The short version
- Virginia Cooperative Extension says carpenter ants nest in live trees with some decay, dead trees, rotting logs and stumps, and use wood only as a nest, not as food.
- Large numbers of carpenter ants on a tree suggest wood decay and a tree that may be hazardous, per Virginia Cooperative Extension.
- Purdue and Iowa State say the ants are not directly harmful to the tree, and killing them is not needed for the tree's health.
- Do not fill or seal the cavity. Have an arborist look at a tree near a house, walkway or driveway.
Roanoke Tree Removal is a local referral service: we pass your request to an independent, local tree crew. We are not a contractor or a government office, and this page is general information, not legal advice.
What carpenter ants are doing in your tree
Virginia Cooperative Extension's carpenter ant fact sheet says the ants dig into wood to house their colonies, but the wood is used only as a nesting site. Their natural diet is insects, honeydew from aphids and plant juices. The wood they remove gets dumped in piles outside the nest entrances, which is the sawdust you see at the base of the trunk.
Iowa State Extension says carpenter ant nests are very common inside trees, especially older trees that are hollow or have a lot of dead limbs. The nests are usually in rotted wood, though some extend into sound heartwood in the center of the tree. The ants get in through knots, cracks, holes and old insect tunnels.
How to tell it is carpenter ants
| What you see | What it suggests | Source |
|---|---|---|
| Large ants, black, reddish-brown or red and black, with a pinched waist | Carpenter ants. Workers run about 1/4 inch and queens up to 3/4 inch. | Virginia Cooperative Extension, Checked Oct 17, 2026 |
| Coarse sawdust piled at the base, below a crack or wound | Ants clearing out a nest inside the trunk. | Iowa State, Checked Oct 17, 2026 Virginia Cooperative Extension, Checked Oct 17, 2026 |
| Smooth, clean tunnels in the wood | Carpenter ants. Termite tunnels are lined with moist soil. | Virginia Cooperative Extension, Checked Oct 17, 2026 |
| Long, matchstick-like shavings in branch crotches of a maple | Rule out Asian longhorned beetle before assuming ants. | UMass Extension, Checked Oct 17, 2026 |
Ohio State notes that a good rain can wash the sawdust away, so no pile does not always mean no ants.
Virginia Cooperative Extension says carpenter ants become active outdoors in late spring and early summer, when they show up on tree trunks and sidewalks. Winged queens and males leave the nest on mating flights from May through July.
Do carpenter ants kill trees?
Not directly. Purdue and Iowa State both say carpenter ants in trees are not directly harmful to the tree, because the ants are taking advantage of wood that is already soft and weak. Iowa State puts the blame for that damage on stress, mechanical injury, environmental conditions, disease or other insects, with decay setting in once moisture gets into a wound.
Ohio State makes the same point from the tree's side. A tree can live with heart rot, and with carpenter ants in that rot, and still grow a healthy canopy, as long as its cambium, the living layer that carries water and nutrients, stays healthy. UMass Extension adds a caution: the nest galleries can sometimes weaken the core of the tree, and carpenter ants can speed up the weakening of a tree that is already decayed.
The real issue: decay and fall risk
Virginia Cooperative Extension says large numbers of carpenter ants on a tree suggest wood decay and a tree that is potentially hazardous. It recommends having an arborist check the tree, especially if it stands near a house, walkway or anywhere a falling tree would be dangerous.
Ohio State lists the usual ways water and fungi get in: pruning cuts, broken branches, man-made holes, woodpecker feeding, deer rubbing, mower and string trimmer damage, and lightning strikes. Over time that can cause heart rot, where the center of the trunk decays or goes hollow. It warns that years of internal rot can bring down even a healthy-looking tree in a storm, and suggests an inspection by an ISA-certified arborist trained in tree risk assessment when a tree could hit a structure or vehicles. See how to tell if a tree is dying and our arborist risk assessment page.
Should you treat a tree for carpenter ants?
Extension services do not agree on this, so it helps to see their advice side by side.
| Source | What it says about treating ants in a tree | Link |
|---|---|---|
| Purdue | Control is not necessary for the tree's health. It can reduce ants moving into nearby buildings, but retreatment every year or so may be needed. | Purdue, Checked Oct 17, 2026 |
| Iowa State | Dust insecticides labeled for trees in the landscape, applied into the nest cavity, are suggested if you treat. Controls are not likely to rid the tree of ants for good. | Iowa State, Checked Oct 17, 2026 |
| Ohio State | Controlling the ants will not reverse damage inside the tree. Follow the product label, which is the law. | Ohio State, Checked Oct 17, 2026 |
| UMass | No chemical management is recommended in trees with carpenter ant colonies. The ants point to a bigger problem, such as decay. | UMass Extension, Checked Oct 17, 2026 |
The common thread: treating the ants is about keeping them out of the house, not about saving the tree. Iowa State and Purdue note that a colony in a tree can form satellite colonies inside a nearby home wall. If the tree is sound enough to keep, the decay is what decides its future.
What not to do to the tree
Several old fixes make things worse. Iowa State and Purdue say plugging or sealing tree cavities, or painting wounds with dressings, is not advised: it will not stop decay or carpenter ants. Ohio State says not to fill a hollow with rocks, bricks or cement, which can cause more damage as the tree sways and are a hazard for anyone who later prunes or removes it.
Ohio State also says not to clean out a cavity, since that risks breaking into healthy wood and spreading fungus, and not to drill a hole to drain water, which just makes a new wound. It warns against topping a tree, which leaves open wounds facing straight up into the rain. What can help is keeping water out: Ohio State mentions sheet metal used as a small roof over an upward-facing hole, and says removing limbs with obvious rot may reduce the chance of ants moving in. Iowa State adds that cutting down an otherwise viable tree just because it has carpenter ants is generally not necessary.
Keeping tree ants out of the house
Virginia Cooperative Extension says ants active inside in late winter or early spring, February or March, probably come from a nest inside the house. Large numbers that suddenly appear indoors in late spring may be foragers from outside. Ohio State says mature colonies can split into 1 to 10 satellite nests, foragers can travel more than 300 feet, and ants follow branches and vines that touch the roof or utility lines.
Virginia Cooperative Extension's outdoor advice: store firewood so it stays dry, remove wet, decaying wood near the house, consider removing rotting stumps and logs close by, and cut back vines and tree branches that touch the house. See stump grinding cost and a tree too close to the house.
What it can cost (national)
| Item (national) | Published figure | Source |
|---|---|---|
| Carpenter ant treatment by an exterminator | $250 – $500 | HomeGuide, Checked Oct 17, 2026 |
| Arborist, per hour or per inspection | $100 – $250 | HomeGuide, Checked Oct 17, 2026 |
| Tree branch removal | $75 – $250 per branch | HomeGuide, Checked Oct 17, 2026 |
| Tree cabling | $200 – $350 per tree | HomeGuide, Checked Oct 17, 2026 |
| Tree removal | $300 – $2,000 per tree | HomeGuide, Checked Oct 17, 2026 |
National figures from HomeGuide, not Roanoke quotes. For a larger tree, see dead tree removal cost and hazard tree removal.
Carpenter ants in a tree near your house?
Call (540) 904-1819 or use the form. Tell us the kind of tree if you know it, where the sawdust or ants are, and what the tree could fall on. We will pass your request to an independent local tree crew. If you have also seen woodpeckers working the trunk, our guide to woodpecker holes in trees explains what the holes mean.
Common questions
Do carpenter ants kill trees?
Not directly. Purdue and Iowa State Extension say carpenter ants in trees are not directly harmful, because they nest in wood that is already decaying. UMass Extension notes the galleries can speed the weakening of a decayed tree.
What do carpenter ants in a tree mean?
Usually decay. Virginia Cooperative Extension says carpenter ants do not damage sound wood, and that large numbers on a tree suggest wood decay and a tree that may be hazardous.
Can a tree with carpenter ants be saved?
It can be. Ohio State says a tree can live with heart rot and carpenter ants as long as its cambium stays healthy. An arborist can judge how much sound wood is left.
How do you treat carpenter ants in a tree?
Iowa State suggests dust insecticides labeled for trees, applied into the nest cavity, and says retreatment may be needed. UMass Extension recommends no chemical treatment in trees. Treating the ants does not fix the decay.
Should I fill the hole in a tree with carpenter ants?
No. Iowa State and Purdue say sealing cavities or using wound dressings will not stop decay or ants, and Ohio State says not to fill hollows with rocks, bricks or cement.
Why are carpenter ants in my tree stump?
Virginia Cooperative Extension says carpenter ants nest in rotting logs and stumps, and suggests you consider removing rotting stumps and logs near the house.
Sources
- Virginia Cooperative Extension, Carpenter Ants (ENTO-485NP, revised Dec 8, 2021) (Checked Oct 17, 2026)
- Purdue University Forestry and Natural Resources Extension, Are Carpenter Ants Harmful to My Tree? (Checked Oct 17, 2026)
- Iowa State University Extension and Outreach, Yard and Garden: Carpenter Ants in Trees (July 15, 2020) (Checked Oct 17, 2026)
- Ohio State University Extension, Buckeye Yard and Garden onLine: Carpenter Ants in Trees (Feb 24, 2025) (Checked Oct 17, 2026)
- UMass Extension, Landscape, Nursery and Urban Forestry Program, Insect and Mite Guide: Camponotus pennsylvanicus (Checked Oct 17, 2026)
- HomeGuide, ant exterminator cost (national, Aug 6, 2023) (Checked Oct 17, 2026)
- HomeGuide, arborist cost (national, Feb 4, 2026) (Checked Oct 17, 2026)