Carpenter ants

What are they?

The red carpenter ant and the black carpenter ant are two of the most common types found in Canada. The red carpenter ant has a dark brownish-black body, with a reddish-brown upper body. The black carpenter ant is dark brownish-black all over.

Carpenter ants are from 6 to 25 mm (.24 to 1 inch) long. A carpenter ant's body is divided into three segments, with a very slim waist separating the upper body and lower body. Their antennae are bent and in sections. Male and female adults have wings at mating time.

Should I be concerned?

Carpenter ants are well known for their ability to damage wooden structures. They are also a nuisance in homes as they search for food. Carpenter ants eat both plant and animal matter. Their natural food sources are insects, other small invertebrates, and sweet body fluids from aphids and other insects. Protein and sweet foods found in and around homes also provide food for foraging workers.

Carpenter ants build nests by burrowing into wood. They dig tunnels (called galleries) much longer than those created by termites. The wood is not eaten, but thrown from the nest as sawdust-like shavings.

Alternate Formats

Did you know?

Carpenter ants are sometimes confused with termites, but it is easy to tell the difference between them. The termite has straight antennae and a thick waist, and the carpenter ant has a very narrow waist and "elbowed" (bent) antennae. Termites are found only in certain areas in Canada.

Carpenter ants live in large colonies with hundreds of workers (all sterile females), several males and females that reproduce, and one or more queen. When part of an established colony goes into a nearby structure, it sometimes establishes a smaller satellite colony there. Some experts believe this is the main way carpenter ants invade houses.

How do I know if I have a problem?

Outdoors, carpenter ants are found in dead trunks of standing trees, stumps, or logs, or under fallen logs and stones. They can sometimes mine sound wood, but they usually choose a soft type, like pine.

Indoors, because they prefer moist, decaying wood, carpenter ants can signal a moisture problem, or wooden structures that are decaying. As well as tunnelling in the trim of buildings, wooden steps, and window sills, ant colonies can nest in houses without attacking structural timbers, using hollow spaces like wall voids, attic spaces, and hollow doors. They can even be found behind books in libraries, behind drawers in dressers and cabinets, and in styrofoam insulation.

Carpenter ants get into houses by several ways:

  • windows
  • holes in foundations
  • heating ducts and air-conditioners
  • power or telephone cables
  • points where tree branches or other vegetation come in contact with the house
  • wooden structures attached to houses (like porches and sheds)
  • firewood brought into the house

To find carpenter ants:

  1. Completely inspect areas of high moisture, wood in contact with the soil, areas where ventilation is poor, and exposed structural lumber.
  2. Figure out if there is actually an infestation of carpenter ants or if it is just individual ants wandering in the house. Look for a high concentration of ants in a particular area like under the kitchen sink.
  3. Pay attention to foraging ants and the patterns of their movement. For example, there may be a trail communicating with a parent colony outside. (Note: ants are most active after sunset.)
  4. Notice if there are swarms of winged ants trying to escape to the outdoors, usually in the spring.
  5. Look for piles of sawdust-like borings outside their galleries and slit-like openings in woodwork.
  6. Listen for the sound of an active colony, which will create a dry rustling noise that can be heard best at night during high ant activity and quiet time in the house. Use a wine glass or stethoscope to listen to the walls.

How can I get rid of carpenter ants?

Physical control

  • Clear away any decaying or infested wood from around buildings.
  • Remove firewood from inside buildings and away from the sides of buildings.
  • Do not bury stumps or other wood debris close to your house.
  • Pay attention to the state of landscaping props (like decorative bark, retaining walls, and driftwood).
  • Correct humidity problems in your home.
  • Replace decaying or infested structural wood with sound material.
  • Remove food sources to discourage ants from invading buildings.
  • Keep food in sealed containers and regularly sweep up all crumbs and other food fragments.
  • Keep your home clean to prevent re-infestation.



If you use a pesticide to control your pest problem, read the label to make sure you are choosing the right product for the right pest. Follow all label directions and warnings carefully. Always look for a Pest Control Products (PCP) number on the label so you know the product has been approved by Health Canada. See Use pesticides safely for more information on using pesticides safely

Chemicals can help you eliminate existing nests and prevent new nests from forming. Chemical control works best when you use it along with physical control.

Once a colony is well established, you usually need to locate and treat the actual nest site for permanent or long-term control. In the case of a satellite colony, the parent colony should be located and destroyed for most effective control. In difficult situations, use a professional exterminator.

Various pesticide products for are available for homeowners, and can help reduce the number of ants infesting your house. If you plan to do an indoor application, check the product label to make sure it is registered for use inside your home. There are also several other commercial products available to professional pest control operators.

For commercial food processing or preparation, use products specifically labelled for these areas. Carefully follow all label directions and warnings. Remove or cover all food, packaging material, and utensils before treatment. Afterwards, wash all surfaces that may be in contact with food and rinse thoroughly with water before re-use.

Please note: When applying pesticides, you should leave any dead ant bodies where they are. Other scavenging ants will either eat or bring the dead ant back to the nest to feed the rest of the colony. In this way, the pesticide's effect is passed on.

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