American Dog Ticks (Dermacentor variabilis)
Life Cycle
A fully engorged female D. variabilis drops from the host and in 4 - 10 days lays 4,000 to 6,500 eggs on the ground. Incubation of the eggs during summer is about 35 days, but temperatures can influence this time greatly. When the eggs hatch, the six-legged larvae emerge. Larvae remain on the ground or ascend low-growing vegetation while awaiting a host. Once on an acceptable host, they will engorge for 3 - 12 days (about 4 days on average) then drop to the ground and molt in about a week. The resulting nymphs then emerge and usually engorge on a small rodent for 3 - 11 days (the average being 6 days). Once fed, the nymphs will also, drop to the ground to mol. This molting may take from 3 weeks to several months. After such time, the adult female and male ticks will emerge. Unfed adults may live more than 2 years, but this instar usually soon attacks dogs and other large hosts. Females engorge in 6 - 13 days. Mating between the males and females occurs on the host as the attached female feeds. Like unengorged adults, immatures have considerable longevity in the absence of suitable hosts. Under favorable conditions, the full life cycle may take only three months, however it can be as long as two or more years. Larval and adult activity peak during the spring and early summer. In the southern United States, all stages of the tick can be found throughout the year.
Host Relationships
Dermacentor variabilis is found throughout the United States; however, it is only sparsely found throughout the Rocky Mountain area. Larval and nymphal dog ticks are known to infest a variety of hosts, including: white-footed mice, chipmunks, meadow voles, rats, squirrels, opossums, and raccoons. Adult ticks are usually reported from medium- or large-sized mammals, including: horses, cattle, white-tailed deer, opossums, and raccoons.
Page Last Updated: 4/5/2016 2:59:00 PM