Formosan Termites in California: What the Highland Park and La Verne Finds Mean for the San Gabriel Valley
Formosan subterranean termites have now been confirmed on both sides of the San Gabriel Valley. Here is what has actually been found, how to recognize them, and what to do with a suspect sample.
Formosan subterranean termites (Coptotermes formosanus) are an introduced species with colonies of several million, a foraging range of about 100 meters, and the ability to build nests above ground without soil contact where there is moisture. In California they were first found in La Mesa in 1992 and have since been confirmed in Canyon Lake (2020), Highland Park and Rancho Santa Fe (2021), and Hollywood Hills and La Verne (2022), the last three confirmed by UC Riverside. Nothing has been confirmed inside the San Gabriel Valley yet, but Highland Park and La Verne bracket it, and UC researchers say the pest is probably underreported. The tell is the swarm: Formosan swarmers fly at dusk and into the evening toward lights from late May through early August, are yellowish-brown and 12 to 15 millimeters long with hairy wings, while our native subterranean termites swarm in daylight after rain and are dark brown to black. If you see an evening swarm at a porch light, bag a few, do not spray, and send them to UC Riverside.
Local help: Winged termites at a porch light in the evening between late May and early August? Bag a few, do not spray, and text a photo to (626) 409-1584. We will tell you what they are and whether they should go to UC Riverside. Identification is free.
On this page
- Where Formosan termites have been found in California
- Formosan termites vs. regular termites: what is different
- What do Formosan termites look like? Recognizing the swarm
- Are Formosan termites in the San Gabriel Valley?
- What to do if you think you have them
- How Formosan termites are treated
- What we are doing about it
- Sources
- Quick answers
Where Formosan termites have been found in California
The Formosan subterranean termite is native to China and established across the humid South: Alabama, Florida, Georgia, Hawaii, Louisiana, Mississippi, the Carolinas, Tennessee and Texas. California has had it since 1992, and the list of confirmed sites has grown in the last few years. Every one of these was confirmed by UC Riverside’s Department of Entomology or UC Cooperative Extension.
| Year | Place | County | How it was found |
|---|---|---|---|
| 1992 | La Mesa | San Diego | First California report; eradication attempts failed and the termite is still found at the original site |
| 2020 (June) | Canyon Lake | Riverside | Infestation found by a local pest control company, confirmed by UC Riverside |
| 2021 (June) | Highland Park, Los Angeles | Los Angeles | Swarmers found during a termite inspection by an El Monte-based operator; the first confirmed find in Los Angeles County |
| 2021 | Rancho Santa Fe | San Diego | Confirmed by Dr. Chow-Yang Lee’s lab at UC Riverside |
| 2022 (June) | Hollywood Hills, Los Angeles | Los Angeles | Dead swarmers in a loft around a standing light; no active infestation found on inspection |
| 2022 | La Verne | Los Angeles | Large evening swarm from a neighboring property; slab home, no damage found; suspected source was railroad ties |
UC Riverside’s researchers add the caution that the pest is probably underreported: most of these finds happened because a technician or a homeowner thought the swarmers looked wrong and mailed them in.
Formosan termites vs. regular termites: what is different
| Trait | Formosan subterranean | Western subterranean (native) | Western drywood (native) |
|---|---|---|---|
| Colony size | Several million | Mature colonies up to hundreds of thousands | Small; a fraction of a subterranean colony |
| Foraging range | Up to about 100 meters | Shorter; forages out from the soil nest | None; the colony lives inside the wood it eats |
| Where it nests | Soil, plus aerial nests with no soil contact where moisture and food allow; builds carton nests above ground | Soil, reaching wood through mud tubes | Dry sound wood: framing, eaves, furniture |
| Swarm time of day | Dusk into the evening, attracted to lights | Daylight, on warm sunny days after fall or spring rains | Daylight, warm days in late summer and fall |
| Swarm season (California) | Late May through early August | Fall through spring, after rain | Late summer and fall |
| Swarmer look | Yellowish-brown, 12 to 15 mm with wings, pale hairy wings, two strong veins at the wing base | Dark brown to brownish-black, brownish-gray wings | Dark body with a reddish-brown head (see our drywood guide) |
| Soldier | Light brown oval head, long curved toothless jaws, white sticky secretion from the fontanelle | Rectangular head, no secretion | Large head with toothed jaws |
| Egg laying | Up to about 1,000 eggs a day at maturity | Far fewer | Far fewer |
| Usual treatment | In-ground bait and non-repellent soil treatment for ground nests; aerial nests must be found and treated directly | Bait stations plus targeted soil treatment | Localized treatment or fumigation |
The numbers are why entomologists call it a nightmare: a colony several million strong eating around the clock does in a season what a native colony does in years, and a colony that can live in a wet wall void with no soil contact is one a soil treatment never touches.
What do Formosan termites look like? Recognizing the swarm
You will not identify Formosan workers; even specialists say workers are of little value for identification. You identify the swarm and the soldiers.
- The timing. Winged termites at dusk or after dark, around a porch light, a window or a lamp indoors, between late May and early August. Our native subterranean termites swarm in daylight after rain, and drywood swarmers fly on warm afternoons. An evening swarm in June is the flag.
- The color. Yellowish-brown bodies with pale, translucent wings that look faintly fuzzy under a lens: the wings are covered in fine hairs, with two strong dark veins along the front edge. Native subterranean swarmers are dark brown to black.
- The size. About 12 to 15 millimeters including wings, around half an inch.
- The soldiers. If you can find them in a tube or damaged wood: oval light-brown heads, long curved jaws with no teeth, and a drop of white sticky fluid at the front of the head when poked.
- The still-not-sure test. Bag them. UC Riverside confirms by microscope and DNA; a photo is a start, a sample is proof.
Winged ants at an evening light are far more common than Formosan termites. The termite vs. flying ant checks (straight antennae, equal wings, thick waist) come first.
Are Formosan termites in the San Gabriel Valley?
As of the sources we could verify, no Formosan infestation has been confirmed inside the San Gabriel Valley. The two Los Angeles County finds bracket it: Highland Park is roughly ten miles west of Arcadia, La Verne roughly fifteen miles east, and the Highland Park find was made by a pest control operator based in El Monte, in the middle of the valley. Formosan termites mostly spread by being carried in wood rather than by flying far. Railroad ties, reclaimed lumber, potted plants and used timbers from infested areas are the documented routes, and the La Verne case points at exactly that. The practical conclusion is that a Formosan colony in the valley would most likely be found the same way every California colony has been found so far: someone sees an evening swarm, thinks it looks wrong, and sends it in.
What to do if you think you have them
- Do not spray. Dead swarmers are still identifiable; a sprayed pile scattered across a patio is not.
- Collect ten or more into a zip bag or a jar with a splash of rubbing alcohol. Note the date, time of day and where they were flying.
- Photograph the swarm, the light they came to, and any mud tubes, damp wood or tubes on the foundation.
- Send photos to (626) 409-1584 for a first read, or straight to UC Riverside’s Department of Entomology (entomology@ucr.edu); UC Cooperative Extension’s urban IPM advisor Siavash Taravati has asked to see suspect samples from Southern California.
- Get a full inspection. Attic, crawlspace, the slab edge and every wet spot: Formosan aerial colonies live where water is, so leaking roofs, planters against walls and chronic sprinkler spray matter more than usual.
How Formosan termites are treated
For a Formosan colony nesting in the ground, UC Cooperative Extension says the in-ground baiting used against native subterranean termites may provide adequate control, and the same non-repellent soil treatments apply at entry points. The complication is the aerial colony: a nest in a wet wall, a roof void or a planter with no soil connection, which bait in the ground never reaches and which has to be located and treated directly, with the moisture that supports it fixed. Fumigation kills termites inside the structure but, as with any subterranean termite, does nothing to a colony in the soil. Treatment is therefore an inspection problem first: find every nest, then match the method. Our subterranean termite treatment page covers the bait and soil work, and bait stations vs. liquid treatment explains why we lead with bait.
What we are doing about it
Three things. We look at every subterranean termite sample we collect in the valley with Formosan in mind, and anything that does not match the native species goes to UC Riverside. We treat summer evening swarm calls as urgent identification, not a fall-season annoyance. And we keep moisture at the center of every inspection, because moisture is what lets a Formosan colony live above the soil. If you are on our annual program, that check is already part of the yearly visit. If you are not, a swarm at a June porch light is a good reason to call.
Sources
- UC ANR Pests in the Urban Landscape: Destructive Termite Alert (June 26, 2023)
- UC Riverside Entomology: Formosan Termites Confirmed in Two New Southern California Locations (Aug. 12, 2022)
- Los Angeles County Agricultural Commissioner/Weights and Measures: Formosan Subterranean Termite (July 2021)
- UC IPM Pest Notes: Subterranean and Other Termites (University of California)
- Pest Control Technology: More Formosan Termite Infestations Confirmed in Southern California (2021)
Common Questions
Quick Answers.
Are Formosan termites in California?
Yes, in confirmed pockets. The first California find was La Mesa, San Diego County, in 1992, where eradication failed and the colony persists. UC Riverside and UC Cooperative Extension have since confirmed Canyon Lake in Riverside County (2020), Highland Park in Los Angeles County and Rancho Santa Fe in San Diego County (2021), and Hollywood Hills and La Verne (2022).
Are Formosan termites in Los Angeles?
Yes. The first Los Angeles County find was a Highland Park home in June 2021, confirmed by UC Riverside. Hollywood Hills followed in June 2022, where dead swarmers were found in a loft around a standing light, and La Verne in 2022 after a large swarm from a neighboring property.
What is the difference between Formosan termites and regular termites?
Scale and behavior. A Formosan colony can hold several million termites and forage about 100 meters, versus hundreds of thousands at most for our native western subterranean termite. Formosan swarmers fly at dusk and toward lights in late spring and summer; native subterranean swarmers fly in daylight after rain. Formosan colonies can also nest above ground with no soil contact where moisture allows, which changes how they are treated.
When do Formosan termites swarm in California?
Late May through early August, according to UC Riverside, at dusk and into the evening. A swarm of winged termites around a porch light or a lamp indoors on a warm evening in that window is the single most useful warning sign.
What do Formosan termite swarmers look like?
Yellowish-brown bodies, about 12 to 15 millimeters long including the wings, with pale translucent wings covered in fine hairs and two strong veins at the base of the forewing. Our native subterranean swarmers are dark brown to brownish-black with brownish-gray wings; drywood swarmers fly in daylight in late summer and fall.
What do Formosan termite soldiers look like?
Cream-colored body with a light brown oval head and long, curved mandibles with no teeth. When disturbed they emit a white, sticky defensive secretion from a pore at the front of the head called the fontanelle, which native soldiers do not do.
How did Formosan termites get to California?
By being carried. Wood-destroying pests move easily through human activity: lumber, railroad ties, potted plants and boats. The La Verne find was next door to a property built with many railroad ties the pest control operator suspected came from an area with Formosan termites.
Can bait stations kill Formosan termites?
Often, for colonies nesting in the ground. UC Cooperative Extension says in-ground baiting used for native subterranean termites may provide adequate control for Formosan colonies with ground-based nests, but is unlikely to work on aerial colonies with no soil contact, which have to be located and treated directly.
Who do I report Formosan termites to?
UC Riverside’s Department of Entomology (entomology@ucr.edu) or UC Cooperative Extension urban IPM advisor Siavash Taravati. Keep the sample in a sealed bag, note the date, time and where they were flying, and send photos first. We will help you package it.
Should San Gabriel Valley homeowners worry about Formosan termites?
Be aware, not alarmed. Nothing has been confirmed inside the valley, and every California find so far has been caught by someone who noticed a swarm looked wrong and sent it in. Know the evening-swarm sign, keep up your regular inspections, and report anything odd. That is exactly how Highland Park and La Verne were found.
Are Formosan termites in Pasadena, Arcadia or the San Gabriel Valley?
Not that anyone has confirmed. The nearest confirmed finds are Highland Park, about ten miles west of Arcadia, and La Verne, about fifteen miles east. If you see winged termites swarming at a light on a June or July evening anywhere in the valley, bag a sample and send photos; that is how every California find has been made.
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About the Author
Joshua A. Westad is the owner and licensed operator of ExterMetro Termite and Pest Control in Arcadia, CA. He holds California SPCB Company Registration #8828 (Branch 2 & 3), is a licensed WDO inspector, and has worked San Gabriel Valley homes and businesses for over twelve years — hands-on in the field on every kind of job the valley throws at him.
Think you just found termite evidence?
Bag a few wings or pellets, snap a photo, and text it to (626) 409-1584 — quotes from photos are free, and your job stays under licensed ExterMetro oversight from inspection through follow-up.