Lyme disease is a bacterial infection primarily transmitted to humans through the bite of certain types of ticks. Understanding the appearance of these ticks is important for identifying potential threats and taking preventative measures. This article describes their visual characteristics across different life stages.
Primary Lyme Disease Vectors
In North America, the primary carriers of the bacteria causing Lyme disease are two species of ticks: the blacklegged tick (Ixodes scapularis), often referred to as the deer tick, and the western blacklegged tick (Ixodes pacificus). Both of these Ixodes species are responsible for transmitting the Lyme disease bacterium.
Appearance Across Life Stages
Blacklegged ticks undergo four life stages: egg, larva, nymph, and adult.
Larvae are extremely small, typically less than 1 millimeter, appearing as tiny, six-legged specks. They are often translucent.
Nymphs are slightly larger, roughly the size of a poppy seed, measuring about 1.5 millimeters. They possess eight legs and can range from translucent to grayish or brownish. Their small size and often painless bite make them difficult to detect, yet nymphs are responsible for many Lyme disease transmissions.
Adult blacklegged ticks are larger, typically measuring between 2 to 3 millimeters (about the size of a sesame seed or apple seed) when unfed. Adult female ticks have an oval, reddish-orange body with a distinct dark brown to black shield (scutum) behind their head. When engorged after feeding, a female can swell to about 1/2 inch, appearing gray or dark brown.
Adult male blacklegged ticks are typically smaller than females, measuring around 2 to 2.7 millimeters, and are uniformly dark brown or black. Unlike females, their scutum covers most of their body, preventing significant engorgement. All blacklegged ticks have dark legs.
Key Distinguishing Features
Differentiating Lyme-carrying ticks from other common tick species is important. Blacklegged ticks (both Ixodes scapularis and Ixodes pacificus) possess long, narrow mouthparts and lack ornate patterns or festoons (scalloped edges). Their bodies are generally unpatterned, with the female’s reddish-orange body contrasting with her black scutum.
The American dog tick (Dermacentor variabilis), a larger tick that does not transmit Lyme disease, has distinctive white or silvery-white markings on its back. Female American dog ticks have these markings on their scutum, while males have them streaking across their entire back. The Lone Star tick (Amblyomma americanum) is easily recognized by a single, prominent white dot in the center of the adult female’s back. This species also has a somewhat rounder body shape compared to the oval blacklegged tick.
Where These Ticks Are Found
Blacklegged ticks and western blacklegged ticks prefer specific environments where they can readily find hosts. They are commonly found in wooded areas, tall grasses, brushy zones, and areas with leaf litter. These ticks do not fly or jump; instead, they engage in a behavior called “questing,” where they climb onto low vegetation, such as shrubs or grass, and wait for a passing animal or human to brush against them.
The blacklegged tick (Ixodes scapularis) is widely distributed throughout the eastern and Midwestern United States, including the Great Lakes region, and extends into southern Canada. The western blacklegged tick (Ixodes pacificus) is primarily found along the Pacific coast, with concentrations in northern California. Both species require humid environments to survive, as they are susceptible to drying out. Their presence is often linked to the distribution of their preferred hosts, such as white-tailed deer.