The relatively poor results that have been obtained in controlling or eradicating Culex pipiens fatigans, the urban vector of Wuchereria bancrofti, have made it necessary to obtain as much information as possible about its biology. In this paper the unexpected finding of the influence of cane sugar in delaying oviposition in the gravid female is reported. This is an important finding for those who are investigating the biology of this mosquito in the laboratory and who make use of the age-old practice of keeping adult mosquitos alive by feeding them cane sugar. It is also reported that under certain conditions extensive cane-sugar feeding takes place in nature and it seems possible that this habit may have unsuspected repercussions on behaviour and physiology beyond the confines of the laboratory. One possible development would be the isolation of the attractant present in unrefined sugars and its use in traps in order to assess mosquito populations in the field.