The common term “wood tick” most often refers to the American Dog Tick, scientifically known as Dermacentor variabilis. This hard-bodied arachnid is one of the most frequently encountered ticks across North America. It is commonly found by people and pets spending time outdoors, making accurate identification important.
The American Dog Tick’s Defining Features
The unfed adult American Dog Tick is relatively large compared to many other common tick species, measuring about 3/16 to 1/4 inch long. Its body color is generally a rich reddish-brown or dark brown. The most distinctive feature is the presence of silvery-white or gray ornamentation on its dorsal shield, called the scutum. This scutum covering differs significantly between the sexes, which is a major identification marker. In the adult female, the scutum is a small, patterned shield located directly behind the head, covering only the anterior portion of her back. The adult male, conversely, has this mottled, ornate pattern extending across nearly the entire dorsal surface of its body. Both sexes possess relatively short, broad mouthparts, which is another useful trait for distinguishing them from other tick genera.
Appearance Changes Across Life Stages
The initial stage after hatching is the larva, which is tiny—about the size of a pinhead—and has only six legs. Larvae are typically straw-colored or pale yellow before feeding, and they lack the distinct ornamentation seen in the adults. After feeding on a small mammal, the larva molts into an eight-legged nymph, which is still quite small, measuring less than a millimeter. The nymph is pale yellow-brown and may have a brick-red colored scutum, but it still does not display the pronounced white markings of the adult. Once the adult female feeds, she can swell significantly, sometimes reaching up to 1/2 inch long and 10 millimeters wide. Since the scutum is non-expandable, it remains a small shield near the head, while the rest of the body expands into a large, slate-gray or gray-black sac.
Key Differences from Other Ticks
Distinguishing the American Dog Tick from other common species, such as the Blacklegged Tick (Ixodes scapularis) and the Lone Star Tick (Amblyomma americanum), relies heavily on observing the scutum pattern and overall size. The Blacklegged Tick, often called the Deer Tick, is noticeably smaller than the American Dog Tick in all life stages. The adult female Blacklegged Tick has a dark, plain black scutum contrasting sharply with a reddish-orange body, lacking the American Dog Tick’s distinct silvery-white pattern.
The Lone Star Tick also features an ornate pattern, but it is much simpler and gender-specific. The adult female Lone Star Tick is instantly recognizable by a single, prominent silvery-white spot, or “star,” located in the center of her back. In contrast, the American Dog Tick’s ornamentation is a mottled, marbled pattern rather than a single spot. The American Dog Tick is also a hard tick with festoons, which are small scalloped edges along the rear margin of its body, a feature absent on the Blacklegged Tick.
Geographic Range and Preferred Habitat
The American Dog Tick is widely distributed across the United States, predominantly found east of the Rocky Mountains, though it is also reported in limited areas along the Pacific Coast. This species is highly resistant to drying out, allowing it to thrive in environments that other ticks often avoid. It prefers areas with tall grasses, roadside vegetation, and open, brushy woodlands. Adult ticks of this species commonly quest by climbing to the tips of low vegetation, waiting to latch onto passing large hosts, including humans, dogs, and livestock. Their prevalence along trails and in grassy fields makes them a common outdoor hazard during their peak activity period, which typically runs from mid-April to early September.