Carpenter ants

Quick facts

Carpenter ants are usually seen in homes in the spring. If you see carpenter ants indoors during winter that means there is a nest inside your home.

  • Signs of carpenter ant infestation:
    • Small piles of coarse sawdust
    • Seeing 20 or more ants at at time
  • Prevent carpenter ants by eliminating high moisture conditions
  • Hire a pest management professional to eliminate a carpenter ant nest
Carpenter ants form parent colonies outdoors in moist wood, like this tree stump
Carpenter ant damage in a stump

Carpenter ants nest in moist, decayed wood outdoors. Inside buildings they nest in wet places behind bathroom tiles, tubs, sinks, showers and dishwashers.

Carpenter ants damage wood by digging and creating smooth tunnels for their nest. These tunnels do not contain sawdust or other debris.

Wood damage is greater if the colony is present for a longer time.

Identifying carpenter ants

Carpenter ants are among the largest ants in Minnesota. They are frequently seen in the open, especially after sunset.

  • They have dark-colored bodies, narrow waists, elbowed (bent) antennae and hind wings shorter than front wings.
  • They have a waist with one node (petiole) and a body (thorax) with an evenly rounded upper surface.
  • Several species of carpenter ants maybe found infesting homes and other buildings.
  • Colonies of ants are divided into different castes: workers, queens, and males.
  • Workers are black, or red and black, in color; and range in size from 3/8 to ½ inch.
  • Winged queen ants may be as large as one inch.

Other ants mistaken for carpenter ants may have one or two nodes, an uneven upper surface, and do not infest wood.

Correct identification of the ants is important for control strategies to work effectively.  

Different species of carpenter ants (males, winged females and workers) are of different sizes
Carpenter ant castes - left column winged female (top), winged male - right column - workers of varying sizes
Carpenter ant worker has a waist with one node and an evenly rounded upper surface
Carpenter ant worker with evenly rounded thorax and one segmented petiole
Other ants do not have a rounded upper surface, like carpenter ants have
Non-carpenter ant worker with an unevenly shaped thorax and a two segmented petiole

How to detect carpenter ants

You can locate the nest by observing worker ants between sunset and midnight during spring and summer months.

  • Use a flashlight with a red film over the lens or cover part of the flashlight with your hand to follow carpenter ants.
  • You can find their nest by setting out sweet foods (like honey) where you find workers.
  • During spring carpenter ants look for high protein foods.
Carpenter ant damage in wood. Smooth tunnels in a wooden board.
Carpenter ant damage in header boards

Finding coarse sawdust and large numbers of winged ants indoors (late winter through spring) is evidence of an indoor nest.

The presence of sawdust can indicate an active nest nearby
Coarse sawdust caused by carpenter ants

Carpenter ants can enter from areas where moisture is or has been a problem.

Where to look for them:

  • Stored firewood
  • House foundation
  • Along outside walls (porches, decks)
  • Basements
  • Areas around the plumbing or vent entrances
  • Trees with branches overhanging the house

Sound and moisture detection may be helpful in locating a nest.

  • An active colony may make a dry, rustling sound that becomes louder if the colony is disturbed.
  • Tap the suspected area and press an ear to the surface to hear any sound.
  • Pest management professionals may use a stethoscope to locate a nest.
  • They may also use a moisture meter to find areas prone to carpenter ants.

If one nest is found there maybe more nests in a structure.

Prevention and control

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Life cycle of carpenter ants

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Jeffrey Hahn, Extension entomologist and Stephen Kells, Extension entomologist

Reviewed in 2018

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