Ticks have four life stages: egg, six-legged larva, eight-legged nymph and eight legged adult. Ticks feed once during each stage. The eggs are fertilized in the fall and deposited in leaf litter the following spring. They emerge as larva in late summer and seek their first blood meal, usually a small rodent or bird that may be infected with disease. They return to leaf litter and remain dormant until the next spring when they emerge as nymphs and seek a host which may be mice, rodents, deer, birds, and humans who they then infect with disease. After feeding for several days, they drop off the host onto the ground. After molting into the larger adult tick, they emerge in the fall and feed on a host patricularly deer and again can infect humans. Then the female lays her eggs.
Different ticks are active at different times. The blacklegged tick and the lone star tick are most active from May through August. The dog tick is most active from April through May.
The chart above is the life cycle of the blacklegged tick.