Carpenter Ants
Reviewed by TJ Jackson, Certified ACE · Updated 2026-05-06
Camponotus spp. | Category: Ants | ✓ Covered: All Seasons Pest Plan
If you’ve spotted a half-inch-long black ant marching across your kitchen counter — or worse, found a small pile of what looks like sawdust under a window sill — you’re likely dealing with carpenter ants. Unlike the smaller nuisance ants in the PNW, carpenter ants don’t just visit your home: they tunnel into it. Wet, weather-exposed wood is their dream real estate, which makes Oregon and Washington homes especially vulnerable. The good news: caught early, the damage is fixable, and IPM has been treating carpenter ants in PNW homes for over sixty years.
| Size | 1/4″ – 1/2″ (workers polymorphic, queens up to 5/8″) |
|---|---|
| Color | Black; some species reddish-brown and black |
| Top ID Marker | Sawdust-like “frass” piles below entry holes |
| Active Season | Year-round in PNW; peak activity April through October |
| Nest Sites | Damp/damaged wood, attics, decks, hollow doors, foam insulation |
| Colony Size | 10,000–20,000 workers; one queen; 3–6 year colony maturity |
| Plan Coverage | ✓ Covered under All Seasons Pest Plan |
Quick Answer: Carpenter ants (Camponotus species) are the largest ants in the Pacific Northwest at 1/4″ to 1/2″ long, typically all-black with some reddish-and-black species. Unlike termites, they do not eat wood — they excavate it to build smooth galleries, leaving sawdust-like frass piles below entry holes. They prefer wet, damaged wood: damp window frames, deck joists, attics with roof leaks, and crawl space wood. A mature colony can damage structural wood significantly over 3 to 6 years. Professional treatment is required because parent colonies are usually outdoors, with satellite colonies in the home — DIY sprays kill foragers but leave the queen untouched.
Key facts at a glance: Size: 1/4″–1/2″ · Color: black or red/black · Tell-tale sign: sawdust-like frass · Damages structure: YES · Colony size: 10,000–20,000 workers · Treatment timeline: 2–4 weeks · Plan coverage: Yes — All Seasons Pest Plan.
What You Need To Know About Carpenter Ants
Our Certified ACE technician TJ Jackson breaks down carpenter ants — how to ID them, what frass tells you, and why DIY sprays almost always make the problem worse.
Frequently Asked Questions
How can I tell carpenter ants from termites?
Carpenter ants are larger, dark-colored, and have a pinched waist with bent (elbowed) antennae. Termites are pale, thicker-bodied with no waist constriction, and have straight bead-like antennae. Carpenter ants leave clean smooth tunnels and frass (sawdust-like debris) outside their galleries; termites leave mud tubes and packed soil. If you see piles of fine sawdust mixed with insect parts, it is carpenter ants.
Do carpenter ants eat wood?
No. Carpenter ants do not eat wood — they excavate it to nest. They feed on protein, sweet honeydew from aphids, and sugary household foods. The wood they tunnel through gets pushed out as frass (the sawdust pile you see). This distinction matters because their damage is mechanical, not digestive, and looks different from termite damage.
How do I know if carpenter ants are inside my walls?
Tap suspicious wood with a screwdriver handle — hollow wood is a sign. Listen at quiet times of day for a faint rustling or crinkling sound inside walls. Look for clean piles of sawdust, dead insect parts, and discarded wings below window sills, baseboards, or in basements. Slight kickout holes (about 1/8″ across) in wood are entry/exit points workers use to dispose of debris.
Are carpenter ants dangerous to my house?
Yes — they are wood-destroying organisms (WDOs) and can compromise structural wood over time. While they cause less damage than termites in any given year, mature colonies (3+ years old) can excavate significant volumes of damp framing, decking, or sill plates. Pacific Northwest homes are particularly at risk because of our wet climate. Early intervention prevents costly repairs.
Why do carpenter ants like Pacific Northwest homes?
Moisture. Carpenter ants only nest in wood that has been softened by water exposure. The PNW’s heavy rainfall, leaky gutters, and crawl space humidity create exactly the wet wood conditions they require. Common nest sites in OR and WA homes include deck ledger boards, window frames behind failing caulk, around chimneys with leaky flashing, and any wood in contact with damp soil.
Does the All Seasons Pest Plan cover carpenter ants?
Yes. Carpenter ant treatment is included in Interstate Pest Management’s All Seasons Pest Plan, including the initial treatment, scheduled seasonal services, and free re-service visits if activity returns between visits. For severe or structural infestations, our team may also recommend additional inspection of the parent colony location outdoors.
Why don’t store-bought sprays work on carpenter ants?
DIY sprays only kill foragers — the workers you see are usually less than 10% of the colony. The queen and brood are deep inside the nest (often in a wall void or outside parent colony) and never contact the spray. Worse, repellent sprays can cause satellite colonies to relocate deeper into the structure, making professional treatment harder. Bait and direct nest treatment are required for elimination.
How long does it take to eliminate carpenter ants?
Professional treatment typically eliminates active foraging within 1 to 2 weeks, with full colony elimination in 3 to 6 weeks depending on whether the parent colony is indoors or outdoors. Most cases involve a satellite colony inside the home and a parent colony in a nearby tree, stump, or wood pile — both must be addressed for permanent results.
Signs You Have Carpenter Ants
Most homeowners don’t see a single ant — they see a hundred. Here’s what to look for, in the order it usually shows up:
1. Sawdust-like frass piles
Small piles of fine, smooth sawdust under window sills, in basements, or by baseboards — often mixed with dead ant body parts. This is the single most reliable carpenter ant sign and confirms an active nest nearby.
2. Large black ants foraging at night
Carpenter ants are mostly nocturnal. If you see big (1/4″+) black ants at dusk or in the middle of the night, especially in the kitchen or bathroom, you likely have an active colony in the structure.
3. Faint rustling sounds in walls
Mature colonies make subtle crinkling or papery sounds inside walls, especially near roof lines or around damp windows. Press your ear against suspicious areas at night when the house is quiet.
4. Discarded wings near windows
In spring, winged reproductive (alates) emerge to start new colonies. Finding small piles of translucent wings on window sills means a colony in your home matured and just released swarmers.
5. Hollow-sounding wood
Tap suspect wood — door frames, deck rails, window casings — with a screwdriver handle. Wood with active galleries sounds hollow and dead compared to solid wood. This indicates internal damage.
6. Pinhole exit holes in trim
Smooth, clean 1/8″ holes in baseboards, window casings, or siding that workers use to push frass out. Often surrounded by a faint stain or sawdust ring.
Behavior, Biology & Lifecycle
Understanding how carpenter ants live is the single biggest reason professional treatment succeeds where DIY fails. Here’s what makes this species different:
Parent colony plus satellites
Carpenter ants typically have one outdoor parent colony (a stump, log, or living tree) and one or more satellite colonies inside structures. The parent contains the queen and main brood; satellites contain workers, mature larvae, and sometimes winged reproductives. Both must be treated for complete elimination.
Need wet wood, not dry
Unlike termites, carpenter ants cannot establish in dry, sound wood. They require wood with elevated moisture (typically 15%+ moisture content) — usually caused by leaks, condensation, or ground contact. This is why fixing the underlying moisture problem is part of any complete treatment.
Lifecycle: 6–12 weeks egg to adult
Eggs hatch in 14–28 days, larvae develop for 21 days, pupae form for another 21 days. New colonies grow slowly: a queen lays only 9–16 eggs in her first year. It takes 3 to 6 years for a colony to mature and produce winged swarmers — meaning the colony you found has likely been there a while.
Diet: protein and sweets, not wood
Workers feed on insects (live and dead), aphid honeydew, and sugary household foods. They do not digest cellulose. This dietary preference is why protein-based and sugar-based baits work — workers carry them back to feed larvae and the queen, eliminating the colony from the inside out.
Active April through October in PNW
Foragers leave the colony at dusk during warmer months, traveling up to 100 yards from the nest. In winter, colonies remain alive but mostly dormant inside the structure. Sightings drop dramatically — but the colony does not die.
PNW is prime carpenter ant territory
According to WSU Extension, carpenter ants are one of the most common structural pests in Washington and Oregon, driven by our wet climate, abundant forest cover, and older housing stock with deferred maintenance issues.
DIY Homeowner Steps
Find and fix moisture sources
Carpenter ants only nest in wet wood. Check for roof leaks, plumbing drips, failed caulking around windows, gutter overflow, and damp crawl spaces. Drying out the wood is half the battle.
Inspect outdoor wood near the home
Walk the perimeter looking for stumps, dead tree limbs, woodpiles against the foundation, and railroad ties. The parent colony is usually within 100 yards of the structure. Remove and store firewood off the ground and at least 20 feet from the house.
Trim vegetation off the house
Branches touching siding, shrubs against walls, and ivy on the structure all give ants direct entry points. Maintain a 12″+ clearance between vegetation and your home.
Do not spray visible trails
Repellent sprays scatter satellite colonies deeper into walls and trigger budding. If you’ve identified active carpenter ants in your home, especially with frass present, contact a professional rather than treating yourself.
Carpenter Ants vs. Other PNW Ants
Not sure which species you have? Here’s a side-by-side of the four ants we get called about most often in Oregon and Washington homes:
| Feature | Odorous House Ant | Carpenter Ant | Pavement Ant | Moisture Ant |
|---|---|---|---|---|
| Size | 1/16″–1/8″ | 1/4″–1/2″ | 1/8″ | 1/8″–3/16″ |
| Color | Dark brown/black, uniform | Black, sometimes red & black | Brown to black with darker abdomen | Yellow to light brown |
| Smell when crushed | Rotten coconut | Slight formic acid (vinegar) | None distinctive | Lemony / citronella |
| Damages structure? | No | Yes — excavates wood | No | Often follows existing wood damage |
| Typical nest site | Wall voids, near pipes, baseboards | Damp/damaged wood, attics, decks | Cracks in driveways, sidewalks, foundations | Rotting wood, wet crawl spaces |
| Sawdust piles? | No | Yes (frass) | No | Sometimes |
| DIY spray response | Buds & spreads | Workers die, queens unaffected | Some kill, recurring | Buds & spreads |
| Plan coverage | ✓ All Seasons | ✓ All Seasons | ✓ All Seasons | ✓ All Seasons |
Plans That Cover Carpenter Ants
All Seasons Pest Plan
$39/month
Setup fee ~$260 for initial treatment
Year-round protection from the pests Pacific Northwest homeowners deal with most — ants, spiders, wasps, box elder bugs, and more.
- Recurring exterior treatments
- Seasonal pest coverage
- Free re-service between visits
Pest & Rodent Bundle
$47/month
Setup fee ~$280 for initial treatment
The most complete protection for your home. Full pest coverage plus active rodent monitoring — one plan, one team, one less thing to worry about.
- Everything in Pest & Rodent plans
- Best value for whole-home protection
- Free re-service guarantee
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