This 2008 photograph depicts a dorsal view of a male yellow dog tick, Amblyomma aureolatum, which is a vector of Rocky Mountain spotted fever (RMSF) in the country of Brazil. Note that the back of this tick is completely covered by its hard, scutum, or ?shield?. However, when this feature is compared with that of the female version of this hard tick, of the family Ixodidae, you?ll note that the female?s dorsal abdomen is only partially covered, which allows her abdomen to expand to many times the size seen here when she is ingesting her blood meal. Rocky Mountain spotted fever (RMSF) is the most severe tick-borne rickettsial illness in the United States. This disease is caused by infection with the bacterial organism Rickettsia rickettsii.