In the winter, bees will cluster together in the hive to keep warm. The cluster is very tight and is concentrated around their food source.
However, not all bees get to stick around for winter.
Drones (male bees) are not allowed to stay during the winter. Their only job is to mate with a virgin queen in the spring. After that, they are allowed to stick around until the nectar supply runs out and then they are deemed useless and kicked out if the hive.
Guard bees stand guard ensuring the drones don't sneak back into the hive.
On warm days of winter (usually above 50 degrees), bees will leave the cluster to take a cleansing flight or potty break. Bees are very tidy housekeepers and will not go to the bathroom in their hive.
Housekeeper bees also take care of the bees that have died in the hive. On warm days, these bees drag the dead bees from the hive and dispose of the bodies right outside the hive.
So, if you see a bee in the wintertime, please let them go. They've been holding it for a long time!
Brenda (aka The Blonde Gardener)