A dry rustling inside a wall after dark, or a small heap of sawdust under a window sill, is often the first hint that you need to work out how to get rid of carpenter ants. These ants do not eat wood. They carve galleries through it, usually where it is already damp or decaying, and the damage keeps growing as long as the colony stays.
The ants on the kitchen floor are rarely the whole story. The queens tend to stay outdoors in a tree, a stump or a woodpile, while workers shuttle to smaller nests inside the house, and that split explains why a can of spray almost never ends the problem.
How Do You Get Rid of Carpenter Ants for Good?
Getting rid of carpenter ants for good means destroying their nests, not just killing the ants you see. Carpenter ants live in colonies with one or more queens, and the workers you spot in your kitchen are only the foragers. Before you buy anything, confirm the species and understand where the colony actually lives.
Confirm They Are Carpenter Ants
Carpenter ants are the largest ants you are likely to see in a Canadian home. Health Canada describes two common types here: the black carpenter ant, dark brownish-black all over, and the red carpenter ant, which has a reddish-brown upper body. Adults measure 6 to 25 mm (about 1/4 inch to 1 inch), with elbowed antennae and a very slim waist. Termites, by contrast, have straight antennae and a thick waist, and Health Canada notes they are found only in certain areas of Canada.
Piles of sawdust-like shavings near wood are a classic clue, because carpenter ants tunnel into wood to nest but do not eat it. For the full list of clues, see our guide to the signs of carpenter ants in your house.
Parent and Satellite Nests
Carpenter ant colonies usually have a parent nest outdoors and one or more satellite nests nearby, often inside your home. According to UC IPM, the queens live in the parent nest, which is typically in a live or dead tree, a stump, a woodpile or landscaping wood. Penn State Extension notes that the parent colony is often within 100 yards (about 90 metres) of the house, and workers travel back and forth between nests.
This is why spraying the ants you see rarely solves the problem. UC IPM estimates that only about 10% of a colony is out foraging at any given time, and Penn State warns that if you do not eliminate all the nests, the ants typically return within days or weeks.
The 4-Step Plan
The 4-step plan for getting rid of carpenter ants works on both the parent and the satellite nests:
- Find the nest by following the ants at night.
- Bait the colony with a slow-acting carpenter ant bait placed on their trails.
- Treat the nest directly with an insecticide dust when you can reach it.
- Fix the moisture problem and remove the wood that attracted them.
Health Canada notes that chemicals work best when you combine them with this kind of physical control, so do not skip step 4.
How Do You Find a Carpenter Ant Nest?
Finding a carpenter ant nest is easiest at night, when workers travel between the nest and their food. Carpenter ants are most active after sunset, so a flashlight and a little patience will tell you more than a daytime search.
Inspect After Sunset
Inspecting after sunset gives you the best chance to see busy trails. The University of Georgia Extension suggests starting after sunset, and Penn State recommends checking basements, attics, garages and the outside of the house between 10 p.m. and 2 a.m. from May through July, when foragers are most active.
Follow a Sugar Bait Trail
A sugar bait trail turns the ants into your guides. UC IPM suggests setting out a nontoxic bait, such as sugar milk (equal parts sugar and milk), where you have seen ants, then following the workers as they carry it home.
Listen for Rustling in Walls
A rustling sound in a wall can point to a hidden satellite nest. Health Canada says a dry rustling noise is easiest to hear at night, and that pressing a wine glass or a stethoscope against the wall can help you pinpoint it. Slit-like openings in woodwork and small piles of shavings below them are other clues.
Check Damp Wood Indoors
Damp wood indoors is where satellite nests usually start. Check window sills, door frames, wooden steps, the area under the kitchen sink, hollow doors, attic spaces, wall voids and foam insulation, which Health Canada lists as possible indoor nest sites. A spot with many ants in one place, such as under a sink, is a stronger sign of a nest than a few ants wandering around. If the trail disappears into a wall, our guide to ants in walls explains what to check next.
Search Trees and Stumps Outdoors
Trees and stumps near your house are the most likely home of the parent nest. Walk around large trees at night and shine your flashlight up and down the trunk: a steady line of ants moving up and down suggests a nest (University of Georgia Extension). Look for sawdust-like shavings at the base of trees, in stumps, under fallen logs and in woodpiles, and check landscaping such as decorative bark, retaining walls and old timbers.
How to Use Carpenter Ant Bait
Carpenter ant bait works because workers carry it back to the nest and share it with the queen and the rest of the colony. It is the method the University of Georgia Extension calls the preferred choice in most cases, and it can reach nests you never find.
How Carpenter Ant Bait Works
Carpenter ant bait mixes food the ants want with an insecticide that acts slowly. Health Canada explains that a bait must work slowly enough for the poison to be fed to every member of the nest. A fast-acting product kills the forager before it gets home, so the queen keeps laying eggs and the colony survives.
Choosing a Carpenter Ant Bait
Choosing a carpenter ant bait starts with the label. Many ant baits are made for small sugar ants and not for carpenter ants: for example, TERRO states that its Liquid Ant Baits are not recommended for carpenter ants. Pick a product whose label lists carpenter ants, shows a PCP number (which means Health Canada has registered it), and is approved for indoor use if you plan to use it inside.
Carpenter ants eat both sweets and proteins, from honeydew and fruit juices to insects (UC IPM). Ants can be finicky, so UC IPM recommends offering several baits and letting the ants choose, and Health Canada notes that two different baits used together work better than one. For tested products, see our picks for the best ant killer.
Bait Stations Indoors
Bait stations indoors should sit right on the ants' path. Use childproof plastic stations (University of Georgia Extension) and place them along trails, near baseboards and close to any small piles of wood shavings. Keep them out of reach of children and pets, and use plenty of them rather than one or two. If most of the activity is around food, our guide to getting rid of ants in the kitchen covers cleanup that makes the bait more attractive.
Gel Bait Outdoors
Gel bait outdoors goes where the ants travel, not in random spots. The University of Georgia Extension suggests small piles of gel next to trails or on the bark of a tree that holds a nest, and NC State Extension notes that bait works better near foraging trails. Apply it in the evening: NC State Extension notes that carpenter ants are nocturnal, and other ants that forage in the daytime may eat it before the carpenter ants come out.
How Long Baiting Takes
Baiting carpenter ants takes patience. Health Canada advises keeping baits available for at least two weeks and warns that repeated applications may be needed. Check the stations often and replace bait as the ants eat it. Penn State also notes that ants sometimes ignore baits, so if a product goes untouched for a few days, switch to a different type.
Why You Should Not Spray While Baiting
Spraying while you bait undoes the work. Health Canada warns against using chemical sprays on ants during a bait program, because the bait will not work: the spray kills or scatters the foragers that were supposed to carry it home. Hold off on sprays until the bait has had time to reach the colony.
How Do You Kill Carpenter Ants in the Nest?
Killing carpenter ants in the nest is the most direct way to end an infestation once you know where the nest is. Health Canada's advice is simple: for permanent control, you usually need to locate and treat the nest, and if you find a satellite colony, track down and destroy the parent colony too.
Insecticide Dust in Wall Voids
Insecticide dust is the right choice for a nest inside a wall. The City of Edmonton recommends dust formulations for ants in wall voids, because liquid sprays may damage insulation or cause electrical shorts; Health Canada also says wall voids can be treated with dusts. UC IPM notes you may need to drill holes to reach a hidden nest, and Penn State describes blowing low-toxicity dusts into nests and cavities. Follow the label exactly, and avoid breathing the dust, which UC IPM says can seriously irritate the lungs.
Outdoor Nests
Outdoor nests in stumps, logs or dead trees can be removed or treated. Penn State suggests removing the infested wood or tree, or treating it with an insecticide labelled for carpenter ants. Removing the wood is often the better long-term fix, since it also removes the next nesting site.
Diatomaceous Earth
Diatomaceous earth is a dust you can buy at retail stores, and UC IPM lists it among the dusts that work on carpenter ants. It works on contact, scratching the outer skin of ants (Health Canada), so it only helps where ants walk through it, such as inside a wall void or along a hidden gallery. Our guide to diatomaceous earth for ants explains how to apply it.
Boric Acid
Pest control professionals may apply boric acid dust in nests (Penn State), and for home use in Canada boric acid is usually sold as sealed bait stations or gels, which Health Canada and the City of Calgary note are generally of low toxicity to other animals. Like any pesticide, it still needs to stay away from children and pets. Read our guide to using boric acid to kill ants before you buy or place a bait.
Leave Dead Ants in Place
Leaving dead ants in place sounds odd, but it helps. Health Canada explains that other ants may carry the dead ones back to the nest, spreading the pesticide's effect through the colony. Clean up once activity has stopped.
Pesticide Safety at Home
Pesticide safety starts with the label. Read it to confirm the product suits carpenter ants, look for the PCP number, and follow every direction and warning. Keep products and treated areas away from children and pets, and check local rules, since Health Canada notes that some provinces and municipalities restrict certain lawn and garden pesticides. If you have pets, see our guide to pet-safe ant killers. Some of the strongest products, such as fipronil perimeter sprays and silica gel dust, can only be applied by a licensed applicator (UC IPM).
How Do You Keep Carpenter Ants From Coming Back?
Keeping carpenter ants away comes down to dry wood and no easy bridges into your house. These steps also stop a new colony from moving into the space the old one left.
Moisture Problems
Moisture problems are the main reason carpenter ants move into a home. Penn State notes that they usually avoid sound wood with less than 15 percent moisture content. Repair leaky pipes, roofs, flashing, gutters and downspouts, and improve ventilation in attics and crawl spaces.
Damaged Wood
Damaged wood should be replaced once the ants are gone. Health Canada advises replacing decaying or infested wood with sound material, and Penn State recommends repairing damaged wood as part of removing a nest. Leaving tunnelled wood in place invites the next colony.
Branches Touching the House
Branches touching the house act as bridges for foraging ants. Trim trees and shrubs so they do not touch your roof, siding or wires (UC IPM, Penn State). Health Canada also lists power and telephone cables as common entry routes.
Firewood Storage
Firewood storage matters because woodpiles are ideal nest sites. Store firewood off the ground and several feet away from the house (UC IPM), and only bring in what you will burn right away. Health Canada also advises clearing stumps, logs and wood debris around buildings rather than burying them.
Mulch Depth
Mulch depth around the foundation should stay shallow. UC IPM recommends reducing mulch along the house to a depth of 2 to 3 inches (about 5 to 7.5 cm) and avoiding direct contact between soil and wooden parts of the house.
Entry Points
Entry points around pipes, wires, windows and foundations are how foragers get in. Seal the gaps where utility lines enter, caulk cracks in the foundation, and keep food in sealed containers so foragers have less reason to come inside. For general ant prevention, see our guide on how to get rid of ants.
When Should You Call a Professional for Carpenter Ants?
Calling a professional for carpenter ants makes sense when you cannot find the nest or the ants keep coming back. Health Canada recommends a professional exterminator in difficult situations.
Signs DIY Is Not Working
Signs that DIY is not working include ants still active after several weeks of baiting, ants in several rooms or floors, rustling in walls you cannot reach, or soft and hollow wood in structural parts of the house. Penn State notes that satellite colonies are rarely eliminated without professional-grade materials.
What a Professional Does
A licensed pest control professional should start by locating the nest, or at least a probable nest site, before treating (University of Georgia Extension). Professionals can also use products that homeowners cannot buy. To know what to expect, read our guide to carpenter ant pest control and the cost of ant extermination in Canada, or get a quote from a recommended local exterminator through Pest Agent's referral form. For more ant guides, visit the ant hub.
Frequently asked questions
Do carpenter ants go away on their own?
Usually not. A colony with a nest in or near your home keeps sending out foragers, and Penn State notes that if every nest is not eliminated, the ants typically return within days or weeks. Finding and treating the nests is the only reliable fix.
Can carpenter ants destroy a house?
Carpenter ants can damage a home's structure because they hollow out wood to make room for their nests, according to Health Canada. They usually start in wood that is already damp or decaying. Catching them early and fixing moisture problems keeps the damage limited.
Do carpenter ants bite?
Yes, they can. UC IPM notes that carpenter ants cannot sting, but they can bite and spray formic acid into the wound, which causes a burning feeling. Orkin Canada reports that bites are rare and reactions are usually mild.
Why do I see carpenter ants with wings?
Winged carpenter ants are the males and females that leave the colony to mate. Health Canada notes that they usually swarm outdoors in spring. Penn State notes that winged ants found at indoor windows likely come from a nest inside the house, so treat them as a reason to inspect.
Are carpenter ants the same as termites?
No. Carpenter ants have elbowed antennae and a narrow waist, while termites have straight antennae and a thick waist. Carpenter ants tunnel into wood and push out shavings, but they do not eat it the way termites do.
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