A tick. The "american wood tick", "rocky mountain wood tick", and "brown dog tick" are the ticks that spread rmsf in the United States. Some people get rmsf but do not remember getting a tick bite. A person with symptoms of rmsf who has been in areas where ticks live, but does not recall a tick bite, may be started on antibiotic treatment while awaiting blood tests to confirm rmsf infection.
Arachnids! Technically "insects" do not transmit the bacteria (rickettsia rickettsii) resposible for rocky mountain spotted fever (rmsf). Ticks - which are technically related to spiders rather than insects - do transmit r. Rickettsi. The most common ticks are dog ticks. However a variety of ticks from around north & south america are capable of spreading rmsf including, although rarely, deer ticks.