Warm up and spread your wings: thermoregulation for flight in the stag beetle Lucanus cervus

Flight in insects is a highly energy-demanding activity, requiring precise thermoregulation to ensure optimal muscle performance. In the European stag beetle Lucanus cervus , males exhibit a significant degree of morphological variation, with larger individuals possessing exaggerated mandibles that may hinder agility and increase energetic costs. This study investigates the thermoregulatory mechanisms employed by L. cervus males to prepare for and recover from flight, using thermal imaging. Field observations revealed a distinct pre-flight warmup phase characterized by increased pterothoracic temperature. The temperature in this region, housing the primary flight muscles, reached over 30 °C, 24 while abdominal temperatures remained close to ambient temperatures. Thermal imaging across three flight phases (i.e., stand-by, pre-flight, and post-flight) showed a significant temperature increase in the pterothorax. μCT analysis unveiled a sophisticated tracheal system in which the detailed submillimetric features of the air channels are consistently reproduced across individuals, while the spatial architecture at the whole-body scale varies individually. These observations suggest that tracheal organization may play a role in heat transfer between body regions, potentially contributing to the preservation of muscle efficiency and the protection of vital organs from overheating. However, the functional significance of this variation remains to be experimentally verified. Additionally, field data indicated peak flight activity between 19:30 and 21:00. These findings provide the first evidence of thermoregulatory behavior in L. cervus , highlighting the role of morphological and physiological adaptations in flight performance.