Some observations on the utilization of groundwater habitats by Odonata larvae in an astatis pool of the Rhône alluvial plain (France)

Since 1979, samples of groundwater fauna have been pumped out of the alluvial plain of the Rhône River, upstream from Lyon (France). At several times they revealed early larval instars of Odonata from 0.5 to 2.0 m deep in the water-logged sediment of a neglected, unsilted gravel pit. This astatic pool is an outcrop of the underground water table. The data suggest the possibility for some Odonata (Libellulidae e.g. Sympetrum striolatum (Charpentier), Coenagrionidae) to effect a complete larval cycle in this kind of environment by the utilization of the phreatic biotope.