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Summer 2018 is an Active Year for Carpenter Ants

Categorized: Gardens, Home & Garden Pests

BROOKINGS, S.D. - Throughout summer 2018, SDSU Extension staff have received numerous reports of carpenter ant activity.

"The concern with carpenter ants is that they can become a structural pest if they nest in homes or other buildings," said Patrick Wagner, SDSU Extension entomology field specialist.

So far, Wagner said nearly all of the reported cases have been identified as the same species, Camponotus pennsylvanicus, commonly known as the black carpenter ant (Figure 1).

How to identify carpenter ants?

Carpenter ants can be distinguished from other ants based on a few characteristics:

  1. Most carpenter ants are quite large, ranging in size from 3/8 to 1/2 of an inch long. They also have dark-colored bodies that are either uniformly black or black and red.
  2. Carpenter ants have a uniquely shaped thorax, which is the body segment directly behind the head. Most ants have an indentation on the top of the thorax, whereas on carpenter ants, the top of the thorax is smooth and even (Figure 1).
  3. Carpenter ants have only one node or peak on the pedicel or the thin segment connecting the thorax and abdomen.

"It is important to understand that, unlike termites, carpenter ants do not eat wood," Wagner said. "However, they will burrow through and displace wood as they build their colonies."

One of the main signs of carpenter ant activity is seeing piles of wood dust showing up near dead trees or wood structures (Figure 2).

"Carpenter ants prefer to nest in wood that has been softened by moisture," he said of locations like tree stumps, rotting logs and damp wood in and around buildings. "It is likely that the wet summer experienced throughout much of South Dakota has been favorable for carpenter ants, resulting in their increased activity."


The best management for carpenter ants is to prevent an infestation from occurring in the first place. Below, Wagner outlines some prevention tips:

  1. Allow good air circulation in homes and other buildings to prevent moisture build up.
  2. If there is wood with water damage, replace it if possible.
  3. Remove rotting tree stumps, logs, and wood piles (i.e., firewood) from around buildings. Carpenter ants often migrate indoors from these areas, so it is best to keep them far away from the exterior walls.

"If you suspect a carpenter ant infestation, immediate treatment is recommended," Wagner said. "However, keep in mind that seeing a few carpenter ants indoors does not mean that their nest is also indoors.

One option is to use perimeter sprays which form an insecticide barrier that kills the ants on contact. Wagner explained that this will prevent accidental invasions and also limit populations from making it indoors.

However, these products are only effective for a limited amount of time and fail to eliminate the ants at the source.

Setting out poison ant baits, either granular or liquid, is usually more effective.

"Ants not only consume the bait, but also take it back to their nest and feed it to the rest of the colony," he said.

Ant baits are relatively inexpensive and may be applied either directly or inside specially designed ant traps.

There are a variety of other alternative methods such as using a mixture of boric acid and sugar as poison bait, or sprinkling diatomaceous earth near the nest to kill ants on contact.

For severe infestations, it may be wise to hire a professional pest control company to evaluate and treat the situation.

If you have questions or concerns regarding carpenter ants, please contact your nearest SDSU Extension entomologist for more information. A complete listing can be found at iGrow under the Field Staff icon.

Courtesy of iGrow. Figure 1. Top view of a black carpenter ant (Camponotus pennsylvanicus).

Figure 2. Wooden landscape timbers with piles of wood dust on the ground around them. Courtesy: Edward H. Holsten, USDA Forest Service,

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