Life histories of Enallagma hageni (Walsh) and E. aspersum (Hagen) (Zygoptera: Coenagrionidae)

The life histories of E. hageni and E. aspersum were studied in small ponds near Highlands in western North Carolina, United States. Both species overwintered as larvae short of the final instar, E. hageni in instars F-6 to 1-2 and E. aspersum in instars F-8 to F-l. The life cycle of E. hageni was completely univoltine with an early, relatively synchronized emergence. Although E. aspersum was primarily univoltine, about 8% of the new-year class was bivoltine, completing development and emerging within a single season. Fmergence was temporally dispersed, but there was a distinct peak in early summer. The temporal separation of life cycle events is probably significant in enabling the two species to coexist.