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photo by Gary Fewless, text by V. Medland

Male (top) and female (below) Dog Ticks (Dermacentor variabilis)

These two "wood ticks" might appear to be be basking in the sun, but really they are waiting to grab their next meal. In the Great Lakes States there are several species of wood ticks. These are probably the American dog tick, Dermacentor variabilis. This species is the widely distributed in North America and occurs throughout the eastern and central United States. Although they are called dog ticks the adults will feed on most large mammals. The juvenile ticks (nymphs) feed on small rodents.

Ticks congregate where warm-blooded animals are likely to pass by--so grassy field, paths, and trails are common places to pick up these blood parasites. Since they cannot fly or move very fast at all they climb up to a suitable resting place (like this blade of grass) and hold out their appendages. When they detect that an animal is close by sensing shadows, carbon dioxide , or vibrations they drop onto or grab onto it.

After feeding on blood the engorged female drops from the host and in 4 - 10 days lays 4,000 to 6,500 eggs on the ground. The eggs hatch in about 35 days and tiny six-legged juveniles or nymphs emerge. Nymps remain on the ground waiting for small rodents. After feeding the nymphs drop from their host to rest and molt to a larger size. After two molts the nymphs mature into adults. The life cycle may take only three months, or it can last as long as two or more years depending on the availability of suitable hosts. Larval and adult activity peak during the spring and early summer.

This species can carry Rocky Mountain Spotted Fever, but that disease is rare in the upper Great Lakes area. D. variabilis may or may not be a carrier of Lyme disease. Some individuals have been found with the bacterial spirochaete that causes the disease, but it has not been shown that it can transmit the disease to humans and it may only be a carrier.

The main vector of Lyme in this area is the blacklegged deer tick, Ixodes scapularis. Adult dog ticks can be distinguished from adult I. scapularis by their larger size and the white markings on the upper body surface.

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Last updated on April 15, 2014