Of the many kinds of ants found in and around houses, one in particular spells "double trouble." Carpenter ants tunnel into wood to form nest galleries, as well as becoming a nuisance with their foraging in kitchens for food. These ants, if unnoticed for several years, can cause structural damage. Control measures include prevention and the application of insecticides. Effective control depends upon locating the nest. Often pest control operators can control carpenter ants more efficiently than homeowners.

Identification

Carpenter ants are usually larger than most other house-infesting ants. Those of economic importance as wood destroyers belong to the genus Camponotus, with 14 species occurring in Texas. These ants vary in color from a solid dull black or yellowish-red to a combination of black and dull red or reddish-orange. Mature colonies have several castes or forms of adults, including winged and wingless queens, winged males and several sizes of wingless workers. Winged queens are about 3/4 long, including wings. Only one functional, wingless queen (9/16 long) will be in the colony. The winged males are up to 7/16 inch long.

Workers vary considerably in size. Minor workers average 5/16 inch long and major workers are up 7/16 inch long, but there may be several intermediate sizes between these two extremes.

Winged carpenter ants resemble winged termites and, in Texas, it is not uncommon for both of these important wood-destroying insects to swarm at about the same time. It is important that they be accurately identified since control measures are different for the two. Ants have small pinched-in waists, wings of unequal length (the front pair longer than the hind pair) and the antennae bent at right angles about the mid-length. A termite's body is not narrowed at the middle, the wings are of equal length and the antennae are rather straight with bead-like segments.

Biology and Habits

Carpenter ants are social insects which live in colonies made up of different forms or castes. Each of these castes has its own specific duty or function contributing to the success of the colony. Ants develop through several stages: egg, larva, pupa and adult. Larvae are small, legless, white and grub-like. The pupal stage follows larval development and is completed inside tan or cream-colored cocoons which are often mistakenly referred to as "ant eggs."

From early spring to summer large numbers of winged males and females emerge from established colonies. Emergence is triggered by environmental conditions and may occur over several days or weeks, which allows for interbreeding of individuals from different colonies. Mating occurs in flight, after which the males die and the females begin searching for a nesting site. The new queen breaks off her wings, either just before or after selecting the nesting site.

Outdoors, carpenter ants use dead trees or tree limbs, stumps, logs, firewood or areas under stones as nesting sites. They tunnel into wood only to make nests, not for food. Queen ants may establish new colonies in homes, seeking nest sites in wood shingles and siding, beams, joists, fascia boards or other exposed wood. They prefer moist, decaying wood since it is easier to penetrate, but will enter natural cracks, checks, knotholes or joints.

Probably the most common way in which a home becomes infested is by the movement of all or part of an existing colony from outdoors. Ants can enter when tree branches or utility lines contact a house. They may gain access through cracks and crevices around windows and in foundation walls, through ventilation openings in the attic and through foundation heating or air conditioning ducts. Carpenter ants do not always attack wood when nesting in houses, but can use existing cavities in wall voids above below cabinets, hollow-core doors or old termite galleries. They also may be found on shelves or beneath insulation in attics.

After establishing a nesting site, the female deposits 15 to 20 eggs. Under favorable conditions these eggs progress through the larval, pupae and into the worker stage in about 2 months. The queen cares for the larvae and feeds them with fluids secreted from her body. After becoming adults, these new workers take over the responsibility of expanding the nest as the colony population increases, and providing feed for new broods and the queen. The first generation worker ants are small. The queen's responsibility is to produce eggs for the remainder of her lifetime.

The colony remains small during the first year, but in subsequent years the population grows rapidly, up to 2 or 3 thousand or more individuals. Usually it takes 3 to 6 years for a colony to reach this size, at which time winged reproductives are produced. Once the colony reaches a certain size it rarely grows larger, but workers are continually produced to replace those which die or are lost.

Economic Importance

Carpenter ants generally are not a serious threat to structures in Texas. However, if a nest goes unnoticed for several years while it is continually expanded to accommodate the developing colony, or if other colonies are established in the wood, significant damage may occur. This may result in a need for expensive structural repairs.

Control

Inspection

Once the carpenter ant nest has been located, control is relatively easy. Inspections should be carried out, both indoors and outdoors.

Examine carefully any tree stumps, dead or dying shrubbery, overhanging tree limbs, attached fences, wooden porch floors and columns, window and door sills, roof edges and areas between the roof and the ceiling. These areas are most likely to have wood with a high moisture content, or are likely to have decayed and rotting wood as a result of excessive moisture. Under or against the house, examine carefully any wood in contact with the soil. Because carpenter ants do not confine their nests to damp wood, the interior of a house should be inspected for signs of activity. To locate the nest area, follow foraging carpenter ants to determine the general direction they are traveling. These ants may lead you to their nest site. Look carefully at the edges of the floor, ceiling, windows, and door trims. In addition to wall void areas above windows and doors and inside hollow-core doors. In Texas, carpenter ants are commonly found in attics, nesting in or under fiber-glass or blown in insulation.

The most obvious sign of infestation is seeing large black or black and reddish ants in the kitchen or bathrooms, or large winged ants collected on window sills. Look carefully for piles or scattered bits of the fibrous, sawdust-like frass which the ants have removed from the wood. The frass can be distinguished from construction sawdust or from the frass of other wood infesting insects such as carpenter bees by the fragments of ants and other insects mixed with the wood fibers. Frass is expelled from cracks and crevices or from the slit-like openings or "windows" made by the ants themselves.

Carpenter ant galleries usually are found following the grain of the wood and around the annual rings. The softer spring wood is tunneled first; however, the hard grain is penetrated at frequent intervals to interconnect the galleries. No carpenter ant galleries can be observed from the wood surface. The inner surfaces galleries are smooth and contain no frass or borings. Occasionally ants will make faint rustling or gnawing sounds which can be heard in wall voids or cavities within the wood, particularly when large colony is present.

During the inspection, other wood-infesting insects or the damage they cause may be discovered.

Prevention

Preventing carpenter ants is difficult, but certain measures will greatly reduce the likelihood of invasion. Since carpenter ants are likely to nest in damp or decaying wood, this condition should be avoided or remedied. Insure proper clearance between structural wood and the soil. Provide good ventilation under the house in the attic, and for drainage away from the house. Repair or replace roof flashings and roof eaves, porch supports and other places that are exposed to moisture. Use pressure-treated wood if possible.

Remove stumps, logs and wood debris near the house. Store firewood away from the house. Remove or treat with insecticides any carpenter any colonies found within 100 feet of the house. Keep exposed wood in good condition, with paint sound and all cracks, knot holes, checks or joints properly sealed with wood putty and paint.

Insecticide Use

Once the nest has been located treat it with a residual insecticide applied either as a dust or spray. If insecticides are applied only where ants are seen and not in their nest location, control is unsatisfactory because only isolated individuals are killed. Individual carpenter ants can live for 6 months or more without feeding, so unless the nest is treated control is unlikely. It may be necessary to drill small holes into wall voids, window and door sills, baseboards and other areas to reach the nest or major part of the colony. Dust formulations are particularly effective for this type of application. Attics can also be lightly dusted if the nest is located there. Use insecticide products containing carbaryl (Sevin), chlorpyrifos (Dursban), diazinon or propoxur (Baygon@). Wooden structural members and other exposed wood that is frequently wet may be treated with a wood preservative which retards decay as well as killing any ants that contact treated surfaces. Galleries in wall voids or other indoor areas can be dusted with a product containing silica gel, which will provide long term residual protection if the area treated remains perfectly dry.

Pest control operators are familiar with carpenter ants, the damage they cause and conditions leading to infestations. They have experience in the sometimes difficult task of nest location. They have chemicals and equipment to make safe and effective treatments. In many cases it may be best for home owners to employ a local pest control firm to deal with carpenter ant problems.