Seattle Home Inspector's Blog


Moisture Ants---who invited THEM in?


These little wood destroying organisms are awesome!

Well maybe not so much for your house, but at least the damage will likely stay pretty localized.  Moisture ant carton

Moisture ant towerMoisture Ants are only present if there is a leak or wetness sufficient to cause wood decay/rot. 

What they seem to like is very slow consistent leaks---too much and they don’t seem to be encouraged to build a nest. 

All it takes for them to get started is a little leak at a plumbing fitting or wood that stays wet from some other constant moisture condition. 

Wood in contact with wet soil will often stay wet enough that when the wood decays the Moisture Ants will move in.

Their nests are designed like sponges that will move water to wood that is not decayed and thus promote the spread of the decay.  In this manner, if there is sufficient water supply they can expand the nest quite a distance. 

In the case of a plumbing leak that is small, they might be able build a nest that will successfully absorb all the water to the point that the leak might never show itself---only becoming evident when the wall or ceiling is taken down for some other reason.

On a recent inspection I found a very nice structure of a Moisture Ant colony.  It was built from the crawl space floor up a corner created by a support post and the concrete foundation---as can be seen in the picture above. 

From there it wrapped itself around the leaking bathtub drain.  Once established, the leak, maintained by daily showers of the home's occupants, was sufficient to maintain the Moisture Ant structures.  These structures are called “carton” and have a sponge-like appearance (like the picture at the top right). 

Moisture Ant Carton encapsulating a leak

The moisture in this instance was sufficient for the ants to extend the carton up the walls above the drain area and across the wall behind the toilet.  This is why there were elevated moisture meter readings under the floor and in the wall between the tub and the toilet.

Moisture in floor and wall

In this case, the damage will be perhaps a bit more extensive than most instances---but who really knows until things are taken apart to be repaired.

The ants were not working the day I found this infestation---most likely dormant for the winter.  They will likely be back though---unless the leak gets fixed.

That is one of the best things about moisture ants---fix the leak and they just leave and go find some other rotten wood.  Typically they are only in our homes because, in some way, we have invited them in.


Charles Buell, Real Estate Inspections in Seattle

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Comment balloon 9 commentsCharles Buell • December 21 2012 06:32AM


Hi Charles - I don't think we have anything like that in our nice dry climate, but what we lack in bugs, we seem to make up in spiders. Every climate has its special treats.

Posted by Dick Greenberg, Northern Colorado Residential Real Estate (New Paradigm Partners LLC) over 6 years ago

I have never seen moisture ants, or their little honeycomb you have up there, but if/when I do I will know what they are because of you!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

Charles -- thank you for this enlightening information.  Especially on how to get rid of them.

Posted by Steven Cook (No Longer Processing Mortgages.) over 6 years ago

Dick, these guys are pretty wide spread---but we sure have our share of them---and it does make sense that an area that is wet like ours would have more.  Even Eastern Washington does not have them as much as we do on this side of the mountains

Jay, I don't ever remember seeing them anywhere I lived back east either

Steven, yes---they are perhaps one of the easiest wood destroying organism to get rid of.

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 6 years ago

Don't have them here on right side. I recall finding them or you found them when we did our job back when. 

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) over 6 years ago

Jim, for sure---lots of moisture ants in those buildings----remember the ones in the rotten siding?

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 6 years ago

Interesting term, moisture ants. We have the same critter here but we call them sidewalk ants to distinguish them from carpenter ants.

In spring or summer you may occasionally see one but these are just scouts. They won't come back unless they find water.

However if you see them repeatedly in the same general area, start checking for water.


FYI 'carton' is French for cardboard and that's what the nest material resembles.

Posted by Robert Butler, Montreal Home Inspector | Aspect Inspection (Aspect Inspection) over 6 years ago

Charlie, I have only seen them on rare occasions here. I did get pictures of them during a swarm tough.

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) over 6 years ago

Robert, here "sidewalk ants" are another critter---different from moisture ants.  They are also called "cornfield ants"

Don, I find it fascinating where different insects thrive and don't thrive

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 6 years ago