Vogt, D.: Cold-hardiness in bumblebees.

Muscular thermogenesis enables individual bumblebees to fly while foraging in the cold. However, this ability comes with great risk. Bumblebees are unable to warm-up and fly if they cool to near freezing air temperature or if they have inadequate fuel reserves to sustain a high enough body temperature for flight. Bumblebees were subjected to prolonged exposure to cold air temperatures without a food source to determine some of the limits in performance (activity and flight). No discernable differences were observed between drones and workers. Bees with ample food in the crop were capable of enduring several days at cool air temperatures. Larger body size may increase survival time at near-freezing air temperature. Prolonged exposure to near-freezing air temperature appears to suppress the ability of bees that have been stimulated to warm-up at 22C when compared to bees acclimated to warmer air temperature.