Pest Control Minneapolis MN | MN Carpenter Ant Pest Control

The sight of big, black carpenter ants scurrying across the floor is a creepy sight for homeowners because it might mean that they are nesting somewhere in the house. They are large ants, 6-12 mm long (3/8-1/2 inch); the flying queen ants may be nearly 2 cm long (7/8 inch). For brief periods in the spring and early summer the winged ants swarm into the air on mating flights. The queens are easy to see as they settle, shed their wings and search for decaying wood to begin their nest. Very few of them will find an ideal site, which is usually outdoors. Their presence does not mean that your house is infested. Carpenter ants are actually beneficial predators that feed on small insects, honeydew and dead and decaying material.

Carpenter ants make two types of nests. If the queen finds moist, decaying wood, she tunnels into it to begin the main nest. This site must be permanently moist or the eggs and younger larvae cannot survive. Old nests can contain thousands of ants, but it takes several years for a new nest to build up to a few hundred individuals. Main nests are usually outdoors in rotting stumps, trees or in decaying landscape timbers. They can become established in houses where wood in the structure has begun to decay. Although carpenter ants do not eat wood, they do tunnel into it to make their galleries. Once they establish a nest in damp wood they will eventually damage the structure by tunneling from the decaying wood into the sound wood. Carpenter ants also make satellite nests where they care for the older larvae and pupae that tolerate drier conditions. These nests are often in wall voids and eaves, ceilings or under insulation in attics or crawl spaces. Most nests in houses are satellite nests that maintain communication with the main nest.


The best protection is to maintain dry conditions with proper construction and maintenance, remember that anywhere wood is in contact with soil there is a risk of carpenter ant infestation.

  • Repair wood damaged by moisture, ventilate damp areas, clean gutters to avoid clogging, which leads to water damage to siding or roof.
  • Store firewood on raised platforms, well away from the house.
  • Prune trees so branches don’t touch the house.
  • Remove all nearby rotted stumps or logs. Check for rotting landscaping wood.
  • Ensure that wood of the siding or structure isn’t in contact with soil at any point around the house foundation.


The key to control is finding the main nest, where the queen is laying eggs. This requires thorough inspections and an effort to follow foraging ants back to their nest. If you see more than 10-12 ants in your house in an evening, it is worth investigating whether their nest is in the house. First, make sure the insects in question are carpenter ants. If in doubt, catch some of the largest ones and have them identified. Follow some of the ants until they lead you back to the nest. Sometimes carpenter ants are interested in sweet food in the early spring and you may be able to attract some to jam or honey and then follow them homeward. They use the same trails over and over and are most active at night.

Thoroughly inspect the crawl spaces and attics as well as under porches. Look for signs of nesting activity, such as mounds of loose shavings or sawdust beneath a crack in a wall or eave space. Also, listen for rustling sounds in the walls (use a rolled up paper tube to amplify the noise). Carpenter ants particularly like to nest in wall cavities, under siding, between floors and where wood is in contact with soil. Satellite nests can also be near roof gutters, downspouts and in the ceiling.

  • Find and remove the nest material manually or by vacuuming up the ants. You will know it is a nest if you see ants carrying white, oval pupae or larvae.
  • If not structural damage has occurred, prevent ants from re-entering the space by caulking the entry cracks.
  • If structural damage has occurred, repair it and remedy any underlying moisture problems.
  • To kill ants travelling through walls or to prevent them from re-entering a wall or cavity, apply a very fine dusting of the following:

Boric acid is a stomach poison for insects. Wear a dust mask, gloves and eye protection while applying it. Apply it and store it out of the reach of children and pets because it could be harmful if enough is eaten.

Diatomaceous earth (silicon dioxide) is a non-toxic white powder that kills insects by causing them to dehydrate. Wear a dust mask when applying the dust to avoid respiratory irritation

How to Treat

Apply a fine layer of dust to house wiring and plumbing pipes, wherever they can be reached. Research has shown that ants use these as pathways through the wall voids. Unscrew the cover plates from electrical switches and outlets (turn off main power first!) and insert a dust applicator wand alongside the box. Apply a fine layer of dust to the wires on either side of the box. If the house has a sealed vapour barrier around the electrical box, be sure to reseal this with caulk or plastic tape after applying the dust. Apply dust to any accessible plumbing pipes in walls and crawl spaces.

Entryways for ants (see diagram below):

A Fence joined to house

B Plumbing outlets

C Lower edges of siding

D Edges of fireplace brick

E Crawl space vents

F Gutters

G Window casings

H Door frame

I Vegetation touching house

J Overhead wires

Possible sites of main nests (see diagram above):

1 Wood in contact with soil

2 Woodpiles

3 Decaying tree roots

4 Heartwood of live trees

5 Rotting stump

Severe Infestations

The control measures above may not eliminate established ant infestations in high risk houses, such as those surrounded by woods, those on earthen crawl spaces or those with decaying timbers in the foundation. In this case, or if you are unable to make the necessary inspections, it is advisable to call a licensed professional pest control service to locate the problem. Choose a service that will conduct a thorough inspection for the main nests and that is willing to discuss with you, in detail, the various treatments. To prevent the problem from recurring after treatment, replace or repair any damaged timbers and correct moisture problems.

Carpenter ants can be distinguished from termites by their narrow, wasp-waist and antennae that have an elbow bend in the middle. If you choose to have the pest control expert apply pesticides to the perimeter of the house to prevent future carpenter ant invasions, it is important to know that the only areas it is necessary to treat are along the top of the sill from inside the crawl space, and under the bottom edge of the siding on the exterior.

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