Drywood vs. Subterranean Termites — What Every Southern California Homeowner Needs to Know

If you've been told you have termites — or if you suspect you might — the first and most important question isn't how bad the damage is or how much it will cost to fix. It's which species you're dealing with. Southern California is home to two primary termite species, and they are different enough in their biology, their behavior, and their treatment protocols that confusing one for the other leads directly to failed treatments, wasted money, and continued damage.

Drywood termites and subterranean termites both eat wood. That's essentially where the similarity ends. They live in different places, leave different evidence, require different inspection techniques, respond to different treatments, and call for different warranties. The structural pest control industry in California specifically distinguishes between them on every inspection report, every treatment recommendation, and every license category — because treating them the same is a fundamental error.

The single most important difference between these two species is where they live — and it drives everything else.

Drywood termites live entirely inside the wood they're infesting. The colony — including workers, soldiers, reproductives, and the queen — is contained within the wood structure itself. They don't need soil contact, they don't need external moisture beyond what's present in the wood, and they don't travel between the wood and the ground. A colony can establish in a second-floor window frame, in a piece of attic framing that never touches anything but air, in an antique piece of furniture, or in any exposed wood anywhere in or on the structure.

This has a practical consequence: they're essentially undetectable without finding their evidence or doing an invasive inspection. They don't build visible external structures. They can work inside a wall stud or rafter for years without producing any surface evidence except the occasional frass ejection.

Subterranean termites live underground. Their colony — which can contain hundreds of thousands to millions of workers — is based in the soil, typically at depths of several feet. Workers travel from the colony to wood food sources above, requiring either direct soil-to-wood contact or the construction of mud tubes that allow them to cross inhospitable surfaces while maintaining the humidity they need. When they finish feeding in an area, they retreat back underground.

The underground colony structure means that even an extensive subterranean termite infestation in a structure's framing may be supported by a colony entirely outside the structure — in the adjacent soil, under the slab, or in a neighboring property. Treating the wood itself without addressing the colony below often provides only temporary relief.

Learning to read what each species leaves behind is the most practical skill a homeowner can develop for early detection — because it's the information a licensed inspector uses to determine what you're dealing with before doing any invasive work.

Drywood termites can be anywhere in the structure that has exposed or accessible wood — attic framing, window and door frames, exterior wood trim, wood siding, interior furniture, garage framing. They don't favor any particular part of the structure based on moisture or soil proximity. A drywood colony can establish equally in a ground-floor baseboard or a second-floor attic rafter.

Subterranean termites concentrate their activity in areas near or below soil level: sill plates, cripple studs in the subarea, floor joists, any wood-to-soil contact points on the property, and areas with moisture — subterranean termites are drawn to wood that's been softened by water, so bathrooms with slow leaks, areas of irrigation over-spray, and any location where water consistently contacts structural wood are higher-risk zones. They're rarely found in attics or upper floors except in cases of severe, long-standing infestations.

This is the critical practical implication of getting the species identification right. The treatments are fundamentally different and non-interchangeable.

In California, termite inspections and treatments are regulated by the California Structural Pest Control Board (SPCB). There are three license branches: Branch 1 covers fumigation; Branch 2 covers general pest control; Branch 3 covers wood-destroying organisms including termites.

Termite inspections and treatments specifically require Branch 3 licensure. Before hiring any company for termite work, verify their SPCB license and ask specifically about Branch 3 coverage. A company licensed only for general pest control (Branch 2) cannot legally perform termite work in California.

After any inspection, California law requires the inspector to issue a standardized Wood Destroying Organisms (WDO) report — a formal document that identifies active infestations, evidence of prior infestation, and conducive conditions. A WDO report that says "termites" without specifying species, location, or distinguishing drywood from subterranean is incomplete. A legitimate SPCB-licensed inspection produces a document specific enough that a different inspector could read it and know exactly what was found and where.

Yes — and it's more common than most homeowners realize. A 40-year-old home in Southern California with wood-framed construction has had decades to accumulate multiple termite introductions. A subterranean colony in the subarea and a drywood colony in the attic are not mutually exclusive. In fact, an inspection that finds evidence of only one species in an older home is sometimes incomplete — good inspectors check the full structure, not just the area where the first evidence is found.

When both species are present, treatment is more complex because the approach differs for each. Fumigation addresses the drywood population but does nothing for the underground subterranean colony. Soil treatment addresses the subterranean colony but leaves the drywood colony untouched. A comprehensive treatment plan for a dual infestation addresses both — typically fumigation for drywood combined with soil treatment or baiting for subterranean, with the sequencing determined by what's active and where.