Carpenter ants are a widespread household pest known for tunneling through wood, which can cause structural concerns for homeowners. Unlike many other ant species, these large insects can cause significant damage as they establish colonies within wooden structures. Understanding their behavior, particularly when they are most active, is the first step in managing an infestation.
Activity Patterns and Timing of Foraging
The worker carpenter ant is primarily nocturnal, impacting when homeowners see them. Foraging peaks at night, often starting around dusk and continuing until dawn. This timing allows the ants to avoid predators and extreme temperatures while searching for food and water.
While most active outside at night, the colony remains busy around the clock inside the protected galleries. Temperature plays a large role; foraging slows or stops completely below approximately 50 degrees Fahrenheit. During warmer months, some worker ants may forage during the day, particularly if the colony is large or a desirable food source is nearby.
These ants are scavengers, seeking sweets like honeydew from aphids, plant nectars, and protein from dead insects. This food-gathering occurs under the cover of darkness. Spotting large ants repeatedly indoors at night strongly indicates a nearby established colony.
Key Characteristics and Nest Location
Positive identification is important, as carpenter ants are often confused with termites due to their wood-dwelling habits. They are among the largest ant species in North America, with workers measuring between one-quarter and one-half inch in length. They are usually black or a combination of black and dark red.
A defining characteristic is the single, upward-protruding segment, or node, that forms their narrow waist between the thorax and abdomen. In contrast, termites lack this pinched waist, having a broad connection between their body segments. Carpenter ants possess antennae that are distinctly bent, or elbowed, while termites have straight antennae.
These pests do not consume wood, but excavate it to create smooth, clean galleries for nesting. They prefer to establish parent colonies in moist or decaying wood, as this is easier to chew. Areas prone to water damage, such as around leaking pipes, poorly sealed windows, or roof eaves, are common targets.
A single colony can grow large, leading to the establishment of one or more satellite nests. These secondary nests do not contain the queen or eggs, but house workers, mature larvae, and pupae, and are often found in drier wood within the structure. The presence of multiple nesting sites makes locating and eliminating an entire infestation challenging.
Signs of Infestation and Wood Damage
The clearest physical evidence of an infestation is “frass,” a distinct debris pushed out of their tunnels. Frass is composed of coarse wood shavings created during excavation, often mixed with dead insect parts and waste products. Piles of this sawdust-like material are found directly below small openings, known as kick-out holes, which the ants use to clear galleries.
When inspecting damaged wood, the galleries appear clean, smooth, and sandpaper-like, differing from termite tunnels which are often lined with mud. Carpenter ants chew along the wood grain, creating extensive, interconnected tunnels that can weaken structural timbers. This excavation process leaves the wood with a hollow sound when tapped, which is a useful diagnostic clue.
An auditory sign can indicate an active colony, particularly during quiet, nocturnal hours when the ants are excavating. Homeowners may hear a faint, dry rustling or tapping sound from within walls, which is the sound of workers scraping wood with their mandibles. Finding large, winged reproductive ants, known as swarmers, indoors is a strong sign, indicating a mature colony ready to establish new nests.
Next Steps After Discovery
Upon discovering evidence of carpenter ants, the focus should be on locating the nest and addressing the environmental conditions that attracted them. Since they are drawn to moisture-damaged wood, fixing plumbing leaks, ensuring proper ventilation, and repairing roof or window leaks is paramount. Removing excessive moisture makes the nesting environment less hospitable.
After correcting moisture issues, homeowners should seal all potential outdoor entry points, such as cracks in the foundation, utility line openings, and gaps around window and door frames. This prevents foraging workers from easily entering the structure. However, because the nests are often hidden deep within wall voids or wood, complete elimination usually requires professional intervention.
Pest control specialists use specific strategies, often employing non-repellent dusts or baits. Insecticidal dusts are applied directly into the kick-out holes and galleries. Baits are picked up by foraging workers and carried back to the nest to poison the entire colony, including the queen and brood. Treating only visible ants without destroying the hidden parent and satellite nests is unlikely to resolve the infestation permanently.