Ixodes pacificus

Ixodes pacificus, the western black-legged tick, is a species of tick found on the western coast of North America. The western black-legged tick is a hard tick, i.e., a member of the family Ixodidae. The larvae and nymphs typically feed on lizards and small mammals, while adults typically feed on deer. It is an ectoparasite that attaches itself to the outside of its host and feeds on the host's blood. It can have a heteroxenous lifestyle or monoxenous life cycle depending on how many hosts it feeds on in each cycle. I. pacificus has a four-stage life cycle that takes around 3 years to complete; these stages include egg, larva, nymph, and adult. They prefer dense woodland habitats or areas of brush and tall grass.

It is the principal vector of Lyme disease in that region, while the deer tick, Ixodes scapularis, is the vector to the east.