Wintering and Cold Hardiness of the Small Tortoiseshell Aglais urticae (Linnaeus, 1758) (Nymphalidae, Lepidoptera) in the West and East of the Northern Palearctic

Abstract

The geographic variability of the cold hardiness of poikilothermic animals is one of the keys to understanding the mechanisms of the formation of their ranges under climate change or anthropogenic introductions. A convenient object is the small tortoiseshell butterfly Aglais urticae, which is distributed from the Atlantic Ocean to the Pacific Ocean. On the edges of the distribution range, the difference between the averages of the absolute minimum air temperatures reaches 60 °C. The cold hardiness (supercooling point and lower lethal temperatures) of imago wintering in a supercooled state in the northeast of Russia was assessed in comparison to the previously studied European ones. Despite the huge difference in air temperatures, the mean supercooling points ranges in the east (−23...−29 °C) and the west (−17...−22 °C) differ by only 7 °C; the lower lethal temperatures for this species is near −30 °C. The identified cold hardiness is not enough for overwintering of A. urticae on the vast majority part of the species range in natural shelters above the level of snow cover. The inhabiting of A. urticae in regions with air temperatures below −30 °C is possible only when wintering under snow. This primitive behavioral adaptation probably does not require physiological changes and may not be unique to Lepidoptera.