Carpenter ants nest in tree stumps because they hollow out damp, softening wood for shelter rather than food, and an old stump near the house can hold the main colony that sends foragers and satellite nests indoors. Trace where the ants go after dark, take out the stump and any other wet wood close to the house, and leave ants already living inside the walls to a pest management professional.
Are they carpenter ants?
Start by being sure. NC State Extension describes carpenter ants as among the largest ants in North Carolina, with workers from a quarter inch to five eighths of an inch long, all sizes in the same colony. The black carpenter ant, the species most often found nesting in homes, is mainly black, while other species can be reddish-brown to yellow. The surest clue is what they push out of the wood: coarse, fiber-like shavings mixed with bits of dead insects. Their tunnels run along the grain and look almost sanded smooth inside. Subterranean termite galleries are different, packed with mud-like material instead of clean shavings.
Why a stump suits them so well
Carpenter ants do not eat wood. They chew it out to make room for the nest and throw the shavings away. What they need is wood soft enough to dig and damp enough to stay humid. NC State says they prefer wood with a moisture content of fifteen percent or higher, and Clemson Extension says the most important thing to remember is that they are attracted to moist wood. A stump that has sat in the ground for a few years, soaking up rain from the soil and softening from the inside, is close to perfect. Clemson notes colonies can also nest in soil or under rocks, so the ground round the stump counts too.
Parent nests and satellite nests
This is why a stump outside can mean ants inside. NC State explains that the queen founds a primary nest, and that workers later move out with some of the young to start satellite nests, while the queen stays in the parent nest. Clemson Extension says a colony is usually six to ten years old, with more than two thousand workers, before it forms satellites, and that satellites usually have no queen or eggs. Their favorite spots include hollow porch columns, wall and ceiling voids, insulation, and the space under a bath or shower. So the stump may be the parent and the house the satellite, or the other way round.
Follow the trail after dark
Carpenter ants are mostly active at night. NC State suggests a simple test after sunset: set bottle caps of honey mixed with water along the foundation, wait, then follow the ants carrying it back toward the nest. The nest is usually close, but trails can run up to 300 feet. If they lead away from the house to a stump, a woodpile or a dead tree, the colony is outside. If they disappear into a wall, check the crawlspace and attic. NC State also warns that spraying the foundation may cut foraging for a while but can hide where the nest is, so find it before anyone sprays.
Signs they have moved indoors
NC State lists the warning signs. Winged ants inside the house point to a nest in or under it; swarmers form in fall and fly in spring. Workers turning up at sinks, dishwashers and showers looking for water in early spring is another. So are rustling sounds in a wall, small piles of sawdust-like shavings, and slit-like openings in wood. Because they favor damp wood, NC State notes infestations often line up with moisture problems around doors, windows, roofs and leaks. Any of these means the stump is no longer the whole story, and the house needs an inspection by a pest management professional.
Dealing with the stump
Grinding the stump below grade takes out the block of soft wood the colony lives in, turning it into chips, and that is often the end of an outdoor nest that close to the house. Ants nesting in the roots or soil under it may relocate, so keep watching the trails for a few weeks afterward. Do not rake fresh grindings into a bed against the house, since you would just be laying out new nesting material. Pile them well away from the walls, use them out in the yard, or have them hauled. For other uses of the chips, see stump grindings and where they can go.
Make the house less inviting
Removing the stump is one step. NC State's list for keeping carpenter ants out runs on from there. Keep tree limbs pruned at least twelve inches from the house, so ants cannot walk across. Never stack firewood near or against the home. Remove dead or unhealthy trees near it. Keep gutters clear, fix leaks and dripping spigots, keep the crawlspace dry and seal foundation cracks. Clemson Extension adds sealing where utility lines enter the house, and notes that catching a problem early takes less insecticide. Termites are a separate question with separate answers: see do stumps attract termites.
Common Questions
If carpenter ants are in my stump, are they in my house too?
Not necessarily, but check. Colonies can split into satellite nests, and those often end up in damp spots in a house. Follow the trails after dark to see where the ants go. Winged ants indoors, ants at sinks in early spring, or piles of shavings inside are signs to call a pest management professional.
Should I spray a stump full of carpenter ants before it is ground?
There is usually no need. Grinding destroys the nest wood itself. Spraying the house foundation can make things worse, because NC State Extension warns it can hide where the nest is. If you want a treatment, ask your county Extension office or a pest control company first, and follow the product label.
How can I tell carpenter ant damage from termite damage?
Look inside the tunnels. Carpenter ants leave galleries that are clean and smooth, almost sanded, and push out coarse shavings mixed with insect parts. Subterranean termite galleries are packed with mud-like material and have no shaving piles. If you are unsure, a pest management professional can confirm which you have.
What to Do Next
A soft stump with ants trailing toward the house is a good one to grind before the next swarm season. Send a photo of it, the way in and your town, or call (828) 574-4474. Stump grinding takes it below grade in one visit.