Winter is a stressful time for beekeepers and their bees. Days or even weeks can go by without seeing any sign that the bees are alive, and disturbing the hive at these times can lead to disaster. Beekeepers have devised many ways to check on their bees without opening the hives, from modern high-tech solutions like fiber optic cameras to the ultimate low-tech option: pressing your ear against the side of the hive and listening for a hum (the latter is my modus operandi). I've read stethoscopes can be helpful, but so far I haven't managed to swipe one from my vigilant doctor.
At what temperature can bees fly? Some say, very authoritatively, bees cannot fly when it's below 55 degrees. Anyone who keeps bees in a cool climate will tell you this is a lie.
Here's a video showing one of our colonies, who live in an early version of the Cork Hive, enjoying a break in the rain.