Senescence is the result of age-specific trade-offs among life history traits. Energetic trade-offs among various components of an organism's energy budget can also affect an individual's life span. An increase in reproductive effort, for instance, can result in less energy available for maintenance of body tissues resulting in a shorter life span. We investigated the effects of reproduction on longevity of giant waterbugs (Belostoma flumineum). Female giant waterbugs oviposit eggs onto the backs of males which then provide all post-copulatory parental care. The number of reproductions was manipulated in both males and females, and male waterbugs were divided into groups that provided parental care or did not. This allowed us to determine the relative costs of mating versus parental care. Both male and female waterbugs maintained as virgins outlived those that bred. Parental care incurred a greater cost in male waterbugs than the act of mating, but the number of reproductions had no effect on life span suggesting that a single reproductive event is as costly as many. In both males and females the age at first reproduction was significantly positively correlated with age at death.