The planarian,Dugesia dorotocephala(Woodworth), was studied in the laboratory and field as a predator of all developmental stages ofCulex peusSpeiser. Reproduction by transverse fission was accelerated by higher feeding rates and probably by crowding. Decreased feeding in culture could be offset by increasing the density ofDugesia. Experimental field populations ofCulexlarvae were reduced by 90+% in 26 days during July and August, 1973. Mucus secretions effectively immobilized prey larvae and their body fluid was consumed. Mucus was also used to produce cemented sand anchors for attachment to larvae and pupae. Group feeding without internecine activity was observed whereby as many as 12Dugesiacollectively ensnarled a single prey. Field and laboratory observations indicated optimum temperatures for feeding and reproduction were 20–26°C. Feeding ceased above 29°C; mortality ensued at 30°C.