Ornithodoros hermsi is a soft bodied tick, which is part of the family Argasidae. It is one of the smallest ticks of the species Ornithodoros. Females are larger than the males. O. hermsi has a multihost life-cycle  and some females have been observed to last four years without any blood meals. They are a parasite of rodents and other small mammals. The most favored host is the western chipmunk, Eutamias spp.
As do all other species of ticks, O. hermsi begin as eggs, then larvae, then nymphs, to adult ticks. O. hermsi has two larval molts and has 3 nymphal stages. The nymphal blood meals and the greater volume of blood intake will increase the development from nymphs to adults and decrease the number of nymphal stages.
Ornithodoros hermsi is found in the northwestern region of the United States, in states including Washington, Oregon, California, Idaho, Colorado, and even northern Arizona and New Mexico. Additionally, the species is found in southwest British Columbia, Canada.
The ticks are found in timbered regions and at high altitudes. Wood used for fuel and lumber are common locations, as are hollow pine logs, douglas firs, and wooden cabins. O. hermsi have been found in the nests of birds and rodents.
Medical and veterinary importance
Ornithodros hermsi is a vector of Borrelia hermsii which can cause tick-borne relapsing fever in humans. Tick-borne relapsing fever, TBRF, is spread by the spirochete bacteria in Borrelia hermsii which are spread from O. hermsi to animals to humans or directly to humans. Unlike, hard-bodied ticks, Ixodidae, O. hermsi feeds on a host for a short period ranging from 15–20 minutes. They often feed at night. The bites are not painful nor noticeable which is dangerous as victims of the bite will not know they are affected until symptoms of TBRF appear. There is a higher transmission of Borrelia hermsii in late-stage nymphs and adult ticks because they have larger blood meals and, therefore, longer feeding times.
- Schwan TG, Raffel SJ, Schrumpf ME, et al. (July 2009). "Tick-borne relapsing fever and Borrelia hermsii, Los Angeles County, California, USA". Emerging Infect. Dis. 15 (7): 1026–31. doi:10.3201/eid1507.090223. PMC 2744237. PMID 19624916.
- McCoy, Brandi N.; Sandra J. Raffel, Job E. Lopez and Tom G. Schwan (25 August 2010). "Bloodmeal Size and Spirochete Acquisition of Ornithodoros hermsi (Acari: Argasidae) During Feeding". Journal of Medical Entomology 47 (6): 1164–1172. doi:10.1603/ME10175. Retrieved 11/4/2013.
- Wheeler, Charles M. (February 1943). "A Contribution to the Biology of Ornithodoros hermsi Wheeler, Herms and Meyer". The Journal of Parasitology 29 (1): 33–41. JSTOR 3272745.
- Bay, D.E.; R.L. Harris (1988). Introduction to Veterinary Entomology (A Guide to Livestock Insects). Robert Harris Publisher. p. 72. ISBN 0-9624083-0-1.
- Shapiro, Leo. "Brief Summary". Encyclopedia of Life. Retrieved 5 November 2013.
- Schwan, Tom G; Paul F. Policastro, Zachary Miller, Robert L. Thompson, Todd Damrow, and James E. Keirans (September 2003). "Tick-borne Relapsing Fever Caused by Borrelia hermsii, Montana". Emerging Infectious Diseases 9 (9): 1151–1154. doi:10.3201/eid0909.030280. PMC 3016790. Retrieved 5 November 2013.
- Davis, Gordon E. (10 October 1941). "Ornithodoros hermsi and Relapsing Fever in Oregon". Public Health Reports (1896-1970) 56 (41): 2010–2012. JSTOR 4583889.
- "Relapsing Fever" (Web). Encyclopaedia Britannica Online Academic Edition. Encyclopaedia Britannica Inc. 2013. Retrieved 5 November 2013.
- Bay, D.E.; R.L. Harris (1988). Introduction to Veterinary Entomology (A Guide to Livestock Insects). Robert Harris Publisher. p. 73. ISBN 0-9624083-0-1.
- Lopez, Job E.; Brandi N. McCoy, Benjamin J. Krajacich and Tom G. Schwan (July 2011). "Acquisition and Subsequent Transmission of Borrelia hermsii by the Soft Tick Ornithodoros hermsi". Journal of Medical Entomology 48 (4): 891–895. doi:10.1603/ME10283. Retrieved 5 November 2013.