Male P. longipennis defend shoreline territories, usually at ponds, where most mating and oviposition occur. Relationships between some shoreline characteristics and P. longipennis activity were investigated in New Jersey, USA. Males and females preferred similar, but not identical, regions of the pond edge and avoided others. Preference was positively correlated with vegetation height and with sunlight. Females were more selective than males in use of favored areas, and males were more selective at low than at high populations. Addition of perches and floating vegetation to unattractive areas markedly increased the use of those areas by both sexes. Males guarded their mates as the latter oviposited. Guarded females usually oviposited longer than unguarded females except at very high male densities. Females mated and initiated oviposition at frequencies approximately proportional to their frequency of occurrence but oviposited much less persistently in areas where they rarely occurred. Although a male’s expectation of encountering females and mating was lower in regions of lowest density than in those of intermediate or high density, mated females tended to oviposit more persistently in the lowest density zones. Consequently, males apparently had lowest expectations of fertilizing eggs in regions of intermediate density, despite the fact that energetic costs of territory maintenance probably were higher than at low density. This situation might result from imperfect congruence of male and female perceptions of territory quality. Also, males in regions of higher mating probability might benefit if their mates return to oviposit without remating after leaving the pond. Both males and females could obtain benefits from areas where they occur most abundantly as a consequence of increased larval survival.