Odonata occurrence in caves: Active or accidentals? A new case study

Caves are environments that host unique faunas and may be important for organisms not exclusively dependent on caves. The occurrence of epigean taxa in caves is often considered accidental, but their study can provide useful information on cave colonization. Records of Odonata underground are extremely scarce. We have identified larvae of Cordulegaster bidentata in two caves, one natural and one artificial, from Lombardy in northwestern Italy. They occurred in pools near the cave entrance that have 84 lux of maximum illuminance, reached in early spring. In both caves we found a high density of larvae, and some of them were at very advanced instars. They had an important role in the cave's trophic web, exerting a high predation pressure on larvae of the salamander Salamandra salamandra. The plasticity of some Odonata species may allow them to take advantage of underground springs.