Horses as a major cause of mortality in Coenagrion puella (L.) (Zygoptera: Coenagrionidae)

The aim of this short communication is to show the dramatic effect on the susceptibility to predgtion of a population of emerging damselflies when the emergent vegetation in the pond is greatly reduced by grazing vertebrates. In a two year study of the population dynamics of C. puella, at a pond in northern England, we monitored larval densities monthly, and measured and marked individually, almost every adult emerging from the pond. The pond is roughly circular with a radius of about 10 m. The aquatic vegetation consists of Nuphar lutea and Potamogeton crispus, while the emergent vegetation around the margins of the pond is Glyceria sp. The pond is situated in a small field which was ungrazed in 1983 but grazed in 1984.