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The Three Most Common Tick Species in Marin and Sonoma Counties

November 2020-Ticks are active year-round in Marin and Sonoma counties. Ticks are blood-sucking arthropods that can transmit a variety of diseases such as Lyme disease, Rocky Mountain spotted fever, tick-borne relapsing fever, tularemia, anaplasmosis and ehrlichiosis. Not all tick species are created equal, so let’s take a look at the differences between the three most commonly encountered tick species we see here.

American Dog Tick

American dog ticks (Dermacentor variabilis) are found throughout much of the United States and have also been collected in Canada and Mexico. In Marin and Sonoma counties, these ticks can be found in large numbers in sunny, grassy habitats, particularly those near waterways. Adults can be found throughout the year but are most active March through July. They commonly feed on dogs and people, as well as a variety of carnivorous hosts. The nymphal stage of these ticks feed primarily on rodents and rabbits. Female American dog ticks are very similar to female Pacific Coast ticks both in size and markings, but the markings are more pronounced on the bodies of female American dog ticks. It is fairly easy to tell the males apart as the American dog ticks have more distinctive whitish markings on their bodies. The American dog tick can transmit Rocky Mountain spotted fever and tularemia. 

Pacific Coast Tick

Pacific Coast ticks (Dermacentor occidentalis) can be found in shrublands, chaparral and along hiking trails from Oregon to Mexico. Adults have been collected in California year-round, but are most abundant in the spring. They prefer to feed on deer, cattle, horses, and people. The immature nymphal stage of these ticks are most abundant in spring and summer, and feed primarily on rodents, especially squirrels.

In Marin and Sonoma counties, adults of this species are commonly found in the same habitats as western black-legged ticks. Pacific Coast ticks can be distinguished from western black-legged ticks by their coloring—they are brown with off-white mottling across their backs. The Pacific Coast tick can transmit Rocky Mountain spotted fever, Pacific Coast tick fever, Colorado tick fever, and tularemia.

Western Black-legged Tick

Western black-legged ticks (Ixodes pacificus) are found along the Pacific Coast of the United States, particularly in Northern California. They are usually found locally from October through July. Adults are commonly encountered during the cooler months while the nymphs are found later in the spring and early summer. Larvae and nymphs typically feed on small animals such as rodents and lizards, while adults feed on larger mammals including humans and deer. Both nymphs and adult females can transmit Lyme disease bacteria to humans.

Learn more about ways to protect yourself from ticks and tick-borne diseases:

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