Dermacentor andersoni, commonly known as the Rocky Mountain wood tick, is a species of tick. It can cause tick paralysis. This tick is well known as a vector of the Rocky Mountain spotted fever rickettsia in the northwestern U.S. and Canada, the Colorado tick fever virus, and the bacteria which causes tularemia (hunter's disease).
- The larva only has three pairs of legs.
- The nymph has four pairs.
- A single pair of spiracular openings (stigmata) are seen close to the coxae (leg bases or segments) of the fourth pair of legs (except in larvae).
- A terminal capitulum (mouthparts) is visible from above in all hatched stages.
- A large sclerite called the scutum is present dorsally behind the capitulum. The scutum almost entirely covers the back of the male, but only partly covers the back of the female.
- Eyes, if present, are on the scutum.
- Sexual dimorphism in size and colour is frequent. The female is often larger.
- The posterior margin of opisthosoma is usually subdivided into sclerites called festoons.
- The pedipalps are rigid along the chelicerae, and are not leg-like.