Signs of Carpenter Ants

How to Tell If You Have Carpenter Ants

Scientists estimate that there are almost 700 species of ants in the U.S. and Canada. Of these, about 30 species are carpenter ants. Fortunately, only a few of these actually invade homes. However, the carpenter ants that invade homes often cause serious damage because of their habit of making their nests in wood.

Homeowners get nervous when they think that carpenter ants have invaded their home. An accurate identification is important because ants are all different. The same treatment does not work for all species of ants.

What Does a Carpenter Ant Look Like?

Scientists identify carpenter ants by looking at particular parts of the ant’s body. The scientists make comparisons to decide if the ant is a carpenter ant or not.

  • Is the ant’s thorax rounded or irregularly shaped?
  • Does the pedicel have one node or two?
  • Does the antenna have twelve segments? Does it have a club?
  • Is there a circle of hairs at the back of the abdomen?
carpenter ant worker
photo credit:Univ of Minn
carpenter ant closeup
Carpenter Ant

Some of these characteristics can be hard to see without a magnifying glass. It may be easier for a homeowner to identify the ant in other ways. By considering the ant’s size and behavior, homeowners can identify many common ants, including carpenter ants.


How big are the ants?

carpenter ant sizes
Image credit:Laurel Hansen,

A carpenter ant colony has workers of different sizes. The smallest workers can be less than 1/8″ long. The largest workers can be more than half an inch long. There are black carpenter ants, red carpenter ants, and carpenter ants that are brown and even two-toned ones. Black ants that are all the same size may be acrobat ants.

The queen is usually the largest ant in the colony. In most colonies there is only one queen. However, in colonies of Camponotus vicinus (Mayr), there are several queens. This may be the reason for the colonies of this species of carpenter ant being very large.

During the year, most of the ants in a carpenter ant colony are workers. There are very large workers, called major workers. These can be more than 0.5″ long. There are also small workers, called minor workers. These are often less than 1/8″ long.


Most carpenter ants nest in trees and woodpiles. (Exception: the Florida carpenter ant often nests in the ground under leaves or items that are on the ground.)

As they burrow into wooden beams in houses, carpenter ants are highly destructive. Tiny as they are, the pests easily enter homes through cracks in windows and doors, holes in siding and roofs, and fissures in building foundations. Carpenter ants set up parent nests in addition to several satellite colonies in close proximity to each other, so individuals may encounter multiple nests in infested homes.

Where To Look For Them

Colonies are typically found in moist or decaying wood where there’s plenty of condensation and poor airflow, including under bathroom tiles, around dishwashers, under roofing, around windows, and under tubs, sinks, and showers. When carpenter ants come into homes, they often make nests inside walls and under cabinets.

Nests Inside
If there is wood that is damp or decaying, the carpenter ants will hollow it out and make their nest in it. Has there been a plumbing problem, a roof leak, or a drainage problem? Carpenter ants readily nest in wood in areas where there is dampness. Moisture ants like damp areas too, but they are yellow ants.

However, dry areas like those found in insulation, wall voids, and hollow doors become infested with workers, pupae, and larvae.

Homeowners often hear rustling sounds of carpenter ants moving around in their nest inside the wall.

Nocturnal Activity

When did you see them?
Carpenter ants are active at night. (Outdoors they are also active on cloudy days.) A few workers may forage during the day, so it is possible to see a couple of ants wandering around.) However, at night the workers move around in lines.

They follow trails between their food supply, the water supply, the satellite nests, and the main nest. Homeowners who suspect they have carpenter ants may benefit from making an inspection at night. During the inspection, look outside at window sills, eaves, fences, utility lines, and tree limbs that touch the house. Trails of ant workers will often lead to the nests.