Subterranean termites vs drywood termites is the first question worth answering, because the two live in different places and call for completely different treatment. Homeowners tend to use the word termite as though it names one insect. Around the Bay Area it names two, and telling them apart decides everything that happens next.

This is a practical guide to that difference: where each one lives, the signs each leaves behind, and why a treatment that works on one does nothing at all to the other. It reflects what Banner technicians find in crawl spaces and wall voids from Santa Cruz up through the Tri-Valley.

How do you tell subterranean termites from drywood termites?

Look at what the insects leave behind, and where you find it. Subterranean termites build mud tubes, which are tunnels of packed soil running along foundations, crawl space joists, and interior walls. Drywood termites leave frass instead: hard, wood-colored pellets that gather in small piles beneath window sills, door frames, and drywall voids.

Subterranean Termites Live in the Ground

Western subterranean termites are the ones Banner technicians run into most across the region, and they stay active year-round here rather than showing up in one season. The colony itself never leaves the soil. It sends workers up into wood, which is why the damage usually starts low: crawl spaces, sill plates, the first floor. They can travel up through multiple floors once they are established, so a find on a second floor does not rule them out.

Their giveaway is the mud tube. Subterranean termites cannot spend long in open air, so they build shelter tubes out of packed soil and move through those instead. Run a flashlight along a crawl space wall in Concord or Martinez and find a ribbon of dried mud climbing the concrete, and you have your answer.

What brings them to a house in the first place is wood touching soil. Lumber stacked against a foundation, a planter box built against the siding, a fence post set into a flower bed: every one of those is a bridge from the colony into the structure. Breaking that contact is the single most useful thing a homeowner can do without calling anyone, and it belongs with the rest of keeping pests out of your home: a dry perimeter, no wood stacked against the wall, nothing bridging soil to siding.

Drywood Termites Live Inside the Wood

Drywood termites are less common around the Bay, though they turn up regularly in older housing stock on the Peninsula and in the South Bay. They need no contact with soil whatsoever. A colony can sit in a wall void, a window sill, or a door frame for years, feeding on the wood around it, never once reaching the ground.

Since they live sealed inside the wood, you rarely see the insect. You see the frass. Drywood termite frass is hard and pellet-like, and it piles up directly under whatever it is falling out of. A small cone of pellets on a window sill in an older San Jose home is a drywood find, not dust, and sweeping it away only resets the clock on noticing it again.

One thing worth ruling out before anyone treats anything: wood boring beetles leave frass too, and theirs is finer and more powder-like. The distinction matters because the treatment is not the same, which is a good argument for having someone identify it in person rather than guessing from a photo on your phone.

Why the Difference Decides the Treatment

This is where the distinction stops being trivia. Subterranean termites are treated in the soil. A technician trenches along the foundation, roughly six to twelve inches out from the wall and eight to twelve inches down, then uses injection rods to place a termiticide below the depth of the slab. Where concrete is in the way, the same treatment goes in through half-inch holes drilled about every eighteen inches, plugged with concrete afterward. The products are EPA-registered and applied by a licensed technician following the label.

Drywood termites are treated in the wood. A local treatment means drilling small holes, an eighth of an inch across, into the infested area and injecting a foam that works both on contact and through a residual transfer effect. Six to twenty-four holes is a normal range depending on how much wood is involved, and they get plugged when the work is finished. Expect that residual to take up to three months, and expect minor activity during that window. That is the treatment doing its work, not failing.

That last point catches people out. Fumigation fills a structure with gas over three days, which reaches drywood colonies sealed inside the framing and reaches nothing at all in the ground. Subterranean termites simply retreat down their shelter tubes into soil the gas never touches. Fumigation is a real option for widespread drywood infestations, and Banner arranges it through a fumigation subcontractor rather than performing it in-house.

What Bay Area Conditions Add

Termite pressure here is a moisture story, and this region is a patchwork rather than one climate. Along the coastal fog belt and up through the Santa Cruz mountains, cool damp air, redwood debris, and year-round moisture keep subterranean activity steady in a way inland cities never see. Crawl spaces in Scotts Valley and Aptos stay damp most of the year.

The Tri-Valley works the opposite way. Walnut Creek, Concord, and Livermore get hot dry summers against cold wet winters, so pressure arrives in pulses: soil dries and cracks through August, then saturates once the rains start. Waterlogged soil pushes subterranean workers toward the warm dry structure sitting above it.

No month here is a quiet month for termites, which is exactly what separates them from yellowjackets or ants. What does change through the year is access. Late August is the last dependable stretch of dry weather, and a dry crawl space is a crawl space somebody can actually inspect properly. Once the rains arrive that same sub area is wet, tight, and considerably harder to read.

Moisture, Fungus, and the Damage People Miss

Wood that stays wet invites more than termites. The wood destroying fungi divide into brown rot, white rot, and soft rot, and brown rot causes most of the decay in the softwood framing used above ground. It often gets called dry rot, which is a misleading name, because dry wood does not decay at all. Water is the requirement.

The remedy is mechanical first and chemical second. A technician wire brushes the fungus off the member, then applies a borate-based wood treatment that keeps it from growing back. Kept out of the weather, that treatment carries a long residual, which is why it earns its place on exposed framing in attics and crawl spaces. If what you actually have is mold, that belongs to a different specialist, and Banner will tell you so instead of taking the work.

What an Inspection Actually Covers

Termite work begins with an inspection, and there are two kinds. A limited inspection looks only at the areas already in question. A complete inspection covers the whole structure including attics and crawl spaces, which is what a property sale normally calls for. If you are buying or selling, read up on what a WDO inspection covers before you book anything.

Be clear on what a recurring plan does and does not reach. Quarterly service handles the general pests in the usual household lineup, and most homes do best on a quarterly plan for that work. Termites sit outside it entirely. Wood destroying organisms get their own inspection, their own treatment, and their own warranty, which is why Banner’s termite control service is scheduled separately from general pest service.

On warranties, read the limits rather than the headline. A local treatment carries a retreatment warranty covering the area that was treated; a full subterranean treatment or a fumigation carries a longer one covering the structure. Each of them means re-treating at no additional cost. None of them covers repairing the damage, work carried out by the owner, or conditions that were present but not evident at the time of inspection. Anyone offering more than that is offering something the paperwork behind it does not.

The reason inspection leads is the same reason integrated pest management leads everywhere else in this trade: you treat the source you have confirmed, never the one you assumed. A guess about which termite you have is really a guess about which treatment to buy, and those two guesses cost the same season.

The Bottom Line

Getting subterranean termites vs drywood termites right is most of the job, because the two overlap in name and in almost nothing else. Mud tubes on a foundation point to a colony in the soil and a treatment that goes into the ground. Frass under a window sill points to a colony inside the wood and a treatment that goes into the wood. Guess between them and you lose a season while the real colony keeps working.

If you have found something and you are not certain which it is, the next step is simple: call Banner and book an inspection. A local technician will walk the property, get into the crawl space or the attic if that is where the answer is, and tell you what is genuinely there before anyone starts talking about treatment. No upsell. No pressure.