Termite Damage You Can't See: How to Know When to Call a Professional
About the Author: Jameson Elam is the owner and operator of Good Sense Termite, serving Alameda, Santa Clara, San Mateo, and Santa Cruz counties. With over 14 years of hands-on experience in the termite control industry, Jameson specializes in thorough inspections, accurate diagnostics, and long-term solutions tailored to California homes. His deep knowledge of local termite behavior and building structures has made Good Sense Termite a trusted name for homeowners and real estate professionals alike.
The most unsettling thing about termites isn't the damage they cause — it's how long they can cause it without you knowing. Both drywood and subterranean termites spend the vast majority of their lives inside wood or underground, completely out of sight. By the time visible evidence appears, activity has often been ongoing for months or years.
This is why "I haven't seen any termites" is not the same as "my home doesn't have termites." Here's what hidden termite activity actually looks like — and the signs that should prompt a call, even when you can't see anything obvious.
Why Termite Damage Stays Hidden So Long
Understanding why termite activity is so hard to detect helps you know where to look and what to take seriously.
Drywood termites live entirely inside wood. A drywood termite colony spends its entire life cycle inside the wood it infests — feeding, reproducing, and expanding its galleries without ever needing to emerge. The only evidence that reaches the surface is frass, which the colony periodically pushes out through small kick-out holes, and the swarmers that emerge briefly during swarming season. Between those events, there's nothing visible at the surface.
Subterranean termites travel underground. Subterranean termite colonies live in the soil and access above-ground wood through mud tubes or directly through ground-contact wood. Most of their foraging activity happens below the soil surface or inside wood — the mud tubes that are the most visible sign are often in the crawl space or on foundation walls that homeowners rarely inspect closely.
Damage accumulates from the inside out. Both species feed on the interior of wood while preserving the outer surface as long as possible. A piece of framing that looks structurally sound from the outside may be extensively hollowed inside. This is why probing with a screwdriver — not just looking — is part of any meaningful termite inspection.
The Indirect Signs Worth Taking Seriously
Because direct evidence (visible termites, obvious damage) often doesn't appear until an infestation is well established, the more important skill is recognizing indirect signs — the things that don't look like termites but often are.
Doors and Windows That Stick or No Longer Align
When drywood termites damage the wood framing around doors and windows — or when subterranean activity affects floor framing and causes subtle settlement — the first symptom is often a door or window that no longer opens and closes the way it used to.
This is easy to attribute to seasonal wood expansion, a house settling, or the previous owner's shoddy installation. And sometimes it is those things. But a door or window that has noticeably changed behavior without an obvious explanation — particularly in an older home, or following a dry summer or wet winter — is worth having a professional look at.
Hollow-Sounding Floors or Walls
Tap on a hardwood floor or a wall surface in an area where you have any reason to suspect termite activity. Sound, undamaged wood produces a solid, dense sound. Wood that has been hollowed out by termite galleries produces a distinctly hollow, papery sound.
This test works best when you have a reference point — tap an area you're confident is undamaged first, then compare. A floor section that sounds noticeably different from surrounding areas, or a wall that sounds hollow when it shouldn't, is worth investigating further.
Blistered, Bubbled, or Unexpectedly Soft Paint
Drywood termites that have established galleries just beneath a painted wood surface sometimes cause the paint above to blister or bubble — the gallery disrupts the surface just enough to be visible as a paint defect. This is easy to mistake for moisture damage, and it can be either, but if it appears on a surface that shouldn't have a moisture source, termites are worth considering.
Similarly, painted wood that feels soft or gives slightly when pressed firmly — without obvious moisture damage — may have compromised structural wood behind it.
Frass in Unexpected Places
Drywood termite frass is the colony's waste product — small, hard, six-sided pellets roughly the size of a grain of sand. It's pushed out of the colony's kick-out holes and falls or accumulates below.
Finding frass is often described as "looking like sawdust" — but it's more regular in shape and harder than sawdust. It can appear on windowsills, on surfaces below wooden eaves, at the base of walls, in light fixtures or on ceiling surfaces below attic framing, and in other locations that don't have an obvious construction or dust source.
A small pile of frass found once might be old, dormant activity. Frass that accumulates again after being cleaned up is a sign of active, ongoing colony activity — and a clear prompt to call a professional.
Mud Tubes in Low-Visibility Locations
Mud tubes are the most definitive sign of subterranean termite activity, but they're often in places homeowners don't regularly see: along foundation walls visible only from outside at ground level, inside the crawl space on floor joists and piers, behind stored items in the garage, or running along the back of cabinets in a utility room.
A mud tube that's been there for years may be old and inactive — break a section of it and check whether it's repaired within a few days. Active colonies will repair a broken tube; inactive ones won't. Either way, the presence of mud tubes warrants a professional inspection to determine current status and whether any damage has occurred.
Unexplained Moisture Readings or Crawl Space Changes
If you have a moisture meter or your inspector has noted elevated moisture readings in previous inspections, changes in those readings — particularly increases in crawl space framing or subfloor — can indicate subterranean termite activity that is compromising wood integrity and allowing moisture infiltration.
Similarly, if you notice water staining on crawl space framing that doesn't correspond to a known plumbing or drainage issue, subterranean termite damage that has created pathways for moisture is worth considering.
The Structural Signs That Mean Act Now
The signs above are reasons to schedule an inspection. The signs below are reasons to call today.
Flooring that has become noticeably soft, spongy, or bouncy in a localized area — particularly near exterior walls, in bathrooms, or above the crawl space — may indicate subterranean termite damage to subfloor or floor joists that has progressed to structural compromise.
A door or window frame that has visibly shifted — not just sticking, but visibly out of square — can indicate structural framing damage significant enough to affect the opening's geometry.
Any visible collapse or failure of wood structural elements — a sagging section of floor, a wall that has developed a visible lean, a ceiling that has shifted — requires immediate professional assessment. Termite damage that has progressed to visible structural failure means the affected framing has lost meaningful load-bearing capacity.
Swarmers emerging from inside the home. Termite swarmers emerging from baseboards, electrical outlets, window frames, or any interior location mean a colony is active inside your home's structure — not in the yard, not in a neighboring tree, but inside the walls or framing. This is one of the clearest possible signs of an established interior infestation and warrants same-day professional inspection.
What a Professional Can Find That You Can't
Even a diligent homeowner doing a thorough walk-through has significant limitations compared to a licensed termite inspector:
Crawl space access and assessment. Most homeowners rarely or never enter their crawl space. A termite inspector assesses it systematically, checking every accessible joist, pier, and sill plate.
Moisture meters. Inspectors use calibrated moisture meters to detect elevated wood moisture that indicates either active termite damage or conditions that make termite activity likely.
Attic inspection. Attic framing is a common drywood termite location that most homeowners never look at closely.
Pattern recognition. An experienced inspector recognizes the difference between old, inactive damage and current activity — and knows where to probe based on patterns in the wood that aren't obvious to an untrained eye.
The WDO report. The written inspection report documents findings with specificity — location, extent, species, and recommended treatment — creating a record that an informal homeowner check doesn't produce.
The Bottom Line
Termite damage that you can't see is still damage. The indirect signs described above — sticking doors, hollow sounds, frass accumulation, unexplained paint bubbling — are the language termites use when they're not ready to be found yet. Learning to read those signs is one of the most practical things a Bay Area homeowner can do.
When any of these signs appear, the right call is a professional inspection — not because every sign definitively means termites, but because the cost of an inspection is trivial compared to the cost of discovering advanced damage later.
Good Sense Termite offers free inspections throughout Santa Clara County. Call or text us at (408) 418-9152 or request your inspection online — we'll give you a clear, honest answer about what's happening in your home.
It's just good sense.
Frequently Asked Questions: Hidden Termite Damage
What are the early signs of termite damage inside walls?
The most common early indicators are doors or windows that suddenly stick or no longer align properly, hollow-sounding walls when tapped, small piles of frass (sand-like pellets) at the base of walls or on windowsills, and blistered or bubbled paint on wood surfaces without an obvious moisture source. None of these are definitive on their own, but any of them in an older Bay Area home warrants a professional inspection.
How do I know if termite damage is active or old?
Active drywood termite colonies continue producing frass — if you clean up a frass accumulation and it reappears within days or weeks, the colony is active. For mud tubes, break a small section and check whether it's repaired within a few days; active subterranean colonies will rebuild it. For structural damage, only a professional inspection with probing and moisture metering can reliably distinguish between old, dormant damage and ongoing active infestation.
Can termites damage my home without any visible signs from the outside?
Yes — this is the norm rather than the exception. Both drywood and subterranean termites can maintain active colonies inside structural wood for extended periods without producing visible exterior evidence. Interior signs — frass, sticking doors, hollow sounds — often appear before exterior signs become obvious, which is why paying attention to interior changes in an older home matters.
How long can termites go undetected in a Bay Area home?
There's no fixed answer — it depends on species, colony size, location in the structure, and how closely the homeowner has been paying attention. Drywood termite colonies can establish and expand in attic framing for several years before producing enough frass to be noticed in living spaces. Subterranean colonies in crawl spaces can forage through floor joists through multiple wet seasons before the damage becomes detectable from above. Annual professional inspections are the most reliable way to catch activity before it reaches this stage.
Should I be concerned about sticking doors and windows if I don't see termites? Yes, if the change is unexplained and has occurred recently in an older home. Sticking doors and windows are commonly caused by seasonal wood movement or normal settling — but they're also a known symptom of termite damage to door and window framing, and of subterranean termite activity affecting floor framing in ways that cause subtle structural shifts. An inspection rules out termites as the cause, which is worth knowing regardless.
What's the difference between termite frass and sawdust?
Termite frass consists of small, hard, six-sided pellets — consistently shaped and roughly the size of a grain of sand. Sawdust is irregular in shape, finer in texture, and varies significantly in particle size. Frass from drywood termites also tends to be a consistent color — ranging from cream to dark brown depending on the wood being consumed. If you're unsure whether what you're seeing is frass, a photo sent to a licensed termite company is usually enough to get a quick answer.
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