Bighorn Sheep Ticks (Dermacentor hunteri) are Hard Ticks in the Family Ixodidae. This species is the most desert-adapted of all ticks and can be found in desert mountain ranges where Desert Bighorn Sheep occur in the Mojave and Sonoran deserts of the southwestern U.S. and northern Mexico, but not in Baja California (Crosbie, et al. 1997).

Adult ticks are found on Desert Bighorn Sheep, primarily in plateau and rocky slopes habitats during winter and early summer. Juveniles are found on Desert Woodrats (nymphs and larvae) and Cactus Mice (larvae) in spring and early summer in the same habitats. The distribution of Bighorn Sheep Ticks may be limited to areas where all three species co-occur (Crosbie and Boyce 1998).

Male and female Bighorn Sheep Ticks look different. Males have a red back with black and white lines, while females have white on the dorsal shield and are otherwise dark colored (black lines on red).

Bighorn Sheep Ticks feed on humans, but fortunately they do not seem to transmit diseases to humans. In part, this is because ticks usually need to be attached for a long time (hours) before diseases are transmitted, and usually we find and remove them in time.

Prior to the spring of 2011, the only place in southern Nevada where I know that ticks are a problem for humans is in the Arrow Canyon Range. I've never seen a tick on a human at Red Rocks, Lake Mead, or Mt. Charleston, places that all have plenty of opportunities for ticks, although there has been at least one case of Lyme Disease on Mt. Charleston.

During the spring of 2011, I saw ticks at Lake Mead NRA and Red Rock Canyon NCA. I also heard about ticks in other areas, such as Mt. Charleston. I don't know what was different this year, but it showed that bighorn ticks can probably be found anywhere bighorn are found. Even so, they are rare and only a minor inconvenience.

References:

Crosbie P.R., and W.M. Boyce. 1998. Dermacentor hunteri (Acari: Ixodidae): seasonal variation in questing adults and on-host juvenile stages, and host associations and feeding behavior of larvae and nymphs. J Med Entomol. 35:1034-43.

Crosbie, P.R., W.L. Goff, D. Stiller, D.A. Jessup, and W.M. Boyce. 1997. The distribution of Dermacentor hunteri and Anaplasma sp. in desert bighorn sheep (Ovis canadensis). J Parasitol. 83:31-37.