Four members of the Ixodes ricinus species complex, Ixodes pacificus, Ixodes 
persulcatus, Ixodes ricinus and Ixodes scapularis, have, between them, a 
worldwide distribution within the northern hemisphere. They are responsible for 
the transmission of several animal and human pathogens, including the causal 
agents of Lyme borreliosis, tick-borne encephalitis, human granulocytic 
anaplasmosis and human babesiosis. Despite the importance of these ticks as 
vectors, the knowledge and understanding of the role that diapause plays in 
their complex life cycles are confused and incomplete. In view of the continuing 
geographic spread of these tick species, as well as the effects of climate 
change on vector-borne diseases, it is timely to encourage research on diapause 
phenomena to improve understanding of their biology and of pathogen transmission 
dynamics. In our review we seek to clarify thinking on the topic and to address 
gaps in our knowledge that require the attention of researchers.