American Dog Tick – Dermacentor variabilis

American Dog Tick – Dermacentor variabilis
Class Arachnida / Order Ixodida / Family Ixodidae
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Live adult dog ticks (also known as wood ticks) photographed in the wild at DuPage County, Illinois.
The American dog tick is the largest of the eastern wood ticks, and the most common tick found in Illinois. They are most active during the moths of April and May, but I have encountered them into July and August; 2005, with its dreadful drought here near Chicago was particularly bad. (However, that may be because I rarely used mosquito repellent at all that summer.)

Ticks are arachnids, and adult ticks have eight legs like spiders. The American dog tick is reddish brown, with white or pale yellow markings. The male tick is about 1/8 inch long, with the female slightly larger. She will be much bigger, about 1/2 inch after feeding.

This is a female dog tick I brought home unintentionally.

Ticks are parasites, and American dog ticks are known as "three host" ticks because they use three different hosts during their development. When the larva hatches from the egg (eggs are laid in the soil), it has only six legs, like an insect. The larva will generally latch onto the first small mammal that happens by – a vole, shrew, chipmunk, mouse or the like. After drinking blood for about four days, the larva drops off the host, and molts (sheds its skin) to become an eight-legged nymph. It then finds the next host – generally a larger mammal such as a raccoon, deer or opossum. Once again, the process repeats and the nymph becomes an adult tick. Adult ticks will find a third host, a large mammal. The male tick supposedly will not feed, but mates with the female while she is feeding. (Male ticks rarely bite, but I can tell you from bitter experience they do bite.) After mating, both genders drop off the host and the female will lay up to 4,000 eggs in the soil.

American dog ticks do not carry Lyme disease, but they can carry Rocky Mountain spotted fever.

Blacklegged Tick
Adult Blacklegged Tick, also commonly called a deer tick [1]

Deer ticks can carry Lyme disease, the most commonly diagnosed tick-borne bacterial disease in the United States. It has also become a veterinary problem, believed to cause joint-related problems in animals (dogs and horses, mostly) exposed to the Lyme bacteria.  Lyme disease was first reported in Connecticut in 1975, and is named after the town of Lyme in which the disease was first observed.

"Ötzi the Iceman," a 5,300-year-old Bronze Age hunter found frozen in the Alps in 1995 had the DNA sequence of Borrelia burgdorferi, making him the earliest known human with Lyme disease.

See also
The lone star tick does not transmit Lyme disease
. Patients bitten by lone star ticks will occasionally develop a circular rash similar to the rash of early Lyme disease. The cause of this rash has not been determined; however, studies have shown that it is not caused by Borrelia burgdorferi, the Lyme disease bacterium.

The rash may be accompanied by fatigue, headache, fever, and muscle and joint pains. This condition has been named southern tick-associated rash illness (STARI).


  1. Photo: Scott Bauer, USDA ARS,  under Creative Commons Attribution 3.0
  2. Arthur V. Evans, National Wildlife Federation Field Guide to Insects and Spiders & Related Species of North America (Sterling, 2007).
Class Arachnida / Order Araneae: Spiders are the largest group of arachnids.  They are easily recognized by their eight legs, and there are few creatures great or small that elicit such irrational fear in mankind. The vast majority of spiders are completely harmless and offer beneficial services, chief of which is keeping the burgeoning insect population in check.
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