[Small Carpenter Ant] Ants aren't always what they seem

Features - Ants

Proper ant identification needs to be the first step in any control program. The additional time spent in identification is an investment towards reducing your time spent controlling the pest and returning on callbacks.

February 28, 2011
Ted Snyder

I had a problem. A pest management professional had brought in an ant for me to identify. It had been showing up on the second story of a two-story office building. His problem was that he couldn’t stop sightings of the ant. My problem was with the identification.

I first thought it was a cornfield ant. Cornfield ants are small ants that nest in turf and fields. They will occasionally enter structures looking for food.

In Figure 1 on page 99, you can see a typical cornfield ant. There are two traits that can give you a fairly rapid identification on this ant: a single node and long palps (palps being the leg-like appendages around the mouth).

Although the ant I had was small and was a one-node ant, the palps weren’t long. That frustrated me.

There are more than 20,000 species of ants, and the majority of them are only occasionally considered pests. If you’ve ever encountered an unusual ant in one of your accounts, where it showed up for a while but then disappeared, and you’ve never seen anything like it again, you may have encountered one of these ants. I chalked this ant up as one of these occasional invaders.

My identification was still wrong. I had an unusual type of carpenter ant.

WAYS TO ID CARPENTER ANTS. I had always thought that carpenter ants were easy to identify. They are large and black, oftentimes with yellow hairs on their abdomen.

These traits could work well if all we ever saw was the black carpenter ant or the Western black carpenter ant, but there are more types of carpenter ants that just those, and we need to use other traits if we are going to consistently and correctly identify carpenter ants.

The right way to identify carpenter ants is to look for two traits. First, a single node. Second, their thorax is evenly rounded, that is to say, it doesn’t have any large dips or depressions in it. Compare Figure 2 below (the ant that was brought to me) with the cornfield ant in Figure 1.

The ant I was dealing with wasn’t just a carpenter ant; it was the small carpenter ant, Camponotus nearcticus, which can be distinguished from other carpenter ants by a couple of traits. First, their small size (3/16 to 1/3 inch). Second, any of the following color combinations: abdomen black; head black, brownish red, or dark red; thorax or legs black, brownish red, or dark red.

BIOLOGY AND BEHAVIOR. In nature, the small carpenter ant nests in tree branches and similar locations. When it nests in structures, it prefers higher areas, especially eaves and soffits, which can, to the ant, resemble tree branches. Like most carpenter ants, it is attracted to moisture damaged wood, but it is more likely to nest in sound wood than the black carpenter ant.

Figures 3 through 5 provide some images of typical nesting locations, although these can also be nesting locations for other types of carpenter ants.

The small carpenter is found throughout the United States and the southern reaches of Canada, except for Colorado, Utah (except the Northwest), southern Nevada, California south of the San Francisco Bay Area, Arizona (except the southeast), southeastern New Mexico, parts of Texas, southern Louisiana, and Florida south of the panhandle.

CONTROL. When I first encountered the small carpenter ant, the pest management professional had tried everything he could think of to control them. He’d baited trails. When I had thought that they may have been an occasional invader ant, he’d used a residual insecticide on the perimeter of the building and on the ivy that grew up the side of the building.

Once I had my identification, I understood why this ant was only showing up on the second floor of the commercial structure. The structure itself was two stories, and the colony must have been in the soffits or the roof!

Also, carpenter ants do not take bait as readily as other species of ants, which explains why the attempts to bait this ant prior to identification had failed.

Carpenter ant control is a four-step process.

First, inspect thoroughly. Look for potential nesting sites. The identification of your carpenter ant will give you some clues. Also, inspect for frass (debris resembling wood shavings with insect body parts in them), water-damaged wood, and small openings that ants may be using to enter the structure. If desired, a small amount of flushing agent can be injected into potential openings. If a number of carpenter ants come out, or if you hear a noise inside the wall that sounds like newspaper crinkling, then you’ve found a nest.

Second, treat the nest. Once you’ve found a nest — or if you suspect an area harbors a nest — treat the cracks or crevices leading into it with an insecticidal dust.

Third, treat other areas. Interview the client to find out where on the interior and exterior carpenter ants have been sighted. These areas need to be treated with a liquid residual insecticide. Best results come from using any of the various non-repellent insecticides.

Fourth, use habitat modification techniques. Determine what was attracting ants to the structure. Some common problems might include moisture-damaged wood, branches of shrubs or trees touching or overhanging the structure, and dead wood (firewood, stumps, etc.) stored adjacent to the structure. Also, as with other ants, poor sanitation conditions indoors can be particularly attractive to carpenter ants.

FINAL THOUGHTS. Proper ant identification needs to be the first step in any control program. The additional time spent on identification is an investment towards reducing your time spent controlling the pest and returning on callbacks.

The author is training & technical services manager at Batzner Pest Management, New Berlin, Wis. He also blogs about pests at www.tedsnyderonline.com. E-mail him at tsnyder@giemedia.com.


Various authors. AntWeb, http://www.antweb.org.

Hansen, Laurel, and Klotz, John. 2005. Carpenter Ants of the United States and Canada.

Mackay, William. 2004. The Systematics and Biology of the New World Carpenter Ants of the Hyperdiverse Genus Camponotus (Hymenoptera: Formicidae).