Class Arachnida: Order Acari
Ticks are a well known and widely despised group of organisms. They are easily recognized by their single body segment and eight legs. All ticks are parasites and must feed on blood to grow and reproduce. Some ticks vector viruses, bacteria, and even protozoans; that is, they are capable of transmitting disease-causing agents from one host to another as they feed. There are actually two groups, or families, of ticks: the hard ticks (the kind that you pull off of your dog) and the soft ticks (which you have probably never seen). They differ in a number of ways including appearance, method of attaining a host, and number of life stages.
Family Ixodidae: The Hard Ticks
California’s varied habitats are home to 31 species of hard ticks. These ticks have four life stages: egg, two sub-adult stages (larva and nymph), and adult. Both sub-adults and adults may be found in grass, brush, leaf litter, on tree trunks and rocks. Hard ticks are exposed in the environment in an attempt to hitch a ride on a passing host. The tick climbs on, attaches and feeds for multiple days. A hard tick’s appearance changes drastically as it feeds; what starts off looking smooth and hard becomes swollen and distorted. Adult females gorge on so much blood that they increase in size by as much as ten times. Once a sub-adult feeds, most drop off of the host and molt to the next life stage. A few species of hard ticks remain on a single host, molting and feeding repeatedly. Adults feed once to become sexually potent (males) or to produce eggs (females). In Lake County, three types of hard ticks are commonly encountered by people and outdoor pets. Large images of all three species are available at Tick Encounter, a website maintained by the University of Rhode Island. Additional information about tick ecology and tickborne disease (diseases spread by ticks) may be found at the California Department of Public Health and the Centers for Disease Control.
Western Black-legged Tick (Ixodes pacificus), aka Deer Tick
Western Black-legged adults have dark bodies and, not surprisingly, black legs. This is a cool weather species; adults are usually active from the first fall rains through spring (October through May). Adults feed on a variety of large mammals including deer, horses, people and dogs. Sub-adults have been collected year-round but are most abundant in the spring. These primarily parasitize western fence and alligator lizards, ground foraging birds and small rodents but will also feed on larger hosts including people. This tick is commonly collected in chaparral and mixed oak woodlands in Lake County.The Western Black-legged Tick is the primary vector of Borrelia burgdorferi (the bacteria that causes Lyme disease) in the western United States. The Centers for Disease Control (CDC) report that Lyme disease is the most commonly reported vectorborne disease (those that are spread by ticks and insects) in the nation. Reports of illness are comparatively high in the northeast relative to the west. Both adults and nymphs may be vectors of the disease and infection rates vary significantly by location and year. In 2013, nymphs collected in Lake County had infection rates ranging from approximately three to nine percent.
Pacific Coast Tick (Dermacentor occidentalis), aka Dog Tick
Adults of the Pacific Coast Tick are brown with off-white mottling across the male’s entire back and a portion of the female’s. The latin word “occidentalis” means western, an appropriate name for a tick which is only found in Oregon, California, northern Baja California, and Mexico. Adults have been collected in California year-round but are most abundant in the spring. Among adult hosts are deer, cattle, horses, and man. Sub-adults are most abundant in spring and summer and feed primarily on rodents, especially squirrels. In Lake County, adults of this species are commonly collected in the same habitats as the Western Black-legged Tick.The Pacific Coast Tick has been found naturally infected with a virus and multiple bacteria that cause disease in humans: among these is the bacterium Rickettsia 364D. The first human infection with this pathogen was reported in Lake County in 2008 (Shapiro et al. 2010).
American Dog Tick (Dermacentor variabilis), aka Dog Tick
Female American Dog Ticks are very similar to female Pacific Coast Ticks. It is fairly easy to tell the males apart; the former have more distinctive whitish markings than the latter. American Dog Ticks are found throughout much of the United States, and have also been collected in Canada and Mexico. In Lake County, adults are rarely collected in chaparral where Western Black-legged and Pacific Coast Ticks are abundant. They can be found in large numbers in sunny, grassy habitats particularly those near waterways. Adults have been collected in California throughout the year but are most active March through July. They commonly feed on dogs and people as well as a variety of carnivorous hosts. Sub-adults feed on rodents and rabbits.
The American Dog Tick is an important vector of Rocky Mountain spotted fever and also transmits the bacteria that cause tularemia. A bite from this tick may cause tick paralysis.
Family Argasidae: The Soft Ticks
Soft ticks are irregular in shape, and textured in appearance which makes them well-camouflaged. These are odd-looking creatures; not unlike a clump of dirt with legs. Soft ticks hide until a host lays down nearby, then rush out to feed. These fast-moving ticks typically feed for 30-60 minutes at a time. Soft ticks have between nine and twelve life stages: egg, larva, six to nine nymphal stages, and adult. Because these ticks feed quickly they grow incrementally. Mature females feed repeatedly and produce many small batches of eggs during their life. There is only one soft tick commonly found in Lake County.
Pajahuello Tick (Ornithodorus coriaceus)
The Pajahuello Tick is found near resting places of its large mammalian hosts (primarily deer and cattle) but will readily take blood from almost any warm-blooded animal. Although many people will never encounter this tick, the likelihood of exposure increases if you come in contact with host bedding sites, (ie. deer beds) during activities such as hiking, hunting or camping. For humans, the bite of this tick is notoriously painful, and may result in a localized inflammatory response due to a toxic substance introduced into the bite site during feeding. This tick is not known to vector disease to people.