The Lone Star Tick (Amblyomma americanum) is a common species found throughout much of the eastern United States. Its ability to transmit several pathogens to humans and animals makes proper identification a relevant public health concern. Recognizing this arthropod across its life cycle requires understanding its unique combination of color, size, and distinctive markings.
The Defining Feature of the Adult Female
The adult female Lone Star Tick is easily identified by the unique marking that gives the species its common name. When unfed, the female’s body is a striking reddish-brown color with an oval, flattened shape, measuring approximately 4 to 6 millimeters in length (the size of a sesame seed). The most distinct feature is a single, silvery-white or iridescent spot located centrally on her scutum, the hard shield behind the mouthparts. This bright, isolated dot contrasts sharply with the dark reddish-brown body. The scutum does not cover the entire back, allowing the abdomen to expand significantly after a blood meal.
Appearance of Adult Males and Engorgement
The adult male Lone Star Tick appears distinctly different from the female, lacking the single white spot. Males are slightly smaller, generally measuring between 2 and 5 millimeters in length. Their dark brown to reddish-brown body is patterned with subtle white, cream, or silver markings. These markings appear as streaks or mottled bands along the margins of the dorsal shield, covering the male’s entire back and giving it a marbled appearance.
The appearance of both sexes changes drastically after feeding on a host, a process known as engorgement. As the tick consumes blood, its body swells, transforming from a flattened oval to a plump, sphere-like shape. An engorged female can balloon up to 16 millimeters, reaching the size of a small grape. The reddish-brown color is replaced by a slate-gray or grayish-blue hue due to the ingested blood. This swelling stretches the body wall, making the female’s white spot and the male’s marginal markings less visible and harder to use for identification.
Appearance Across Immature Life Stages
The immature forms of the Lone Star Tick are the most frequently encountered and the most challenging to identify due to their small size. The larval stage, often called “seed ticks,” is the smallest, measuring less than 1 millimeter, about the size of a poppy seed. Larvae have only six legs, distinguishing them from all older life stages. Their color is typically a pale, light tan or yellowish-white, and they are frequently found in large, dense clusters on vegetation or a host.
The nymph is the intermediate stage, slightly larger than the larva, generally ranging from 1 to 2.5 millimeters in size. Nymphs possess eight legs, similar to adults, and have an oval shape that is reddish-brown or lighter brown. Due to their size and uniform coloration, nymphs are often mistaken for the adult forms of other tick species, such as the blacklegged tick.
Geographical Range and Preferred Habitat
The Lone Star Tick is broadly distributed across the eastern, southeastern, and midwestern United States. Its established range extends from central Texas north to Iowa and eastward along the Atlantic coast, reaching as far north as coastal Maine.
The preferred habitat consists of forested and wooded areas that feature thick underbrush and dense ground cover. They are commonly found in ecotonal areas, which are the transition zones between open fields and forests. Populations thrive in areas near creeks and rivers, where moisture is high and wildlife, particularly white-tailed deer, tends to rest. The tick actively seeks a host by a behavior called questing, climbing onto the tips of low-lying vegetation to wait for a passing animal or human.