The honey bee colony forms a cluster or “ball” of bees crowding in together once temperatures get to about 59° F or lower. The warmer it is, the bees hang out in a looser, less tightly crowded condition. The colder it gets however, the more tightly they pack in next to each other.
Each bee is a walking thermometer and there are “outer bees” in the cluster and there are “inner bees” in the cluster. The bees take turns being inner and outer bees over time. All of the bees in the cluster generate heat by using “micro-vibration” in the thorax of the flight muscles. To watch them, you can’t even tell that they are making any movements of that sort.
“Inner” bees are packed together less tightly than bees on the outside of the cluster. That’s beecause their jobs, even while clustered, generate heat as well as care for the queen and any brood depending on the time of year. When there is brood to care for honey bee clusters can and will maintain temperatures of up to 95° F and maintain it as long as there is enough food to keep burning the energy.
“Outer bees”, those that make up the variably one to thee inches of the cluster “shell” as it were, cluster much more tightly together in order to “insulate” the inside of the cluster through increasing bee density and minimizing the amount of surface area that gets cold. When there is no brood to care for, bee clusters will “chill out” just a bit working enough to hold temps at about 55-ish ° F. Enough to keep bees alive and able to move their muscles.
Bees typically “hold it” and wait to empty the waste in their bodies for times when the weather allows them to fly out and away from the hive to do so. Unless they are ill or otherwise affected, bees won’t make a mess inside the hive. At least, that kind of mess.
When the temperatures are warmer, the cluster loosens up and sometimes breaks into smaller clusters allowing bees to travel across the combs and even to move the whole cluster ball upwards towards the area where honey or food is still stored. As the temperatures drop, the cluster re-forms and tightens up again. Those bees that don’t make it back to the cluster often die. Clusters that break up into smaller clusters spread apart in the hive that get caught unable to reform the larger cluster are also at risk of killing off the whole colony because there just aren’t enough bodies to keep each “mini-cluster” warm enough.
Bees that get too cold experience something called “torpor” which leads to dead bees. It’s not the typical behavior of bees to put themselves in such a situation to experience torpor, but it can and does happen far more than any beekeeper would like to see. Otherwise, honey bees cluster up and stay active and awake inside the hive all Winter long.
And that is what they are doing in there.