Dermacentor variabilisAmerican dog tick(Also: Common wood tick; Wood tick)

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Geographic Range

American dog ticks are found in the United States, mainly east of the Rocky Mountains (from Montana to south Texas), with some reports of the species from California and the Pacific Northwest, west of the Cascade and Sierra Nevada Mountains. They are most commonly found in the United States along the east coast. This species is also found in parts of Canada, east of Saskatchewan, as well as in northern Mexico. (Chan and Kaufman, 2008)

Habitat

American dog ticks are generally found in forests, densely wooded areas, and grasslands, which support a large number possible hosts. They are also commonly found in areas regularly visited by potential mammalian hosts, such as vegetation on the sides of roads, near trails, and in grassy areas near highway rest stops. (Chan and Kaufman, 2008; "Medical Entomology", 2008)

Physical Description

American dog ticks are typically larger than other Ixodes species, and are characterized by ornate, light-colored dorsal patterns including various shapes such as diamonds and other geometric designs on an otherwise brown to reddish-brown body. These ticks have rounded or oval bodies. Their coxae (first leg segments) are split into two parts, which have characteristic spurs. Shortened mouthparts and palps, along with their ornate dorsal patterns, distinguish American dog ticks from similar tick species. Adults and nymphs of this species have eight legs, though larvae have only six. Nymphs also lack a genital pore, which is found on the underside of adults. (Chan and Kaufman, 2008; Robert, 1969)

This species is sexually dimorphic. Females range in size from 4 mm before a meal to as high as 15 mm long and 10 mm wide following, and their dorsal patterning only covers the anterior portion of their scutum (dorsal shields). Males are smaller and their patterning extends over the entire scutum. (Chan and Kaufman, 2008; Robert, 1969; Shearer and Wall, 1997)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • male more colorful
  • Range length
    3.6 to 15 mm
    0.14 to 0.59 in
  • Average length
    4 mm
    0.16 in

Development

American dog ticks hatch from eggs as 6-legged larvae and then become 8-legged nymphs, before finally reaching adulthood. A blood meal from a different host is required before each stage. This can make development a long process, as suitable hosts are not always readily available. After hatching, larvae wait on the ground for a small mammal host such as a mouse for their first blood meal. They then drop off this first host and wait for a second host, typically a larger mammal such as a raccoon. This process is repeated until adulthood is achieved, generally taking at least 54 days but possibly years, depending on host availability, as feeding takes several days at each stage and these animals may have to wait for several months to a year for subsequent hosts. After adult females find final hosts, they feed and engorge a last time before dropping off to mate, lay eggs, and die. (Campbell and Harris, 1979; Chan and Kaufman, 2008)

Reproduction

American dog ticks mate once yearly, typically in mid-April after emerging from over-wintering in soil. Adult females partially engorge while on their host and then release pheromones to incite males to drop off their hosts. Once males have been attracted and copulation is complete, females finish feeding before dropping off to lay eggs. While females die after laying eggs and so only mate with one male, a single male may mate with multiple females. (Campbell and Harris, 1979; Louly, et al., 2008; "Medical Entomology", 2008)

American dog ticks reproduce sexually with breeding occurring in the spring (most typically in mid-April). Once a male has dropped off his host, attracted by pheromones released by a female, he approaches her. After making contact, a male mounts a female, locates her genital opening, and inserts a spermatophore into her using his mouthparts. Mating takes place on the host. Within 5-14 days, females drop from their hosts, fully engorged. Four to ten days later, once egg development is complete, females will lay up to 6500 eggs before dying. The number of eggs laid is positively correlated with temperature and amount of blood taken during the final blood meal, up to temperatures exceeding 35°C or final blood meals exceeding 665 mg. (Campbell and Harris, 1979; Chan and Kaufman, 2008; Louly, et al., 2008; "American dog tick", 2006; "Medical Entomology", 2008)

  • Breeding interval
    American dog ticks breed once yearly.
  • Breeding season
    Breeding season is in the spring, most often mid-April.
  • Range number of offspring
    4000 eggs to 6500 eggs
  • Range gestation period
    4 to 10 days
  • Range age at sexual or reproductive maturity (female)
    1 to 17 months
  • Average age at sexual or reproductive maturity (female)
    3 months
  • Range age at sexual or reproductive maturity (male)
    1 to 17 months
  • Average age at sexual or reproductive maturity (male)
    3 months

Males exhibit no parental investment following copulation. Females protect and nourish eggs in the body, before dying after egg laying is complete. Once eggs hatch, larvae search for their first small mammal host without any parental assistance. (Chan and Kaufman, 2008)

Lifespan/Longevity

Longevity of American dog ticks depends on whether hosts are found for feeding in a appropriate amount of time. Larvae can survive 11 months before their first feeding, nymphal stages can survive 6 months without feeding, and adults can survive 2 years without feeding. The life cycle of this species can be completed in as few as 54 days but may take up to two years. Adult females die soon after breeding, while males may live to breed over multiple seasons. (Carrol and Nichols, 1986; Goethert and Telford, 2009; Lyon and Restifo, 1998)

  • Range lifespan
    Status: wild
    2 to 24 months
  • Average lifespan
    Status: wild
    11 months

Behavior

This species is solitary and parasitic, moving from host to host between developmental stages. Between hosts, these ticks typically wait in a wooded or grassy area well traveled by humans and other mammals such as a nature trail. This movement to the edge of trails, known as "questing," may be initiated by odors left by potential hosts. Adult ticks looking for a new host often climb a blade of grass and cling to it, holding on with their third pair of legs. When a potential host passes, they grab on with their free legs. Once a host is located, American dog ticks insert their mouthparts (a jaw-like structure known as a hypostome, with teeth and chelicerae) and secrete a cement-like substance that anchors them to their hosts. Once feeding is complete, another substance is secreted to dissolve the "cement" and the tick falls off the host. (Dharmarajan, 2009; Mans, et al., 2002; "American dog tick", 2006)

Home Range

While feeding, the home range of these ticks is limited to their hosts and the ranges of these hosts. When not feeding, these ticks wander in search of hosts but no specific information is available regarding how widely they may travel in this search.

Communication and Perception

These ticks locate hosts by climbing a blade of grass or small plant and extending their legs in anticipation of a mammal host. There is evidence suggesting that ticks "quest" on paths followed by mammals, led by their odors. Males are attracted to females by sensing pheromones. In addition, all ticks of the suborder Ixodida have a sense organ on their first legs termed Haller's Organ. This organ contains sensilla that are sensitive to carbon dioxide and infrared radiation, likely aiding them in locating hosts. (Hwang, 2006; Mans, et al., 2002; Stewart Jr., 1998)

Food Habits

This species parasitizes almost all mammals and feeds exclusively on blood, making it an obligate sanguivore. Feeding occurs periodically for 3-11 days at a time and these animals can live for long periods of time without feeding, at all stages of development. Adult ticks, which consume greater quantities of blood, prefer larger hosts. Though this list is not all-inclusive, some specific mammals known to be hosts of this tick include dogs, humans, rabbits, raccoons, rats, mice, porcupines squirrels, and voles. (Carrol and Nichols, 1986; Koehler and Oi, 2003)

  • Animal Foods
  • blood

Predation

Although American dog ticks are very well protected by their exoskeletons, they do have some natural predators, including centipedes, newts, salamanders, skinks, spiders, toads and turkeys. ("American Dog Tick", 2013)

Ecosystem Roles

American dog ticks are obligate ectoparasites in all stages of development. Larvae and nymphs target smaller mammals such as mice and other rodents, while adults target larger mammals such as dogs, raccoons, cattle, and humans. Different abundance patterns are observed for engorged and non-engorged ticks. For example, engorged tick abundance is primarily a function of host age, with younger hosts more easily supporting engorged ticks. Non-engorged tick abundance depends more on abiotic factors such as season or collection site. A wooded or grassy area in the spring will have a high abundance of non-engorged ticks. (Chan and Kaufman, 2008; Koehler and Oi, 2003)

American dog ticks are carriers of the pathogen which causes Rocky Mountain spotted fever (Rickettsia rickettsii, a type of coccobacillus), as well as Francisella tularensis (a bacteria), which causes tularemia, also known as "rabbit fever." They can also carry and transmit Cytauxzoon felis, a protozoan, from wild cats to domestic cats. (Blouin, et al., 1984; Chan and Kaufman, 2008)

Species Used as Host
  • Mammals
Commensal/Parasitic Species
  • Cytauxzoon felis (Class Aconoidasida, Phylum Apicomplexa)
  • Francisella tularensis (Class Gamma Proteobacteria, Phylum Proteobacteria)
  • Rickettsia rickettsii (Class Alphaproteobacteria, Phylum Proteobacteria)

Economic Importance for Humans: Positive

This species provides no known economic benefits to humans.

Economic Importance for Humans: Negative

American dog ticks are vectors for diseases such as Rocky Mountain spotted fever and tularemia. Dogs and humans may also be affected by tick paralysis if they become hosts. Rocky Mountain spotted fever is a disease that affects small blood vessels, causing an initial rash followed by other symptoms that include fever, vomiting, and diarrhea. There is an approximate 20% mortality rate if untreated, but ticks must remain attached for at least 6 hours in order to transmit the disease. Tularemia has a mortality rate of approximately 7% if untreated; symptoms include chills, fever, and swollen lymph nodes. Tick paralysis can occur in dogs and humans, and is caused by a neurotoxic protein produced in a tick's salivary glands that may enter the bloodstream during feeding. The mortality rate is about 10%, but individuals are likely to recover if the tick is removed. (Chan and Kaufman, 2008; Goethert and Telford, 2009; Lyon and Restifo, 1998)

Conservation Status

This species has no special conservation status. (IUCN, 2012)

Contributors

Matt Paterini (author), University of Michigan-Ann Arbor, Jeremy Wright (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal

chemical

uses smells or other chemicals to communicate

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

infrared/heat

(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

internal fertilization

fertilization takes place within the female's body

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynous

having more than one female as a mate at one time

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

sanguivore

an animal that mainly eats blood

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

semelparous

offspring are all produced in a single group (litter, clutch, etc.), after which the parent usually dies. Semelparous organisms often only live through a single season/year (or other periodic change in conditions) but may live for many seasons. In both cases reproduction occurs as a single investment of energy in offspring, with no future chance for investment in reproduction.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

taiga

Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

vibrations

movements of a hard surface that are produced by animals as signals to others

References

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Michigan State University. 2006. "American dog tick" (On-line). Insects and Arthropods. Accessed January 17, 2012 at http://www.pestid.msu.edu/InsectsArthropods/AmericandogtickDermacentorvariabilis/tabid/277/Default.aspx.

Purdue University. 2008. "Medical Entomology" (On-line). Ticks. Accessed January 17, 2012 at http://extension.entm.purdue.edu/publichealth/insects/tick.html#top.

Blouin, E., A. Kocan, B. Glenn, K. Kocan, J. Hair. 1984. Transmission of Cytauxzoon fells Kier, 1979 from Bobcats, Felis rufus (Schreber), to Domestic Cats by Dermacentor variabilis (Say). Journal of Wildlife Diseases, 20/3: 241-242. Accessed January 24, 2013 at http://www.jwildlifedis.org/content/20/3/241.full.pdf.

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Goethert, H., S. Telford. 2009. Nonrandom Distribution of Vector Ticks (Dermacentor variabilis) Infected by Francisella tularensis. PLoS Pathogens, February 2009: 0-10. Accessed January 17, 2012 at http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1000319.

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