Dermacentor andersoni

ORDER

Acari

FAMILY

Ixodidae

TAXONOMY

Dermacentor andersoni Stiles, 1908.

OTHER COMMON NAMES

English: Paralysis tick, Rocky Mountain spotted fever tick.

PHYSICAL CHARACTERISTICS

Includes a large collection of diverse types of mites, chiggers, and ticks; carries parasites and disease; has adult length of 0.08–0.65 in (2.1–16.5 mm). Specifically, unengorged females have length of 0.11–0.21 in (2.8–5.4 mm), adult males a length

of 0.08–0.24 in (2.1–6.1 mm), and engorged females a length of up to 0.65 in (16.5 mm) and a width of up to 0.45 in (11.4 mm). The body, covered with hard protective covering, is pear shaped, and is dorsoventrally flattened (top to bottom). Immature instars and adult females possess a strong pro-dorsal scle-rite, with the opisthosoma being covered with soft cuticle to permit engorgement. Holodorsal shield is found on adult males; posterior idiosoma is flattened, anterior gnathosoma is articulated. Tectum is well developed. Coxal glands are absent, and water control is performed through salivary glands.

Color of adult females is reddish brown with grayish white dorsal shield (scutum) near front of body, which changes to grayish color when engorged; adult males are spotted with brown and gray, and do not have distinctive white shield; they possess simple eyes, located on the margin of scutum. Capitulum is apparent from above; basis capitulum is rectangular in shape with sides not laterally produced and approximately length of mouthparts. There are 11 abdominal festoons. Anal groove is located posterior to anus. Broad spiracular plates, located on underside of body, possess blunt process that usually reaches dorsum; goblets, located within spiracular plates, are moderate in size and number.

DISTRIBUTION

Widely distributed in North America, primarily throughout Rocky Mountain states and into southwestern Canada. Specific areas are central British Columbia through southern Alberta into southwestern Saskatchewan; south through eastern Washington, Oregon, and California; all of Montana, Idaho, Wyoming, Nevada, and Arizona; western Oklahoma to northern New Mexico and Texas.

HABITAT

Mostly woods and meadows; those arid, brushy areas that provide food and protection for its usual hosts such as livestock, wild mammals, and humans. Over-winters in ground debris.

BEHAVIOR

Usually attached to its host, but when without host it will hide in cracks and crevices or in soil. If without a host at the beginning of winter, it will over-winter under groundcover to resume seeking host in spring. It will also stop looking for hosts during hottest summer months. Generally, adults will climb to top of grasses and low shrubs to attach to hosts that brush against them. Host attachment is accomplished by secreting cement-like substance around mouthparts and inserting it into host.

FEEDING ECOLOGY AND DIET

Adults generally feed for less than one hour at a time; parasitic, feeding primarily off of terrestrial birds, reptiles, and mammals and typically feeding only from late February until mid-July. All three stages (larva, nymph, and adult) can survive for more than one year without feeding. Engorged larvae, nymphs, and unfed adults normally spend cold months in grasses and leaf litter. Larvae feed throughout the summer, with nymphs continuing possibly to late summer. Males feed for about five days without engorging, become sexually mature and ready to mate, and then will resume feeding. Females feed for up to seven days (until fully engorged), during which time they mate. Fully engorged female will increase body weight from about 0.000176 oz (5 mg) to more than 0.0247 oz (700 mg). Each stage feeds on a unique host individual. Larvae, nymphs, and adults climb grass stems and bushes while searching for host. Can detect the presence of chemicals such as carbon dioxide associated with mammals, which indicates animal's presence.

REPRODUCTIVE BIOLOGY

Semelparous (reproduces once during lifetime, after which it dies). Requires blood meal before developing into its next life stage and for egg development. Mating takes place primarily on host, with female usually on top of male. Males do not become engorged. After feeding for 4–17 days, mated female descends from host and seeks protected area to lay eggs. In spring, after a preoviposition period of usually 3–11 days, she lays single cluster of usually 3,000–5,500 (but possibly 2,500–7,400) yellowish brown ellipsoidal eggs over period of 10–33 days. Female then dies within 1–14 days. During next 7–38 days, eggs hatch if temperature is 72–90°F (22–32°C).

Young six-legged larvae begin crawling in search for small rodent host (such as mice, voles, and chipmunks), dying within 30 days if unsuccessful. Unengorged first instar larva is about 0.0236 in (0.6 mm) in length. Usually feeds for 2–8 days (usually three) to engorgement, and then drops to ground to molt within 6–21 days. May survive for more than 300 days if unfed during this time. After finding suitable small- to medium-sized host (such as rabbits, ground squirrels, marmots, and skunks), nymphs reach engorgement in 3–11 days. Second instar eight-legged nymphs are 0.0551–0.0591 in (1.4–1.5 mm) in length. After completing engorgement, they drop off again and molt into adults usually in 14–15 days (possibly in 12–120 days). Adults can survive more than a year (usually about 600 days) unfed, but after finding a suitable medium- to large-sized host (such as dogs, deer, and humans), they mate on host after partial feeding. Life cycle is 1–3 years (typically 20 months), depending primarily on host availability and various environmental stresses and conditions.

CONSERVATION STATUS

Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

Females may carry and transmit several diseases to humans, including Rocky Mountain spotted fever, tularemia, and Colorado tick fever in the United States, with only rare occurrences in Canada.