Emergence site selection in the endangered Southern Damselfly Coenagrion mercuriale in its UK stronghold, with observations on the Small Red Damselfly Ceriagrion tenellum

Emergence site selection was compared between the damselflies Coenagrion mercuriale and Ceriagrion tenellum in one of the UK strongholds for the former species. The mean height of exuviae above water level was 3.64  0.36 cm (n=74) for C. mercuriale and 2.35  0.18 cm (n=68) for C. tenellum. For both species there was a significant difference between observed and expected (based solely on relative abundance) plant species used as emergence perches. Eleocharis palustris and Juncus articulatus were used more, and Hypericum elodes less, often than expected. The national vegetation community in 13 cages was M29 i.e. Hypericum elodes-Potamogeton polygonifolius mire. Two other cages contained S19a and S19b which is Eleocharis palustris swamp. Broadly, suitable emergence habitat consisted of semi-submerged communities of Hypericum elodes (mean % cover 50%  4.4%), Potamogeton polygonifolius (mean % cover 5.8%  1.9%), Eleocharis palustris (mean % cover 19.2  2.6%), Juncus articulatus (mean % cover 3.2%  1.1%).