Wood-Destroying Organisms & Rot
~11 min read · Distinguish termite evidence, carpenter ants and fungal rot — and probe where they hide.
Wood-destroying organisms eat houses from the inside: subterranean termites commuting through mud tubes, carpenter ants excavating galleries, and fungal rot dissolving wood wherever moisture persists. The inspector's tools are a flashlight, a probe, and knowing each destroyer's signature.
Termites
Subterranean termites (the main US threat) nest in soil and commute: their signature is the mud tube — pencil-width earthen tunnels up foundations, piers, and in cracks; galleries follow the SOFT springwood leaving a layered, dirt-packed excavation; swarmers (winged reproductives) and piles of shed wings in spring are colony evidence. Conducive conditions are half the report: wood-soil contact, mulch to siding, moisture, foam insulation bridging grade. Drywood termites (southern/coastal): no soil contact, kick-out holes with six-sided fecal pellets. Damage often hides behind paint — probe and sound (paper-thin surfaces, hollow notes).
- Mud tubes = the subterranean signature; break one, check for traffic
- Dirt-packed layered galleries; wings and swarmers in season
- Report conducive conditions, not just live evidence
- Drywood: pellet piles, no tubes
Carpenter ants and other insects
Carpenter ants don't eat wood — they EXCAVATE it (usually moist/rotted wood): galleries are clean and smooth (no mud), with frass — sawdust-like debris mixed with insect parts — kicked out below; large black ants trailing indoors, especially at night, complete the picture; their presence usually flags a moisture problem first. Powderpost beetles: small round exit holes and fine flour-like powder, typically in hardwoods and older joists; active vs historic judged by fresh powder.
- Ants: clean galleries + frass piles (vs termites' muddy ones)
- Ant infestations mark moisture — find the wet wood
- Beetles: pinholes + fresh flour powder = active
Fungal rot
Brown rot ('dry rot' — a misnomer; all rot needs moisture) leaves brittle, darkened wood cracked into cubes; white rot leaves pale, spongy, stringy wood. Requirements: moisture (~20%+ wood moisture), oxygen, temperature — so rot maps the moisture map: sills, rims, sub-bath framing, deck connections, siding bottoms. Probe suspected areas (a screwdriver sinking = finding); report rot AND its water source together. Scope note: many states separate the WDO/termite report (a licensed pest inspection) from the home inspection — the home inspector reports visible evidence and refers.
Worked example
In one crawl space: pencil-width mud tubes climb two piers; a sill section sounds hollow and the probe sinks in, revealing dirt-packed layered galleries; under the kitchen, a joist shows clean smooth galleries with a cone of sawdust-and-body-parts below; and the rim by the hose bib crumbles in brown cubes. Identify each organism and frame the report.
Four signatures. The mud tubes + dirt-packed layered galleries in the sill: subterranean termites — active pathway evidence; note conducive conditions feeding them. The clean galleries + frass cone: carpenter ants — and their presence predicts wet wood there (check the kitchen plumbing above). The cubical brown crumble at the hose bib: brown rot — the leaking bib is the water source; probe to size the damage. Report structure: visible WDO evidence by type and location (conditions), structural members affected (probe results), water sources and conducive conditions, and referral to a licensed pest-control operator for treatment scope plus contractor repair — the home inspector documents and refers; treatment prescriptions belong to the licensed WDO professional.
Common exam pitfalls
Confusing termite and ant galleries.
Termites pack mud and layers into soft grain; ants leave clean smooth tunnels and dump frass outside.
Reporting rot without its water source.
Rot is a moisture symptom — the finding pairs the damaged wood with the leak, contact, or condensation feeding it.
Believing 'dry rot' happens to dry wood.
All decay fungi need moisture — the name describes the brittle result, not the cause.
Mud means termites, clean-and-frass means ants, cubes mean rot — and every one of them drinks before it eats.
Recap
- Subterranean termites: mud tubes, dirt-packed layered galleries, swarmers
- Conducive conditions are reportable findings
- Carpenter ants: clean galleries, frass, moisture flag
- Beetles: pinholes and fresh powder
- Rot: brown cubical vs white stringy — probe and pair with water
- Document, refer to licensed WDO/pest professionals
Prove it: 10 questions on this topic
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