Carpenter ants are one of the most common wood-destroying insects in California, and unlike termites, they don’t eat wood. They excavate it, carving out galleries and tunnels to build their nests. The damage starts slowly, usually in wood that’s already damp or decaying, but a mature colony can expand into sound, dry wood and compromise structural integrity over time.
How to Identify Carpenter Ants
California is home to several species of carpenter ants in the genus Camponotus. They’re among the largest ants you’ll encounter, with workers ranging from about a quarter inch to over half an inch long. Most are black or dark brown, though some California species have reddish-brown coloring on parts of their body. The easiest way to distinguish them from other large ants is their smooth, evenly rounded thorax (the midsection between head and abdomen) when viewed from the side.
If you see large winged ants indoors, especially in spring, those are reproductive “swarmers” leaving a mature colony to start new ones. Their presence inside your home is a strong indicator that a colony has been established nearby for several years.
Where They Nest in California Homes
Carpenter ant colonies operate with a two-nest system. The parent nest is usually outdoors, located in a dead or living tree, a tree stump, a woodpile, or landscape timbers. From that base, colonies establish satellite nests in nearby structures. The indoor nest you discover is almost always a satellite, connected to a larger parent colony outside by trails of workers moving back and forth.
Parent nests require moisture because the eggs need humidity to survive. That’s why initial infestations start in wood damaged by water leaks, condensation, or poor ventilation. Common entry points include areas around windows, where wood contacts the foundation, and anywhere plumbing runs through walls. Satellite nests, however, don’t house eggs, so they can set up in relatively dry spots: wall voids, hollow doors, insulation, and sound wood. This is what makes them tricky. By the time you notice ants in a dry, interior wall, there’s likely a moisture problem somewhere else that started the whole chain.
In California specifically, kitchens and bathrooms are prime targets because of the higher humidity. Under dishwashers and sinks, where hidden leaks create perfect nesting conditions, is a particularly common location. Crawl spaces where insulation meets wooden beams are another hotspot.
Signs of an Infestation
The most reliable sign is frass: small piles of wood shavings that carpenter ants push out of their galleries as they excavate. Carpenter ant frass looks like the output from a pencil sharpener, with rough, fiber-like, uneven bits of different sizes. The piles often include soil, dead ants, insect parts, and cocoons mixed in. Fresh frass is loose and light-colored, matching the wood being excavated. Darker, brown frass typically means the ants are working through damp or rotting wood.
Where you find frass tells you where to look for the nest. A pile beneath an exit hole almost always means the colony is directly above or behind that spot. Check window sills, door frames, baseboards in kitchens and bathrooms, and built-in cabinets where they meet walls or floors. If you find frass on more than one floor of your home, the colony has likely established multiple satellite nests.
A few indicators suggest a well-established problem:
- Frass in multiple rooms or piles that reappear after you clean them up
- Rustling sounds in walls near frass piles, especially at night
- Cocoons in the frass, which means the colony is actively breeding and has been established for at least three to six years
- Winged swarmers indoors, confirming a mature colony
- Frass near load-bearing wood or structural beams, which raises the stakes considerably
When and How They Forage
Carpenter ants are primarily nocturnal. Workers leave the colony in late afternoon or early evening, forage through the night, and return by early morning. This is why you might never see them during the day even if a colony is active in your walls. If you suspect an infestation, checking with a flashlight after dark along baseboards, counters, and exterior walls is far more revealing than daytime inspections.
Their diet is varied: living and dead insects, sweets, meat, fats, and honeydew (the sugary substance produced by aphids and scale insects on garden plants). Workers can forage several hundred feet from the nest, which means the ants you see in your kitchen may not be nesting anywhere in your house. They carry food back intact or swallow it and regurgitate it to feed nestmates. In early spring, workers from an indoor colony start foraging before food is available outdoors, which is often when homeowners first notice them. They’re drawn to water sources in kitchens and bathrooms, and to sugary items like fruit, soda, and candy left on counters.
Carpenter Ants vs. Termites
The distinction matters because the damage pattern and treatment approach are different. Carpenter ants excavate wood to create living space but get their nutrition from food sources outside the wood. Termites actually consume wood as food. In practice, this means carpenter ant galleries are clean and smooth, almost sandpapered in appearance, while termite damage is rougher and packed with mud or fecal material. The presence of frass piles (wood shavings pushed outside the nest) is a carpenter ant signature; termites leave no such piles.
Carpenter ants also cause damage more slowly than subterranean termites, which are the other major wood-destroying pest in California. But “slower” doesn’t mean insignificant. A large colony with multiple satellite nests can create an extensive network of galleries that weakens joists, beams, and framing over years.
Getting Rid of Carpenter Ants
Killing the ants you see foraging is almost useless. The colony, including the queen, is hidden in the nest, and foragers represent a small fraction of the population. Effective control means locating and eliminating both the satellite nests indoors and the parent nest outdoors.
Start by following the ants. Since they forage at night along consistent trails, you can trace their path from a food source back toward the nest. Look for trails along foundation edges, utility lines entering the house, and branches touching the roofline. Outside, check dead trees, stumps, woodpiles, and landscape timbers within a few hundred feet of your home.
Bait products that ants carry back to the colony are generally more effective than sprays for reaching the queen and the rest of the nest. Because carpenter ants eat a range of foods, baits combining sugar and protein tend to work best. Place them along known foraging trails in the evening. Perimeter sprays around the foundation can reduce the number of ants entering the structure but won’t eliminate a colony that’s already established inside.
For infestations that have spread to multiple rooms, involve structural wood, or have been present for years (indicated by cocoons in frass), professional pest control is the practical choice. A pro can use tools like moisture meters and acoustic detection to pinpoint nest locations in walls without tearing them open.
Preventing Infestations
Moisture control is the single most important preventive measure. Fix leaking pipes, especially under sinks and behind dishwashers. Make sure crawl spaces have adequate ventilation. Replace water-damaged wood rather than just drying it out, since decayed wood remains attractive to carpenter ants even after it dries. Ensure gutters direct water away from the foundation.
Eliminate bridges between outdoor colonies and your home. Trim tree branches and shrubs so they don’t touch the house. Store firewood well away from the structure and elevated off the ground. Remove dead stumps and logs from the yard. Seal gaps around utility lines, pipes, and wires where they enter the building.
Inside, reduce food availability by storing sweets in sealed containers and cleaning up spills promptly. Pay special attention in early spring, when indoor colonies are most actively foraging for the sugar and water sources that California kitchens provide in abundance.