Termite Swarm Season in California: 2026 Timing & Risk
5 species, peak swarms September 15 – November 15, infestation probability zone I (very heavy) — plus whether today is swarm weather in Sacramento, Fresno, South Lake Tahoe.
Swarm season is open — checking today's conditions…The California termite year at a glance
Typical window, checked against today's dateCoastal and Southern California sit in the IRC very-heavy band — UC IPM notes that thousands of California housing units require termite treatment every year, much of it drywood work on attic framing and eaves.
Is today swarm weather in California?
Subterranean termites launch on the first warm (70°F+), humid, calm days after a soaking rain inside their window; drywood and dampwood species fly on warm, still late-summer evenings. The rows below read today's high, humidity, the last 48 hours of rain, and wind for California's three reference cities and score them against the species windows that are open right now (Western subterranean, Drywood, Dampwood).
| City | High today | Humidity | Rain, last 48 h | Wind | Swarm conditions |
|---|---|---|---|---|---|
| Sacramento | … | … | … | … | Loading |
| Fresno | … | … | … | … | Loading |
| South Lake Tahoe | … | … | … | … | Loading |
Score 0–10: Unlikely 0–2.9 · Possible 3–5.4 · Likely 5.5–7.4 · Swarm conditions 7.5+. Weather from api.open-meteo.com, read in your browser when the page loads. A high score means conditions favor a flight somewhere nearby — not that your house is infested.
Which termites swarm in California, and when
Western subterranean termite
Reticulitermes hesperus- Swarms in California
- September 15 – December 15, daytime after rain
- Local notes
- Swarms after the first fall rains statewide, with a smaller spring flight in March–April.
- Damage pattern
- The West Coast's main subterranean species; same mud tubes and foundation entry as its eastern cousin.
Drywood termite
Incisitermes and Cryptotermes species- Swarms in California
- August 15 – November 15, evening
- Local notes
- The western drywood termite is California's signature pest — attic framing, eaves, window frames — flying on warm, sunny late-summer and fall afternoons and evenings, especially in Southern California.
- Damage pattern
- Lives entirely inside dry wood — attics, furniture, trim — no soil contact; leaves six-sided fecal pellets.
Dampwood termite
Zootermopsis species- Swarms in California
- August 1 – October 31, evening
- Local notes
- Pacific dampwood termites in coastal and foothill homes with wet wood; dusk flights toward lights.
- Damage pattern
- Only attacks wet, decaying wood; a dampwood find is a moisture problem first.
Formosan subterranean termite
Coptotermes formosanus- Swarms in California
- May 1 – June 30, evening
- Local notes
- A handful of separate introductions: San Diego County (La Mesa, Rancho Santa Fe), Riverside County (Canyon Lake), and Los Angeles County (Highland Park and nearby). UC ANR has found these populations genetically unrelated to one another, so this is repeat arrival rather than one spreading front. Evening flights.
- Damage pattern
- Colonies of several million that can hollow a joist in months; builds above-ground carton nests in walls.
Desert subterranean termite
Heterotermes aureus- Swarms in California
- July 1 – September 30, night
- Local notes
- Desert subterranean termites in the Coachella and Imperial valleys; night flights after summer storms.
- Damage pattern
- Arizona's number-one structural pest; thin mud tubes that drip from ceilings and hang from joists.
California is in termite infestation probability zone I
The International Residential Code's Termite Infestation Probability Map (built on US Forest Service survey data) divides the country into four bands. Local jurisdictions use it as the basis for the termite-protection requirements they write into the code; homeowners can use it to set expectations. The figure names those bands rather than numbering them — the zone I–IV shorthand here is ours, not the code's, and the figure warns its lines are approximate. California: zone I, very heavy. The Gulf and Deep South — Louisiana, Mississippi, Alabama, Georgia, Florida, South Carolina, and eastern and coastal Texas — plus nearly all of California. The band's northern edge runs near the North Carolina line, and we place North Carolina here on the strength of its coastal plain. (We place Hawaii here too; the code figure maps only the lower 48.) Termites reach most structures eventually, and in this band the code also bars below-grade foam plastic on foundation walls and slabs.
Very heavy
The Gulf and Deep South — Louisiana, Mississippi, Alabama, Georgia, Florida, South Carolina, and eastern and coastal Texas — plus nearly all of California. The band's northern edge runs near the North Carolina line, and we place North Carolina here on the strength of its coastal plain. (We place Hawaii here too; the code figure maps only the lower 48.) Termites reach most structures eventually, and in this band the code also bars below-grade foam plastic on foundation walls and slabs.
Moderate to heavy
The mid-South, the Mid-Atlantic, the lower Midwest, and the interior and desert Southwest — Arizona, Nevada, and New Mexico included. Infestations are common; routine inspection is the norm in home sales. In the low-desert metros the local pressure runs well above what this band suggests.
Slight to moderate
The northern tier, the Rockies, and the Pacific Northwest. Colonies are localized; carpenter ants cause more wood damage than termites do.
Bands are assigned to each state's populated core; several states straddle a boundary (the state note above says which parts). No public-domain copy of the IRC map is available, so the zones are listed rather than drawn.
California termite hotspots
Los Angeles and Orange County
The largest drywood termite market in the country — nearly every older home has had some drywood history — with separate Formosan introductions confirmed in several Los Angeles County neighborhoods.
San Diego
Mild, humid coast with heavy drywood and western subterranean pressure; Formosan confirmed at La Mesa and Rancho Santa Fe.
The Bay Area and Sacramento Valley
Western subterranean termites in older Oakland, San Jose, and Sacramento neighborhoods; dampwood along the coast.
Signs of termites in California homes
Swarmers vs. flying ants
Termites: straight antennae, thick waist, four equal wings twice the body length. Ants: elbowed antennae, pinched waist, front wings longer than hind. Save a few in a bag — identification decides everything that follows.
Discarded wings
Swarmers shed their wings minutes after landing. Piles of identical translucent wings on a windowsill, in a spider web, or on a tub floor are the most common first sign — often with no insects left in sight.
Mud tubes
Pencil-width earthen tunnels climbing a foundation wall, pier, or plumbing penetration. Subterranean termites build them to stay moist between soil and wood. Break one open — live workers inside mean an active colony.
Frass (drywood pellets)
Drywood termites push six-sided, sand-like pellets out of kick-out holes — tiny piles under a window frame, rafter, or furniture. Drywood termites are established in California, so this is a sign to take seriously here.
Hollow or blistered wood
Baseboards that sound papery when tapped, paint that bubbles like water damage, doors that suddenly stick. Subterranean galleries run with the grain and are packed with mud; drywood galleries are clean and cross the grain.
Wet wood and dampwood termites
Dampwood termites are common in California and only attack wet, decaying wood. Finding them means finding a leak — fix the moisture and the termites lose their habitat.
What to do when you see a swarm in California
Preventing termites in California
Prevention is mostly moisture and wood-to-soil management, and most of it costs a weekend rather than a contract. In a zone I state, these are the habits that keep a home off the treatment list:
- Keep 6 inches of visible foundation between soil or mulch and any siding, trim, or sill plate. Mulch piled to the siding is the most common entry invitation inspectors find.
- Move water away. Downspout extensions, grading that slopes away from the house, and a crawlspace vapor barrier remove the moisture subterranean colonies need.
- Break wood-to-soil contact. Deck posts on metal standoffs, no firewood or lumber stacked against the house, stumps removed, and fence posts that don't touch the foundation.
- Seal slab and foundation penetrations where plumbing and conduit enter — termites need a crack the width of a business card.
- Fix leaks fast. A dripping hose bib or AC condensate line against the foundation creates a permanent wet spot that colonies home in on.
- Screen attic and crawlspace vents with fine mesh and seal cracks in exposed rafter tails and fascia — drywood swarmers enter through the smallest openings in exposed wood.
- Watch the trees. Formosan colonies nest in live oaks, pecans, and other yard trees and reach the house from above ground — a carton nest in a tree within 100 feet of the home is a treat-now signal.
- Inspect annually — a $75–$150 professional inspection (or a thorough flashlight walk of the crawlspace and foundation each spring) catches mud tubes years before structural damage.
California termite swarm FAQ
More California pest timing
More West termite swarm seasons
Swarm windows are climatological typicals compiled from land-grant extension guidance (UF/IFAS, LSU AgCenter, Texas A&M, UC IPM, and state extension services) and from the IRC Termite Infestation Probability map; any single year runs 1–3 weeks either side. Cost ranges are general industry figures, not quotes. Live conditions from Open-Meteo. California extension guidance: ipm.ucanr.edu/PMG/PESTNOTES/pn7415.html. National picture: where termites are swarming right now →
Hero image: “Formosan termite alates” — USDA Agricultural Research Service (Scott Bauer) — Public domain