Department of Entomology
BIOLOGY AND CONTROL OF CARPENTER ANTS
By: Michael Waldvogel, Extension Entomology
Insect Note - ENT/rsc-14
|In North Carolina,
as in other southern states, carpenter ants are generally considered of
lesser importance compared to termites in the amount of structural damage
they cause. However, a carpenter ant problem that is ignored or goes unnoticed
can lead to signficant damage. The term "carpenter ant" is applied broadly
to several species of ants that nest in or around wood. Our concern is with
ants in the genus, Camponotus. Some of these species actually tunnel
into the wood, while other species prefer to nest in existing cavities.|
Carpenter ants are among the largest species that you will find in North Carolina. Like other ant species, carpenter ants are social, i.e, they live in a colony and have several "castes" or adult forms that perform different jobs in the colony. The queen usually reaches 9/16 inch in length. The workers range in size from 1/4 to 7/16 inch. So, if you see different sized ants, they could all be from the same colony. All of these ants are adults regardless of their size, so they do not grow. Only the queen produces offspring in the nest. Immature ants (larvae) are white, legless, and maggot-looking in appearance. They remain in the nest and are fed by the workers. The larvae develop into pupae, which are tan and capsule-shaped. Eventually, new adults emerge from these pupae. Adult ants will vary in color depending upon the species. The black carpenter ant, the species that most commonly nests in homes, is primarily black in color. Other carpenter ant species may be more reddish-brown to yellow in color.
In the spring, carpenter ants swarm, i.e., winged
adults emerge from the colony. The swarmer's sole purpose is reproduction.
Shortly after mating, the female (queen) loses her wings and searches
out a cavity in wood or soil where she begins to lay eggs and produce
her colony's first workers. These workers care for the queen as she produces
more offspring, and they assume the tasks of foraging for food, maintaining
and expanding the nest, and caring for the young. After 3-6 years, the
colony will contain 2000-3000 workers, and will start to produce swarmers.
The swarmers are actually produced in the fall, but they wait until the
following spring to emerge. Swarming is not the only means for carpenter
ants to produce new nests. "Satellite" colonies may be formed by workers
that move out of the main nest, carrying larvae and pupae with them. Eventually,
these secondary colonies produce their own reproductives.
Nesting and Feeding Habits
Unlike termites, carpenter ants do not eat wood; they tunnel through wood while building or expanding their nests. Typical outdoor nesting sites include tree holes, tree stumps, logs, standing dead trees, and planter boxes. When conditions are suitable, carpenter ants may establish nests indoors. Typical indoor nesting sites include structural wood, wall voids, attic areas, insulation (foam or fibreglass), hollow doors, window/door casings, voids beneath kitchen/bathroom cabinets, as well as hollow beams (e.g., decorative beams that may cover pipes or girders. In the case of carpenter ant species that nest in existing cavities, the workers may subsequently invade and damage nearby structural wood while expanding their nest site. Carpenter ants prefer wood with a moisture content of 15% or higher, so the problem is often associated with moisture. The ants often invade homes through cracks and crevices in the foundation masonry, around windows and doors, through foundation, as well as heating/AC vents. They may travel along tree limbs or shrubs that touch the siding and roof, gaining access to attic areas. Telephone, electric and cable TV lines also provide ready means of entering the home. The primary food of carpenter ants is honeydew, the sugary secretions of certain plant-feeding insects, such as aphids and scales. For that reason, worker ants are often found traveling up tree trunks and on to limbs in search of honeydew on the leaves. The ants will also feed on plant secretions and fruit juices, as well on the remains of insects, including dead members of their own colony. When the ants invade homes, they usually seek out sweet items, such as sugar, but they also will feed on fats, grease and meats. Water is also important to the ants. Outdoors, you will often find ants collecting water dripping from water spigots, gutter downspouts or air conditioner drain lines. Indoors, the ants are often seen near sinks, bathtubs and dishwashers.
Signs of an Infestation
There are several indications of an infestation:
Swarmers - The appearance of swarmers indoors is a likely indication of a nest in or under the house. Winged ants will emerge from around baseboards, window casings, vents or other openings in floors or walls, and will often congregate around windows. Swarmers found outdoors on porches, siding or around windows are merely a sign of a nearby colony, which is most likely located outdoors. However, it is well worth the effort to inspect your home for other signs of ant activity.
Workers - Beginning in early spring, worker ants will often be found foraging for water around bathroom/kitchen sinks, dishwashers or showers. Foraging activity is usually greater at night when the lights are off, but you will find ants during the daytime, as well. In some cases, you may be able to trace the insects back outdoors where they are traveling to and from a nearby nest. With extensive foraging, your will find trails that the ants maintain clear of debris. These trails may extend up to 300 feet from the nest.
Noise - With mature colonies infesting a house, you can actually hear rustling or gnawing sounds coming from the wood or void where they are nesting.
Sawdust - As the ants expand their nest, they throw out piles of fiber-like wood debris and frass (fecal material). Debris with a dark appearance is likely an indication of decaying wood, and can be used as a clue in searching for the nest. The frass may have a sawdust-like appearance, but will also contains the remnants of ants and other insects on which the colony has been feeding.
Damage - wood that is damaged by carpenter ants may have
slit-like openings through which the ants expel the sawdust and frass.
The galleries will usually follow the wood grain, with the softer "springwood"
portion of the annual rings being excavated first. Tunnels through the
harder summerwood connect these galleries. The gallery walls will be relatively
smooth, resembling drywood termite damage. However, the galleries of drywood
termites are usually filled with small, hard, seed-like fecal pellets
that do not resemble the wood fiber debris that carpenter ants remove
from their galleries. Wood damaged by subterranean termites also has excavated
areas, but the gallery walls have a coating of a mud-like fecal material.
Preventing Carpenter Ant Problems|
Anytime there are trees, stumps or other wood items around our home, there is always the potential for a carpenter ant problem. However, there are important steps that you can take now to prevent carpenter ants from becoming a problem. Prevention starts with common sense and inspection, not with a monthly or periodic pesticide application. Proper maintenance of your home and surroundings greatly reduces the likelihood of a carpenter ant problem. The key point to remember is that carpenter ants are usually associated with moisture, particularly where wood is involved:
Controlling Carpenter Ants
It is important to remember that finding carpenter ants foraging inside your home does not necessarily mean that they are nesting indoors. Do not panic and do not resort to spraying insecticides indoors where you see ants. Although spraying stops ant foraging for a while, it only serves to detour them elsewhere (possibly elsewhere indoors) and they will likely return when the chemical residue is gone. More importantly, you may be delaying the inevitable discovery that the ants are actually damaging your home. The first step in controlling carpenter ants is to determine if they are nesting indoors. Spraying your foundation with any of the commonly available insecticidesmay keep foraging ants away temporarily, giving you a clue as to the source of the ants. (Check the NC Agricultural Chemicals Manual for a list of chemicals that can be use). If ant activity continues at about the same level, then you may very well have an indoor infestation. As an alternative to spraying, you can try baiting the ants outdoors. Put small amounts of honey mixed in water into bottle caps (or similar small containers) and place them along the foundation. Carpenter ants are more active at night, so do your investigation after sunset. Try to follow the ants as they move away from the baits and back to their nest. In most situations the ant nest is located nearby, although it could be as much as 300 feet away from where you find foraging ants. The main purpose of this baiting is simply to see where the ant trail leads. If the ant trails move away from the house, you can use one of the control methods mentioned below for outdoor infestations. If the ants appear to be nesting indoors, the next step is to carefully inspect for likely nesting sites. Concentrate first on those areas around your home that are most vulnerable to moisture problems. Probing the wood with a screwdriver or ice pick is a good way to uncover damage by a number of wood-destroying pests, including carpenter ants and termites. Careful inspection of the attic and crawlspace are important. Because of the time-consuming and tedious nature of a thorough inspection, you may want to enlist the help of a pest control company that has the experience and the ability to quickly find and eliminate the ants.
Indoor infestations - Simply spraying surfaces where you where you see ants foraging is not likely to solve the problem. The ants are likely to move to some other area (still indoors) and may return later when the chemical residue is diminished. Ant baits, particularly those containing hydramethylnon, sulfluramid, avermectin or boric acid, can be effective if the ants are foraging for food. If the ants are gathering around water sources (e.g., a sink), they may not be attracted immediately to the bait. In general, baits are the best approach to dealing with ants. They are more effective in the long term and are less hazardous (compared to sprays) when used properly. However, they may require 7-10 days before ant activity declines significantly. You must be willing to tolerate some ant activity to give the foragers enough time to carry the bait back to the nest where it will be fed to the larvae, other workers and to the queen. Do not spray areas where you will place the bait; otherwise, the ants will avoid these areas and not pick up the bait. If ant activity continues at about the same level for several weeks, then you need to take additional steps to deal with the problem. Before spraying, you should first determine the extent of any structural damage caused by the ants. The may require removing siding or portions of sheetrock (indoors). If the damage is severe, repairing and/or replacing wood (and subsequently removing the nest) may be more important than any treatment, and may solve the problem in the process. If damage is minor, then you can use of a pesticide that is labeled for application to wood to eliminate the nest. Effective control often requires the injection of insecticidal dusts or sprays into voids or into the nest. These treatments are complex and may be too difficult for the average person to carry out safely. Contact a pest control professional for help in these situations.
Outdoor treatments - If the ants are foraging from an outdoor nest that cannot be found, then a perimeter treatment can help. Liquid or granular insecticidesapplied to/along the foundation will cut foraging activity temporarily, but they will not prevent ants from returning at some later date. A list of these products can be found in the NC Agricultural Chemicals Manual . A better choice might be a granular ant bait sprinkled in a 8-12" area on the soil along the foundation. Combat®, which is available in most retail stores, as well as the professional ant baits Maxforce® and Advance® are commonly used for ants, including carpenter ants. Other baits may also be available. Note: Granular baits are not the same as the granular insecticides that are often used for controlling lawn pests. Granular insecticides may be helpful, but must be watered into the soil.
Read the product labels carefully to be sure that you buy the right product.
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ENT/rsc-14 (June 1996). Web version last updated - 08/07/08
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