Figure 4

Ixodes scapularis is a small, reddish brown tick. The tick has three active stages: immature larval, nymphal, and mature adults. Larvae are extremely minute and possess only six legs; all other stages have eight legs. Larvae are not infected with the Borrelia bacteria. Nymphs of Ixodes scapularis are about the size of a pinhead, adults are larger, about the size of a sesame seed. Females have a reddish brown dorsal "shield" located behind the mouth parts and, when engorged, have a reddish brown body. Males are smaller than females and completely brown (Figure 4 ).

Figure 5 depicts the 2-year life cycle of ticks in the eastern United States. The tick life cycle is 2-3 years.

Figure 5

Exposure to Lyme disease is greatest in spring and summer months when nymphal ticks are most active, and much less in late fall and very early spring when adult ticks are active. Most cases of Lyme disease are caused by the nymphal tick.