Emergence of the damselfly Pyrrhosoma nymphula (Sulzer) (Zygoptera: Coenagrionidae) from two adjacent ponds in northern England

Emergence of the damselfly Pyrrhosoma nymphula was followed closely at two similar and adjacent ponds in northern England. Males emerged earlier than females at both ponds (significantly so at one). The sex ratio was significantly male biased at both ponds. Size of emerging adults declined through the emergence period at both ponds. Adults emerging from one pond did so significantly earlier and were significantly larger than those from the other pond. The density of larvae was approximately twice as high in the pond from which larvae emerged early; this pond was also slightly deeper and usually achieved higher maximum daily water temperatures. These findings are discussed in the light of the conventional view of seasonal regulation in a spring-emerging damselfly.