Ixodes scapularis Say
Adult ticks are eyeless and have no distinguishing coloration or markings. Males are quite small in size and mostly black in appearance. Female ticks are generally larger than males, and unfed body coloration is described as brown-orange below overlayed with a dark brownish-black scutum. Blood-engorged females are smaller than other ixodid species, teardrop shaped and charcoal gray in color.
The blacklegged tick is found from the New England states westward to the Great Lakes and south throughout the Atlantic and Gulf Coast states including Texas and Oklahoma. Outside the US, this tick has also been reported from parts of northern Mexico.
Hosts: Larvae and nymphs feed primarily on small mammals especially rodents, birds, and lizards. Adult ticks attach to a wide number of large mammals including deer, cattle, horses, feral swine, and humans. Blacklegged ticks exhibit little attachment site preference and are commonly found attached to the axillaries, dewlap, genitals, escutcheon, and tail-head regions in livestock; some of these infestations by adults are severe especially in winter and early spring.
Biology: A three-host tick, the blacklegged tick completes its life cycle over the course of two years. In southern parts of the US, immature ticks become active in spring and summer, while adult activity spans autumn to spring.
Associated Disease Pathogens:
The blacklegged tick is the primary vector of Lyme borreliosis (Lyme disease) across the northern part of its range. This tick also transmits the protozoa Babesia microti to humans in the northeastern and north-central US, and is known to be one of the tick vectors involved in transmitting Anaplasma phagocytophilum, the bacterial disease agent responsible for causing human anaplasmosis, formerly known as human granulocytic ehrlichiosis (HGE), and Anaplasma marginale (bovine anaplasmosis) to cattle.
Similar Species: There are numerous other species of the genus Ixodes that at a glance are similar in appearance and distribution to the blacklegged tick within the US. However, most of these species are not commonly encountered and most often require thorough microscopic examination to verify identity to species.