The predatory efficiency of Sphaerodema rusticum on Culex quenquefasciatus has been assessed based on its predatory behaviour and the predator-prey relationship. Sequential behavioural strategies and duration of each event of the predation on prey were observed. Predator efficiency was assessed by prey death in different densities of prey groups, sex of predators and the prey sizes. S. rusticum recognizes and approaches its prey, C. quiquefasciatus. Sometimes the predator waits until a prey reaches its vicinity. At higher prey density, they quickly capture the prey by their fore legs, pierce the body using their proboscis and suck the contents. S. rusticum uses its visual sense to recognize and capture the prey. Blocking the visual sense experimentally resulted in poor predatory efficiency, when compared to that of the control. The predatory efficiency was much less in those insects whose tibial hairs of the fore legs were coated with moulten wax. Studies on the predator-prey relationship indicate that the rate of predation increases along with predator size. The fifth nymphal instar and adult stage show the maximum predatory efficiency than the earlier nymphal instars. Between the sexes, rate of predation is higher in females than in males. The rate of predation significantly increases with an increase in the density of the prey. The nymphs and adults of S. rusticum feed on all the larval stages of the mosquito. Hence, S. rusticum can be used as an efficient bio-controlling predator of mosquito larvae in fresh water bodies.