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 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).
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.
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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WA State, Home Inspector Advisory Licensing Board