Spatial and temporal segregation of six coexisting species of Ophiogomphus (O. anomalus, O. aspersus, O carolus, O. howei, O. mainensis, and O. rupinsulensis) were studied in a 137.7 km reach of the Aroostook River in northern Maine. Collections of exuviae showed that O. mainensis was most abundant and dominated the assemblage at sites in the upper reaches of the study area and was in low numbers and percent of total Ophiogomphus at sites in the lower reaches of the study area. Ophiogomphus rupinsulensis was most abundant and dominated the assemblage at sites in the lower reaches of the study area but was absent or in low numbers and percent of total Ophiogomphus at sites in the upper reaches. Ophiogomphus anomalus and O. carolus were present at all sites and O. anomalus was generally more abundant and made up a higher percent of the total Ophiogomphus spp. than O. carolus. Ophiogomphus howei and O. aspersus were present at only a few sites in low abundance and percent of the total Ophiogomphus. Several species of Ophiogomphus coexisted as larvae in 0.20 m² areas of the substrate.

There was little evidence of temporal segregation among the six species. All species had short seasonal emergence periods in June. Diel emergence was during the morning and early afternoon. Timing of seasonal and diel emergence either differed little or not at all among the six species. Species that we were able to identify in all larval stages (O. mainensis,O. anomalus, and O. howei) were present in a wide range of instars on all sampling dates (May to October) suggesting overlapping generations and multivoltine life histories. In all six species, some larvae remained in the final instar for almost a year before emerging as adults.