In this guide
Formosan termites are a subterranean termite species from East Asia that builds very large colonies and can do serious damage to wood in a house. In San Diego County they are rare. UC researchers first confirmed them in California in La Mesa in 1992, found another colony close to that site in 2018, and documented one in Rancho Santa Fe in 2021. If you live in the county, the termites in your garage are far more likely to be a native species.
So what should you actually do? Learn the few signs that separate a Formosan termite from the usual suspects, keep a sample if you see swarmers between late May and early August, and get any suspected infestation looked at by a licensed inspector. The rest of this page walks through each step, with links to the agencies that track this pest.
Where Formosan termites have been found in San Diego County
The story starts in La Mesa. According to UC Agriculture and Natural Resources (UC ANR), a pest control operator sent soldier termites from a La Mesa home to university scientists in February 1992, and they turned out to be Coptotermes formosanus, the Formosan subterranean termite. It was the first record of the species in California.
Efforts to eradicate that colony did not fully succeed. In 2018 an inspector found a new colony in La Mesa about half a mile from the 1992 site, and UC genetic testing showed the two populations matched. UC ANR has since documented a colony in Rancho Santa Fe in 2021 and a few more finds in La Mesa and in Los Angeles County, and its Pests in the Urban Landscape blog keeps homeowners posted on new alerts.
That is a short list for a county this size. The species is worth knowing about because a colony can be very large and hard to get rid of once established, and because early reports help UC scientists map where it is spreading.
Formosan termites vs. the termites you already know
San Diego homeowners mostly deal with two kinds of termites: native subterranean termites, which live in the soil and travel through mud tubes, and drywood termites, which live inside the wood itself and leave small piles of pellets. Formosan termites belong with the first group. They need moisture and contact with soil or a damp space, just like native subterranean termites.
| Feature | Formosan subterranean | Native subterranean | Drywood |
|---|---|---|---|
| Where the colony lives | Soil, sometimes damp spots above ground | Soil | Inside dry wood |
| Typical sign | Mud tubes, swarmers in early summer | Mud tubes, swarmers after spring rain | Small fecal pellets below wood |
| Soldier head | Oval or teardrop, amber | Long, rectangular | Large, with strong jaws |
| Swarmer color | Light, yellowish to amber-brown | Dark, almost black | Reddish to orange-brown |
| California swarm timing | Late May to early August | Mostly spring, after rain | Varies by species |
The swarm timing for Formosan termites comes from UC ANR. The soldier and swarmer descriptions follow UC Riverside's notes on the La Mesa finds and the University of Florida IFAS Extension's species profile, since Florida has dealt with this termite for decades.
What a Formosan soldier looks like
Soldiers are the caste experts use to identify the species. A Formosan soldier has a pale body and a head shaped like an egg or a teardrop, with an amber color that stands out against the body. When disturbed, soldiers can release a drop of white, glue-like fluid from an opening on the front of the head. Native subterranean soldiers have a longer, squarer head. Workers of the two species look almost the same, which is why a handful of workers alone is not enough for an ID.
What the swarmers look like
Swarmers (also called alates) are the winged adults that leave the colony to start new ones. UC Riverside notes that Formosan swarmers have a lighter body than the dark native subterranean swarmers and differ from the orange-brown drywood swarmers. The University of Florida describes them as about half an inch long (12 to 15 mm) including wings.
When to watch: the early summer swarm
Most San Diegans think of termite swarms as a spring thing, and for native subterranean termites that is usually right. Formosan termites run later. UC ANR gives their California swarming season as late May through early August, and the inspectors who found the La Mesa colonies were told to watch for swarms at dusk in summer.
If you see a cloud of pale winged insects around a porch light on a warm June evening, it may be nothing more than ants or a native termite flight. It is still worth a closer look. Many swarmers indoors, or piles of shed wings on windowsills and near light fixtures, point to a colony close by.
Signs of subterranean termites around your home
Formosan or native, subterranean termites leave similar clues. Walk around your house once in a while and check these spots:
- Mud tubes, pencil-width tunnels of soil, climbing a foundation wall, a pier, a pipe or the side of a step.
- Wood that sounds hollow or crumbles when you press it, especially near the ground or near leaks.
- Shed wings in a small pile, often on a sill or near a door after a swarm.
- Bubbling or soft spots in paint or drywall close to the floor.
Moisture makes all of this worse. Subterranean termites need it, and a slow leak or a sprinkler that soaks the same patch of stucco every morning gives them what they want. The County's watering rules already push you toward less irrigation, and our guide to water-use rules in San Diego County explains where to check what applies to your address. Keeping soil and mulch from touching wood siding, fixing drips under sinks, and keeping crawl spaces vented all help.
Older wood-frame houses deserve an extra look. Neighborhoods full of early 1900s bungalows, like the ones described in our North Park neighborhood guide, have raised foundations and crawl spaces where a mud tube can go unnoticed for years.
What to do if you think you have Formosan termites
Don't spray first
Store-bought sprays kill the insects you can see and scatter the rest, and they can make it harder for an inspector to judge where the activity is coming from. Take the sample and photos first.
Get a licensed inspection
In California, termite inspections and treatments for structures are regulated by the Structural Pest Control Board, a state agency within the Department of Consumer Affairs. A licensed inspector writes a wood-destroying organism (WDO) report that describes the evidence found in visible and accessible areas and recommends any corrective work. The Board's online license lookup lets you confirm a company's or an individual's license, check its status and see any disciplinary history. Do this before you sign a contract.
Tell the inspector that you suspect Formosan termites and show them your sample. Formosan colonies can be larger than native ones, so treatment plans may differ. That decision belongs to the licensed professional, and getting more than one inspection for a big job is common practice.
Tell UC
Because the species is still rare in California, UC ANR has asked people in Southern California who find termites resembling Formosan termites to contact its urban IPM advisors, and it has published an identification poster for that purpose. Your local office is UC Cooperative Extension San Diego. A confirmed report helps researchers track how far the species has spread beyond La Mesa.
If you rent
Report what you see to your landlord or property manager in writing, with the date and your photos. Treatment of a building is normally handled by the owner and their licensed operator, not by tenants.
Reading more
UC IPM's Pest Notes on subterranean termites cover prevention and treatment options in more depth, and the Structural Pest Control Board's consumer pages explain what a WDO report includes. For more home and everyday topics, browse the rest of our Living in San Diego section.
In a nutshell
Formosan termites: quick answers before you call anyone
What is the single best clue that a termite is Formosan?
The soldier's head. Formosan soldiers have an oval or teardrop-shaped amber head on a pale body, while native subterranean soldiers have a longer, squarer head. Workers of both species look almost the same.
It's covered in the section What a Formosan soldier looks like
I saw winged termites at dusk in late June. Should I worry?
Take a closer look. UC ANR puts the California swarm season for Formosan termites from late May through early August, often around dusk. Many swarmers indoors or piles of shed wings point to a colony nearby, but ants and native termites also fly, so save a sample before deciding.
It's covered in the section When to watch: the early summer swarm
How do I keep a sample for an inspector?
Put a few soldiers or swarmers in a small jar or zip bag with rubbing alcohol, note the date and address, and take a clear photo.
It's covered in the section When to watch: the early summer swarm
Should I spray the termites I can see?
No. Store-bought sprays kill the visible insects and scatter the rest, which makes it harder for an inspector to find where the activity comes from. Collect the sample and photos first.
It's covered in the section Don't spray first
Who regulates termite inspections in California?
The Structural Pest Control Board, part of the Department of Consumer Affairs. Its online lookup shows a company's license type, status and disciplinary history.
It's covered in the section Get a licensed inspection
Next up: Out of the house for a while: plan a walk on the Torrey Pines trails
Questions readers ask
Are Formosan termites common in San Diego County?
No. UC researchers have documented them in only a handful of places in Southern California, including La Mesa (first found in 1992 and again in 2018) and Rancho Santa Fe (2021). Most termites San Diegans find are native subterranean or drywood species.
When do Formosan termites swarm in California?
UC Agriculture and Natural Resources puts the California swarming season for Formosan subterranean termites from late May through early August. Swarms are often reported around dusk.
How can I tell a Formosan termite from a native one?
Look at the soldiers: Formosan soldiers have an oval or teardrop-shaped amber head, while native subterranean soldiers have a longer, more rectangular head. Formosan swarmers are lighter in color than the dark native swarmers. A sample checked by an expert is the only sure way.
How do I check that a pest control company is licensed?
Use the license lookup on the California Structural Pest Control Board website (pestboard.ca.gov). It shows the license type, status and any disciplinary history.
