(Baetis vernus)
Baetis vernus is a species of ephemeropteran insects inthe family Baetidae. This species is part, with Baetis buceratus and Baetis tenax, of those called "medium olive" by fly fishermen. Baetis is a genus of mayflies inthe family Baetidae, the most species - richof any genera in this family. Species of the genus Baetis constitute one of the components of aerial plankton. They are like all mayflies in decline, probably due to water and sediment pollution, but also due to degradation of the nocturnal environment by light pollution and possibly also due to the polarized light pollution, a growing phenomenon that can cause ecological sinks and ecological traps for species sensitive to polarization of light, including mayflies.