Carpenter ants are in your house because they found moisture, wood they can nest in, or food worth foraging for. Usually it’s a combination of all three. Unlike termites, carpenter ants don’t eat wood. They hollow it out to build nests, pushing the debris out behind them. Your home is attractive to them for the same reasons it’s attractive to you: it’s warm, sheltered, and has a reliable water supply.
Moisture Is the Biggest Draw
The single most common reason carpenter ants move into a home is moisture-damaged wood. Damp wood is softer and easier for the ants to chew through, and the warm, humid conditions inside wall cavities help their colonies grow and reproduce. They can nest in dry wood too, but they strongly prefer areas that have been wet.
The trouble spots are predictable: around and under windows, roof eaves, decks, porches, chimneys, skylights, and anywhere plumbing runs. Carpenter ants have been found nesting under bathtubs, inside dishwashers, in wall voids beneath window sills, inside hollow doors, under fiberglass insulation in crawl spaces, and behind siding. If you’ve had a slow leak anywhere in your home, even one you’ve already fixed, the wood it softened could still be inviting ants in.
Your House May Be a Satellite Colony
Here’s something most people don’t realize: the ants inside your house probably aren’t the main colony. Carpenter ant colonies have a parent nest that needs a steady moisture supply, so it’s usually located outdoors in a dead tree stump, a rotting log, or landscape timbers. From that parent nest, the colony establishes satellite colonies in drier, protected locations like the inside of your walls. Workers travel between the two, sometimes foraging as far as 100 feet from the parent nest.
This means the ants you’re seeing indoors could be commuting from a stump or woodpile in your yard. It also means that killing the ants inside your house without addressing the parent colony often doesn’t solve the problem. They’ll keep sending workers back.
They’re Also Looking for Food and Water
Even if carpenter ants aren’t nesting in your walls, they may be foraging inside for food. They eat proteins and sugars: meat scraps, pet food, honey, syrup, fruit, candy, and soda. In early spring, workers from an indoor colony start searching for food before much is available outside, which is why you’re most likely to notice them in your kitchen or bathroom during March through May. They’re also drawn to standing water in sinks, pet bowls, and damp countertops.
During spring, carpenter ants are particularly attracted to protein sources. As the season progresses, they shift toward sweets. If you’re finding a handful of large black ants near your kitchen counter or trash can, they’re likely scouts following a scent trail back to the colony.
How to Tell It’s Carpenter Ants
Carpenter ants are among the largest ants you’ll find indoors, typically a quarter to half an inch long, and usually black or dark brown. The clearest sign of an active nest is frass: small piles of coarse, shredded wood shavings that the ants push out of their tunnels. You’ll find these piles beneath baseboards, window trim, or along walls. The debris looks rough and fibrous, sometimes mixed with insect body parts or bits of insulation.
If you’re seeing winged ants inside your home, especially in spring, that’s a strong indicator of a mature colony nearby. Winged carpenter ants are sometimes confused with termite swarmers, but they’re easy to tell apart. Carpenter ants have elbowed antennae, a narrow pinched waist, and two pairs of wings that are different lengths. Termites have straight antennae, a thick waist, and wings that are all the same length. If you’re seeing winged ants indoors during winter or early spring, they’re almost certainly emerging from a nest inside the structure.
How Quickly They Cause Damage
Carpenter ants are slow workers compared to termites. A new colony takes up to six years to fully mature, and it takes months for eggs to develop into adult workers. You’re unlikely to see serious structural damage from a colony that’s only been active for a season or two. That said, a large, established colony that goes undetected for years can weaken beams, joists, and framing, especially in areas already compromised by moisture. The damage is cumulative, and because it happens inside walls, it’s easy to miss until it’s significant.
What’s Attracting Them From Outside
Before carpenter ants get inside, something in your yard draws them close. Dead tree stumps, stacked firewood, old landscape timbers, and fallen branches all serve as nesting sites for parent colonies. The longer wood sits undisturbed on the ground, the more likely it is to become infested. Trees with openings or cavities near the house are also attractive nesting spots. Branches or shrubs that touch your siding, roofline, or windows give ants a direct bridge from their outdoor colony to your home’s interior.
How to Fix the Problem
Because carpenter ants are driven primarily by moisture, the most effective long-term fix is eliminating the water source. Repair leaky roofs, windows, doorframes, and plumbing. Replace any wood that’s been water-damaged, rotted, or previously infested by ants or termites. Make sure there’s no place where wood contacts soil directly, since that wicks moisture up into the structure.
Outside, remove dead stumps and store firewood off the ground and away from the house. Trim trees and bushes so no branches touch the building. Seal any openings in living trees near the structure. These steps remove both the nesting sites that support a parent colony and the pathways ants use to reach your home.
For active infestations, bait systems tend to be more effective than sprays alone. Baits work slowly, which is the point: foraging ants carry the bait back to the colony and share it, eventually reaching the queen. Perimeter sprays can kill the workers you see, but if the parent colony outdoors stays intact, new workers will replace them. If you’re finding frass in multiple locations or seeing large numbers of ants consistently, a pest control professional can help locate both the satellite and parent nests, which is often the hardest part of getting rid of them for good.