Ticks are small arachnids that can attach to hosts and feed on blood. Understanding their visual characteristics is helpful for identification, as various species exist with differing appearances. Identifying ticks accurately can aid in recognizing potential health risks, since some species are known to transmit pathogens. This visual guide provides details to help distinguish common ticks and understand how their appearance changes.
General Physical Traits
Ticks are arachnids, related to spiders and mites. Adult ticks possess eight legs, while insect adults have six legs. Unlike insects, ticks do not have antennae or wings. Their bodies are oval and flattened before they feed, allowing them to easily attach to a host.
A defining feature of hard ticks is the presence of a hard shield-like plate on their back called a scutum. In male hard ticks, this scutum covers most of the dorsal surface, while in females, nymphs, and larvae, it only partially covers the front part of the body. This difference in scutum size allows the female’s body to expand considerably during feeding. Unfed adult ticks range in size from about 3 to 5 millimeters long, comparable to a small seed.
Common Tick Species and Their Distinctive Looks
Different tick species display unique visual characteristics, making distinction possible. The Deer Tick, also known as the Blacklegged Tick (Ixodes scapularis), is small. Unengorged adult females are about 1/8 inch long, while males are slightly smaller, around 1/16 inch. These ticks are orangish-brown with an oval shape, and their legs are darker than their bodies.
The American Dog Tick (Dermacentor variabilis) is larger than the Deer Tick. Unfed adults are reddish-brown with distinctive cream or grayish markings on their scutum. Females have a large silver-colored spot behind the head, while males have fine silver lines on their backs. Unengorged adult females are around 3/16 inch long.
The Lone Star Tick (Amblyomma americanum) is a common species. These ticks are medium-sized and reddish-brown to tan in color. Adult females are recognizable by a single, silvery-white spot located on their scutum. Males may have scattered white spots on their backs. Unfed adults are about 1/3 inch long.
Appearance Changes Throughout Life Stages
A tick’s appearance can change significantly depending on its life stage and whether it has recently fed. Ticks undergo four life stages: egg, larva, nymph, and adult. Larval ticks are small, less than 1 millimeter, and are sometimes called “seed ticks.” They have six legs, unlike the eight legs found in nymphs and adults.
Nymphs are the next stage and are slightly larger than larvae, about the size of a poppy seed or pinhead. They have eight legs, similar to adults, but are still small. Adult ticks are the largest stage before engorgement.
When a tick feeds, it engorges with blood, which alters its size, shape, and color. An unfed tick is flat and oval, but after a blood meal, it can become larger and more rounded. For example, an adult female American Dog Tick can swell from 3/16 inch to about 5/8 inch long after feeding. An engorged female Deer Tick can reach 10 millimeters in length, and an engorged American Dog Tick female can grow up to 15 millimeters. The color can also shift, becoming grayish, bluish-gray, or slate gray.