Tick Identification

The Black-Legged Tick (Deer Tick) — Lyme Vector

Ixodes scapularis (East/Midwest) and Ixodes pacificus (West Coast) are the only ticks that transmit Lyme disease in the United States. Adult females are reddish-orange with a dark brown shield behind the head. Males are entirely dark brown. In their nymph stage — when they cause most human infections — they are roughly 1–2 mm in size, about the size of a poppy seed. Easy to miss against skin.

The Lone Star Tick

Amblyomma americanum — identified by the distinctive white spot on the back of adult females. Aggressive and found predominantly in the Southeast and East. Does NOT transmit Lyme but can spread ehrlichiosis, tularemia, and STARI (Southern Tick-Associated Rash Illness), which produces an EM-like rash.

The American Dog Tick

Dermacentor variabilis — among the most commonly encountered ticks in the eastern US. Larger than deer ticks with distinctive white or yellowish markings. Does NOT transmit Lyme. Can transmit Rocky Mountain spotted fever and tularemia.

The Rocky Mountain Wood Tick

Dermacentor andersoni — found primarily in Rocky Mountain states at elevations of 4,000–10,500 feet. Similar appearance to the dog tick. Can transmit Colorado tick fever and Rocky Mountain spotted fever. Does not transmit Lyme disease.

Why Size Matters — The Nymph Problem

Deer tick nymphs are responsible for the majority of human Lyme disease cases. They feed in spring and early summer — peak outdoor season — and are so small they often go undetected. Adult deer ticks are easier to spot (sesame seed size) and are most active in fall.