension 6-3425. Request: #1261:
Carpenter Ants, or #1222: Choosing an Exterminator
(For more information on "DialExtension", see: http://king.wsu.edu/gardening/dialextension.htm)
The following publications are also available via free download or, for a
small fee, through your local WSU Extension Office:
The following publications have good information and graphics about carpenter ants but be aware that chemical recommendations listed there may not be legal in Washington State. Diazinon and Dursban (chlorpyrifos) in particular will soon be unavailable for home use in Washington.
University of Kentucky also has a very good carpenter ant publication.
For further information contact your local WSU Extension Office.
Prepared by Sharon J. Collman, Former County Extension Agent, Dr. Laurel Hansen,
Spokane Falls Community College, Dr. Roger Akre, Department of Entomology, Washington
State University (deceased), Dr. Arthur L. Antonelli, Extension Specialist,
Washington State University. Link Updated 09/12.