Three stages of the black-legged tick,Ixodes scapularis also known as the deer tick. Within the fish hook (the largest specimen) is the female I. scapularis (upper left), below her is a male and directly in front of the female are two nymphal deer ticks. Nymphs are thought to be responsible for most human Lyme cases due to their small size and because they are active in April, May, and June, In the Northeastern US, the male and female are active in the Fall. The largest tick in view (outside the hook) is a female American dog tick, Dermacentor variablis, which is shown for comparison. A ruler (in 16ths of an inch increments) is on the top. The fish hook is a #8 for those familiar with sizes. Ixodes scapularis can transmit Borrelia burgdorferi (the Lyme spirochete), Babesia microti (the causative agent of babesiosis) and the causative agent of human granulocytic ehrlichiosis, HGE. The American dog tick does not play a role in the ecology of Lyme disease. Photo by Jim Occi.