A tiny tick can be seen on a man's skin in Norden (Lower Saxony, Germany) on June 18.

If you think that Lyme disease and other illnesses caused by tick bites aren’t a problem that Californians have to worry about, you’d best think again. 

While Lyme disease is most prevalent in the Northeast, Mid-Atlantic and Upper Midwest regions of the United States, as the climate continues to warm, the risks posed by ticks also continue to grow. 

The western black-legged tick, the species that carries Lyme disease in California, is already well established in the woodlands of Marin, San Mateo, Santa Cruz and Sonoma counties, and in the foothills further inland. State data show that an average of 5% to 15% of nymphal blacklegged ticks in California carry the Lyme bacterium. 

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And other potentially dangerous tick species keep turning up in new parts of the state.  

In 2025, research teams that were part of our UC Davis study funded by Bay Area Lyme Foundation, found that the lone star tick, a species first documented in Mendocino County in 2018, is gaining a foothold on the coast. 

That study has now logged 76 lone star tick reports across the state, including recent finds in the Bay Area. Climate modeling shows coastal California offers exactly the conditions the species needs. It isn’t established here yet. But the risk is real, and the lone star tick is the primary........

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