Carpenter ants are the largest ants found inside your home. They may range in size from 1/5 to 3/4 inch. Winged ants or reproductive, (swarmers) are typically found in the spring and summer months. Carpenter ants are a nocturnal insect, the presence of an infestation may be heard at night or in the early morning hours. The sounds of carpenter ants are similar to the sound of rustling cellophane. You may also see sawdust piles (frass) often in conical piles inside the crawlspace, basement, or inside the home.
Carpenter ants damage wood by excavating and creating galleries and tunnels. These areas are clean, i.e. they do not contain sawdust or other debris, and are smooth, with a well sanded appearance (see photo to right).
The damage to wood structures is variable. The longer a colony is present in a structure, the greater the damage that can be done. If structural wood is weakened, carpenter ant damage
can be severe.
It is common to find carpenter ants in homes during spring. It is important to try to determine whether the ants are coming from an outdoor or an indoor nest, although this can be difficult. Their presence is not sufficient evidence to conclude that there is a nest in your home. You may be able to make a more accurate determination based on when you first see carpenter ants. If you find carpenter ants in your home during late winter or early spring, that suggests the ants are coming from a nest in the building. However, if you see activity later in the year, it is less clear if the nest is in the building.
You may also see carpenter ant swarms (i.e. the reproductive queens and males, during spring. Carpenter ants produce large numbers of queens and males during late summer. They emerge from nests the following spring for their nuptial flights. After mating, queens search for suitable sites to begin new nests. Once they land, their wings break off and each queen attempts to construct a new nest.
When carpenter ant nests are indoors, mating swarms become trapped inside. Finding large numbers of winged ants indoors is a sure sign that an indoor nest exists and may give the approximate location of the colony.
Finding one to several winged queens does not automatically mean a nest is present indoors. It is more likely the queens have just mated and have entered the home, searching for nesting sites. Wingless queens (figure 1) found walking indoors are new queens that have recently shed their wings but are still searching for nesting sites. They are not an indication of an indoor nest.
In almost all cases, carpenter ants seen indoors during winter are an indication that there is an inside nest. One exception is when ants are brought indoors in firewood. Workers from firewood are not able to start nests in homes, nor do they damage wood structures in buildings.
Workers may become active during winter if the nest receives sufficient warmth from sunlight, mild outdoor temperatures, or from indoor heat. It is not clear whether just a few workers break dormancy or the entire nest becomes active. When ants are active during winter they will forage at night, searching for moisture. It is common for a home dweller to enter a room early in the morning, turn on the lights, and see ants scurrying for cover. Common places to sight them are cabinets, sinks, dishwashers, rolled-up towels, bathroom tubs, sink and toilet areas, or other places where moisture is abundant. On a bright sunny day, ants may be seen walking randomly through different areas of the house.
It is also possible for a carpenter ant nest to exist in a house during winter but not be noticed. If the nest exists at a site that does not receive sufficient indoor heat or sunshine, e.g. a north-facing outside wall, the ants will remain dormant until spring.