The impact of incidental summer snowfall on two alpine metapopulations of Somatochlora alpestris (Selys) (Anisoptera: Corduliidae)

In the course of a 2-yr mark-resighting study on S. alpestris at 2000 m a.s.l. in the Central Alps of Switzerland snow fell during the beginning of the reproductive period in July 2000. The snow cover was up to 30 cm thick and remained for about 8 days. Only 3% of the individuals marked as tenerals and 4% of those marked as matures before the cold spell were resighted afterwards. In 1998 (a season without snow) the corresponding resighting proportions amounted 10% and 54% respectively. In 2000, at a second study site at 1700-1800 m, 11 % of the individuals marked as matures before the cold spell were found again. It is concluded that, unlike the aquatic stages, the imagines of S. alpestris are not well adapted to survive cold periods with snowfall lasting more than a few days. Various survival strategies focused on egg and larval development of the sp. are discussed with respect to adaptation to a subarctic climate.