Lyme Disease Tick

In the United States, two closely related tick species - Ixodes scapularis and Ixodes pacificus - have been identified as harboring and transmitting the disease - causing Borrelia bacterium to people and animals. I. scapularis, the black-legged tick, is found in the eastern U.S., and I. pacificus, the western black-legged tick, is on the West Coast. Keep in mind that Ixodes species are smaller than the common American "dog tick," which does not transmit the Lyme Disease-causing spirochetes.

Illustration of ticks
Actual Size
(left to right) of larva, nymph, adult male, adult female, and engorged adult female Ixodes ("Deer Ticks") and adult male and female Dermacentor ("Dog Ticks")

Photo of four ticks
Four Forms
of the Ixodes tick - larva, nymph,
adult male, and adult female are shown.
Photo: M. Fergione.

Photo of two ticks
Adult Female Ticks
Ixodes ("Deer Tick") - left,
and Dermacentor ("Dog Tick")
Photo: M. Fergione.