If we are discussing “organisms,” one could argue that it might be wood decay/rot. If we are only talking about “wood destroying insects” the answer would likely be Subterranean Termites (if you live east of the mountains) or likely Anobiid Beetles (if you live west of the mountains).
I have no hard proof of this, but my opinion is based on what I see in the field. Other choices would be Carpenter Ants, Dampwood Termites, and Moisture Ants. In my experience, while there may be exceptions, Carpenter Ants and Dampwood Termites and Moisture Ants tend to do more localized damage.
Carpenter ants can be treated and often no one even knows exactly where the infestation was until remodeling occurs later on. Since the home remained standing all those years, it is testament to the fact that Carpenter Ants only rarely cause catastrophic structural damage. Because the insects have no clue where they are mining the wood in terms of the relative structural importance of wood they are mining, serious structural damage would likely be rare. Once again it would be localized. Engineering redundancy provides additional structural protection. They certainly have no “intention” to destroy your home as well as their own—that would be self defeating.
Dampwood Termites, unlike Carpenter Ants, are not even a real wood destroying insect, in the sense that there isn’t anything you can do to protect your home from them. They are only present if you have been foolish or ignorant enough to allow the home to be damaged by water in the first place. They are not going to be happy with dry wood—as their name implies. So when you fix the water problem, the Dampwood Termites are fixed as well.
The same thing can be said for Moisture Ants. If you don’t have rotten wood in your home you do not have Moisture Ants. Again when you fix the water problem, the Moisture Ants are fixed as well.
Enter the Anobiid Beetle.
Even the presence of the Anobiid Beetle is indicative of our not taking good care of our homes. In this case however, the lack of care may be less obvious. The problem with Anobiid Beetles is that often their presence goes unnoticed until after they have done significant structural damage. While I have never seen houses whose entire floor structures had to be replaced as a result of Carpenter Ants, Dampwood Termites or Moisture Ants, I have seen this several times with Anobiid Beetles. I have very limited experience with Subterranean Termites as they are exceptionally rare in the urban areas in which I inspect, but they can do extensive structural damage—often hidden damage where they do occur. I know my inspector friends on the East side of the mountains unfortunately have much more to say about them in the context of their home inspections. Of course in Southern states they can be a HUGE problem.
Anobiid Beetles love a wood moisture content of between 13% and 18%. Depending on drainage conditions around the home, related moisture issues in the crawl space, missing vapor barrier/ground covers in the crawl space, and inadequate crawl space ventilation, it is not difficult to achieve these ideal moisture levels in the wood structures of a crawl space. Once the wood is infested, the larvae that are boring and eating the wood, will be happy even if the moisture levels fluctuate slightly above 18% and below 13%. The next two pictures show the moisture content in the bottom edge of a floor joist followed by a picture of what the area looks like after probing.
Clearly the wood with the moisture meter does not reveal just how poor a condition the wood is behind the surface.
The life cycle of the beetle is for it to land on the wood and then lay its eggs in the tiny crevasses of the wood surface. They are VERY tiny eggs which turn into VERY tiny larvae. The larvae then bores back into the wood where it grows and tunnels and eats for 5-6 years until it emerges as a beetle and starts the process all over again.
As one can see in the first picture above of support post cross-bracing, their emergence holes are very tiny and unless the observer knows what they are looking at they might not even recognize the holes as a problem. The surface remains pretty much intact while inside the wood, the wood is literally turning into powder. This powder (frass) is actually what is left of the wood after they are done eating it and it is why these beetles are improperly referred to as “Powder Post Beetles.” This next picture shows what one of those cross braces looked like after whacking it with probe.
In this next picture we can see the amount of internal damage to shims under a support post.
Even other inspectors in the NW refer to these beetles as Powder Post Beetles. However, true Powder Post Beetle is a whole different animal with a much different treatment protocol. They primarily infest hardwoods and are officially in the Lyctid Family as opposed to the Anobiid Family. Lyctid beetles are not dependent on wood moisture content and in fact prefer dry wood. One can see why they would be especially problematic in a home. Here in the NW we primarily find them in furniture and hardwood floors shipped in from other parts of the country. Typically the materials will need to be replaced.
In this next picture we can easily see the hundreds of Anobiid Beetle emergence holes—some are open—some are packed with their light-colored frass. Just to the right of “A” one can see the characteristic pile of frass that has developed under a hole in the wood above. Just to the right of “B” one can see a “waterfall” of frass that has collected on the surface of the wood below an emergence hole.
Sometimes there will be rows of frass on the ground beneath infested beams and joists.
The control of Anobiid Beetles is to fix the conditions that are allowing the wood in the crawl space to be above 13%, to replace damaged wood, and to treat the wood with sodium borates. The borates do not kill the beetles but the larvae don’t survive to re-infest the wood. Since the issue is crawl space humidity, as opposed to actual ponding water and plumbing leaks (although they could be a part of the puzzle), one can see why these little beetles can do so much damage—and go unnoticed for a long time—especially when considering their 5-6 year life cycle.
A home that has not been professionally inspected for wood destroying organisms for many years, may have gone through several beetle life cycles and the cable guy or plumber crawling around in your crawl space will not likely notice or care about the beetles. If the home has not been inspected in 30 years, the whole home could be a loss.
Talk about “deal killers.”
Charles Buell, Real Estate Inspections in Seattle