Ticks are arachnids, related to spiders and mites, not insects. These small, eight-legged parasites are common throughout California’s diverse landscapes, where they latch onto hosts to feed on blood. Ticks pose a serious health risk because they can transmit various disease-causing bacteria and viruses during feeding. Understanding the specific species, their preferred environments, and their seasonal activity is key to effective personal protection.
Primary Tick Species and Associated Risks
The greatest concern in California centers on the Western Blacklegged Tick (Ixodes pacificus), the primary transmitter of the bacterium causing Lyme disease in the western United States. Larval and nymphal stages often feed on small animals like lizards and rodents, while adult ticks prefer larger mammals, most commonly deer. Nymphs are particularly hazardous to humans because their small size makes them easily overlooked, despite a high rate of infection in some areas. This species can also transmit the agents responsible for anaplasmosis and hard tick relapsing fever.
California is home to other tick species that carry different health risks. The Pacific Coast Tick (Dermacentor occidentalis) is widespread across the state, found from coastal regions to sagebrush habitats. This species transmits Rickettsia phillipii, which causes Pacific Coast tick fever.
The American Dog Tick (Dermacentor variabilis) is generally found in lower elevations and grassy areas. It is present in California and can transmit the bacteria that cause Rocky Mountain Spotted Fever and tularemia. The Brown Dog Tick (Rhipicephalus sanguineus) is unique because it can complete its entire life cycle indoors, posing a risk to pets and humans, and is also a vector for Rocky Mountain spotted fever.
Geographic Distribution and High-Risk Habitats
Ticks are widely distributed across California, reported in almost all 58 counties. The highest probability of encountering ticks, particularly the Western Blacklegged Tick, occurs in the humid north coastal regions and along the western slope of the Sierra Nevada foothills. These areas provide the necessary moisture and host availability for tick survival.
High-risk environments include transition zones where forests meet meadows, such as oak woodlands, chaparral, and coastal scrub. Ticks do not fly or jump; instead, they engage in “questing,” climbing to the tips of low-lying vegetation like tall grasses or brush. They wait there for a host to brush against them, meaning walking through overgrown areas can lead to attachment.
In the Sierra Nevada, habitat ranges from oak woodlands near the valley floor, through chaparral in the foothills, and up to mixed conifer forests around 4,500 feet. While populations concentrate in northern California, ticks are also found in the mountainous and coastal areas of Southern California. Staying on marked trails and avoiding dense vegetation reduces the chance of an encounter.
Seasonal Activity and Personal Prevention Strategies
The activity period for ticks in California can span year-round, though the risk of exposure changes depending on the specific life stage and species. Adult Western Blacklegged Ticks are most active during the cooler, wetter months, generally from late fall through early spring, which can be October through March in some regions. The nymphal stage, which poses a greater risk for Lyme disease transmission, is typically active during the late winter and spring months, from February to early May or June.
Personal prevention begins with clothing choices and repellents when entering wooded or grassy areas. Wearing long pants and long-sleeved shirts helps to block tick access to the skin, and light-colored clothing makes it easier to spot a tick crawling on the fabric. Tucking pants into socks or boots prevents ticks from crawling up the legs, which is a common path of attachment.
Applying an EPA-registered insect repellent containing at least 20% DEET to exposed skin offers protection against tick bites. Clothing and gear can also be pre-treated with permethrin, a product that kills ticks on contact, though it should never be applied directly to the skin. After returning indoors, it is important to perform a thorough tick check of the entire body, focusing on warm, dark areas like the hairline, underarms, and groin.
For clothing, tumbling them in a dryer on high heat for at least ten minutes will effectively kill any ticks that may have attached. If a tick is found attached, prompt and proper removal is necessary to minimize the risk of disease transmission. Using fine-tipped tweezers, grasp the tick as close to the skin’s surface as possible and pull straight upward with steady, even pressure. After removing the tick, the bite area and hands should be thoroughly cleaned with soap and water.