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Rot, mold, or insects: how do we distinguish among these types of infestation & damage on or in buildings? How do we distinguish between carpenter ants and termites, how do we identify carpenter ant damage, carpenter bee damage, powder post beetle or old house borer damage and termite damage.
What building construction details increase the risk of insect damage, and how do we evaluate the extent of structural impact of existing insect damage on a building. Preventing damage by wood destroying insects (termites, carpenter ants, powder post beetles) by good design and by building maintenance is preferred to simple chemical applications around a property. When use of pesticides is required, there are some important choices.
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Here we outline major topics of concern regarding insect infestation or insect damage and we link to more in-depth diagnosis and repair information.
For our complete list of building insect problem detection, diagnosis, repair & prevention articles please see the detailed article links listed at Related Topics beginning beneath INSECT INFESTATION / DAMAGE.
If we do see insects in or on the building, it's pretty easy to tell CARPENTER ANTS (stomping around boldly in view, often near water or a sink or tub drain indoors) from a TERMITES (rarely in view unless swarming, but may fall out of a disturbed mud tube).
If you want a single rule, ants have a segmented body with a very very narrow waist (below left) while termites look more wormlike in their body (below right). CARPENTER BEES look like a big slow-moving non-aggressive bumble bee. A female carpenter bee is shown in our third photograph. You won't see POWDER POST BEETLES just their dust and damage.
Below from the left we illustrate carpenter ants, including swarming winged carpenter ants, a termite (sketch) and a carpenter bee. Common flies such as cluster flies are illustrated separately at FLIES, REMOVE or REPEL.
The first course in recognition of types of insect activity in or on a building is often the observation of the actual damage to wood materials in the structures. That's because depending on the type of insect, season, temperature, and other conditions we won't always see the wood destroying insects themselves.
Insect Damage Photos
At below left you can see typical powder post beetle or old house borer damage to a wood joist or beam. At below right you may notice the characteristic mud tubes we associate with termite damage.
Below our photos illustrate typical carpenter ant damage (below left) and termite damage (below right).
Wood Rot Photos
Below our photos illustrate typical wood rot. All wood rot is caused by wood decaying fungi, typically basidiomycetes, some assisted by certain bacteria.
Wood rot (below left) tends to show breaks in the wood grain across the grain and in more or less rectangular forms.
Insect damage involves holes penetrating the wood and removal of the softer summer wood, tending to leave latewood or winter-wood behind to form walls and galleys (below right where my pen points to remaining hardwood).
Watch out: because moisture is involved in most wood destroying insect infestations (excepting drywood termites), you may find multiple sources of wood damage all together: wood rot along with termite or carpenter ant damage. (Carpenter bees prefer more dry wood and burrow right through both winter and summer wood in a board).
How do We Determine the Difference Between Carpenter Ant Damage, Carpenter Bee Damage, Powder Post Beetle Damage & Termite Damage in Buildings? Comparison photos:
For this discussion please also review the example photographs we provide above showing all of these insect types and what their damaged wood looks like. Also see the individual articles for each insect or topic. Carpenter ants, carpenter bees, termites, even powder post beetles or old house borers all provide visible indications of insect activity such as entry or exit holes, mud tubes, or the presence of the insects themselves.
Carpenter ant damaged wood will show cleanly excavated wood passages - the frass is brought outside of the area of excavation. And seasonally you'll find carpenter ants or carpenter ant bodies.
Details are at CARPENTER ANTS
Carpenter bee damaged wood will be on the exterior of the building, typically well above ground, in wood trim, siding, decks, etc. You will observe 5/16" to 1/2" diameter round holes, usually penetrating the edges of boards and when the bees are active you'll find coarse fresh sawdust below the working opening.
Details are at CARPENTER BEES
Probing you will find powdery sawdust and damaged wood just below this skin.
The older the powder post beetle (or old house borer beetle) damage is, the deeper into the wood the damage will extend. For this reason, strategic probing is important to assess the depth of damage to the wood and thus to the wood structure.
When powder post beetles are active you may see light dusting of fine wood powder around some of these holes as well as on surfaces below.
Details are at POWDER POST BEETLES
Termite damaged wood typically will include the presence of visible mud tubes and mud-like substance inside the excavated wood galleys.
It's rare to see an active termite unless you disturb (break apart) a mud tube while it's in use - in that case you'll see pale termites fall out. You will see termites if they are swarming however. (Watch out for "winged ants" that are not).
Details are at TERMITES
Wood rot itself does not produce insect entry/exit holes nor mud tubes, but of course both wood rot and insect damage are often found together and may even be found within the same wood member or board.
Mold is a very broad kingdom of fungi, among which some molds, particularly the basidiomycetes are wood rotters. So not all mold causes wood rot, but basically all wood rot in homes is thanks to one or more mold genera/species. (With some help from bacteria).
Details are at
How do We Evaluate the Extent of Insect or Rot Damage on or in Wood Structures? Structural Damage Assessment Procedure
The general approach to repairing damage from wood destroying insects involves these steps:
The Point of View of the Termite Inspector May Affect the Strategy as Well as The Cost to Cure an Active Insect Problem
Watch out: Many of the large number of expert sources available on the detection and prevention of building damage from wood destroying insects (see References, related articles) have been written from the viewpoint of academics or by pest control and related industry associations.
These experts offer valuable information about insect pests, often from the pest control operator's viewpoint.
Our own point of view is that of very experienced building inspectors, diagnosticians, and repair contractors.
Taking this more broad view of the topic adds two benefits: an improved ability to detect insect infestation by knowing where to look (as do experienced pest inspectors) and additional options that may reduce the ultimate cost of building insect damage repair or insect damage prevention.
Example of WDI Inspection Report Concluding Treatment of Active Infestation was Not Feasible
During a building inspection for a home buyer in Hyde Park, NY the pest control inspector (from a local pest control operator or PCO) observed termite infestation in the first floor structure of a home. He also observed that a private water well was located just a few feet from the foundation wall. This pest control operator issued a "WDI Termite Report" report that concluded:
Needless to say, the home seller, buyer, realtor, were all quite upset with this result. What was less obvious was the thinking of the PCO which went as follows:
In other words, as the adage [with some rewording] goes:
But wait! Let's go back to the original adage:
I [DF] was asked for a "second opinion" about the un-solvable termite problem at this Hyde Park home. I am no smarter than the PCO inspector, and I saw the same things he did.
But I also noticed and confirmed by some probing and poking into the area of damage that the actual termite infestation had entered up one narrow area of the foundation wall and entered the wood floor structure beneath a leaky toilet in a first floor bathroom. The entire area of infestation was less than ten square feet of material. That suggested an alternative five-step solution to the active termite problem, a "carpentry approach" and perhaps for that reason, one that the PCO had not considered.
5-Step Termite Damage Repairs Without Requirement for Chemical Treatment
The building owner hired a contractor who cured the termite infestation by the following steps:
Following these repairs the building owner hired the same PCO to perform a follow-up inspection. All of the investigation, repair, and PCO report documentation was provided to the home buyer and buyer's lender. The result was a "clear" or no infestation found report, permitting the home sale to proceed.
Flies are not wood destroying insects but can be a pest in buildings and in some circumstances may spread disease. See FLIES, REMOVE or REPEL.
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Frequently Asked Questions (FAQs)
Question: can you identify the type of insect that appears to have infested this wood seen in our attic?
What kind of pest do you think makes this? - MJS 10/24/2012
I can't say, MJS, but what is quite apparent from your photograph is that what appears to be insect activity, perhaps from a type of borer beetle, occurred before the tree was harvested and cut into lumber.
You can see that the flat sawn and planed surface of the wood has left cross-sectional slices of exposed, sawdust-filled voids in the wood. To me the damage looks like a type of wood boring beetle, powder post beetle or old house borer, but that's uncertain.
We publish your photo here to invite other readers to comment, and I'll also review our text library for some comparison images of similar wood damage.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.