Stages of Development of Libellula depressa Dragonfly Larvae (Odonata, Libellulidae) in the Central Caucasus

Libellula depressa L. dragonfly larvae inhabit aquatic biotopes no more than 30 cm in depth with clay and detrital sediments of the plain, foothill, and mountain zones of the Central Caucasus to the altitude of 1700 m above sea level. The onset of metamorphosis and emergence of adults begin when the water warms to 18 ± 1°C in all zones, shifting in time from April on the plain to mid-June in the mountains. The development of larvae includes 14 age stages and lasts 76–110 days (or 101–137 days, taking into account the egg phase). The increase in the development period begins from the 7th stage, and the last (14th stage) is the longest. The development is characterized by the formation of complexes of morphological and linear features that reliably determine the stage. Morphological changes affect significant systematic features that appear or are lost at a particular stage. Seven age groups include one to four development stages with common morphological parameters.