Ixodes scapularis (blacklegged or “deer” tick)

This section will provide information pertaining to Ixodes scapularis, also known as the blacklegged or deer tick.  This tick is the vector of the bacteria that cause Lyme Disease and Anaplasmosis.  In recent years, the distribution of Ixodes scapularis in Wisconsin has changed dramatically, so that these ticks can now be found in many parts of eastern Wisconsin where they had not been seen before (Lee et al. 2013).  Click on the map (dropdown menu under Ixodes scapularis) to see a recent update on locations in Wisconsin where I. scapularis has been found.

Scientific Name: Ixodes scapularis. (Note: in 1993, Ixodes dammini was determined to be the same species as Ixodes scapularis (Oliver et al. 1993).  Much of the older scientific literature refers to the vector of Lyme disease as Ixodes dammini, which can be confusing.)

Description and Identification: 

Ixodes scapularis small scutum

Blacklegged (deer) ticks have three life stages during their development from eggs to adults.  Click on the life cycle button in the drop down menu for more detailed information on the life cycle.

The three stages after hatching from eggs are the larva, nymph and adult. The size and coloration of the three stages of the blacklegged tick is distinct. Adult female blacklegged ticks are dark brown to reddish- orange in color and are less than 1/8 inch long or about the size of a sesame seed. Females have a dark brown to black patch or “dorsal shield” or “scutum” on their upper body (circled with arrow in photograph) while adult males are dark brown to black in color with no reddish coloration on their body. Adults females are most commonly slightly larger than males.

Nymphs are tiny (< 2 mm in size or about the size of a poppy seed) and very difficult to see while larvae are even smaller at approximately less than 1 mm in size or about the size of a period at the end of a sentence. Adults and nymphs have four pairs of legs while larvae have 3 pairs of legs. In adults, the legs are dark brown to black in appearance hence the common name “blacklegged” tick. Coloration and size of adult females who have fed on the blood of an animal or human can vary depending on the degree of engorgement (how swollen in appearance they are) from light yellowish or grayish-blue to darker brown (Patnaude and Mather, 2000; Keirans and Litwak 1989).  

Image courtesy of: The Comprehensive Deer Tick Control Manual, EcoHealth Inc. http://www.ticktubes.com/downloads/deertickmanual.pdf

Distribution in Wisconsin: See the section titled “Ixodes scapularis Maps.”  http://labs.russell.wisc.edu/wisconsin-ticks/presence-of-ixodes-scapularis-on-hunter-killed-deer-in-wisconsin-2008-09/

Life Cycle: see the sub-section titled “Ixodes scapularis Life Cycle” for more detailed information.

Medical and Veterinary Significance: 

The blacklegged tick is a vector of three bacterial diseases, one protozoal disease and one arboviral disease in humans in Wisconsin. A disease vector is, a living intermediary (person, animal or microorganism) which may carry and transmit disease-causing pathogens (e.g viruses, bacteria, etc.) from one susceptible host to another. Here is a link to a chart “Characteristics of Tick-borne Diseases in Wisconsin” by the Wisconsin Division of Public Health with more detailed information on diseases, etiologic agents, animal reservoirs, vectors, incubation range, clinical signs and symptoms, available tests and treatments (ISDA guidelines). 

http://www.dhs.wisconsin.gov/communicable/tickborne/PDFfiles/Tickborne%20chart_04%2013%202012_final.pdf

Bacterial diseases:

  1. Lyme disease (Borrelia burgdorferi)- see the section on Lyme disease under tick-borne diseases for more detailed information on this bacterial organism.
  2. Anaplasma phagocytophilum (HGA or human granulocytic anaplasmosis) – see the section under tick-borne diseases on Anaplasmosis for more detailed information concerning this bacterial organism.
  3. Probable vector for Ehrlichia muris-like (EML)- see the section on Ehrlichia muris-like (EML) under tick-borne diseases for more detailed information concerning this bacterial organism. 

Protozoal disease:

  1. Most commonly Babesia microti– see the section on Human babesiosis under tick-borne diseases for more detailed information concerning this protozoan parasite. 

Arboviral disease:

  1. Powassan virus or deer tick virus (Flavivirus)- see the section on Powassan virus under tick-borne diseases for more detailed information concerning this virus. 
Diseases of Veterinary Significance associated with Ixodes scapularis as a vector:
 
  1. Lyme disease (Borrelia burgdorferi) in domestic animals
  2. Canine granulocytic anaplasmosis (Anaplasma phagocytophlium) in domestic dogs

Surveillance and Management: See the section titled “Integrated Tick Management” for more information on  tick-borne disease surveillance, prevention and control on humans, pets and in your yard. 

References: 

Keirans JE and Litwak TR. 1989. Pictorial Key to the Adults of Hard Ticks, Family Ixodidae (Ixodida: Ixodoidea), East of the Mississippi River. J. Med. Entomol. 26(5): 435-448. http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA233445

Lee X., Hardy K., Johnson D., and Paskewitz S.M.  2013.  Hunter killed deer surveillance to assess changes in the prevalence and distribution of Ixodes scapularis in Wisconsin.  Journal of Medical Entomology.50:632-639.
 
Oliver, J.H., M.R. Owsley, H.J. Hutcheson, A.M. James, C.S. Chen, W.S. Irby, E.M. Dotson, and D.K. MClain. 1993. Conspecificity of the ticks Ixodes scapularis and Ixodes dammini (Acari, Ixodidae). Journal of Medical Entomology. 30: 54-63.
 
Patnaude MR and Mather TR. (2000). Ixodes scapuarlis Say (Arachnida: Acari: Ixodidae). Featured Creatures from the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Published: July 2000. Revised: September 2008. Reviewed: December 2011. This document is also available on Featured Creatures website at http://entomology.ifas.ufl.edu/creatures. Please visit the EDIS website at http://edis.ifas.ufl.edu.
 

Wisconsin Division of Public Health. Characteristics of Tick-borne diseases in Wisconsin. Revised 8/29/2011. Accessed 6/20/2012. http://www.dhs.wisconsin.gov/communicable/tickborne/PDFfiles/Tickborne%20chart_04%2013%202012_final.pdf