Common species in California
California follows the split authority source pattern. The species below are drawn from the state-authority sources listed in the sidebar Data Row.
- Western blacklegged tick
- Pacific Coast tick
- American dog tick
- Asian longhorned tick (CDPH + CDFA surveillance; not yet established in California as of latest reports)
When ticks are most active
Wet-season pattern, NOT the Northeast May-July pattern. Western blacklegged adults peak November-April (when ground is wet); nymphs peak April-June in coastal + foothill chaparral. Pacific Coast tick adults peak winter-spring. Dry summers reduce tick activity in most of California except along the coast. Microclimate matters — oak woodland leaf litter holds humidity year-round.
Where you're most likely to encounter ticks
Bay Area open-space preserves and East Bay oak woodland (Briones, Tilden, Mt. Diablo), Marin + Sonoma + Mendocino redwoods + oak-bay forest, Sierra foothill trails, North Coast hiking, Central Coast (Santa Cruz, Big Sur, Santa Lucia) chaparral, Lake Tahoe + Sierra Nevada day-hikes, San Diego County backcountry, dog walking in oak-woodland edges, hunting properties in NorCal.
Disease context
Each disease named below carries an evidence tag per the Data Row policy. Pills indicate the strength of state-specific evidence, not the severity of the disease. Symptoms should always be routed to a clinician; this is orientation, not diagnosis.
- Lyme diseasestate surveillance confirmed
CDPH reports Lyme in CA. Lower per-capita incidence than Northeast, but Northern California oak woodlands carry real risk; nymph prevalence varies sharply by habitat (leaf litter > chaparral)
- Anaplasmosisstate surveillance confirmed
- Babesiosisstate surveillance confirmed
- Pacific Coast tick fever (Rickettsia philipii / 364D)state unique angle
California-specific spotted-fever-group rickettsiosis transmitted by Pacific Coast tick (Dermacentor occidentalis); CDPH-tracked
- Tickborne relapsing feverstate surveillance confirmed
Soft-tick TBRF documented in CA mountain cabins + rodent-infested structures
- Tularemiastate surveillance confirmed
- Rocky Mountain spotted fevernon diagnostic mention only
Lower CA incidence than RMSF-belt states
- Ehrlichiosisnon diagnostic mention only
If you find a tick — what to do
Map resolution notes
mixed resolution.CDPH publishes county-level surveillance for several tickborne diseases. UC ANR / IPM supports habitat-resolution claims (oak woodland > chaparral > grassland for nymphal blacklegged density). County vector-control districts (especially in the Bay Area) publish very-local surveillance — Alameda, Contra Costa, Marin, and Santa Cruz counties all have active programs. CDC maps support national comparison. Do not infer fine-grained county or habitat risk in non-cited counties — California's tick ecology varies sharply by habitat moisture, not just by latitude.
State sources
- Primary species source
- California Department of Public Health (CDPH) Vector-Borne Disease Section + CDPH Tick-Borne Diseases hub; UC Agriculture & Natural Resources (UC ANR) Integrated Pest Management for tick biology + identification; California Department of Fish & Wildlife (CDFW) for wildlife context.
- Primary health source
- CDPH Vector-Borne Disease Section reports on Lyme, anaplasmosis, babesiosis, Pacific Coast tick fever, TBRF, and tularemia; county vector-control districts (e.g. Alameda County Vector Control Services District) for local surveillance; CDC pages and maps for national guardrails.
- Primary extension source
- UC ANR / UC IPM Statewide Integrated Pest Management Program publications on western blacklegged tick, Pacific Coast tick, and the wet-season activity pattern that distinguishes CA from Northeast tick ecology.
- Surveillance
- CDPH Vector-Borne Disease Section + Mosquito-Borne Virus Surveillance Reports (where overlapping); California Department of Food & Agriculture (CDFA) for animal-health + Asian longhorned tick watch; county vector-control districts for local-resolution surveillance; UC ANR / IPM publications for habitat-resolution claims; CDC for national comparison.