Although there are 21 species of hard ticks in San Mateo County, the list below are the most common ticks that people and pets contact in the environment.

Western Black-Legged Tick (Ixodes pacificus)

• Adults quest along trails primarily November through April
• Adults feed readily on humans, horses, dogs, and other large mammals
• Larvae and nymphs are most active March to early August, peaking in April to June
• Larvae and nymphs feed primarily on lizards but may also attach to rodents and people
• Primary vector of Lyme disease to humans in California

Pacific Coast Tick (Dermacentor occidentalis)

• Adults reach peak activity from April through May, but are present along trails from November through August
• Adults feed on cattle, horses, deer, dogs, and humans
• Larvae and nymphs are most active April through July
• Larvae and nymphs feed on small rodents and other small mammals in spring and summer
• Vector of Tularemia and various uncommon Rickettsial diseases

American Dog Tick (Dermacentor variablis)

• Adults quest along trails primarily from March through July
• Adults feed on dogs and large mammals, including humans
• Larvae and nymphs are most active April through July
• Larvae and nymphs feed on rodents and other small mammals
• Vector of Tularemia and various uncommon Rickettsial diseases

Rarely, we receive a tick to identify that is a brown dog tick (Rhipicephalus sanguineus). To learn more about brown dog ticks, visit HERE or HERE.

Page last reviewed: November 20, 2023