American Dog Tick

Dermacentor variabilis

Primarily found east of the Rocky Mountains, but also found in limited areas along the Pacific coast, American Dog ticks (Dermacentor variabilis) are found predominantly in areas with little to no tree cover, such as grassy fields and along walkways and trails. They feed on a variety of hosts, ranging in size from mice to deer, and can survive for up to 2 years at any given stage if no host is found. Females can be identified by their large off-white scutum against a dark brown body.

American Dog Tick (adult female)Adult Female

American Dog Tick (adult male)Adult Male

American Dog Tick (nymph)Nymph

American Dog Tick (larvae)Larvae

American Dog Ticks have a dark brown body; with females having an off-white scutum (dorsal shield), while adult males look more mottled. They are flat and oval in shape, and usually brown with whitish-gray markings. Similar to the Blacklegged “Deer” Tick, these ticks have 6 legs as larvae but have 8 legs when they are nymphs and adults. They range anywhere from 5 mm to 15 mm in size depending on whether or not they are engorged.

American Dog Tick

The American Dog Tick exhibits a three-host tick life cycle. In warmer regions of its southern range all three stages may be active on hosts throughout the year with a pronounced increase of occurrence during spring. In northern regions, larvae and nymphs are active spring to autumn while adult questing appears to be highest in spring. Gravid females may lay from 4,000–6,500 eggs.

American Dog Ticks develop from the egg stage, to the 6-legged larva, to the 8-legged nymph, and finally to the adult. The cycle requires a blood meal before progression from larva to nymph, from nymph to adult and by the adult for egg production. This cycle also requires three different hosts and requires at least 54 days to complete, but can take up to two years depending on the host availability, host location and the temperature.

After five to 14 days of blood feeding, a fully engorged female D. variabilis drops from the host. She digests the blood meal and develops her egg clutch over the next four to 10 days. She then lays anywhere from 4,000 to 6,500 eggs on the ground. About 26 to 40 days later, depending on the temperature, the eggs hatch into larvae.

After hatching, larvae remain on the ground or climb growing vegetation where they wait for small mammals, such as mice, to serve as hosts for their first blood meal. This host location behavior is called questing. Under favorable conditions, larvae can survive up to 11 months without feeding. After contacting and attaching to a host, larvae require from two to 14 days to complete blood feeding. After feeding, larvae detach from their host and fall to the ground where they digest their blood meal and molt into the nymphal stage. This process can take as little as a week, although this period is often prolonged.

Nymphs can survive six months without a blood meal. After successfully questing for their second host, which is normally a slightly larger mammal (such as a raccoon or opossum), the nymphs will blood feed over a three to 10-day period. After engorging, they fall off the host, digest their blood meal and molt into an adult. This process can take anywhere from three weeks to several months.

Adults can survive two years without feeding, but readily feed on dogs or other larger animals when available. Questing adult ticks climb onto a grass blade or other low vegetation, cling to it with their third pair of legs, and wave its legs as a potential host approaches. As the hosts brush the vegetation, the ticks grab onto the passing animal. Mating occurs on the host and the female engorges within six to 13 days after which she drops from the host to lay her eggs and then she dies, thus completing the cycle.

Medical Importance

American Dog Ticks are carriers of the bacteria that causes Rocky Mountain Spotted Fever, a serious tick-borne illness with a mortality rate of over 20% if not treated early. Symptoms include high fever, chills, muscle aches, headaches, and sometimes a rash spread across the extremities 2-4 days after the fever begins. In order for transmission to occur, however, the tick must be attached for six to eight hours and in some cases transmission requires more than 24 hours.

These ticks are also known vectors of Tularemia, a disease transmitted from rabbits, mice, squirrels and other small animals. Symptoms include an ulcer at the bite site, fever, chills and tender lymph nodes.

 

Veterinary Importance

Canine Tick Paralysis can occur due to the feeding of D. variabilis. In this case, the tick will attach to the back of the dog’s neck, or at the base of the skull, and feed for at least five to six days. It is believed to release a salivary gland protein into the body. Paralytic symptoms then become visible through unsteadiness and loss of reflex actions. If the tick is not removed, respiratory failures can be fatal. Such paralysis is not limited to dogs, as it can happen to children as well. Once the tick is properly removed, recovery is usually within one to three days. In the U.S., the fatality rate is about 10% in the Pacific Northwest, and most of those who die are children.

American dog ticks prefer grassy areas with low vegetation where larger animals commonly pass by and thrive in areas that are also accessible to humans. When these ticks latch on to dogs, they are brought into the home and can potentially be transferred to humans. American dog ticks are extremely resilient and are able to survive for 2-3 years without feeding.

Widely distributed east of the Rocky Mountains. Also occurs in limited areas on the Pacific Coast.

Range Map - American Dog Tick

Adult American dog ticks overwinter in the soil and are most active from around mid-April to early September. Larvae are active from about March through July and nymphs are usually found from June to early September. In northern areas, such as Massachusetts and Nova Scotia, adults appear from April to August with a peak in May and June.

In central latitudes of the U.S., such as Virginia, adults are found to be active from April to September/October with peaks in May and July. In Ohio, adult activity occurred between April and September with a peak in May/June and a second smaller peak in August/September.

A study done in Lexington, Kentucky, found the duration of D. variabilis’ spring activity was related to its overwintering success. This study also concluded that overwintering adult D. variabilis ticks remained active throughout the entire season.

That same study reported that adult activity began a week or two earlier than in more northern states, such as Ohio, and a week or two later than in more southern states, such as Georgia. In Georgia, adult ticks are active from late March to August with peaks from early May to late June. While in Florida, adult D. variabilis activity occurs from April to July.

The American Dog Tick occurs primarily in wooded, shrubby and long-grass areas. However, it is possible for residential areas to support populations of this tick. Shrubs, weeds, tall grass, clutter and debris on the property attracts the rodents that are hosts for immature ticks. By maintaining grass short, removing possible rodent harborage, and sealing cracks and crevices in and around the property one can directly reduce or prevent local tick populations.

Keeping grass and weeds cut short decreases humidity, which helps kill ticks or makes an area undesirable for ticks and rodents. Additionally, it makes it difficult for ticks to climb on the vegetation and wait for its host. If pesticides are applied, cutting the vegetation short increases effectiveness and allows for better coverage. Removing rodent harborage areas may reduce an infestation.

Because dogs can easily pick up ticks while walking on infested grass or roaming through wooded areas, it is necessary to treat the pet properly. There are many products that can be applied to prevent or treat a tick infestation on an animal including topical treatments and sprays. Regularly grooming, washing bedding, and examining the dog are strongly recommended to prevent tick infestations.