Tick on a leaf

Nnymphal blacklegged tick, Ixodes scapularis.  Most human cases of Lyme disease in the U.S. are transmitted by bites of nymphal blacklegged ticks like this one.  The nymphs wait in or on the leaf litter for vertebrates (like people) to pass by, then they climb on and eventually bite, sometimes transmitting the bacteria to the host.