Western Deer Tick

Ixodes pacificus

The Western “Deer” tick (Ixodes pacificus), actually called the Western Blacklegged tick, can transmit the organisms responsible for causing Anaplasmosis and Lyme disease in humans. Wild rodents (such as white-footed mice) and other mammals are likely reservoirs of these pathogens. This tick is distributed along the Pacific coast of the United States. Larvae and nymphs feed on birds and small rodents, while adult ticks feed on deer and other mammals. Both adult and nymphal ticks are known to transmit disease to humans.

Quick Overview:

  • Commonly found in deciduous forests and shrubs bordering forests along the West Coast of the United States in CA, OR, WA, and some parts of NV, AZ and UT.
  • Not typically found in open fields or in grassy areas.
  • Diseases transmitted: Lyme disease, Babesiosis, Anaplasmosis, Ehrlichiosis, and Powassan Virus.
  • Male ticks are not known for transmitting infections.
  • Females typically lay their eggs (~2000 or so) in late May. Eggs then hatch in late summer.
Western Blacklegged Deer Tick

American Dog Ticks have a dark brown body; with females having an off-white scutum (dorsal shield), while adult males look more mottled. They are flat and oval in shape, and usually brown with whitish-gray markings. Similar to the Blacklegged “Deer” Tick, these ticks have 6 legs as larvae but have 8 legs when they are nymphs and adults. They range anywhere from 5 mm to 15 mm in size depending on whether or not they are engorged.

Tick ID Plot Western Blacklegged Tick

The life cycle of the deer tick takes approximately two years to complete. Their development is dependent on environment and the availability of hosts. Under favorable conditions, they may be capable of developing in less than one year.

All three of the deer tick’s development stages require blood meals from hosts. Deer ticks attach themselves to and feed on one host during the larval stage, another during the nymphal stage and a third during their adult stage. Deer tick larvae and nymphs both molt after feeding.

After laying eggs, female deer ticks die. However, one female is capable of laying up to 3,000 eggs. Six-legged larvae emerge from these eggs and begin to search for a host. Larvae feed for approximately four days before dropping to the ground to molt into nymphs. Resulting nymphs have eight legs and search again for hosts. They, too, will feed and molt into adults.

Medical Importance

The Blacklegged Deer tick is the primary vector of Lyme disease across the northern part of its range. This tick also transmits Babesiosis to humans in the northeastern and north-central U.S., and is known to be one of the tick vectors involved in transmitting Human Anaplasmosis; formerly known as human granulocytic Ehrlichiosis. It is also thought to transmit Bovine Anaplasmosis to cattle.

It is important to note that the pathogen that causes Lyme disease is maintained by wild rodent and other small mammal reservoirs, and is not transmitted everywhere that the western blacklegged tick lives. In some regions, particularly in the southern U.S., the tick has very different feeding habits that make it an unlikely vector in the spread of human disease.

Habitat Gulf Coast

Most commonly found in the habitats of white-footed mice and white-tailed deer, deer ticks are predominantly found in the leaf litter and taller grasses and shrubs of deciduous forests (e.g., maple and oak) and surrounding grassy areas.

This three-host tick tends to have a serial host preference. Larvae feed primarily on small rodents (especially white-footed mice), birds, and reptiles. Nymphs feed on various small rodents, birds, cats, and humans. Adults feed on larger mammals including cats, dogs, and of course, humans.

Western Blacklegged ticks are only found on the western coast of the U.S.; throughout Washington, Oregon, and California. Colonies have also been found in Arizona, Utah, and Nevada.

Range Map - Western Blacklegged Deer Tick

The Western Deer tick is very similar to Ixodes scapularis, the deer tick. Geographically the western black-legged tick inhabits the west coast of the US, where it is commonly found in coastal California, Oregon, and Washington.

Morphologically, it is small, red, has long, thin mouthparts, and no festoons. All species of blacklegged ticks are very small and hard to spot.