Ixodes scapularis is commonly known as the deer tick or blacklegged tick (although some people reserve the latter term for Ixodes pacificus, which is found on the West Coast of the USA), and in some parts of the USA as the bear tick. It is a hard-bodied tick (family Ixodidae) of the eastern and northern Midwestern United States. It is a vector for several diseases of animals, including humans (Lyme disease, babesiosis, anaplasmosis, etc.) and is known as the deer tick owing to its habit of parasitizing the white-tailed deer. It is also known to parasitize mice, lizards, migratory birds, etc. especially while the tick is in the larva or nymph stage.
The image shown at the upper right—and in fact, most images of Ixodes scapularis that are commonly available—show an adult that is unengorged, that is, an adult that has not had a blood meal. This is natural, since the ticks are generally removed immediately upon discovery to minimize the chance of disease. However, the abdomen that holds blood is so much larger when engorged and looks so different from the rest of the tick that it would be easy to assume that an engorged specimen of Ixodes scapularis is an entirely different tick (see photo at left).
When the deer tick has consumed a blood meal its abdomen will be a light grayish-blue color, whereas the tick itself is chiefly black. In identifying an engorged tick it is helpful to concentrate on the legs and upper part of the body.
I. scapularis has a two-year life cycle, during which time it passes through three stages: larva, nymph, and adult. The tick must take a blood meal at each stage before maturing to the next. Deer tick females latch onto a host and drink its blood for four to five days. Deer are the preferred host of the deer tick, but it is also known to feed on small rodents. After she is engorged, the tick drops off and overwinters in the leaf litter of the forest floor. The following spring, the female lays several hundred to a few thousand eggs in clusters. Transtadial (between tick stages) passage of Borrelia burgdorferi is common. Vertical passage (from mother to egg) of Borrelia is uncommon.
Ticks are very hardy creatures and I. scapularis is no exception. Expect them to be active even after a moderate to severe frost, as daytime temperatures can warm them enough to keep them actively searching for a host. In the spring, they can be one of the first invertebrates to become active. Deer ticks can be quite numerous and seemingly gregarious in areas where they are found.
As disease vector
Ixodes ticks also can transmit Ehrlichia, a gram-negative obligate intracellular bacteria that is responsible for Ehrlichiosis.
Ticks that transmit Borrelia burgdorferi to humans can also carry and transmit several other parasites, such as Theileria microti and Anaplasma phagocytophilum, which cause the diseases babesiosis and human granulocytic anaplasmosis, respectively. Among early Lyme disease patients, depending on their location, 2%–12% will also have HGA and 2%–40% will have babesiosis.
Co-infections complicate Lyme symptoms, especially diagnosis and treatment. It is possible for a tick to carry and transmit one of the co-infections and not Borrelia, making diagnosis difficult and often elusive. The Centers for Disease Control's emerging infectious diseases department did a study in rural New Jersey of 100 ticks, and found 55% of the ticks were infected with at least one of the pathogens.
Although they are the preferred mammalian hosts, deer cannot transmit borrelia spirochetes to ticks. Ticks acquire Lyme disease microbes by feeding on infected white-tailed mice and other small rodents.
Guinea Fowl, chickens, and fire ants are known predators to ticks. None have been proven to be effective in populations on a large scale, but there is anecdotal evidence to support localized control of tick populations.
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- Varde S, Beckley J, Schwartz I (1998). "Prevalence of tick-borne pathogens in Ixodes scapularis in a rural New Jersey County". Emerging Infectious Diseases 4 (1): 97–99. doi:10.3201/eid0401.980113. PMC 2627663. PMID 9452402.
- Information on Tick-Related Health Threats and Deer Tick Fact Sheet from the National Pest Management Association
- blacklegged tick, Ixodes scapularis on the UF / IFAS Featured Creatures Web site
- Ixodes scapularis, black-legged tick, deer tick overview as a vector for Lyme disease, developmental stages at MetaPathogen
- Ixodes scapularis genome sequence at VectorBase
Please read to protect yourself from Deer ticks that may cause Lyme disease. Public Health Fact Sheet: Lyme Disease