Dermacentor occidentalis

Marx, 1892

Pacific Coast tick

Dermacentor occidentalis, commonly known as the Pacific Coast , is a hard tick in the Ixodidae native to western North America. Unfed measure approximately 4.5 mm in length with a distinctive silvery-gray . This is a known of several human including , Pacific Coast tick fever, and , though it does not transmit . The tick exhibits a three- , feeding on a wide range of mammalian, avian, and reptilian hosts throughout its development.

The life history and bionomics of some North American ticks (1912) (14748516866) by Internet Archive Book Images. Used under a No restrictions license.

Dermacentor occidentalis -Harmony Headlands State Park, California, USA-8 (1) by Jerry Kirkhart from Los Osos, Calif.. Used under a CC BY 2.0 license.

The life history and bionomics of some North American ticks (1912) (14584877289) by Internet Archive Book Images. Used under a No restrictions license.

Pronunciation

How to pronounce Dermacentor occidentalis: //dɛr.məˈsɛn.tɔr ˌɒk.sɪˈdɛn.tə.lɪs//

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Dermacentor occidentalis can be distinguished from the western black-legged tick (Ixodes pacificus) by the position of the anal groove: D. occidentalis has the anal groove below the (cup-shaped, opening upward), while I. pacificus has the anal groove above the anus (inverted U-shape, opening downward). This character is diagnostic and visible with magnification. The silvery-gray coloration and patterns help distinguish it from other Dermacentor . () occurs in overlapping ranges but has different coloration patterns and is more common in eastern and central regions.

Images

Habitat

Found in coastal California biome and adjacent regions. Occurs in chaparral, grassland, and woodland-edge . show clumped distributions along trails with aggregated spatial patterns. Vegetation types include tall grass, brush, rocky areas with logs and fallen leaves. Ticks position on vegetation tips to contact passing .

Distribution

Native to western North America. Documented throughout California and in southwestern Oregon (Curry, Coos, Douglas, Lane, Josephine, Jackson, and Klamath counties). Records from Mexico. Distribution closely tied to coastal and near-coastal extending inland in suitable vegetation zones.

Seasonality

active in spring through early summer with peak activity varying by year and location. Nymphal activity patterns vary diurnally in relation to meteorological factors and activity periods. Seasonal activity influenced by temperature and moisture conditions.

Diet

Obligate blood feeder throughout all active life stages. Larvae, nymphs, and each require blood meals for development and .

Host Associations

Homo sapiens - bite humans
Neotoma fuscipes - dusky-footed woodrat; stages
Peromyscus spp. - deer mice; stages
Sylvilagus spp. - cottontail rabbits; stages
Lepus spp. - jackrabbits; stages
Canis latrans - coyote; stages
Procyon lotor - raccoon; stages
Mephitis mephitis - striped skunk; stages
Spilogale putorius - spotted skunk; stages
Vulpes vulpes - red fox; stages
Urocyon cinereoargenteus - gray fox; stages
Odocoileus hemionus - mule deer; stages
Ovis canadensis - bighorn sheep; stages
Spermophilus beecheyi - ground squirrel; stages
Thomomys bottae - pocket gopher; stages
Scapanus spp. - moles; stages
Sorex spp. - shrews; stages
Perognathus spp. - pocket mice; stages
Dipodomys spp. - kangaroo rats; stages
Reithrodontomys megalotis - harvest mouse; stages
Microtus californicus - vole; stages
Rattus norvegicus - Norway rat; stages
Mus musculus - house mouse; stages
Zonotrichia leucophrys - white-crowned sparrow; stages
Passerella iliaca - fox sparrow; stages
Pipilo maculatus - spotted towhee; stages
Melozone crissalis - California towhee; stages
Toxostoma redivivum - California thrasher; stages
Aphelocoma californica - scrub jay; stages
Corvus corax - common raven; stages
Cyanocitta stelleri - Steller's jay; stages
Colaptes auratus - northern flicker; stages
Sphyrapicus spp. - sapsuckers; stages
Picoides spp. - woodpeckers; stages
Meleagris gallopavo - wild turkey; stages
Callipepla californica - California quail; stages
Zenaida macroura - mourning dove; stages
Columba livia - rock dove; stages
Tyto alba - barn owl; stages
Buteo spp. - hawks; stages
Accipiter spp. - hawks; stages
Falco spp. - falcons; stages
Cathartes aura - turkey vulture; stages
Pituophis catenifer - gopher snake; stages
Lampropeltis getula - common kingsnake; stages
Crotalus spp. - rattlesnakes; stages
Sceloporus occidentalis - western fence lizard; stages
Uta stansburiana - side-blotched lizard; stages
Elgaria multicarinata - alligator lizard; stages
Phrynosoma blainvillii - horned lizard; stages
Plestiodon skiltonianus - skink; stages
Crotaphytus bicinctores - collared lizard; stages
Sceloporus graciosus - sagebrush lizard; stages
Urosaurus ornatus - tree lizard; stages
Cnemidophorus tigris - whiptail; stages
Gambelia spp. - leopard lizards; stages
Xantusia spp. - night lizards; stages
Anniella spp. - legless lizards; stages
Coluber spp. - racers; stages
Lampropeltis zonata - mountain kingsnake; stages
Masticophis flagellum - coachwhip; stages
Salvadora hexalepis - patch-nosed snake; stages
Sonora semiannulata - ground snake; stages
Tantilla spp. - flat-headed snakes; stages
Thamnophis spp. - garter snakes; stages
Trimorphodon spp. - lyre snakes; stages
Hypsiglena torquata - night snake; stages
Arizona elegans - snake; stages
Phyllorhynchus decurtatus - leaf-nosed snake; stages
Rena humilis - western blind snake; stages
Charina bottae - rubber boa; stages
Lichanura trivirgata - rosy boa; stages
Python molurus - Indian python (introduced); stages

Life Cycle

Three- : , larva, nymph, and . Larvae hatch with six legs, feed on host blood, then to eight-legged nymphs. Nymphs feed again and molt to adults. Adults feed, mate, and females lay eggs. Each active stage requires a blood meal and typically feeds on different host individuals. In cooler climates, the life cycle may extend across 2-3 years.

Behavior

Exhibits questing : climbs vegetation and extends forelegs to contact passing . Starved ticks show increased questing activity and metabolic rate compared to recently fed individuals. Ticks sense carbon dioxide and host cues to initiate questing. Can enter state with reduced metabolism when host cues absent. Salivary gland activity increases with starvation, producing cement-like substances for host attachment. host-seeking patterns vary with vegetation type and meteorological conditions. Drop-off rates during sampling affected by , substrate roughness, and distribution pattern.

Ecological Role

Serves as a for multiple between wildlife and humans. Acts as a for endosymbiotic bacteria including Francisella-like endosymbionts (FLE) which may interfere with pathogenic . Microbiome composition varies with geographic location and host association. Male ticks harbor greater bacterial diversity than females. Ticks not infected with spotted fever group Rickettsia show microbiome similarities to canine skin microbiomes, suggesting host influence on microbial .

Human Relevance

Bites humans and is a for ( rickettsii), Pacific Coast fever (Rickettsia philipii strain 364D), (Francisella tularensis), anaplasmosis, and . Does not transmit . Two novel bunyaviruses (Nairovirus and Phlebovirus ) detected in tick with high , though human unconfirmed. Prompt removal within 24 hours reduces transmission risk. Tick testing services available for identification and detection.

Similar Taxa

Ixodes pacificusOverlapping range in California; distinguished by anal groove position above (inverted U-shape) versus below anus in D. occidentalis; I. pacificus transmits while D. occidentalis does not.
Dermacentor variabilisCongeneric with similar patterns; D. variabilis more common in eastern and central North America with different geographic distribution; both and .
Dermacentor andersoniOverlapping distribution in western states; Rocky Mountain wood tick with different preferences and associations.

Misconceptions

Contrary to common belief, ticks do not fly, jump, or fall from trees. They do not embed their in skin; rather, mouthparts are adapted to penetrate and hold fast with cement-like secretions. The does not transmit despite being a common human-biting in California. Burning ticks with matches or applying petroleum jelly are ineffective removal methods and may increase transmission risk.

More Details

Pathogen Prevalence

In San Diego County , philipii str. 364D detected in 2.3% of ticks and R. rhipicephali in 8.2%. Francisella-like endosymbiont present in 70% of ticks in Mendocino County . Two novel bunyaviruses present in 20-91% of ticks depending on collection year.

Microbial Interference

Inverse relationship observed between Francisella-like endosymbiont (FLE) abundance and , suggesting FLE may interfere with spotted fever group Rickettsia establishment in ticks.

Collection Methods

Flagging along trails effective for sampling ; clumped distributions require adequate spatial sampling. Drop-off rates during flagging affected by and substrate characteristics.