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Temperature regulation in a winter cluster

A winter cluster can be thought of as a ball of bees dissected by sheets of honeycomb. Clusters begin to form when the outside air temperature falls to about 57°F (14°C). Bees in these clusters are in no way hibernating but are actively moving, eating, and performing hive duties.

The comb in the very center of the ball contains a small amount of brood and the queen bee. The brood and the queen are kept at the correct temperature by the surrounding workers. The workers have several ways of regulating temperature and air flow throughout the cluster.

The cluster is not of uniform density. The outermost layers of the cluster form the densest portion, whereas the bees in the core are able to move freely and carry out the regular chores of brood rearing and caring for the queen. Although brood rearing may be almost non-existent in early winter, as the day length increases, so does the amount of brood rearing.

When no brood is present, the core temperature is kept somewhat less than 85°F (29°C), but brood needs to be kept warmer—at a constant temperature of about 93°F (34° C).

To warm the cluster, the workers vibrate their wing muscles—an action which burns calories and gives off heat. The temperature in the brood rearing area is further regulated by the expansion or contraction of the cluster. If the “nursery” becomes too hot, the cluster expands which increases the air flow around each bee and cools the nursery. If the nursery becomes too cold, the cluster contracts which decreases the air flow.

Bees on the exterior surface of the cluster become so cold that they appear motionless and dead. However, in a way that is not completely understood, these outside bees get pushed towards the center of the cluster by warm bees who then exchange places with them.

Clustered bees need a constant supply of food and, as the winter progresses, the cluster will slowly move toward stored honey. If the cluster loses contact with the stored honey, the bees can quickly starve. Clusters of bees that are too small—that is, they don’t have enough bee bodies to maintain adequate nest temperatures—will soon die as well.

Rusty

Comments

skirtmuseum
Reply

@HoneyBeeSuite thanks, i needed that post

mycomya
Reply

Do you remove the varroa mite bottom tray during winter, to increase ventilation?

Rusty
Reply

Mycomya,

I do, actually. But when it gets into the 20s I put them back in. So far this winter I’ve put them in and taken then out twice. See http://www.honeybeesuite.com/?p=2500 for more.

mycomya
Reply

Thanks!

Sarah
Reply

Let me try my comment again and let’s see if I can make it coherent this time! Between autocorrect and typing fast because I’m excited about what’s going on in my hive, that comment was nearly illegible.

My bees are flying like crazy here on this mid-50s day in southern Colorado. I opened all the hives to see where the cluster is and to check on honey stores (I leave 2 deep hive bodies and a medium super on each, to be sure they make it through the winter). To my surprise, one of the colonies had brood in the super! I’ve never seen this before, and am unsure how to proceed. Should I move that super below a deep? Or put a candy board on top of it? Leave well enough alone? The deep below feels plenty heavy yet, so I think I’ve got enough honey, but it’s below the brood nest (or, below at least PART of the brood nest). This is my strongest hive, so I don’t want to lose it by messing something up by moving the super, but at the same time, I don’t really want brood leavings in my honey foundation.

Rusty
Reply

Sarah,

Honey bees really do move up in the winter. The driving force for this is related to the temperature gradient in the hive. Air that has been warmed by the cluster will rise and move toward the top of the hive, so the warmest place inside any hive (other than the cluster itself) is the area just above it. The rest of the hive is relatively cold. For more on this see: Physics for beekeepers: temperature in the hive. Bees that leave the cluster to fetch more food are more likely to search in the warmest areas, which is why they go up. Meanwhile, frames below and to the side of the cluster remain untouched. Later, once the outside air warms up so the inside is more comfortable, the bees may begin using the other stores.

The same principle often applies to the winter brood nest, so I’m not at all surprised that you found brood in your honey super. Many beekeepers use a queen excluder for that purpose.

You can do a couple of different things. You can reverse the upper two boxes (brood box and honey super) but only if the nest is completely in the one box. You don’t want to split the nest in half, because the bees may not be able to keep both halves warm.

If the lowest brood box is empty of brood but contains honey, you could take that box and put it on top of the honey super. Or you could rearrange frames in the hive to make sure full honey frames are right next to the brood nest. Or you could put a candy board immediately above the honey super, if you don’t want to dig out the lowest brood box.

At this point, your honey super is going to be your brood rearing area for a few generations. I don’t see a way around it. Just go ahead and order some new frames/foundation for the honey season if you don’t want to use the ones darkened with cocoons. The cocoons won’t hurt your honey crop (unless you were planning on comb honey) but they don’t look as attractive once they’re lined with cocoons.

If it were me, I would probably do nothing at this point. It sounds like the bees are doing well, raising brood, eating honey. Life is good. But if the weather stays cold and they eat their way through that honey super, you may have to add a candy board. Watch them carefully because with new bees in the making, they will eat through a lot of food in a hurry.

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