Subterranean termites are the most destructive wood-destroying pest in California, responsible for more structural damage than drywood termites, fires, and storms combined. At least three species live in the state, they swarm primarily between March and June, and a single mature colony can contain hundreds of thousands of individuals silently feeding on your home’s framing. Here’s what California homeowners need to know about identifying, preventing, and treating infestations.
Species Found in California
For decades, entomologists recognized two subterranean termite species in California: Reticulitermes hesperus, the western subterranean termite found throughout the state, and R. tibialis, the arid-land subterranean termite more common in drier inland areas. A 2025 study led by researchers at UC Riverside upended that picture by confirming a third distinct species, now named Reticulitermes rusti, had been hiding in plain sight in Southern California.
The discovery matters beyond taxonomy. R. rusti behaves differently from R. hesperus, which may explain why some past pest control efforts fell short. Treatments designed for one species aren’t always effective against another, and pest management professionals are now working to develop species-specific strategies. If you’ve had a stubborn reinfestation in Southern California, this third species could be part of the reason.
How to Spot an Infestation
Subterranean termites live underground and need constant moisture to survive, so they rarely expose themselves to open air. Instead, they build shelter tubes (commonly called mud tubes) from soil, saliva, and bits of wood or drywall. These pencil-width tunnels run up concrete or stone foundations, connecting the colony in the soil to the wood it’s feeding on. Mud tubes are the single most common visible sign of an active infestation.
There are four types worth knowing:
- Working tubes run from the soil nest up to wooden structures and serve as the colony’s main highway.
- Exploratory tubes rise from the soil but don’t connect to wood yet. They indicate termites are actively searching for new food sources.
- Drop tubes extend downward from wooden structures back toward the soil.
- Swarm tubes are temporary exit routes built so winged reproductive termites can launch into the air during swarming season.
If you break open infested wood, you’ll find hollow, enclosed cavities that follow the grain. Subterranean termites prefer the softer springwood and leave the harder summerwood intact, creating a distinctive layered pattern that looks almost like pages of a book. You may also notice light-brown fecal deposits inside the tunnels. This damage pattern alone can distinguish subterranean termite activity from drywood termites, which excavate across the grain and leave hard, sand-like pellets.
When Swarming Season Starts
In most of California, subterranean termite swarming begins in late February or March and runs through May or June. The trigger is weather: termites typically emerge on warm, sunny mornings immediately following a heavy rainstorm. The spike in soil moisture and humidity creates ideal conditions for winged reproductives (called alates) to leave the colony, pair off, mate, and search for damp wood near foundations to start new colonies.
Swarms usually happen during morning or early afternoon hours. You might see a cloud of small, dark-winged insects near your foundation, or find dozens of discarded wings on windowsills and near exterior doors. A swarm inside your home is a strong indicator that a colony is already established nearby. A swarm outside doesn’t necessarily mean your house is infested, but it does mean active colonies are foraging in your soil.
How Fast They Cause Damage
Subterranean termite colonies grow slowly at first but can eventually reach enormous sizes. Mature colonies average roughly 300,000 individuals, though some contain several million. A colony of about 60,000 termites can consume one linear foot of a standard 2×4 board in approximately five months.
That pace sounds slow, and it is, on a daily basis. But termites work 24 hours a day, 365 days a year, and multiple colonies can be foraging under the same house simultaneously. Because the damage is entirely hidden inside walls and under floors, years of feeding often accumulate before anyone notices. By the time mud tubes appear on a visible surface or a floor feels spongy underfoot, significant structural damage may already exist.
Treatment Options
Two main approaches dominate professional subterranean termite control, and they work in fundamentally different ways.
Liquid Soil Barriers
The traditional method involves applying a liquid termiticide into the soil around and beneath your home’s foundation. This creates a continuous chemical barrier that termites cannot cross without being killed. Modern products are non-repellent, meaning termites don’t detect them in the soil and walk right through the treated zone. They pick up the active ingredient, carry it back to the colony on their bodies, and spread it to nest mates through normal grooming and feeding. Non-repellent barriers have proven more reliable than older repellent products, which termites could sometimes detect and route around.
Bait Stations
Baiting takes a different approach. Plastic stations containing cellulose (essentially processed wood) laced with a slow-acting growth disruptor are installed in the ground around your home’s perimeter, typically 10 to 15 feet apart and about 1 to 2 feet from the foundation. Termites find the stations while foraging, feed on the bait, and share it with colony members. The slow action is deliberate. If termites died immediately, other workers would notice dead bodies accumulating near the stations and avoid them. Instead, the active ingredient spreads through the colony over weeks, and entire colonies can be eliminated.
Additional stations are often placed near known problem areas like woodpiles, tree stumps, and spots with previous termite damage. Depending on the system and the pest control company’s protocol, stations are checked monthly, quarterly, or annually. Baiting is less invasive than trenching around a foundation for liquid treatment, but it requires ongoing monitoring to stay effective.
Prevention for California Homes
Subterranean termites need two things to reach your home: soil contact and moisture. Removing either one dramatically reduces your risk.
Exterior wood siding, trim, and framing should sit at least 6 inches above the soil line. In crawl spaces, beams should clear the ground by at least 18 inches, which also gives inspectors room to spot problems during routine checks. No structural wood should touch soil directly, period. This includes fence posts that butt against the house, planter boxes built against siding, and decorative lattice that bridges the gap between soil and framing.
Moisture control is equally important. Fix leaky faucets and irrigation lines near the foundation. Grade soil so rainwater drains away from the house rather than pooling against it. Keep gutters clean and downspouts directed well away from the foundation. In crawl spaces, a vapor barrier over exposed soil helps keep humidity down. Subterranean termites cannot survive without moisture, so a dry perimeter is one of the strongest deterrents you have.
For new construction on a concrete slab, the soil beneath the slab should be treated with termiticide before the concrete is poured, applied at a rate of 1 gallon per 10 square feet of fill material. A vertical chemical barrier around foundation elements adjacent to the slab adds another layer of protection. These pre-construction treatments are far easier and cheaper than retrofitting a barrier after the home is built.
Inspections and California Home Sales
California’s Structural Pest Control Board oversees termite inspections statewide. Most lending institutions require a Wood-Destroying Organism (WDO) inspection before financing a home loan. A licensed inspector examines accessible areas of the property and files a report categorizing findings into two sections: Section 1 covers active infestations and visible damage, while Section 2 covers conditions likely to lead to future infestation, such as excessive moisture or wood-to-soil contact.
These reports are filed with the Structural Pest Control Board and remain searchable for two years. If you’re buying a home in California, you can look up any property’s inspection history through the Board’s online Property Address Search to check whether a WDO report is on file. Knowing whether a home has a history of termite activity, and what was done about it, gives you a clearer picture of what you’re walking into.