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Species profile

Rocky Mountain wood tick

Dermacentor andersoni

A hard tick of the Rocky Mountain states and southwestern Canada. Adults are the principal stage associated with pathogen transmission to humans.

Adult female Dermacentor andersoni on the left and adult male on the right with scutum differences marked
mixed · Adult · unfed

Image credit:James Gathany / CDC Licence termsSource

CDC dorsal scientific illustration of an adult female Dermacentor andersoni Rocky Mountain wood tick
female · Adult · unfed

Image credit:CDC / Andre J. Brooks / CDC Licence termsSource

Also known as: Rocky Mountain tick

Image gallery

Adult female Dermacentor andersoni on the left and adult male on the right with scutum differences marked
Adult female and male

Image credit:James Gathany / CDC Licence termsSource

CDC dorsal scientific illustration of an adult female Dermacentor andersoni Rocky Mountain wood tick
Adult female, dorsal illustration

Image credit:CDC / Andre J. Brooks / CDC Licence termsSource

Quick facts

Family: Ixodidae. Genus: Dermacentor. Hard tick. Taxonomic authority: Stiles, 1908. Life stages: egg, larva, nymph and adult. CDC reports a two-to-three-year life cycle.

Identification

Adults are ornate Dermacentor ticks with short mouthparts, eyes and festoons. Females have a cream-patterned anterior scutum; males show pale mottling across most of the dorsum.

Short mouthparts, eyes, festoons and an ornate dorsal shield. Adult morphology is the most useful field-visible stage, but definitive separation from related Dermacentor may require expert examination.

May be confused with Dermacentor variabilis. Location and altitude are useful context but do not replace morphology.

Photographs alone cannot always confirm this species. Geographic location, host and colour are supporting context, not conclusive identification; expert morphological examination may be required.

Sex and appearance differences

Adult females have a relatively small cream-patterned anterior scutum and an expandable posterior body. Adult males have an ornate scutum covering nearly the whole dorsum. The accepted CDC image displays adult female and male together.

Life cycle

Three-host life cycle that may require two to three years. Adults feed mainly on large mammals; larvae and nymphs feed largely on small rodents.

Life stages

  • Egg
  • Larva
  • Nymph
  • Adult

Seasonal activity

Adult Dermacentor activity is mainly spring through autumn, often highest in late spring and early summer. Local elevation and climate alter timing.

Hosts

  • Humans (Homo sapiens)
  • Small mammals
  • Large mammals
  • Livestock
  • Dogs (Canis lupus familiaris)

Habitats

  • Rocky Mountain rangeland
  • Grassland and shrubland

Distribution

Occurs in Rocky Mountain states and southwestern Canada, commonly at elevations reported by CDC from approximately 4,000 to 10,500 feet. This is a regional distribution statement, not a prediction of encounter risk at every location.

Presence, established populations, habitat suitability and disease risk are distinct evidence categories.

Countries and regions

  • United States — established_regional

    Occurs in Rocky Mountain states and southwestern Canada, commonly at elevations reported by CDC from approximately 4,000 to 10,500 feet. This is a regional distribution statement, not a prediction of encounter risk at every location.

  • Colorado — present

    Colorado State University Extension identifies the Rocky Mountain wood tick as the most common tick species that bites people in Colorado.

  • Idaho — present

    University of Idaho Extension identifies the Rocky Mountain wood tick in northern Idaho.

  • Montana — present

    Montana State University Extension identifies the Rocky Mountain wood tick as frequently found on companion animals in Montana.

  • Nebraska — present

    Nebraska DHHS includes the Rocky Mountain wood tick among medically important ticks monitored in Nebraska.

  • New Mexico — present

    New Mexico Department of Health includes the Rocky Mountain wood tick in its state hard-tick list.

  • Oregon — present

    Oregon Health Authority records the Rocky Mountain wood tick in Oregon.

  • South Dakota — present

    South Dakota State University Extension identifies the Rocky Mountain wood tick among common ticks in South Dakota.

  • Utah — present

    Utah State University Extension identifies the Rocky Mountain wood tick as the tick most commonly encountered by people and pets in Utah.

  • Washington — present

    Washington Department of Health records the Rocky Mountain wood tick primarily in eastern Washington.

  • Wyoming — present

    Wyoming's 2025 Tick Blitz identified Rocky Mountain wood ticks in statewide collections.

  • Canada — present

    The Public Health Agency of Canada identifies the Rocky Mountain wood tick among tick species found in Canada.

  • Alberta — present

    Government of Alberta surveillance guidance identifies the Rocky Mountain wood tick in Alberta.

  • British Columbia — present

    Government of British Columbia identifies the Rocky Mountain wood tick among ticks found in British Columbia.

  • Saskatchewan — present

    Government of Saskatchewan lists the Rocky Mountain wood tick among ticks found in Saskatchewan.

Medical and veterinary relevance

A confirmed vector of Rickettsia rickettsii, Colorado tick fever virus and Francisella tularensis, and a species associated with tick paralysis. Adult ticks are the primary human exposure stage.

Adults feed on livestock, dogs and wild large mammals; infestation and tick paralysis are veterinary concerns.

Pathogens and diseases

  • Rocky Mountain spotted fever — disease

    A rickettsial disease transmitted in the United States mainly by American dog ticks, Rocky Mountain wood ticks and, in certain areas, brown dog ticks.

  • Colorado tick fever — disease

    A viral disease transmitted by infected Rocky Mountain wood ticks.

  • Tularemia — disease

    A disease caused by Francisella tularensis; several tick species can act as vectors in defined regions.

  • Tick paralysis — condition

    A toxin-mediated condition associated with feeding by certain tick species; it is not an infectious disease.

Detection of a pathogen in a tick does not by itself establish that the species is a confirmed vector.

Vector and pathogen evidence

CDC lists Rocky Mountain spotted fever, Colorado tick fever and tularemia among diseases transmitted by Dermacentor andersoni. Tick paralysis is toxin-mediated rather than infectious.

Medical importance

Adults bite humans and are the stage mainly associated with pathogen transmission. National encounter data place this species among the most frequently recorded U.S. human-biting ticks.

Veterinary importance

Feeds on livestock, dogs and wildlife and can cause infestation or toxin-mediated paralysis.

Prevention and removal guidance

Prevent tick bites by using current public-health guidance, walking in the centre of trails where practical, using appropriate repellents, treating clothing or gear where suitable, and performing thorough tick checks after exposure.

Remove an attached tick promptly with fine-tipped tweezers or a purpose-designed tick-removal tool. Grasp close to the skin and pull upward steadily without twisting or crushing the tick. Seek professional medical or veterinary advice when symptoms or concerns arise.

Important identification and health information

Educational information and limitations

Photographs and visible features may be insufficient for definitive identification.

This educational information is not a diagnosis or a substitute for medical or veterinary advice.

This educational information does not replace examination or advice from a qualified veterinary professional.

Presence, established populations, habitat suitability and disease risk are distinct evidence categories.

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