Observed optimum temperature for activity in German populations is 20–22 °C (68–72 °F) (Heimes 1988) and they are rarely recorded below 16 °C (61 °F) or above 25 °C (77 °F), other observations for Ukrainian populations (Ščerbak et Ščerban 1980) put minimum activity temperature from 19 °C (66 °F) and optimum to 21–26 °C (70–79 °F). Above around 27 °C (81 °F) they try to avoid exposure to direct sunlight and cease activity with more extreme heat. The snakes will exhibit a degree of activity even during hibernation, moving around to keep a body temperature near 5 °C (41 °F) and occasionally emerging to bask on sunny days.