Tick Identification

This page will provide more detailed information concerning tick identification. We will identify species if the specimen or a digital image is provided (contact smpaskew@wisc.edu for identifications).

IXO SCA F & M and DER VAR F & MFigure 1.  Adult deer ticks on the top (female on left, male on right) and adult wood ticks on the bottom (female on left, male on right).

IXO SCA 4 STAGESFigure 2.  All 3 life stages of Ixodes scapularis.  Upper Left, Nymph.  Upper right, larva.  Lower left, Adult female.  Lower right, adult male.

cropped-all-3-with-nymph-1000pixel.jpg

Figure 3.  From the left:  Wood (dog) tick, lone star tick, deer tick (all adult females) and a nymph of the deer tick (far right).

Note to Readers: 

In 1993 Ixodes dammini was shown to be the same species as Ixodes scapularis and and taxonomists decided to retain the older name, I. scapularis. Those who read peer-reviewed papers or utilize keys with references to I. dammini, should make note of this (Oliver et al. 1993).

1. Blacklegged or Deer Tick 

Common Name: blacklegged or deer tick

Scientific Name: Ixodes scapularis Say (Arachnida: Acari: Ixodidae)

Description and Identification: 

Adult female deer ticks are dark brown to reddish in appearance and are less than 1/8 inch (3.12mm) long. Adults exhibit sexual dimorphism with females being slightly larger than males. Nymphs are tiny (< 2 mm in size) 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 that are dark in coloration while larvae have 3 pairs of legs. Adult blacklegged ticks have no distinguishing markings or ornamentation on the dorsal area, are eyeless and lack festoons. The scutum, or dorsal shield just behind the mouth parts in hard-bodied ticks, covers the entire dorsal area in males while only covers the anterior portion of the dorsum in females. Unfed females also typically have orange to red coloration behind the scutum as seen in the photo to the right. Coloration of blood fed females can vary depending on the degree of engorgement from light yellowish or gray to darker brown. The scutum is also broadly rounded in comparison to other less common Ixodes species found in Wisconsin. Ixodes species also have a distinctive anal groove on the ventral side which extends anteriorly around the anus and helps distinguish Ixodes species from other species of ticks in Wisconsin (Patnaude and Mather, 2000; Keirans and Litwak 1989). 

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 several bacterial diseases, one protozoan disease and one arboviral disease in humans in Wisconsin.

Bacterial diseases:

  1. Lyme disease (Borrelia burgdorferi, Borrelia mayonii)- see the section on Lyme disease under tick-borne diseases for more detailed information on these pathogens.
  2. Anaplasma phagocytophilum (HGA or human granulocytic anaplasmosis) – see the section under tick-borne diseases on Anaplasmosis for more detailed information concerning this pathogen.
  3. Ehrlichia muris eauclairensis (EML)- see the section on Ehrlichia muris under tick-borne diseases for more detailed information concerning this pathogen. 
  4. Borrelia miyamotoi-see the section on tick-borne relapsing fever for more detailed information on this pathogen.

Protozoal disease:

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

Arboviral disease:

  1. Powassan virus (Flavivirus)- see the section on Powassan virus under tick-borne diseases for more detailed information concerning this and the related deer tick virus pathogens. 

2. Wood tick or American dog tick

Common Name: wood tick or American dog tick

Scientific Name: Dermacentor variabilis (Say) (Arachnida: Ixodida: Ixodidae)

Description and Identification: American dog tick adult females generally are about 1/4 inch (6.35mm) in length when unfed and are reddish brown in color. Adult females have a scutum or dorsal shield that covers only the anterior portion of the dorsum that has creamy-white to silvery-gray markings or striations. Females will vary in size depending on whether they have taken a blood meal. Blood fed or engorged females can enlarge to up to 15 mm long and 10 mm wide (Chan & Kaufman 2008). Adult male ticks are slightly smaller in size (3.6 mm in length) than females, and are also reddish brown with similar cream to silvery-gray colored vertical markings or striations on the dorsal scutal surface. The scutum or dorsal shield covers the entire dorsum on the males. The anal groove never extends anteriorly around the anus as does in Ixodes species. Adults have eleven festoons along the posterior edge of the abdomen and also have “eyes” along the dorsal anterior marginal edges bilaterally. The basis capituli is rectangular in shape with the palpi about as long as the basis capituli (Keirans and Litwak 1989). Adult and nymphal stage Dermacentor variabilis have eight legs while larval stages have six legs (Chan & Kaufman 2008).

Nymphs are approximately 0.9 mm long and pale, yellowish brown before taking a blood meal. Nymphs become light gray in color when engorged. Larvae are smaller than nymphs (~0.6 mm in length), also yellowish brown in color before a blood  mealand then turn grey in color when engorged (Smith and Whitman 1992). Both immature larval and nymphal stages have red markings near their eyes and lack any coloration or markings on the scutum. Nymphs can also be distinguished from adults because they lack a genital opening (Chan & Kaufman 2008).

Distribution in United States and Wisconsin: The American dog tick is widely distributed east of the Rocky Mountains and is also found in Canada east of Saskatchewan and in limited areas along the Pacific coast (west of the Cascade and Sierra Nevada Mountain ranges) (Chan & Kaufman 2008). In Wisconsin the American dog tick can be found distributed throughout the entire state particularly associated with woodland, shrubby or tall grass habitats.  

Seasonality: In Wisconsin, all life stages of Dermacentor variabilis are most active throughout the warmer months (May-August). Peak abundance and activity of D. variabilis varies within North America with adults being most abundant in June and July in temperate zones and July and August in sub-tropical zones (Cilek & Olson 2000).

Hosts: Dermacentor variabilis larvae typically feed on small mammals, and nymphs feed on small-to medium-sized mammals. Adults will occasionally feed on humans but are more commonly found on domestic dogs and other medium-sized mammals (Merten and Durden 2000; Campbell & MacKay 1979).

Medical and Veterinary Significance: 

The American dog tick is capable of transmitting the organism that causes Rocky Mountain spotted fever, Rickettsia rickettsii, (Azad & Beard, 1998) but this disease is very rare in Wisconsin (WI-DHS, 2012). Cases that are reported in Wisconsin residents are usually associated with travel to other states where Rocky Mountain spotted fever more commonly occurs.

Dermacentor variabilis, is also one of the main implicated vectors for the disease tularemia or rabbit fever caused by the bacterium Francisella tularensis. This disease is also rarely reported in Wisconsin. There were a total of three human cases of tularemia in Wisconsin from 2001-2010 reported to the Centers for Disease Control and Prevention (CDC, 2011).

Although the bacteria which causes Lyme disease, Borrelia burgdorferi, has been isolated from Dermacentor variabilis, it has not been proven to be a competent vector and Dermacentor variabilis does not transmit the Lyme disease bacterium (Piesman and Happ 1997; Mukolwe et al. 1992; Mather & Mather 1990; Soares et al. 2006). 

3. The Lone Star tick (Amblyomma americanum)

Important note: This tick is rarely found in Wisconsin and it is currently unknown whether there are established populations within the state. There are occasional reports every year, especially in the southern half of Wisconsin.

Common Name: Lone star tick

Scientific Name: Amblyomma americanum Linnaeus(Arachnida: Acari: Ixodida: Ixodidae)

Description and Identification: Amblyomma tick species are more rounded in shape versus Dermacentor and Ixodes species which have more of a tear-drop shape that tapers at the mouthparts. Adult females are reddish-brown in color and can be easily distinguished from other ticks by the presence of a distinctive white spot or “star” on the dorsum. The spot  may vary in color from whitish to cream or gold to bronze and is often iridescent in appearance upon closer inspection. The spot appears closer to the basis capitulum when the female is engorged. Females are generally larger than males and average 4-6 mm unfed and up to 16 mm or larger when fully fed. The basis capituli is rectangular in shape with the palpi much larger than the basis capituli and palpal segment two much longer than broad (Keirans & Litwak, 1989). Adult males average 2-5 mm in size with a scutum that is dark brown in coloration. A reticulated pattern or whitish ornamentations are usually apparent along the outer margins and festoons on the posterior dorsal body surface of males. Both males and females have eyes along the dorsal anterior margins of the back and festoons along the posterior dorsal margins. 

Distribution in the United States and Wisconsin: 

A. americanum is found west-central Texas, north to Iowa and eastward. It is most widely distributed in the eastern and southeastern United States (Childs & Paddock 2003; Means & White 1997). Over-wintering populations are established as far north as coastal Maine (Keirans & Lacombe 1998).

This tick is rarely found in Wisconsin and it is currently unknown whether there are established populations within the state. There are occasional reports every year, especially in the southern half of Wisconsin.

Hosts: A. americanum species are three-host ixodid ticks that are aggressive, generalist feeders at all three life stages. A. americanum larvae and nymphs tend to feed on small mammals, ground-feeding birds as well as white-tailed deer and domestic cattle.          A. americanum adults frequently parasitize white-tailed deer, domestic cattle, horses and sheep, feral swine and domestic dogs and humans (Allan et al. 2010; Childs & Paddock 2003; Kollars et al. 2000). 

Life Cycle:  Lone star ticks are most often found in woodland habitats, especially young, second-growth forests with dense understory (Childs & Paddock, 2003). The abundance of A. americanum is influenced by the availability of suitable hosts for all three life stages and the availability of appropriate habitat for both the tick as well as it’s potential hosts (ibid).

References:

Allan BF, Goessling LS, Storch GA, Thach RE. (2010). Blood meal analysis to identify reservoir hosts for Amblyomma americanum ticks. Emerg Infect Dis; 16(3): 433-440. http://wwwnc.cdc.gov/eid/article/16/3/09-0911.htm

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