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June 20, 2001

People who work outdoors need to be aware of ticks and how to identify them. Three species commonly attack people in Illinois: the blacklegged tick, lone star tick, and American dog tick.

The American dog tick, also called the wood tick, is found throughout Illinois. Only the 3/16-inch, reddish brown, teardrop-shaped adults attack people, dogs, and cats. As with other ticks, they are flattened dorsally, which keeps them from being brushed off the hostís body. Females have a silvery white shield behind the mouthparts; males have indistinct, wavy, silvery lines running the length of the back. This tick transmits Rocky Mountain spotted feverĖa disease uncommon in Illinois.

The lone star tick also occurs throughout the state but is more common in the southern third. Adults are round, brown, and about 1/8 inch in diameter. In the middle of the back, the female has a large white spot, from which the species gets its name. Not only adults but also nymphs bite humans. Nymphs are pinhead-sized, brown, and round. The lone star tick can transmit human ehrlichiosis.

The blacklegged tick occurs in two populations, both in Illinois and the United States generally. Ticks in the northern states, and the northern half of Illinois, are the deer tick form. It feeds on mice as a larva and carries Lyme disease. In the southern states, and southern Illinois, the blacklegged tick larvae are thought to feed on lizards and birds; ticks in this population have not been found to carry Lyme disease. Adult blacklegged ticks are reddish, teardrop-shaped, and about 1/8 inch long. Nymphs are brownish and pinhead-sized. Both adults and nymphs attack people. Nymphs are numerous and active during June.

Author: Phil Nixon


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