Dermacentor andersoniRocky Mountain wood tick

Geographic Range

Rocky Mountain wood ticks are mostly found in arid areas of the Rocky Mountain region (Nebraska, South Dakota, Arizona, New Mexico, etc.) including California, where it is only found east of the Sierra Nevada mountains. They can also be found in various parts of southwestern Canada, including British Columbia, Alberta, and Saskatchewan. ("The Genera Dermacentor and Otocentor (Ixodidae) in the United States, with Studies in Variation", 1938; "Dermacentor andersoni", 2012; "Geographic distribution of arthropod-borne diseases and their principal vectors", 1989; Yee, 2006)


Adult Rocky Mountain wood ticks are generally found in elevations of 2100 m to 2500 m. Temperature may be important in determining its geographic range as these ticks show a preference for lower elevations (1600 m to 2200 m) at higher temperatures and higher elevations (2350 m to 2500 m) at lower temperatures. This species also prefers brushy areas of foothills and mountains as these areas host small mammals and other host organisms. (Eisen, 2007)

  • Range elevation
    1600 to 2500 m
    5249.34 to 8202.10 ft
  • Average elevation
    2300 m
    7545.93 ft

Physical Description

Rocky Mountain wood ticks are generally brown or reddish brown in color. Females have a distinct dorsal silver-gray ornamentation (known as the 'shield') which turns more gray when the tick feeds, while males are spotted gray and white with no distinctive shield marking. Both sexes are mottled in this fashion over portions of their legs and mouthparts (basis capitulum). Their bodies are flat and pear-shaped, ranging anywhere from 2 to 5.3 mm in length, though fully engorged females may reach up to 16.5 mm. This species is sexually dimorphic; in addition to the marking differences mentioned above, females range from 2.8-5.4 mm long (13.8 to 16.5 mm when fully engorged) while males range from 2.1 to 6.1 mm. Body mass ranges from .005 to .7 g. This species is also polymorphic, with a lot of physical variation between individuals. Features that distinguish this species from other ticks include the number and size of goblets (used in aeration/respiration) on its spiracular plates, with this species having 100-200 goblets on average. Females produce a neurotoxin in their oral secretions that prevents the release of acetylcholine, a neurotransmitter necessary for muscle contractions, often causing paralysis even in larger mammals such as dogs and humans. (Furman and Loomis, 1984; Lysyk, 2010; Richard and Farrow, 1991; "Dermacentor andersoni", 2012; "Dermacentor andersoni", 2009; Yee, 2006)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • female more colorful
  • Range mass
    .005 to .7 g
    0.00 to 0.02 oz
  • Range length
    2.1 to 16.5 mm
    0.08 to 0.65 in


The life cycle of Rocky Mountain wood ticks is characterized by three stages: larval, nymph, and adult. Progression through these stages can take 1-3 years. Individuals usually take a single blood meal from a mammalian host before progressing to the next stage and the size of hosts increases along with the size of ticks. Host availability may cause variation in timing and duration of mating, ovipositing, egg hatching, molting, and overall growth. The life cycle begins when eggs are deposited on vegetation by engorged females during early summer. Larvae remain inactive until outside stimulation (i.e. temperature, light, humidity) cause them to seek their first mammalian host (usually some sort of rodent). Following a feeding period ranging from 2 to 6 days, larvae drop off and form nymphs via a molting process. Nymphs display behavior similar to larvae, remaining dormant until stimulated by the presence of a potential host. Following attachment to the second host, males and females demonstrate different behaviors. In preparation for mating, females feed on the host for long periods (5 to 15 days) while males feed for shorter periods and spend more time copulating with partially fed females. After females are fully engorged, they drop off their hosts and seek a place to deposit their eggs. Males and females die shortly after completing reproduction. ("Rocky Mountain Wood Ticks", 2012; "Dermacentor andersoni", 2012; "Dermacentor andersoni", 2009; Yee, 2006)


This species has a polygynous mating system, where males disrupt their adult stage feeding period to begin copulation with partially fed females. Mating occurs in the third and final life stage. Females release 2,6-dichlorophenol during feeding, allowing males to identify them as potential mates. Once females have consumed enough blood, they release cholesteryl oleate, signaling that they are ready to mate. These two chemicals are common to hard ticks (Family Ixodidae). (Sonenshine, et al., 1982; Sonenshine, 2004; Sonenshine, et al., 1988; Sonenshine, et al., 1989; Sonenshine, et al., 1986)

These ticks are reproductively active from May through June, with some variation possible due to host availability, temperature, humidity, and other environmental factors. This species is known to have a single breeding season in late spring with adults dying soon after copulation. When grown in ideal conditions in a lab, maturation and reproduction have come to completion in approximately 68 days; in the wild, it takes both males and females approximately a year to reach sexual maturity. Females may lay anywhere between 2500 and 7400 eggs, depending on their nutrition levels, over the course of 10 to 33 days. ("Scorpions Spiders Mites and Ticks: Arachnida - Rocky Mountain Wood Tick (Dermacentor andersoni): Species Account", 2012; "Dermacentor andersoni", 2012; "Dermacentor andersoni", 2009; Yee, 2006)

  • Breeding interval
    Rocky Mountain wood ticks breed once yearly between the months of May and June.
  • Breeding season
    This species breeds from late spring through early summer.
  • Range number of offspring
    2500 to 7400
  • Average number of offspring
  • Range age at sexual or reproductive maturity (female)
    1 to 3 years
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Range age at sexual or reproductive maturity (male)
    1 to 3 years
  • Average age at sexual or reproductive maturity (male)
    1 years

Neither males nor females invest in their young beyond females' investments in their eggs. ("Dermacentor andersoni", 2012; Yee, 2006)


The primary determinant of lifespan for Rocky Mountain wood ticks is the availability of the blood meal required to reach each life stage. Larvae can survive up to a month without a blood meal; however, with a single meal they are able to molt into nymphs, which can then survive upwards of a year before needing another blood meal. With yet another single feeding, nymphs are able to morph into adults, which can survive up to 2 years without feeding. Members of this species will typically live 1-3 years total in the wild. The longest recorded lifespan in captivity for this species is 4 years. Variation in life span may be influenced by external factors such as humidity, temperature, and host availability, which may cause these ticks to be dormant for longer periods of time between life stages. ("Life Span", 2012; "Scorpions Spiders Mites and Ticks: Arachnida - Rocky Mountain Wood Tick (Dermacentor andersoni): Species Account", 2012; "Dermacentor andersoni", 2012; "Dermacentor andersoni", 2009; Yee, 2006)

  • Range lifespan
    Status: wild
    1 to 4 years
  • Average lifespan
    Status: wild
    3 years
  • Range lifespan
    Status: captivity
    3 to 4 years
  • Typical lifespan
    Status: wild
    1 to 4 years
  • Average lifespan
    Status: wild
    2 years
  • Typical lifespan
    Status: captivity
    2 to 4 years


Rocky Mountain wood ticks are parasitic ticks with a 3-stage life cycle, each of which is associated with a different host. They are mostly sessile for the first two life stages, only moving when seeking a host. Adults are highly mobile as they scramble to find mates, which they encounter on what is known as the definitive host. Once attached to a host, the ticks remain there, dropping off only once they have consumed a sufficient amount of blood to transition into the next life stage or complete breeding. To engage in feeding, these animals must first be stimulated by changes in the external environment, sensed via a front-leg structure known as Haller's organ, which senses changes in stimuli such as humidity, temperature and carbon dioxide levels (produced by potential hosts). Once they sense a prospective host, these ticks attach using cushioned pads on their feet known as pulvilli, which secrete an adhesive substance. Rocky Mountain wood ticks use their palpus to feed, which they inject into an exposed area of their hosts' dermis, proceeding to draw blood. This species does not have social hierarchies and does not display any complexity in its social system. ("Dermacentor andersoni", 2012; "Dermacentor andersoni", 2009)

Home Range

In the adult stage, home range is typically limited to the host. ("Rocky Mountain Spotted Fever (RMSF)", 2011; "Dermacentor andersoni", 2012; "Geographic distribution of arthropod-borne diseases and their principal vectors", 1989)

Communication and Perception

The primary sense organ, Haller's organ, is common to both hard and soft-bodied ticks. There are slight differences in the organ from species to species, but it is generally located on the dorsal surface of the tarsi (leg segments closest to head of the tick). Haller's organ plays a key role in finding hosts as setae on the organ respond to changes in humidity, carbon dioxide levels, and olfactory stimuli. This organ is also important in pheromone detection during mating season. In addition to Haller's organ, these ticks also have many setae on their scutum and legs. Longer, curved setae on the ventral surface aid in chemosensory and tactile responses while shorter, straighter setae act as temperature receptors. Rocky mountain wood ticks have a pair of simple eyes that are more or less parallel to the second pair of legs, just past the head. (Sonenshine, et al., 1986; "Dermacentor andersoni", 2012; "Dermacentor andersoni", 2009; Woolley, 1972)

Food Habits

Rocky Mountain wood ticks are sanguivores (most typically of mammals) who take a single blood meal from their hosts at each of their three life stages. ("The Genera Dermacentor and Otocentor (Ixodidae) in the United States, with Studies in Variation", 1938; "Dermacentor andersoni", 2012; "Dermacentor andersoni", 2009; Woolley, 1972; "Geographic distribution of arthropod-borne diseases and their principal vectors", 1989)

  • Animal Foods
  • blood


The main defensive mechanism of this species against typical tick predators such as ants, beetles and spiders is the secretion of allomones, a special set of substances which influence predator behavior in favor of the tick (i.e. discouraging pursuit if following scent). The main component (nearly 25% of mass) of these allomones is squalene, a biochemical precursor to steroids. These allomones are secreted by large wax glands on the underside of the tick's legs. Once depleted, these wax reservoirs take up to 10 days to replenish, a period during which the tick has little defense against predation. (Sonenshine, et al., 1993; Sonenshine, 2004; Yoder, et al., 1993)

  • Known Predators
    • Ants
    • Beetles
    • Spiders

Ecosystem Roles

As an obligate parasite, Rocky Mountain wood ticks rely on mammalian blood to provide the nutrition necessary to transition through their various life stages. During their lifespan, these ticks also play an important role as host to various types of bacteria, two of which are Arsenophonus and Wolbachia. Of the two, Wolbachia has a special relationship with many other arthropods and is noted for its ability to alter the reproductive abilities of its hosts by infecting the testes and ovaries. Such infections may result in "male killing" where males are killed during larval development, "feminization" where infected males develop as females or (infertile) pseudo-females, or sometimes leading to the development of parthenogenesis, where females reproduce without coming into contact with a male. The most important effect of hosting Wolbachia, however, is "cytoplasmic incompatibility", where Wolbachia-infected males are unable to reproduce with uninfected females. This has been suspected as a potential cause of speciation. Rocky Mountain wood ticks are also known hosts of Rickettsia bacteria, specifically R. prowazeki and R. rickettsii; infection with these bacteria is most often deadly for Rocky Mountain wood ticks and can be passed to host species as well. Rickettsia rickettsii, for example, is known as a cause of Rocky Mountain Spotted fever, the most common fatal tick-borne disease in humans found in the United States. (Burgdorfer, et al., 1973; Dergousoff and Chilton, 2010; Niebyiski, et al., 1999; Samish and Rehacek, 1999)

Species Used as Host
  • Class Mammalia
Mutualist Species
  • Arsenophonus
  • Wolbachia
  • Rickettsia prowazeki
  • Rickettsia rickettsii

Economic Importance for Humans: Positive

Rocky Mountain wood ticks provide no known economic benefit to humans.

Economic Importance for Humans: Negative

One of the important ecosystem roles carried out by Rocky Mountain wood ticks is that they serve as a vector for the tick-borne disease known as Rocky Mountain Spotted Fever (RMSF). Upon biting a host, the tick passes on the disease-causing gram-negative coccobacillus, Rickettsia rickettsii, which is an obligate intracellular parasite and is the true disease-causing agent. Symptoms characteristic of this disease include a rash beginning in the palms of the hands and soles of the feet, fever, nausea, emesis, severe headache, muscle pain, and loss of appetite. Although lethal in some cases, the disease is treatable. Taking antibiotics upon infection, for example, greatly reduces the mortality rate from an alarming 20% chance to a relatively low 5%. Although not known from this particular species, species in the genus Dermacentor are also known to serve as a vector to Tularemia, also known as Pahvant Valley plague or rabbit fever. As with RMSF, this disease is caused by a bacterial endosymbiont (Francisella tularensis), which is also a non-motile gram-negative coccobacillus. What makes this different from RMSF, however, is that it does not rely on direct contact in order to be spread. It can be waterborne, inhaled, or ingested (i.e. poorly-cooked meat). ("Rocky Mountain Spotted Fever (RMSF)", 2011; Burgdorfer, et al., 1973; Cunha, 2011; Dergousoff and Chilton, 2010; Kim, et al., 2010; Kwaik, et al., 2007; "Geographic distribution of arthropod-borne diseases and their principal vectors", 1989; Yee, 2006)

Conservation Status

This species has no special conservation status. (Furman and Loomis, 1984; "Scorpions Spiders Mites and Ticks: Arachnida - Rocky Mountain Wood Tick (Dermacentor andersoni): Species Account", 2012; "Geographic distribution of arthropod-borne diseases and their principal vectors", 1989)


Jean-Claude Michel Munyarubuga (author), University of Michigan-Ann Arbor, Jeremy Wright (editor), University of Michigan-Ann Arbor.



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


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


uses smells or other chemicals to communicate


a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females


union of egg and spermatozoan


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


(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


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.


having the capacity to move from one place to another.


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.


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


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


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


having more than one female as a mate at one time


"many forms." A species is polymorphic if its individuals can be divided into two or more easily recognized groups, based on structure, color, or other similar characteristics. The term only applies when the distinct groups can be found in the same area; graded or clinal variation throughout the range of a species (e.g. a north-to-south decrease in size) is not polymorphism. Polymorphic characteristics may be inherited because the differences have a genetic basis, or they may be the result of environmental influences. We do not consider sexual differences (i.e. sexual dimorphism), seasonal changes (e.g. change in fur color), or age-related changes to be polymorphic. Polymorphism in a local population can be an adaptation to prevent density-dependent predation, where predators preferentially prey on the most common morph.


an animal that mainly eats blood

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season


remains in the same area


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.


non-motile; permanently attached at the base.

Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa


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


lives alone


uses touch to communicate


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).


Living on the ground.


uses sight to communicate


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