Bee activities are reducing with falling temperatures
Depending on the subspecies, most bees stop flying when the temperature drops below 9°C
To be able to fly the body temperature of a bee needs to be 35°C. A bee needs to prepare herself for flight by raising the body temperature. Bees achieve this by generating heat with their body.
Likewise, a bee colony needs to maintain a constant brood nest temperature of 34°C in winter and 35°C in summer. They achieve this with so called "Heater Bees" who can generate a body temperature of over 43°C with their wing muscles whilst disengaging their wings and pushing their body into so called Heater Cells, i.e. empty cells randomly placed among the brood cells. They also press their immobilised body onto the brood comb for up to 30 minutes, transferring their body heat onto the comb. The energy for heating is obtained from honey.
Honey serves as fuel; pollen provides the proteins bees need in their diet. To survive a lengthy period of time without bringing in fresh nectar and pollen bees rely on their stores of pollen and honey, the only reason they store it - not as a gift for the beekeeper.