How to Get Rid of Carpenter Ants: Find the Nest, Fix the Damp, Bait the Right Way

First, make sure it is a carpenter ant

Before you work out how to get rid of carpenter ants, check the ant. A carpenter ant worker is 1/4 to 1/2 inch (6 to 13 mm) long, black or red and black, with one node at the waist and a smooth, rounded back. If one check fails, you may be treating the wrong pest.

This matters because the plans really differ. Small kitchen ants take a sweet bait and little else. Termites need a termite company. However, carpenter ants need you to find a nest and fix damp wood. If you want to know how to get rid of big black ants, start here, because most of them in a house are carpenter ants.

Our carpenter ant identification guide has the side-view checks, the size table and what a sighting means by season. Small ants with a heart-shaped abdomen are acrobat ants, the ant most often mistaken for carpenter ants. Winged ones at a window may be termites, so check our termite guide before you buy anything. For tiny trailing ants, the plan in our guide to small house ants is the right one.

How to get rid of carpenter ants, step by step

Here is how to get rid of carpenter ants in 8 steps, and the first 4 cost little or nothing. Confirm the ant, find the nests at night, fix the moisture and cut off their routes. Then remove or treat the nest, or bait the trail if it stays hidden. Allow several weeks.

Why carpenter ants are so hard to kill

Carpenter ants are hard to kill because you only see a small part of the colony. Only 10 to 15% of the workers are outside the nest at any time, Illinois DPH says. The queen stays hidden in a parent nest, often outdoors, while the ants in your kitchen may live in a separate satellite nest.

So spraying the ants on the counter kills a few foragers and nothing else. The queen keeps laying eggs, and new workers take their place. That is why so many people say they sprayed last year and the ants were back in spring.

A large colony also spreads out. The parent nest holds the queen, the eggs and the young larvae. It needs damp, decaying wood, so it is usually outdoors in a stump, a dead tree or old timbers. Satellite nests hold workers, older larvae and pupae. Because they have no eggs to keep moist, they can sit in drier places such as insulation, hollow doors and wall voids.

The two kinds of nest can be far apart. The trail between them may run up to 100 yards (90 m), and the workers move back and forth along it. As a result, wiping out one satellite nest in a wall can still leave the parent nest free to send more ants next year.

Their diet is the last problem. Carpenter ants eat insects, honeydew from aphids, and household sweets and meats. Their tastes change through the year, so a bait they love in May may sit untouched in August. That is also why the advice below keeps saying to watch the bait and swap it.

Step 1 in practice: find the nests at night

The best time to find a carpenter ant nest is between sunset and midnight in spring and summer. Workers leave the nest about 15 minutes after sundown. Put out a lure, wait, then follow the ants that carry food away. Two or three evenings of watching usually show you the trail.

• Use red light. Tape red film or red cellophane over a flashlight. The University of Minnesota says the ants cannot see red light, so they keep working while you watch.
• Pick the lure by season. In spring the ants want protein, so use a small piece of tuna packed in water (not in oil). Later in the year, honey or sugar water works better.
• Follow the food. An ant carrying food is heading home. Mark where it disappears with painter’s tape. The nest may still be a few feet inside the wall from that point.
• Listen. Tap gently on the suspect wood and put your ear to it. A disturbed colony makes a dry rustle, like crinkling cellophane.

Our carpenter ant guide has the full seven-step method for tracking a nest, with the sawdust and damp-wood checks. Here, the point is to look for both kinds of nest, because removing only one is why treatments fail.

Where the parent nest hides outdoors

Walk the yard in daylight and check every piece of old, damp wood near the house. Look in stumps, tree roots, dead branches and hollow trees, firewood stacks, landscape timbers, old fence posts and boards lying on the ground. A cone of coarse sawdust at the base of a tree or a stump is a strong clue.

Where satellite nests hide indoors

Indoors, start where water collects. Check under sinks, behind the toilet, around tubs and showers, below windows and skylights, around the dishwasher and near the chimney. Then check the dry spots satellite nests also use: attic insulation, hollow doors and wall voids. Fresh sawdust that comes back after you sweep it means the ants are still working above it.

If you find one nest, keep looking. The University of Minnesota warns that a building may hold more than one.

Fix the moisture first: the step that costs nothing

Fixing moisture is the cheapest part of how to get rid of carpenter ants for good. The ants dig their nests in wood that has been wet. Penn State notes they will not infest sound wood with a moisture content under 15%. Dry the wood out and replace what has gone soft, and an indoor nest loses its home.

• Find the leak. Check the roof, flashing, chimney, skylights, window seals and every pipe near the ants.
• Clear the gutters and make sure downspouts carry water away from the walls.
• Stop condensation. Insulate pipes that sweat, and vent attics, crawl spaces and bathrooms.
• Test the wood. Press a screwdriver into suspect trim and framing. Wood that gives easily needs replacing.
• Lift wood off the ground. Remove places where siding, decks or porches touch soil.

If exclusion and sanitation are successful, insecticide treatments are not required. This is also the honest answer for anyone searching for how to get rid of carpenter ants naturally. Drying the house, removing the nest wood and sealing the gaps use no pesticide at all. For scents and kitchen remedies, see our natural ant repellent guide, though no scent will move a nest out of wet wood.

Carpenter ant bait: how to make it work

Carpenter ant bait works when the workers carry it home and share it with the queen and the young. That takes time, so baits are slow by design. The University of Minnesota says baiting can take weeks or months. Use bait when you cannot find the nest, choose one whose label lists carpenter ants, and check it within 24 hours.

Why slow is the point

A bait is food mixed with a slow-acting poison. Workers eat it, walk home and pass it mouth to mouth to other workers, the larvae and the queen. If the poison acted fast, the foragers would die on the trail and the nest would never get a dose. UC IPM stresses this because only about 10% of the ants forage at once.

That is also why you should never spray near a bait. A spray kills the carriers before they get home, and it can wipe out the scent trail the others follow.

Sweet or protein? Match the bait to the season

Carpenter ants change what they want to eat. In spring, colonies need protein to raise their young. Purdue University researchers found that the ants crave protein in spring and switch to sugar in the fall. The University of Wisconsin adds that baits work best in spring and early summer.

So in practice, offer a choice. Put a protein or combination gel bait and a sweet liquid bait side by side, as UC IPM suggests for ants in general. Keep whichever one the ants feed on, and drop the other.

Where to put the bait, and how to check it

• Only where you see ants. Put small dabs or a station right on the trail, near where they come out.
• Check within 24 hours. If they ignore it, clean it up and try a different bait.
• Add more when they eat it. An empty bait cannot keep working.
• Leave the crowd alone. A mass of ants at the bait means it is working.
• Keep it out of reach of children and pets, inside a sealed station where you can.

Do carpenter ant baits really work?

Sometimes. This is the one point where extension services disagree, and you should know it before you spend money. Some see baits as a useful tool. Others say carpenter ants are too picky for baits to be reliable.

Our reading: bait is the fallback when the nest stays hidden, not the first move. It works best with a product made for carpenter ants, placed in spring, checked daily and swapped when ignored. Finding and treating the nest is faster and more certain.

How long does it take to get rid of carpenter ants?

Plan on several weeks. A nest you find and treat directly can go quiet within days. Bait is slower: NC State says activity may take 7 to 10 days to drop, and the University of Minnesota allows weeks or months. Any plan that promises the whole colony in 2 or 3 days is promising too much.

Built from the University of Minnesota, NC State, UC IPM and the University of Wisconsin, plus what readers report on forums. Your timing will vary with the size of the colony and the season.

Treating a carpenter ant nest you have found

A nest you have found is the best target you will get. Take out nest wood outdoors. For a nest you can see, use a ready-to-use product labeled for carpenter ants on that site. For a nest inside a wall, a professional drills holes about 1/8 inch (3 mm) wide and puffs in an insecticidal dust.

An exposed nest is the easy case. You may open one while replacing rotten trim or a window frame. Treat it then, because the University of Minnesota notes that the exposed part of the colony will try to move. After that, replace the damaged wood.

A nest inside a wall needs care. The University of Minnesota says to leave the drilling to a professional. The University of Nebraska adds that liquid insecticide should never go into a wall void, where water can harm the insulation, the drywall or the wiring. Dusts are used instead, in small, light amounts.

The dusts used for this include boric acid, diatomaceous earth and silica gel. UC IPM says drying dusts stay effective as long as they stay dry, and that you should avoid breathing them in. Our carpenter ant guide’s sawdust and galleries photos show what a nest looks like once the wood is open.

Does diatomaceous earth kill carpenter ants?

It can, slowly, when a registered diatomaceous earth dust is puffed into a nest or a void and stays dry. The University of Nebraska lists several registered dusts of this kind for carpenter ants. It does not work as a ring around the house, and it stops working when it gets wet. Use only a product sold as an insecticide, into cracks and voids, never spread across floors or lawns.

What kills carpenter ants? Products compared

The carpenter ant killers that work are the ones that reach the nest: slow baits the workers carry home, and dusts placed in the nest itself. Contact sprays reach only the 10 to 15% of workers out foraging. The most effective products, such as fipronil sprays, are for licensed applicators only, UC IPM and the University of Kentucky note.

Common bait ingredients include avermectin, borax and boric acid, fipronil and spinosad. A carpenter ant spray sold in shops is usually a pyrethroid such as deltamethrin. It earns its place only on a nest you can see. Oregon State is blunt: the most effective insecticides for carpenter ants are not sold in retail stores.

Getting rid of carpenter ants outside: the parent nest

Outdoors, the goal is the parent nest, because it holds the queen. Remove the stump, log, woodpile or rotten timber it lives in, or have it treated. Remove stumps and waste wood within 100 yards (90 m) of the house where you can, Penn State advises. A colony left outside can send workers back in.

A nest in a living tree is often best left alone. The University of Minnesota says the ants use wood that is already decayed and do not harm the tree itself. Instead, trim the branches that touch the roof and wires, so the colony has no bridge into the house. Ask an arborist about a tree with large dead or hollow sections.

A perimeter treatment is a professional’s call. A non-repellent spray applied outside lets foragers carry the product home, and Penn State notes that usually one treatment is needed. On the other hand, injecting insecticide into the soil around the house, as for termites, is unnecessary for carpenter ants, the University of Nebraska says.

Homemade borax bait: what is true and what is risky

No extension service we found publishes a homemade borax bait for carpenter ants. The popular forum mix, 1/2 cup sugar, 1 1/2 tablespoons borax and 1 1/2 cups water on cotton balls, has helped many people. But it is stronger than the 0.5 to 1% borate that UC IPM gives for liquid ant baits, and it carries no label.

Strength matters. A strong bait can kill the foragers before they reach the nest, or taste too bitter to eat. A dry version, a third borax and two thirds sugar sprinkled along the trail, is stronger still. Worse, it leaves open powder on floors where children and pets walk.

Borax and boric acid are not the same thing either, as Iowa State points out, though readers often mix them up. Laundry borax is sold as a cleaner, not as an insecticide. So there are no label directions for using it around a family.

Is it safe? Not as safe as forum posts claim. The National Pesticide Information Center says people who swallow boric acid can get nausea, vomiting and diarrhea. In pets, signs of poisoning can start within 2 hours. It also reports seizures and deaths more often in infants with long-term exposure than in adults.

Our advice: a sealed, labeled bait station gives you the same idea with tested strength and a case small hands cannot open. If you still mix your own, keep it in a closed container the ants can enter, well out of reach, and remove it when you are done. For other home remedies and how well they work, see our natural ant repellent guide.

What does not work against carpenter ants

The 3 most common mistakes are spraying the trail, setting off a fogger and using kitchen remedies. Each one goes after the ants you can see and leaves the nest, the queen and the damp wood alone. Here is what the extension sources say about the methods people try first.

• Myth 1

  Myth: “Spraying the trail will get rid of them.”

  Truth: The University of Minnesota says spraying foragers is not effective and may only reduce the ants you see for a while. Most of the colony stays home.

• Myth 2

  Myth: “A perimeter spray around the foundation keeps them out.”

  Truth: Illinois DPH says spraying the foundation or an open attic usually gives little or no control, and it exposes people and pets for nothing. NC State adds that sprays mostly repel the ants elsewhere.

• Myth 3

  Myth: “A bug bomb will clear the house.”

  Truth: The University of Wisconsin says foggers do not work well on carpenter ants because they do not get into walls. EPA also warns to keep foggers away from flames and pilot lights.

• Myth 4

  Myth: “Vinegar, peppermint or cinnamon will drive them out.”

  Truth: Plant oils kill ants on contact but last very little time, UC IPM says, and soapy water only wipes a scent trail. None of them reaches a nest in wet wood.

• Myth 5

  Myth: “Borax bait kills the colony in 2 to 3 days.”

  Truth: Extension sources give weeks: 7 to 10 days before activity drops at best, and weeks or months for full control.

• Myth 6

  Myth: “A ring of diatomaceous earth around the house will stop them.”

  Truth: It stops working when it gets wet, and the nest is not touched. Registered dusts work only inside the nest or a void.

• Myth 7

  Myth: “Once the ants are gone, the job is done.”

  Truth: Killing a satellite nest leaves the parent nest outside, and Illinois DPH says it can reinfest later. Fix the moisture, or a new colony can move in.

• Myth 8

  Myth: “Carpenter ants need monthly spraying all year.”

  Truth: The University of Nebraska says regularly scheduled sprays are not needed. Treat the colony, then watch to see if it worked.

When to call a pro, and what treatment involves

Call a licensed pest professional when the nest is inside a wall, ceiling or floor, when you see carpenter ants indoors in winter, or when ants still trail after 2 rounds of bait. Most of the time, a good treatment is a careful inspection, then nest treatment with a dust or a bait, not monthly spraying.

Knowing how to get rid of carpenter ants yourself does not mean every nest is a DIY job. Professionals have tools you do not. The University of Minnesota lists experience finding nests, moisture meters and listening devices, and professional insecticides such as fipronil. A typical visit includes:

• An inspection inside and out, looking for trails, sawdust, damp wood and the parent nest.
• Drilling and dusting any nest in a wall, door or frame.
• Baits placed where ants trail, if the nest cannot be reached.
• A non-repellent perimeter spray outside, in some cases.
• Advice on the leak and the wood to replace. Some firms also seal gaps.

Tell the technician when, where and how many ants you have seen. Your night trail notes make their inspection faster.

How much does carpenter ant treatment cost?

It varies with your region, the size of the house and how hard the nest is to reach. No university or government source publishes prices. One consumer cost guide, This Old House, puts carpenter ant removal at $250 to $500, with follow-up visits at $40 to $70. Treat any quote outside that range as a reason to ask questions.

Get two or three quotes, and compare the treatment, the guarantee and the price, as the University of Wisconsin advises. Wisconsin also notes that a correct treatment of the nest should usually end it in one visit. UC IPM suggests asking for baits and spot treatments rather than monthly sprays.

Do you need a year-round pest contract?

For carpenter ants alone, usually not. A plan that sprays inside and out every month does not find the nest, and the University of Nebraska says regularly scheduled sprays are not needed. It is fair to ask a company what each visit will treat, and why. A follow-up visit to check the nest is a different thing, and a sensible one.

Carpenter ants when you rent

If you rent, carpenter ants are usually your landlord’s job, because they point to a leak or rotten wood, and that is a repair. Rules vary by state. Minnesota law (section 504B.161), for example, makes the landlord keep the unit in reasonable repair, and the state Attorney General lists exterminating insects among the landlord’s duties.

• Report it in writing, with dates, photos and where you see the ants, and keep a copy.
• Point out any leak, stain or soft wood near the ants. That is the part the owner must fix.
• Do not set off a fogger. It will not reach the nest, and it can drift into other units.
• Sealed bait stations labeled for ants are a reasonable stopgap in your own unit, out of reach of children and pets.
• In a condo or HOA, ask who is responsible for the walls and exterior. Nests often sit in shared structure.

How to keep carpenter ants from coming back

To keep carpenter ants away, keep wood dry and keep their bridges cut. Trim branches at least 12 inches (30 cm) from the house, keep mulch to 2 to 3 inches (5 to 8 cm) deep, and store firewood off the ground and away from the walls. Then walk the house each spring, when colonies wake up.

• Firewood: bring in only what you will burn soon, and never stack it against the house, on the porch or in the garage.
• Stumps and old timbers: remove them near the house, since they are favorite parent nest sites.
• Gaps: seal where pipes, cables and wires enter, and around doors and windows.
• Hoses and cables: coil garden hoses off the ground, and keep cables away from branches.
• A spring check: look for soft wood, stains and sawdust around windows, skylights, the chimney and the bathroom.

Winged ants at a window in spring need their own check, because some are termites. Our flying ants guide shows the difference. Round holes in bare wood belong to the carpenter bee, which needs its own fix.

Pest control disclaimer. Photo-based identification can help, but it is not always perfect. For dangerous spiders, large infestations, or anything you are unsure about, contact a licensed pest control professional.