San Diego County has the dubious distinction of hosting both major termite categories that damage homes in North America: drywood termites and subterranean termites. Most homeowners use “termite” as a single word, but the two species are as different as cats and dogs in terms of biology, behavior, treatment, and cost. The wrong treatment on the wrong species wastes money and leaves the damage progressing.

Here’s how to identify which one you have, and why the distinction matters for anyone buying, selling, or maintaining a home in San Diego.

Drywood termites: they live inside the wood

Drywood termites (Incisitermes minor and related species) are the variety most San Diego homeowners actually see. They live their entire life cycle inside the wood they’re eating — attic rafters, window sills, door frames, eave fascia, deck posts. They don’t need soil contact. They don’t need external water. They pull moisture from the wood itself and from the humidity in the air.

Drywood colonies are relatively small compared to subterranean colonies — usually a few hundred to a few thousand individuals, versus subterranean colonies that can have millions. But there can be multiple drywood colonies in the same structure, and each one is independently eating away at the wood around it.

Signs you have drywood termites

The telltale evidence is frass — the pellets drywood termites push out of the wood through small “kick holes.” Drywood frass is dry, granular, and looks like tan or light-brown coarse sand. It often accumulates in small piles on windowsills, under picture frames, on baseboards, or on the garage floor beneath exposed framing. Color can vary from pale tan to dark brown depending on the wood species the termites are eating.

You may also see swarmers — winged reproductive termites that emerge in late summer and early fall (typically August through October in San Diego) to start new colonies. They’re attracted to light and often appear at windows. After the swarm flight they shed their wings in piles, which is the most commonly noticed sign.

Other evidence: hollow-sounding wood when you tap on it, a screwdriver pushing into trim or fascia too easily, or blistered paint on woodwork caused by termites eating from the inside out.

Where drywood termites are most common in San Diego

Drywood termites thrive in older coastal homes. The combination of original Douglas fir framing (which drywood termites particularly like) and coastal humidity gives them ideal conditions. North Park, Kensington, Normal Heights, Coronado, Mission Hills, and the older parts of La Jolla all see heavy drywood pressure. Homes built between 1900 and 1960 without later remediation are especially likely to have activity somewhere.

Newer production homes in Carlsbad, Oceanside, and the inland subdivisions see less drywood activity because the framing is typically younger and the wood species used (often SPF — spruce-pine-fir — rather than Douglas fir) is less preferred.

Subterranean termites: they come up from the soil

Subterranean termites (Reticulitermes hesperus is the dominant species in Southern California) live in underground colonies and come up through the soil to access wood above. They can’t survive long without soil contact and moisture from the ground, so they build distinctive mud tubes — pencil-thick tunnels of mud and saliva — to travel from their underground colony up to wood.

Subterranean colonies are enormous. A single colony can contain hundreds of thousands to several million individuals and extend across an entire property and into neighboring yards. Unlike drywood termites, they eat wood faster and can do substantial structural damage before anyone notices.

Signs you have subterranean termites

Look for mud tubes on the foundation, the interior of a crawl space, the exterior stucco, or inside a garage wall. They’re thin (typically 1/4 to 1/2 inch wide), brown-gray, and made of dried mud. Active tubes will have live termites inside if you break one open; abandoned tubes are dry and hollow.

Damaged wood from subterranean termites looks different than drywood damage — the galleries are packed with a mixture of mud and wood particles (subterranean termites do not clean their galleries like drywood do, which is why drywood produces frass but subterranean doesn’t). Wood looks soiled or muddy when the surface is broken open.

Swarmers appear in early spring (February through April) after rain, which is a different timing than drywood. Western subterranean swarmers are small, dark, and have two pairs of equal-length wings.

Where subterranean termites are most common in San Diego

Subterranean pressure is driven by irrigation and soil moisture, so newer tract homes with lush landscaping see the most activity — ironically, the same homes that see less drywood pressure. El Cajon, La Mesa, Escondido, San Marcos, and East County generally have significant subterranean activity, especially where homeowners irrigate right up against the foundation. Any home with wood-to-soil contact is at elevated risk regardless of neighborhood.

Why the treatment is completely different

Drywood termite treatment targets the wood where the termites live. Options include:

  • Local treatment — drilling small holes into infested wood and injecting a foam or liquid termiticide directly into the galleries. Cost-effective when activity is localized and accessible.
  • Borate treatment — applying a borate-based solution to bare wood where termites are or might be. Good for preventive treatment on accessible framing.
  • Whole-structure fumigation — tenting the entire house and filling it with Vikane gas for 2–3 days. The only option that guarantees all drywood termites in the structure are eliminated. Required when activity is widespread or inaccessible.

Subterranean termite treatment targets the soil around the structure or the colony itself:

  • Trenching and soil treatment — digging a trench along the foundation and applying a non-repellent termiticide (like Termidor) that termites unknowingly carry back to the colony, eliminating it.
  • Bait stations — installing in-ground bait stations (Sentricon, Trelona) that termites find and feed on. The bait contains a slow-acting insect growth regulator that eliminates the entire colony over several weeks.

Fumigation does not work on subterranean termites because the colony is in the soil, not the structure. Trenching does not work on drywood termites because they have no soil connection. Put the wrong treatment on the wrong species and you’ve spent money without solving the problem.

Real estate: why this matters for WDO inspections

If you’re buying or selling a home in San Diego, a Wood Destroying Organism (WDO) inspection is almost certainly going to be required. The inspector produces a report listing Section 1 findings (active infestation or damage requiring treatment) and Section 2 findings (conditions conducive to future problems, like wood-to-soil contact or plumbing leaks).

Older homes in the central San Diego neighborhoods routinely come back with drywood Section 1 findings — often affordable to treat locally, but sometimes requiring fumigation that can cost $2,000–$4,500 depending on square footage. Homes with active subterranean activity typically need soil treatment plus ongoing monitoring. Both items can be negotiated into real estate contracts, but the buyer and seller need to understand what treatment is actually being quoted — a fumigation estimate for subterranean activity doesn’t make sense, and a soil treatment for drywood doesn’t either.

The bottom line

Drywood termites live in the wood, leave dry pellet frass, and need either local treatment or fumigation. Subterranean termites live in the soil, build mud tubes, and need soil treatment or colony baiting. Same word, different species, different treatment.

If you’re seeing pellets, wings, mud tubes, or hollow-sounding wood, don’t guess which one you have. A proper inspection identifies the species before any treatment is proposed. Call us at (858) 808-6055 for a free termite inspection — we’re SPCB Branch 3 licensed and we’ll document findings clearly for real estate transactions or homeowner peace of mind.