When bees get cold they cluster together in the center of the hive. a puppy-pile of bees all nestled into one another, with the Queen snuggled securely in the middle. Like stones warmed by the sun, warm honey in the surrounding comb has insulating properties that help keep the cluster at a constant temperature. No matter what the outside temperature, it’s 90 degrees in the middle where the Queen rests.
The constant temperature takes a lot of energy to maintain. Bees on the outside of the cluster act as a blanket to keep everyone on the inside warm. They stay there until they’re too cold. Cold bees then burrow into the center to warm up as the next batch of bees takes over blanket duties.
Some of these blanket bees, only a handful of them at a time, have a rather unusual technique for creating heat. When the colony needs an extra jolt of heat on the outer layer, some of the bees will volunteer to become “heater bees.”
When humans are cold we shiver. Heater bees do something like that but with an interesting twist. First the bee uncouples her wing muscles so her wings don’t move air. With her wing muscles disengaged, she shivers the tiny steering muscles she uses while flying. The shivering motion moves each shoulder muscle against the muscle doing the opposite action, like in isometrics. Imagine the motion of flapping your arms up and down except do that while letting your arms limply hang. Move your shoulder muscles really fast, pitting one muscle against the other.
Like shivering or jogging in place, this raises the heater bee’s metabolism and creates hot spots in the cluster that warm nearby bees, helping them last longer on the outside. Once that little heater bee wears herself out, she burrows back into the warm center to replenish her heat.