Is this a carpenter ant?

Asked July 19, 2013, 12:43 PM EDT

Could you look at these photos of an ant I found in my home office, and tell me whether it's a carpenter ant? Unfortunately, I squished it a little. I've been seeing big dark-colored ants like this since my wife and I moved into our house last year in the spring. Usually I see only one or a handful at a time, and I see them in two places--around an outdoor faucet and coming out from the gap between our bathtub spigot and the tiles. I was concerned until someone told me they're not carpenter ants, but recently a construction guy spotted one at the outdoor faucet and said it was a carpenter. If my squooshing makes the specimen hard to identify, please let me know I'll try to collect another more gently using alcohol. Thanks!

Multnomah County Oregon insect issues

11 Responses

Good day and thank you for using Ask an Expert, also for including the excellent images which reveal critical identification characteristics. (So, thank you for limiting how much you sqooshed!) The most common species in Oregon are Camponotus modoc and C. vicinus.

Yes, your specimen is a carpenter ant. Even so, you have plenty of time to evaluate if and where any damage is, also how you want to manage them.

Here’s an overview of the situation:
- Carpenter ants often establish a nest in moisture-damaged wood. If so, it’s important to determine the source for the moisture and repair it, then replace the damaged wood.

- If you’re seeing only a few random ants, but not in a 2-way trail, they are scouts looking for food and/or water. (The locations of your sightings make me think that the structure is infested.)
- If carpenter ants are using a 2-way trail in and out of the structure, they’re traveling between the main nest somewhere nearby and the nest in the structure. Follow the trail to the main nest; if it’s on your property, it’s wise to have it treated.
- If, during spring, you see multiple winged forms indoors, issuing from a wall, from under baseboard, etc., you have a nest in your house.
- If your structure is infested, you’d be wise to hire a professional pest company.
- Killing the ants you see won’t control them.
- Retail ant baits don’t work for carpenter species in the Northwest

You will need professional assistance to treat the infestation but, first, you need to do some sleuthing to help make the treatment as effective as possible:
1. Locate possible nest sites in the house. Look for what appear to be fresh shavings in the attic space and crawl space.

2. Locate all sources of water damage in the house, perhaps the plumbing, roof, or overflowing gutter, as well as plants or other items holding moisture against the siding. Trim any necessary plants and repair water leaks.

3. If your structure is infested, locate the main nest outdoors so that it, too, can be treated by the professional company.

To determine whether or not your house is infested, do the following:
1. Several times between April and October, go outdoors with a flashlight between 10PM and 2AM.
2. Circle the house looking for 2-way trails of carpenter ants. Such trails indicate the ants are traveling between the main nest and your house.

3. Once you find the 2-way trail, follow it to the main nest. If the main nest is treated, the house is less likely to be re-infested. If the main nest is somewhere off the property, it’s wise to repeat the annual inspections several times between April & October.

Resources for you:
(Please note that, currently, baits and sprays are available to pest control professionals that don’t require drilling to treat wall voids.)

- Carpenter Ants
- Carpenter Ants

Please let me know if you have further questions,

Thank you very much...though of course I don't much like the news you had to give me. Since I took those photos of the big ant you say is a carpenter, they've become scarce all around and outside I've been noticing some small ones. So for the possibility of corroboration and/or insight into nest cycle, I thought I'd ask if you could ID one of these small ones too:

Do you think it's part of the same infestation, or just an innocent bystander?

Thanks again!

- Oliver Baker


Thank you for sending the images of the smaller ants. Unfortunately, it’s difficult to know for certain without having the ant in hand. The partial profile in the final image (#5) suggests this may be a carpenter ant. If so, it may be an intermediate worker, as is shown in the second link I included in my previous response. They may or may not be from the same colony.

At this time, I think you have several alternatives:
1. Carry out several night-time inspections (between 10 PM and 2 AM, between April and October) as outlined in my previous response. If you see one or more two-way trails of carpenter ants, contact several pest control companies for cost estimates for treatment. If you don’t see any 2-way trails, repeat the inspection one or more times this season.

2. Take several mid-sized ant samples – 6 or more is helpful – to the Multnomah County Master Gardeners who can identify them for you. The office is in Montgomery Park, 2701 NW Vaughn St. Suite 450, Portland, OR 97210. Hours are 10 AM to 2 PM, Monday through Friday, closed holidays. If the ants are determined to be carpenters, see #1.


I've got my best photos yet, which I thought I might as well show you.

I haven't gotten over to the county gardeners, and saw nothing in my walks around the perimeter of our foundation (besides some scary big Black Widows), but made an appointment anyway with an exterminator.




Good detective work! The final image of the group reveals the characteristic that says "this is a carpenter ant.” It’s the large node between the thorax and abdomen.

Before you hire a pest control company, repeat the inspections between 10 PM and 2 AM as is suggested in my earlier response. It’s important to locate the main nest because, if it is treated, you’re unlikely to have further invasions from that particular population.

From your description, it sounds like you probably have some water damage. An important part of the treatment for carpenter ants is to locate and repair the leak, then replace the damaged wood.

As for the black widows, know that they’re quite uncommon in our region. It’s likely you’re seeing a close relative, the false black widow, a Steatoda species, which isn’t dangerous.

Thanks for the additional images as they confirmed our suspicions,

Thanks, Jean! For the compliment, the ID and the info about my likely false identification of the Black Widow-like spider. According to the exterminator from Antworks who's coming tomorrow, the two toxins he'll be using (one to be injected behind the siding and another to be painted around the concrete perimeter) both get carried back to the nest. One of them he said kills 5 in the nest for every forager that brings it back. He also said they guarantee you'll be ant-free for a year. I guess this could all be consistent with failing to kill the whole colony and only setting it back a generation. I'd be curious to know if that's part of why you stress finding it.


It sounds like the pest control company is using the newer chemicals. And that’s a good thing because they are baits released just several years ago that our carpenter ants accept. And, as you’ve been told, they take the bait home to their family.

I emphasize locating the main nest and treating it because that is what the university researchers who study our carpenter ants advise. As I mentioned, treating the main nests decreases the likelihood that the ants will re-infest the house.

I also advise that during subsequent years, you verify your house is still free of ants by doing several of the inspections each summer – you know, at night, and sometime between April and October.


So with the guidance of the exterminator I found tore off piece of a rotted stump in our front yard and unleashed a swarm of them. So we found at least one nest. Two neighboring conifers look like they have been colonized as well, so the exterminator will be treating those as well. Actually I got the amplification factor wrong, and he says he expects actually 30 nest ants to die for every forager that brings back the poison (20 for species that don't eat their sick and ailing). "Termidor" is the insecticide he'll be injecting in the walls. Although at first I thought he said the stump nest could account for the ants I saw in our upstairs bathroom, his last word was that we probably have a nest inside as well--which is the reason for the injections. Before I tore open the stump, he did a lot of tsk tsking as we walked around the house and he saw our decaying fence and wood on dirt retaining our driveway extension, not to mention the piles of bark mulch we have everywhere. Apparently we're asking for ants. Based on the size on the ones we've seen--in particular that half-incher of the last photos I showed you, which he said was a soldier and not a worker--the ones we have must have heard the call at least three years ago. Anyway, thanks, Jean, again, for helping me to see that we have a problem.

Yes, if I knew about all the rotting wood, I would also be tsk tsking. Sounds like you have excellent advice at hand, and you're well underway in managing the ants.


Hi, Jean,

Not a question really so much as a development and another chance to show off my photographic documentation skills. (Hopefully not to show off again my proof-reading laziness. Sorry about that last note. ) I thought I'd show you that I just saw one of these
which I reckon is a winged carpenter. Neither I nor the exterminator had seen one, which if I recall right is why he dated the infestation as only about three years old and therefore a couple years short of being ready to explode.

Coincidentally it's 21 days since the exterminator visited, which seems to be legal the window in which you're not allowed to complain that the treatment didn't work. However, this exterminator told me that, with respect to his poisons and protocols, I shouldn't worry even up to 28 days later if I see an ant. The ant in the photo was slow and wobbly enough for me to stop it with my foot, so I'm not inclined to say the treatment isn't working.

- Oliver


It’s tough to confirm an identification without also having an side view. Even so, it does appear that it may be a winged carpenter. The winged forms normally leave the nest early in the year after spending the fall and winter months in the nest. But when nests are treated, it typically “flushes out” some nestmates, including this specimen.

It sounds as if you’re well underway in managing the ants. Even so, recall that you need to remain alert and repeat the periodic inspections as I previously suggested.

Thanks for the update,