Ticks are small, blood-feeding parasites belonging to the class Arachnida, making them related to spiders and mites. They are obligate parasites, meaning they must feed on blood to survive and progress through life stages. Since ticks can transmit various pathogens, knowing how to identify them is important for personal safety. A tick’s appearance changes based on its life stage, sex, and whether it has recently fed.
General Anatomy and Size of the Unfed Tick
An unfed adult tick is small and flat. Like all arachnids, adult ticks possess eight legs, unlike insects which have six. They lack antennae and have a distinctive, flattened, oval-shaped body. Adult ticks are typically about the size of a sesame seed or apple seed, while the smaller nymph stage is roughly the size of a poppy seed. Most North American species are “hard ticks,” characterized by a rigid, shield-like plate called the scutum, located on their back just behind the mouthparts. Unfed ticks are typically dark, ranging from reddish-brown to black, depending on the species.
Visual Changes After Feeding
Once a tick attaches and begins to feed, its appearance changes significantly, a process known as engorgement. The tick’s abdomen swells as it fills with blood, changing the shape from a flat oval to a round, balloon-like sac. A fully engorged tick can swell to several times its original size, growing up to two-thirds of an inch and resembling a small, grayish-blue sphere. This expansion causes a color change; the dark outer shell stretches, and the abdomen takes on a pale gray, bluish, or greenish-white hue. The hard scutum near the head does not expand, remaining dark and providing a small, contrasting spot on the front of the swollen body.
Identifying Common North American Species
Visual markers are used to differentiate the most common North American ticks, even in their unfed state. Identification focuses primarily on the scutum and color patterns.
The Blacklegged Tick
The Blacklegged Tick, often called the Deer Tick, is known for its small size and color contrast. Unfed adult females have a reddish-orange body with a prominent, solid black scutum located just behind the mouthparts. In contrast, the adult male is uniformly dark brown or black, with the scutum covering most of its back.
The American Dog Tick
The American Dog Tick, commonly known as the Wood Tick, is noticeably larger than the Blacklegged Tick. Adult females have a dark brown body with distinct white or silvery markings confined to the scutum. Adult males are dark brown with white or silvery streaks that cover much of the back.
The Lone Star Tick
The Lone Star Tick is easily recognizable, particularly the female, which features a single, distinct white or silver spot on the center of her back, giving the tick its common name. Males are brown and possess scattered, faint spots or streaks around the edge of the body rather than a single central mark.