In 4 small peat bogs and 2 little lowland marshes of northeastern and central Switzerland the larval habitats of this stenotopic sp. were studied with reference to structural, physical and chemical parameters as well as the vegetation and the accompanying odon. fauna. The "classical" peat bog habitats (i.e. natural, shallow and partly overgrown basins or peat diggings) are characterized by acid water, free of carbonate and with low concentrations of electrolytes. The vegetation consists of Scheuchzerio-Caricetum limosae. The investigated larval habitats in lowland marshes are covered with Caricetum fuscae or C. diandrae. The water is slightly acid to neutral. It contains low carbonate concentrations, whereas the electrolytes values are rather high. Based on this evidence, an attempt is made towards the definition of ecological factors which determine the habitat selection. It is assumed that the habitat structural appearance plays the main role. Various other components are presumably but indirectly involved. Tentative conservation measures are suggested and the horizontal and vertical distribution of the sp. in Switzerland (57 known sites) is summarized and discussed with reference to the local temperature conditions.