Top Row: Ixodes scapularis (dammini), the deer tick which transmits Lyme disease.  Left to right: nymph, adult male, adult female, engorged adult female.  Nymphs are most common May through July. Adults appear in the fall and early spring.

Bottom Row: Dermacentor variabilis, the American dog tick, which is not thought to transmit Lyme disease.  Left to right: adult male, adult female, engorged adult female. Adults are most common in May, June, and July.  Note that the adult dog ticks are somewhat larger than adult deer ticks, and have characteristic white markings on the dorsal (top) side.