There are about 50 different species of ticks in California, but only a few species transmit diseases to humans in California.

Ticks are divided into two groups: “hard ticks” (Ixodid ticks) and “soft ticks” (Argasid ticks). Most soft ticks live in the nests of birds or wild animals like squirrels or rabbits. These ticks feed exclusively on animal hosts and are rarely seen by people.

Hard ticks (Ixodids) are more commonly encountered by humans and pets in San Mateo County. There are 28 species of hard ticks in California, 21 of which are found in San Mateo County. Most of these ticks feed on specific groups of animals (e.g., birds, bats, rodents, rabbits, etc.) and are closely associated with the nests, burrows, or bedding areas of these animals. These ticks are almost never encountered by humans and can only be found by examining wild animals or their nests.

Hard ticks have a three stage life cycle: larva, nymph and adult. All three stages feed on blood and a blood meal is required to molt to the next stage or lay eggs. The different life stages of a tick often feed on different kinds of hosts. For example, larvae and nymphs of the Pacific Coast tick (Dermacentor occidentalis) feed on mice and other rodents. The adult stage of this tick feeds on deer or other large animals.

Hard ticks feed by attaching themselves to their host. They remain attached for 3-7 days, depending on life stage, and will swell to many times their usual size while feeding. When they are finished, they drop off, digest the blood, and complete their development to the next life stage or lay eggs. Completion of the entire life cycle can take many months or even a couple of years.

Page last reviewed: December 28, 2023