Dermacentor variablis
American dog tick

North America east of Rocky Mountains, also found in some Western states.

D. variabilis are often found in grassy meadows or wooded areas across North America, east of the Rocky Mountains. Common near stables, kennels, barns or any other areas in which animals are kept. Ticks most often await their next host by climbing into tall grasses and shrubs (U.S. Forest Service,1996)

Hard body is divided in two segements with eight legs, the cephalothorax and abdomen are fused with no sign of external division. Most ticks are flattened dorsoventrally in unfed state, then bloat out to rounded state as they feed. Often with white pattern on brown dorsal plate. Highly visible mouthparts, unlike soft-bodied ticks.

After hatching, the six legged larvae attach to rodents, feed, then drop off and molt into eight legged nymphs which remain inactive until the next spring. The following spring these nymphs, which are also known as "seed ticks," are sometimes present in such numbers that the only effective way to remove them is by ripping them off your skin with a strip of duct tape before they can effectivly burrow in (U.S. Forest Service. 1996). Nymphs climb high grasses or shrubs and await a passing host, usually a somewhat larger animal, such as a dog or human, or die. If a host is found, the nymph feeds, then drops off to molt into an adult. The adult remains inactive throughout the winter and attempts to find another, larger host, usually a cow, on which to feed and breed the following spring. Adults die following mating and egg laying. There is no known social system.

D. variabilis uses its modified chelicerae to cut an entrance into its host's skin, then inserts its mouthpart. The hypostome (feeding tube) has several rows of recurved barbs that serve to anchor the tick to its host. Blood is pumped up by a muscular pharynx and special glands secrete an anti-coagulant in order to prevent the host's blood from coagulating during the lengthy feeding period. Feeding occurs only once yearly and is followed by a long inactive molting period. During its three to four year life cycle, D. variabilis will feed on a sucessively larger host each year, for example, rat (larvae), human (nymph), then cow (adult).

Dermacentor variabilis are prime vectors of several important diseases caused by bacterial pathogens that live in their bloodstream and are tranmitted to the host through the tick's saliva. In addition to Anaplasmosis and Tularemia (rabbit fever), Rocky Mountain Spotted Fever and Colorado Tick Fever are the two main diseases caused by the bite of D. variabilis, both of these diseases can be fatal if not treated in time. Colorado Tick Fever has been reported by California epidemologists as the State's least reported infectious disease. Rocky Mountain Spotted Fever is caused by a rickettsial bacterium. Its symptoms include chills, fever, general aches and pains and a reddish-purplish-black rash in the extremities. Tick paralysis can also be caused by D. variabilis. With this disease, no pathogen is involved. The cause is a neurotoxin produced in the ovaries of female ticks. This neurotoxin enters the host while the tick is engorging, which can be as long as six to seven days (Campbell, 1996). The result is gradual paralysis from the legs upwards. Death can result in humans if the tick is not properly removed in time. In addition to being dangerous to humans, these ticks are vectors for a number of cattle diseases and are responsible for considerable annual economic loss (U.S. Forest Service,1996).

In some areas of Latin America, Dermacentor variabilis are being genetically engineered to produce proteins in their guts that can be used to immunize cattle against diseases for which ticks are vectors. This will benefit the the cattle industry by providing a specialized drug that targets tick vectored diseases specifically. Hopefully this will be more effective and less dangerous than the widespread use of antibiotics(Vasquez, 1996) .

We are trying to come up with new ways to kill these little suckers as fast as we can. They are on mankind's hit list, not on the endangered species list.

Tick control is very important in livestock rearing and rural living. Insecticide application is the most effective means of control, but this has serious and possibly greater negative aspects, including damage to non-target species and general eco-system deterioration. Other methods include mowing down high grasses or individual immunization (U.S. Forest Service,1996).