We investigated behavioural consequences of life history states in Aquarius (Gerris) remigis, a hemipteran surface predator and scavenger of small North American streams. A repeated-measures field study comparing reproductive and non-reproductive first summer generation females and males during the same time in summer showed that non-reproductive males and females, which were foraging to survive the winter, behaved essentially alike, often being territorial. In contrast, reproductives of both sexes were more mobile than non-reproductives, reproductive males being much more mobile than reproductive females, always in search of and attacking potential mates. This resulted in reproductive males showing litde territoriality and having lower foraging success than all other categories, while reproductive females had higher foraging success than non-reproductive females or males, thus likely increasing their fecundity. Many behavioural variables did not change with time. Exceptions were a decrease in the mating activity of reproductives of both sexes, the number of mating attempts, mobility, and the stride rate of reproductive males, and an increase in overall foraging activity of all individuals. This indicates that the behaviour of reproductive males converged towards that of non-reproductive males as the season progressed. Individuals were assigned to either state post-hoc according to whether they had been seen mating at least once during the study period (July and August). Females were further tested to ascertain if they laid eggs. These results support the hypothesis that diapause and reproductive state to some degree predetermine behaviour, thus constraining behavioural flexibility. Attributing behavioural variation to various proximate causes can be central to the interpretation of alternative strategies and tactics.