Dermacentor occidentalis

Host Type: 3-Host Tick

Pacific Coast Tick ID:

Pacific Coast Ticks have a dark brown body; with females having a mottled off-white scutum (dorsal shield), while adult males look more mottled and “spotty”. They are flat and oval in shape, and usually brown with whitish-gray markings. Similar to the American Dog Tick, these ticks have 6 legs as larvae but have 8 legs when they are nymphs and adults. They range anywhere from 3 mm to 15 mm in size depending on whether or not they are engorged.

Diseases it can transmit:

All life stages of this tick can transmit Rocky Mountain spotted fever (Rickettsia rickettsii) to humans, cats, and dogs. Nymphs and adults can transmit 364D rickettsiosis (Rickettsia phillipi) to humans, tularemia (Francisella tularensis) to humans, cats, and dogs, and bovine anaplasmosis to cattle. These ticks also have been implicated in cases of tick-bite paralysis in cattle, deer, and ponies. 

NOTE: Up to 11% of adult Pacific Coast ticks carry the spotted fever group rickettsia Rickettsia phillipii. This germ is associated with the formation of a cutaneous lesion called an eschar as well as Pacific Coast tick fever, and infection with R. phillipii can be mistaken in diagnostic tests for the more dangerous Rocky Mountain spotted fever.

Distribution in the United States:

This is one of the most widely distributed ticks in California. It is found throughout the state except for the very dry regions of the central valley and the southeastern desert region. The only other areas it has been collected in are Oregon and Baja, Mexico.