LoneStarMapTick species • Field guide
Brown dog tick (Rhipicephalus sanguineus)
The brown dog tick (Rhipicephalus sanguineus) is a uniform reddish-brown, dog-loving tick found across the United States. It is unusual among ticks in that it can complete its entire life cycle indoors, so it can infest homes, dog kennels, and yards even in cold climates where other ticks cannot survive winter outside. Dogs are its strongly preferred host at every life stage, and it bites people far less often — but it can and does. Its main public-health importance is as a vector of Rocky Mountain spotted fever in the US Southwest, where year-round outbreaks are tied to heavy infestations on free-roaming dogs. This page is educational and not medical advice.
Last reviewed: 2026-07-20 · Educational only — not medical advice.
How to identify it
- Uniform reddish-brown with an elongated, narrow-oval body and no pale markings or ornamentation on the back.
- Hexagonal (six-sided) basis capituli — the base plate where the mouthparts attach — is the classic identifying feature and separates it from nearly all other US ticks (best seen under magnification).
- Adult male: the hard shield (scutum) covers the entire back. Adult female: the scutum covers only the front portion, leaving the rear free to swell during feeding.
- Engorged females balloon into a gray to blue-gray, raisin-like blob many times their unfed size.
- Context is a clue: most often found on dogs and indoors — along baseboards, wall cracks, and up kennel walls — rather than in tall grass, leaf litter, or deep woods.
Size: Larvae are about 0.5 mm, nymphs roughly 1.1–1.3 mm, and unfed adults about 1/8 inch (2.3–3.2 mm long). A fully engorged female can enlarge roughly a hundredfold, reaching about 1/2 inch (up to ~12 mm) — about the size of a raisin. Males take only small blood meals and change little in size.
Where it lives & when
Found throughout the continental United States (and worldwide) — it is considered the most widespread tick species on Earth. Because it can live and breed indoors, it establishes in homes and kennels even in colder regions where outdoor ticks cannot overwinter. Human Rocky Mountain spotted fever transmission by this tick is concentrated in the US Southwest — notably tribal communities in Arizona and areas along the US–Mexico border — where cases occur year-round and are linked to heavy tick infestations on free-roaming dogs. Elsewhere in the country it is common as a dog and household pest but is a much smaller human-disease concern.
Season: Because it can live indoors, the brown dog tick can be active year-round. In the Southwest RMSF-endemic areas, human cases occur throughout the year rather than only in a warm-weather peak, so vigilance is not limited to summer.
- Homes, dog kennels, and yards — closely tied to domestic dogs
- Indoor cracks and crevices: along baseboards, behind furniture, around window and door frames, and up walls or kennel surfaces
- Fenced yards and resting spots dogs use, rather than tall grass, leaf litter, or wooded trails
Diseases the brown dog tick can carry
Tick presence is not the same as personal disease risk. Not every bite transmits a pathogen.
Look-alikes
Its plain, unornamented reddish-brown back can be confused with other brown ticks. The American dog tick — the other main US RMSF vector — is a useful contrast: American dog tick adults have an ornate, mottled off-white pattern on the shield, while the brown dog tick is uniformly reddish-brown. The single best distinguishing feature is the hexagonal (six-sided) basis capituli, best seen under magnification. Engorged females of many species look alike as gray blobs, so context helps: a tick found on a dog or indoors is very often a brown dog tick. Note that in the US "Rhipicephalus sanguineus" is a species complex (sensu lato), and confident species-level identification may require a specialist.
Compare all tick species →Brown dog tick — frequently asked questions
Do brown dog ticks bite people?+
Dogs are the strongly preferred host at every life stage, so people are bitten far less often than dogs. But brown dog ticks can and do bite humans, and in parts of the US Southwest those bites can transmit Rocky Mountain spotted fever, which is a medical emergency if it develops.
Can brown dog ticks infest my house?+
Yes. Unlike most ticks, this species can complete its entire life cycle indoors, so a dog can bring ticks home that then breed in cracks, along baseboards, and in kennels. Infestations can build up in homes and kennels even in cold climates. Control usually means treating the dog, the home, and the yard together — often with help from a veterinarian and a pest-control professional.
Does the brown dog tick carry Lyme disease?+
No. Lyme disease is spread by blacklegged (deer) ticks, not the brown dog tick. The brown dog tick's main human-disease concern in the US is Rocky Mountain spotted fever, especially in tribal communities in Arizona and other parts of the Southwest.
How is it different from the American dog tick?+
Both can transmit RMSF, but they look and behave differently. American dog ticks have an ornate, mottled shield and live in grassy, brushy outdoor areas; brown dog ticks are a plain reddish-brown with a distinctive six-sided mouthpart base and stay close to dogs, homes, and kennels.
Sources used
- Rocky Mountain Spotted Fever (RMSF)CDC
Spread by American dog, Rocky Mountain wood, and brown dog ticks. Most US cases are in South-Central states; can be fatal without prompt doxycycline.
- Where Ticks LiveCDC
The Lone Star tick is widely distributed in the Northeast, South, and Midwest U.S.
- TickEncounter Resource CenterUniversity of Rhode Island
Tick identification, prevention, and reporting resources.
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Brown dog tick (Rhipicephalus sanguineus)
The brown dog tick (Rhipicephalus sanguineus) is a reddish-brown, dog-associated tick that can breed indoors and transmits Rocky Mountain spotted fever in the US Southwest. Learn how to identify it, its US range and life stages, and its real risks. Educational, not medical advice.