TICK INFORMATION SHEET The Black-Legged or Shoulder Tick Ixodes scapularis (Say, 1821)
DISTRIBUTION AND SEASONAL ACTIVITY Ixodes scapularis is common in the southeastern United States, Texas, eastern Oklahoma, along the Atlantic coast as far north as Massachusetts, and it also has been reported in Wisconsin and Minnesota. The adult ticks are more abundant on hosts from late autumn to spring, whereas larvae and nymphs are more numerous in the spring and summer.
HOSTS AND LOCATION ON HOST Adult ticks prefer to feed on large mammals such as cattle, horses, deer, dogs, sheep, hogs, and humans (Fig. 1). Larvae and nymphs primarily feed on birds, small mammals, and, occasionally, lizards. The adults usually attach to the head and neck of their hosts (Fig. 2).
LIFE CYCLE SUMMARY Ixodes scapularis is a three-host tick. • • • • • • • • • • •
The female lays up to 3000 eggs. The preoviposition period is 10 to 19 days. The incubation period is 48 to 135 days. Larvae engorge in 3 to 9 days. Larvae molt in 22 to 49 days. Nymphs engorge in 3 to 8 days. Nymphs molt in 25 to 56 days. Females engorge in 8 to 9 days. Unfed larvae survive more than 75 days. Unfed nymphs survive more than 60 days. Unfed adults survive for an undetermined time .
Under normal conditions, the black-legged tick apparently completes one life cycle each year. Veterinary Clinics of North America: Small Animal Practice- Vol. 21, No. 1, January 1991
TICK INFORMATION SHEET
Figure 1. Dorsal and ventral body views of the adult male Ixodes scapularis tick.
Ixodes scapularis has been incriminated as transmitting Babesia microti, a protozoal pathogen of field mice and deer mice, to humans on Nantucket Island, Massachusetts. However, recent studies indicate that Ixodes dammini, a newly described species, is the primary vector of Babesia microti. The black-legged tick has been found naturally infected with Francisella tularensis, the causative agent of tularemia, and the tick may be responsible for the transmission of anaplasmosis in some areas. Ixodes scapularis nymphs are competent vectors of Borrelia burgdorferi, which
Figure 2. Dorsal and ventral body views of the adult female Ixodes scapularis tick.
THE BLACK-LEGGED OR SHOULDER TICK
suggests a possible role for this tick in the ecology of Lyme borreliosis in the southern United States.
SELECTED REFERENCES 1. Harris RL: Biology of the black-legged tick. Journal of the Kansas Entomology Society 32:61-68, 1959 2. Hooker WA, Bishopp FC, Wood HP: The life history and bionomics of some North American ticks. U S Department of Agriculture Bureau Entomology Bulletin 106:1-239, 1912 3. Piesman J, Sinsky RJ: Ability of Ixodes scapularis, Dennacentor variabilis, and Amblyomma americanum (Acari: Ixodidae) to acquire, maintain, and transmit Lyme disease spirochetes (Borrelia burgdorferi). J Med Entomol 25:336, 1989 4. Schmid GP, Kornblatt AN, Connors CA: Clinically mild tularemia associated with tickborne Francisella tularensis. J Infect Dis 148:63-67, 1983 5. Strickland RK, Gerrish RR, Hourrigan JL, et a!: Ticks of Veterinary Importance, no. 485. Washington D.C., Animal and Plant Health Inspection Service, U.S. Department of Agriculture, 1976, pp 50-51