Dermacentor andersoni

Dermacentor andersoni

Order: Ixodida

Family: Ixodidae

Rocky Mountain Wood Tick (Dermacentor andersoni) is an ornate hard tick of western North America. It is a compact, reddish-brown to gray-brown tick with pale markings on the scutum, claw-tipped legs, and a flattened body built for clinging to passing hosts and vegetation.

For representative images and visual context, see the page: Rocky Mountain Wood Tick in the Gallery section.

Description

Dermacentor andersoni is generally recognized by:

• Overall form: a hard tick with a low, dorsoventrally flattened body and a compact, oval to pear-shaped outline.
• Body length: an unfed adult female is a few millimeters long; engorged females become much larger after feeding.
• Body regions: ticks do not show the spider-like separation of cephalothorax and abdomen. The visible body is compact, with the mouthparts and capitulum projecting from the front.
• Scutum: pale, ornate shield on the upper body. In females, the scutum covers only the front portion of the back; in males, the shield extends over most or all of the dorsal surface.
• Color pattern: reddish-brown to gray-brown body and legs with contrasting pale or whitish ornamentation on the scutum.
• Eyes: small eyes may be present on the outer margins of the scutum.
• Mouthparts: relatively short mouthparts at the front of the body; the rectangular basis capituli can be useful in close examination.
• Legs: eight legs in nymphs and adults; larvae have six legs. Adults have sturdy, claw-tipped legs used for gripping hosts, vegetation, and smooth surfaces.
• Posterior margin: festoons, or small scalloped divisions, are visible along the rear margin in suitable close views.
• Sex differences: females show a smaller pale scutum with the rear body exposed; males are more extensively patterned across the back.
• Immature differences: larvae and nymphs are smaller and are much less likely to be noticed in ordinary field photography.

The photographed individual appears consistent with an adult female: the pale scutum is concentrated on the front portion of the back rather than covering the entire body. This is a useful field clue, but species-level confirmation in Dermacentor can depend on location and close structural details.

Habitat and Behavior

Typical habitats include:

• shrublands, open grasslands, lightly wooded areas, trail edges, pastures, and brushy margins
• low vegetation where adults can quest with their front legs extended
• western North American habitats, especially the Rocky Mountain and northwestern regions

Behavioral notes:

• Activity: adults are most often encountered in spring and early summer, with activity dropping during hot, dry periods.
• Resting posture: adults often hold a low, flattened posture but may extend the front legs when questing or moving.
• Hunting style: ticks do not hunt prey like spiders. They quest from vegetation and attach to a host that brushes past.
• Movement: slow, deliberate walking with strong gripping ability from the claws at the ends of the legs.
• Feeding: adults feed on medium to large mammals, including wild ungulates, livestock, dogs, and people.
• Immature hosts: larvae and nymphs more often use small mammals such as mice, squirrels, gophers, or related hosts.
• Seasonality: adults are the stage most likely to be noticed by people and pets; larvae and nymphs are smaller and less commonly encountered.
• Life cycle: a three-host tick, with larvae, nymphs, and adults each feeding on a separate host before leaving the host to molt or reproduce.

Identification

Key features for field diagnosis:

• Size and build: compact hard tick with a flattened body and sturdy legs.
• Color and markings: reddish-brown to gray-brown body with pale scutal ornamentation.
• Scutum pattern: adult female with a pale anterior scutum and exposed rear body; adult male more fully patterned across the back.
• Posterior features: festoons along the rear edge can be visible in sharp macro views.
• Legs: eight legs in nymphs and adults, with clawed tips for gripping.
• Mouthparts and capitulum: close views of the front of the body may show the compact mouthparts and rectangular basis capituli.
• Habitat or seasonal clues: western range, spring to early summer adult activity, and association with open or lightly wooded habitats support the identification.
• Photo-identification limits: Dermacentor andersoni can be difficult to separate from similar Dermacentor species by photos alone. Location, season, and very close views of structural features are often important; microscopy or expert review may be needed for high-confidence separation from similar wood ticks.

For this page, the identification should be treated as photo-supported and range-dependent. If the specimen was photographed outside the Rocky Mountain or northwestern range, consider comparing carefully with American dog tick and other regional Dermacentor species.

Similar Species

Use this section to distinguish Dermacentor andersoni from likely lookalikes.

• American Dog Tick (Dermacentor variabilis): very similar in general shape and ornate scutum. Geography is often an important clue; microscopic characters may be needed to separate it confidently from the Rocky Mountain wood tick.
• Western American Dog Tick (Dermacentor similis): a western member of the American dog tick complex recognized in some modern treatments. It may require specialist review or specimen-based confirmation.
• Pacific Coast Tick (Dermacentor occidentalis): another ornate western Dermacentor tick. It is most relevant in Pacific Coast regions and can look similar in casual photos.
• Winter Tick (Dermacentor albipictus): often associated with large mammals such as deer, elk, and moose. Shape, host association, season, and close structural details help separate it.
• Western Blacklegged Tick (Ixodes pacificus) and other Ixodes ticks: usually less ornate, with a different body shape and proportionally longer mouthparts. Adult female Ixodes often shows a dark scutum and contrasting rear body rather than the pale ornate scutum typical of Dermacentor.

Focus on:

• range and habitat
• season of adult activity
• presence and pattern of pale scutal ornamentation
• festoons on the rear margin
• mouthpart length and body proportions
• whether the identification is based on a photograph or an examined specimen

Ecology and Notes

Dermacentor andersoni is a three-host tick: each life stage takes a blood meal from a different host and then leaves that host to continue development. Adults generally use larger mammals, while larvae and nymphs are associated more with small mammals. This host shift makes the species part of both wildlife and domestic-animal edge habitats.

Adult Rocky Mountain wood ticks are often encountered along trails, vegetation edges, grasslands, lightly wooded areas, and other places where hosts move through low vegetation. They are well adapted for gripping, and the macro photographs show how effectively the claws can hold onto a smooth curved surface.

This species can transmit pathogens of medical or veterinary importance in parts of its range, and some female ticks can be associated with tick paralysis. This page is intended for natural-history and identification notes, not medical diagnosis. Attached ticks should be removed promptly and bite concerns should be handled through appropriate medical or veterinary guidance.

Identification notes:

• The gallery individual appears to be an adult female based on the smaller anterior scutum.
• A photograph can often support a Dermacentor identification, but species-level separation may depend on geography and close structural features.
• Similar-looking ticks occur in nearby or overlapping regions, so range and collection location are especially important.

References

• University of Rhode Island TickEncounter — Rocky Mountain Wood Tick
  https://web.uri.edu/tickencounter/species/rocky-mountain-wood-tick/

• CDC Stacks — Rocky Mountain wood tick (Dermacentor andersoni) distribution map
  https://stacks.cdc.gov/view/cdc/27721

• Western College of Veterinary Medicine, University of Saskatchewan — Dermacentor andersoni: the Rocky Mountain wood tick
  https://wcvm.usask.ca/learnaboutparasites/parasites/dermacentor-andersoni-the-rocky-mountain-wood-tick.php

• iNaturalist — search for Dermacentor andersoni
  https://www.inaturalist.org/search?q=Dermacentor%20andersoni

• BugGuide — search for Dermacentor andersoni
  https://bugguide.net/index.php?q=search&keys=Dermacentor+andersoni&search=Search