Carpenter ants seen indoors in winter usually mean a colony is living inside the building, because it is too cold for them to be active outdoors. They nest in wood without eating it, and they favor damp, enclosed spots such as the area around windows, doors, sinks and leaking pipes. Finding the nest and repairing the moisture that feeds it is the job, not chasing the ants you can see.
Key takeaways
- Carpenter ants seen indoors in winter, when it is too cold for them outdoors, strongly indicate a colony inside the building.
- Carpenter ants nest in wood but do not eat it, so the nest is the thing to find rather than the damage on the surface.
- Winged carpenter ants seen indoors in summer do not by themselves mean a nest is present.
- Indoor nests favor permanently damp, enclosed space, such as around windows and doors, showers, bathtubs, dishwashers and leaky pipes and drains.
- Nests have also been found in hollow-core doors, in foam insulation and under leaky roof shingles or roof vents.
- Control means locating the nest and treating it directly, then repairing whatever keeps that area damp.
Why would carpenter ants be inside in January?
Carpenter ants are active outdoors in warm weather. In a cold winter, an ant indoors is usually a sign that a colony has taken hold inside the structure itself.
Michigan winters are cold and snowy, and carpenter ants are not active outdoors at those temperatures. An ant that appears on a kitchen floor, along a basement sill or beside a bathroom in January has only a short list of places it could have come from. The most likely one is a colony inside the building, which is why a winter sighting deserves more attention than a summer one.
Michigan State University Extension treats indoor winter sightings as one of the clearest signals of a nest. The sighting does not reveal where the nest is, only that one probably exists. That is why a technician looks for the source of the ants rather than treating the trail alone, and why the search starts at the places where moisture collects.
What do carpenter ants actually do to a house?
Carpenter ants nest inside wood but do not eat it. The question that matters is where the nest is, not what the ants are feeding on.
Carpenter ants are among the largest and most common ants in Michigan. The most useful thing to know about them is that they build nests in wood without eating the wood. Their presence is a sign of where they have set up home. A line of ants along a window frame or a baseboard shows a route, and the end of that route is the part that matters.
Because they do not feed on the wood, the signs of their presence can be easy to miss. A homeowner may see only a few ants at a time, and often in the same spot. That repetition is worth noting, because it points to a place where the colony is active rather than to a one-time visitor. A few ants that appear once and then vanish tell a different story. Looking at the ants alone rarely settles the matter, since the same colony can be reached from several places in a building.
Where do indoor carpenter ant nests start?
Indoor nests favor permanently damp, enclosed space. The usual starting points are around windows and doors, under sinks, in showers and bathtubs, and wherever a pipe or drain leaks.
The pattern in Michigan buildings follows the moisture. Typical places include the area around windows and doors, showers and bathtubs, dishwashers, and leaky pipes and drains. Each of those keeps a piece of wood wet for long enough that a colony can settle in and stay there, and a nest that finds a steady supply of moisture has little reason to move.
Older farmhouses with crawl spaces, dirt floors or unfinished stone basements can hold damp wood near the sill plate, and that wood is worth checking first. A house with a dry, well-ventilated space has less of that moisture to work with. The aim of the inspection is to find the wet spot, not to guess at it from the ants alone. Checking the damp spots in order, from the wettest to the driest, keeps the search organized.
Where else do carpenter ants turn up in a building?
Beyond the obvious damp spots, carpenter ants have been found in hollow-core doors, in foam insulation and under leaky roof shingles or roof vents. Each is a place where moisture and concealed space meet.
Roof areas are an easily overlooked location for an indoor nest, especially when a leak or a vent lets water into the wood. A nest under leaky shingles or near a roof vent is hard to see from inside the house. The first sign is often ants that keep showing up in the same room, sometimes on an upper floor, and the ants are only the visible end of the problem.
Hollow-core doors and foam insulation are less obvious. Both give an ant a sheltered cavity, and neither looks like wood from the outside. A technician who finds ants near a door will look at whether the door is hollow and whether a gap or leak nearby keeps the area damp. Looking at the whole path the ants take gives a better picture than looking at one spot. Recording each place the ants are seen, and returning to the same list after a few weeks, shows whether the activity is shrinking or continuing.
Are winged carpenter ants in summer a sign of a nest?
Not by themselves. Winged carpenter ants seen indoors in summer do not on their own show that a nest exists in the building, so the season matters when a sighting is read.
Winged carpenter ants seen indoors in summer, by themselves, are not a reliable sign of a nest. The same ant in January is a different case, because the cold removes the outdoor explanation. The season changes the question, which is why a summer sighting is a reason to look and not a diagnosis.
A useful habit is to note when the ants appear, where they walk and whether they keep returning to one place. A few in summer that vanish is a different situation from ants that show up every month in a heated room. A technician will ask those same questions before deciding where to look first.
How is a carpenter ant nest found and treated?
Control means finding the nest and treating it directly, then repairing whatever keeps that area damp. Treating only the ants you can see leaves the source in place.
Locating the nest is usually the hard part, because it sits inside a wall, behind a door or in a roof space rather than in plain view. Treatment is aimed at the nest, not at the trail on the floor. A damp spot left as it is will draw ants back, so the moisture has to be dealt with as part of the job. Looking closely at the carpenter ant control work will show how the two fit together.
A technician works from the inside out, checking the sills, the window and door frames, the plumbing and the roof areas for signs of moisture and activity. Repairs that let an area dry out, such as sealing a gap that admits water or fixing a leaking pipe or drain, belong in the same plan as the treatment. Without them, the conditions that drew the colony stay in place.
What should a homeowner do before the technician arrives?
Write down when and where the ants appear, and leave the area undisturbed where you can. Note whether the ants come from a wall, a window, a sink or a roof vent.
A short written record helps a technician more than a general description does. Note the dates the ants were seen, the room, the exact spot, and whether the sightings happen in winter or summer. Photographs of the trail, taken safely, are useful as well, particularly of any spot where the ants gather repeatedly. Note also whether the ants are seen near a spot where water has been, since a damp location is the feature these nests are known to favor.
Avoid treating the trail yourself. A surface treatment does not reach a nest inside a wall or a door, and it leaves the moisture problem untouched. Keep watch for wet wood, drips, staining or soft spots, and tell the technician about any you find. Those details often point straight to the spot that needs attention.
When should you call about carpenter ants?
Call when ants appear indoors in winter, or when they keep returning to the same spot over several weeks. Phones are answered 24/7, and a visit the same day only when a technician is free.
Winter sightings are the clearest reason to call, because they point to a colony inside the building rather than a stray. Ants that keep returning to one spot, or that appear near a window, door, sink or drain you already know is damp, are also worth reporting. Early contact makes it easier to find the nest before the damp spot becomes the whole problem. A sighting that comes back after an earlier visit is worth reporting too, because it suggests the source has not yet been found.
You can reach the line at (855) 974-4733. Phones are answered 24/7, and a same-day visit happens only when a technician is free. No arrival time is promised. When you call, describe the location of the ants, the season you first saw them, and any damp or leaking spots you have noticed, and the person who answers can pass that on.
Frequently asked questions
Do carpenter ants eat wood?
No. Carpenter ants nest in wood but do not eat it, and that is the main thing to know about them. The concern is where the colony sits, because a nest in a damp sill or wall is the source of the trouble you see on the floor. A trail of ants on the kitchen floor is usually the visible end of a route that leads to a nest somewhere else. The ants can be present for a while before anyone notices a pattern, which is one more reason to write down what is seen.
If I see one carpenter ant in January, is there a nest?
Possibly, and it is worth paying attention. Carpenter ants seen indoors in winter, when it is too cold for them outdoors, strongly indicate a colony inside the building. A single ant that never returns may be a stray, but a second sighting in the same spot is a reason to look more closely.
Does a summer sighting of winged carpenter ants mean I have a nest?
Not by itself. Winged carpenter ants indoors in summer do not on their own mean a nest is present. The reading changes with the season, the location and whether the ants keep coming back. A technician asks those same questions when deciding where to look first.
Where in the house should I check first?
Start where moisture stays. Look around windows and doors, under sinks, around showers and bathtubs, near dishwashers, and along leaky pipes and drains. Roof areas under leaky shingles or near roof vents are also worth a look. A damp, enclosed spot is the most likely location for a nest. Start in the room where the ants are seen, then work outward toward the nearest possible source of water.
Can I just spray the ants I see?
A surface treatment on the ants you can see does not reach a nest inside a wall, a door or a roof space. It leaves the source in place, so the sightings are likely to continue. Treating the nest directly and repairing the damp are the parts that address the cause. Even when a spray is used on the ants, the location of the nest still has to be found.
Do I need to fix the damp before treatment?
In practice the repairs belong to the same plan. Control is to locate and treat the nest directly and to repair whatever keeps the area damp, so a leak left running works against the treatment. Sealing a gap that lets water in, or fixing a leaking pipe or drain, removes the condition that made the spot attractive to the colony.
This guide is general information for Montcalm County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.