De Noordse winterjuffer (Sympecma paedisca (Brauer)) in de Weerribben en de Kuinderplas

Two populations of Sympecma paedisca, a rare species in The Netherlands, are described. They were discovered in 1997 and 1998 in the Weerribben (province of Overijssel) and the Kuinderplas (Flevoland). It was the first time in more than 20 years that populations of this species were found in the Netherlands. The populations are present in a lake created by sanding (Kuinderplas) and a lowland mire (the Weerribben). Similarities between the two Dutch locations are a forested environment and non-acidic, clear water with reed-beds. The reed-beds are characterised by an open vegetation structure and locally dead floating plant material. The fact that the species only survived here is somewhat surprising as both habitat-types were not mentioned in the Dutch literature as favoured habitats. In both areas neither groundwater nor water-level fluctuations play a major role. This is also in contrast with habitat information in foreign literature. The last two years Sympecma paedisca was found from half August onwards into autumn. In the spring of 1998 the species was observed from the beginning of May until the beginning of June. Most reproductive activity took place during a warm spell in the beginning of May. The flight period in spring was later than expected on account of historical observations. The choice of substrate for oviposition was restricted, in both areas nearly only dead floating plant material was used (especially stalks of reed and reed-mace). The question why Sympecma paedisca only survived here and its habitat requirements are discussed. The answer on the first question is rather speculative. Perhaps the acidification of the balks (‘legakkers’) and the intensity of haymaking during the summer are important factors. The habitat requirements are largely unclear. The Dutch populations survived under conditions which lacked elements that were thought to be essential. Minimal requirements for reproduction are non-acidic water which is available during the summer and is partly overgrown with water vegetation. For adult survival certain structural conditions must be met.