This species is widely distributed throughout California except for the very arid areas of the central valley and south eastern desert region. It has also been found in Oregon and Baja California. The immature stages feed on rodents, especially squirrels, while the adults prefer large mammals such as cattle, horses, deer and humans.
Adults are found year-round with peak activity in April and May. Nymphs are most common during spring and summer. Adult hosts tend to be cattle, horses, deer and humans. Rare on dogs and bears. Nymphs tend to feed on rodents and other small mammals.
Capable of transmitting many diseases. Vector of bovine anaplasmosis. Has been found naturally infected with Colorado Tick Fever virus, the Rickettsia of Q Fever and the bacterium that causes Tularemia. Known to cause tick paralysisin cattle, horses and deer. Spotted fever group Rickettsiae have been found in ticks collected from Mendocino County. Bite wounds are commonly mistaken for wounds caused by biting insects and spiders.