Figure 1. Diagram of Life Cycle of the Blacklegged Tick (I. scapularis) .

Shows the four life stages, egg, larva, nymph, adult, and the times during the life cycle that both abiotic (GDD, PPT), and biotic (acorns and various hosts) factors might exert influence. Year t is the year during which nymphal ticks seek hosts, including humans, and represents the focal year with respect to risk of exposure.