While water striders (Hemiptera: Gerridae) have a global distribution different species have adapted to very different habitat types. Freshwater water striders such as Limnogonus luctuosus live in areas along streams and rivers with little to no flow. Marine water striders, such as coastal species Halobates hawaiiensis, have adapted to life on the surface of the ocean. Since these types of water striders live in such different habitats, and face different environmental factors their food preference and behavior can be quite different. In this study, average density of L. luctuosus individuals was measured along the Opunohu River. Also, food preference, behavior, and the effects of increased density were tested in the laboratory for both L. luctuosus and H. hawaiiensis. Response time and frequency of approach to mobile and immobile prey items were recorded for H. hawaiiensis and L. luctuosus. H. hawaiiensis preferred immobile prey while L. luctuosus preferred mobile prey. Frequency of several behaviors (i.e. movements, moving away from others, approached by others, approaching others, attacking, being attacked, jumping, and cleaning) were compared between species, and within species at increasing densities. There were differences between species in the frequency of movements, approaching others, being approached, jumping, and cleaning. Density affected movements, moving away from others, jumping, and cleaning for H. hawaiiensis. Density affected movements, moving away from others, and cleaning behaviors for L. luctuosus. The different ecology of these two species can be used to explain why differences exist in both food preference and frequencyof behaviors.