Drawing on six months of fieldwork in the state of Rio de Janeiro, Brazil, this master’s thesis provides a portrait of Rio de Janeiro by following activities related to mosquitoes. Mosquito-borne diseases pose grave health and social burdens in many areas of the world, and since the 1980s mosquitoes have been vectors of dengue, and more recently of chikungunya and Zika, in the metropolitan region investigated in this account. Topics such as public health related municipal governance, scientists, global health initiatives, health scares and fragmented cities, often discussed separately by anthropologists, are brought together by this minute, barely visible and mobile agent. Specifically, I will explore this through ethnographic attention to mosquito control and reactions generated by mosquito-borne viral disease outbreaks.