Dermacentor variabilis

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Dermacentor variabilis (click on image to enlarge it)
Author(s): Gary Alpert, Harvard University
Source: IPM Images

Dermacentor variabilis (Say) - (American dog tick)

The tick is found in eastern North America with a limited distribution along the Pacific coast. Although there is a record of this species from Sweden (Jaenson et al., 1994), it apparently did not become established there. It frequently bites humans, dogs and other mammals. D. variabilis is the main vector of Rocky Mountain spotted fever (Rickettsia rickettsii) and can also transmit tularemia (Francisella tularensis). The tick lives in forests or in areas with shrubs and grasses, especially in places where rodents are common. Management involves keeping dogs away from tall grasses, regular inspections and treating areas around residences with acaricides.

Vernacular names
• Deutsch: Amerikanische Hundezecke
• English: American dog tick
• Español: garrapata americana del perro
• Français: tique américaine du chien

The tick has 3 hosts during its life time and feeds for about 2 weeks on each host. Female ticks leave their host and lay eggs on the ground. After emerging from the eggs, the larvae climb on grasses and wait for a small mammal like a mouse or squirrel to pass by and to attach themselves.

The larvae can survive without a host for almost a year. After a blood meal, they leave their host and molt to nymphs which parasitize slightly larger mammals. Again they leave the host and molt to an adult which wait for larger mammals. The adults can survive for up to 2 years without feeding and overwinter in the soil. Mating takes place on the host.

Unfed adult females are around 5-6 mm long, males about 3½ mm. The colour is reddish brown with irregular whitish marks and stripes on the scutum of the female and the dorsal parts of the male.