I’ve found that while people understand the bee’s job during the Spring and Summer, with their pollinating and honey making, many don’t understand what exactly bees do during the Winter. After asking a few friends of mine, the general responses are either dying off or hibernating, neither of which is technically correct all the time. Different kinds of bees do different things, so I’ll be talking about honey bees and bumblebees.
The above answers make sense; bees disappear around Winter time because of the lack of flowers and foraging opportunities. Around Winter you may also see many dead bees on the ground around a hive. Let’s start with the latter idea; bees don’t just die around Winter, they stick it out inside their hives. The bee carcasses you see are one of two things: one, it’s the last of the summer bees, who only live for around 3 weeks, dying off, or two, it’s the drones who are forcibly kicked out of the hive. The drones’ only purpose is to mate with a new queen in late Spring, so if they’re still hanging around by Autumn they’re wings are chewed off and they’re left for dead outside of the hive so they stop consuming resources. If you feel bad, keep in mind the drones can literally only do one thing; they can’t even feed or clean themselves.
Moving on to the former idea that bees hibernate in Winter. This is a bit tricky because some bees do, namely bumblebees (and most solitary bees). Bumblebee queens leave in late Autumn to mate and then find themselves a nice hole to sleep in for the long Winter months. Honey bees on the other hand do not hibernate, although they do stick themselves inside the hive, since the cold can easily kill them. As I alluded to earlier, in the Autumn most of the summer bees die off and are replaced by Winter bees, which live anywhere between 3-6 months, to take care of the hive while they’re unable to rear any more brood. They form a ball, roughly, inside the hive (yes even Langstroth hives, the ball is just spread across the frames of one box), with the queen in the centre. The workers vibrate their wing muscles to create warmth, keeping the hive at a toasty 10º-25º Celsius. They also take turns on the colder outside of the ball.
For bumblebees, since they’re hibernating they don’t need to store any food in the place they hibernate; instead they gorge themselves on honey before they leave the hive to sustain them for the Winter months. Honey bees require more food storage because they’re exercising––vibrating their wings––and they’re awake. If they don’t have enough honey, because of a poor forage year or because of beekeepers or wild animals, the hive is unlikely to survive the Winter. If the hive is too cold, because of a lack of workers or persistent very cold weather, the honey may solidify and the hive is unlikely to survive. If the bees are sick, with varroa, poor nutrition, or other, they are unlikely to survive; this one goes for bumblebees too.
Two sources were used for this post for the life cycles of honey bees and bumblebees:
“Bombus Sp.” The Virtual Nature Trail at Penn State New Kensington, information gathered by Katie Kirstein. Penn State University, Oct 2013. www.psu.edu/dept/nkbiology/naturetrail/speciespages/bumblebee.html
Döke, Mehmet, A. Frazier, Maryann, and Grozinger, Christina M. “Overwintering Honey Bees: Biology and Management.” Current Opinion in Insect Science, Vol 10, August 2015, Pages 185-193. doi.org/10.1016/j.cois.2015.05.014