Sixteen monthly visits were made to the Ndumu game reserve when resting Aedes circumluteolus mosquitoes were collected on the ground. The population density reached exceedingly high levels 7 or more days after the Usutu and/or Pongola rivers inundated their flood plains, and was related mainly to river flooding and far less to local rainfall. During dry months male Ae. circumluteolus disappeared while females persisted at very low levels. Blood-feeding and ovarian development occurred throughout the year and precipitin tests showed the preferred host was almost exclusively antelope (Bovidae), the dominant large mammal present. It was concluded that Ae. circumluteolus is a floodwater mosquito. Owing to the low density of females during dry months and low infection rates with arboviruses it is considered unlikely that Ae. circumluteolus would support viral transmission throughout the year. It is more likely that viruses survive in overwintering eggs and are transovarially transmitted.