Most important group of ticks in the United States as pests of man and other animals, both as blood-sucking parasites and as disease vectors.
Some species feed regularly on man and other animals; transmit the causative organisms of Spotted Fever, Tularemia, Colorado Tick Fever, possibly Q Fever, and Anaplasmosis; and pass many of the causative agents of these diseases transovarially and transtadially.
Specimens of D. variabilis and D. andersoni are the ticks most frequently involved in cases of tick paralysis in the United States.
Dermacentor ticks are ornate, with pale markings on the scutum, eleven festoons, eyes, and short palpi.
The basis capituli is quadrangular dorsally.
The American dog tick, Dermacentor variabilis,
Commonly Carry: Rocky Mountain Spotted Fever, Tularemia, 364D Rickettsiosis
Markings: pale whitish or yellowish markings on the scutum
Common Hosts: Adults prefer dogs, although it feeds readily on large mammals, including man.
Where Found: East of the Rocky Mountains, on the Pacific Coast, and in parts of northern Idaho and eastern Washington
Larvae: The newly hatched larvae are about 0.6 mm long, without spiracular plates, and are yellow with red markings near the eyes. Engorged larvae are about 1.5 mm long and are slate gray to black. Larvae seek the host actively and do not assume the waiting position typical of the adults. Meadow mice, white-footed mice, and pine mice are important hosts of larvae.
Nymph: Nymphs are similar in appearance to the larvae, but have four pairs of legs and are light yellowish brown with red markings near the eyes. Engorged specimens are slate gray and about 4 mm in length. The entire life cycle is from four months to more than a year.
Adult: Commonly found in the spring in their “waiting position” on grass and other low vegetation. The third pair of legs is used to cling to the grass while the others are waved about ready to grasp any host that comes by.
The male remains on the host for an indefinite time, alternately feeding and mating. The female feeds, mates, becomes engorged, and drops off to lay several thousand eggs.
The adult male and females are frequently encountered by sportsmen and people who work outdoors. The males and females have pale whitish or yellowish markings on the scutum. Males may be only 3 mm long, while engorged females may be as much as 13 mm in length.
Males of D. variabilis do not feed enough to alter their size noticeably. Females may increase in size from about 5 mm long and 2.5 mm wide to 13 mm long and 10 mm wide, but their engorgement is retarded if males are not present.
American dog ticks, as well as other species, are attracted by the scent of animals, hence are most numerous along roads, paths and trails. Engorged ticks that drop from animals using the passageways further increase the concentration at these sites. These facts are important to persons applying pesticides for tick control.
The Rocky Mountain Wood Tick, Dermacentor andersoni,
Commonly Carry: Colorado Tick Fever
Markings: It is similar to the American dog tick, but adults of the wood tick in general have more pale coloring and larger goblets on the spiracular plates than the American dog tick.
Common Hosts: The life cycle of this three-host tick is two to three years. The larvae and nymphs attack small mammals, and the adults obtain their blood meals from large mammals including man.
Where Found: in the Rocky Mountain states and in Southwestern Canada. The range of this tick coincides with the area in which cases of Colorado tick fever are contracted.
The Winter Tick, Dermacentor albipictus,
Commonly Carry: Lyme Disease, Anaplasmosis
Markings: The spiracular plates are oval with very large goblets.
Where Found: The Winter Tick is widely distributed throughout North America
Common Hosts: It is a one-host species parasitic on cattle, horses, moose, elk, deer and sometimes man. These ticks may be extremely numerous on these large animals and may cause blood loss leading to anemia and even death.
The Pacific Coast tick, Dermacentor occidentalis,
Commonly Carry: It is a known vector of tularemia, Colorado Tick Fever, and a suspected vector of Rocky Mountain spotted fever.
Markings: The basis capituli has conspicuous tooth-like dorsal projections on the posterior margin known as cornua.
Where Found: The West and Southwest
Common Hosts: is a three-host tick whose life cycle on small rodents and large mammals may be completed in less than three months. It is a serious year-round pest of cattle and will attack man.