Well, I don’t know if the bees are happy, but I certainly am. Whenever I see winter bees dart outside on a cold afternoon and drop a semi-solid parcel, I sigh with relief. I want to say, “See! You can do this! You can make it till spring, one day at a time.”
I’ve never liked the term “cleansing” flight because it reminds me of certain forms of human hocus-pocus. However, a quick flip through a dozen bee books reveals the term is generally accepted. A cleansing flight involves finding a day of relative warmth and brazenly leaving the hive for a quick bathroom break.
Such a trip is fraught with peril. Since bees cannot fly any distance when temperatures get down around 50°F (10°C), any bee traveling too far may get stiff from the cold and be unable to return home. Of course, not defecating is dangerous too. If bee feces builds up inside a hive, disease and unhealthy living conditions can threaten the colony. Although bees can wait long periods between cleansing flights, it seems probable that the shorter the wait, the better.
A mid-winter flight can be multi-purpose
In my hunt for definitions, I noticed that some people use the term “cleaning” flights for a mission that includes ridding the hive of debris. They claim that the removal of dead bees, parasites, wax bits, mouse feces, or defective larvae may be part of the mid-winter cleaning procedure.
Indeed, I have seen bees discard dead nestmates in winter, but from my own observations it seems that defecation is the major issue. Still, if a day is warm enough, a little light housekeeping may also be in order. Like everything else in beekeeping, what the bees dump on a given day will be highly influenced by local conditions.
Snow on the ground makes the entire cleansing process more visible. Sometimes a beekeeper seeing snow dotted with feces and dead bees becomes alarmed that a sudden crisis has befallen the bees. But cleansing, clearing, and cleaning are everyday processes that signal the colony is functioning normally. The snow merely illuminates their activities.
But why so many dead ones?
Beekeepers often claim that all the dead bees near a winter hive perished from prolonged exposure to the cold. Some say the dead are old bees that would have died soon anyway. Others say they were sick bees that sacrificed themselves for the good of the colony.
While each of these may be true, I think some of those dead bees are simply corpses that got dumped during housecleaning. In any case, the process is normal and serves a purpose. Whenever I see a few dead bees on the landing board or a sprinkling of dead bees on the snow, I am comforted by the idea that life in the hive is progressing according to plan.
Upper entrances may aid cleansing flights
On a side note, an article about winter management in The Hive and the Honey Bee (2015) by Currie, Spivak, and Reuter (p. 631) mentions that an arm of the winter cluster may move toward the entrance during the day and back at night. The authors speculate that this arm may be a corridor for bees that want to leave for a cleansing flight. In my own mind I picture this “arm” moving like an amoeba, flowing toward the entrance by day and retracting to the warmth of the cluster by night.
I find this idea fascinating because I have noticed over many years that my colonies with upper entrances in winter seem to do better than those without. I’ve always thought the reason was related solely to ventilation and moisture control. But now I wonder if easy, contiguous access to an exit that is kept relatively warm by an extension of the cluster, may facilitate timely bathroom breaks.
Compare the routes
Compare two bees. The first bee feels warm all the way to the door, flies out, defecates, and returns immediately to the warm extended arm of the cluster. The second bee travels in the cold air below the cluster, down through the depth of a brood box or two to get to the entrance where winter air is rushing in. She then takes her cleansing flight. But on her return, she is not greeted by warmth until she crawls back up through chilly brood boxes to reunite with the cluster.
The difference between the two routes could influence how many live and how many die. If I were a bee, I would opt for the quicker, warmer route.
Warm air leaves at the top
Beekeepers often challenge me on the use of upper entrances. Some claim that the bees crowd the upper opening in order to keep out cold drafts. But this never made sense to me because cold air does not flow into the upper entrance. Instead, warm air flows out.
Hot air rises. Cold air comes in through the lower entrance and is warmed by the cluster. As it warms it rises to the top of the hive and eventually leaves through the upper entrance or ventilation ports. Bees near that upper entrance are going to feel warm, not cold.
If you have any doubt about this, look at this thermal image I posted last week. In this image you can see the warm cluster in the middle of the hive and the warm air above it. You can also see warm air leaving through the upper entrance in front. Compare that area to the lower entrance at the landing board, which looks as cold as ice. The bees lallygagging behind the upper entrance must feel like they’re in a sauna, especially compared to any using the lower entrance.
It is my belief that the bees at the upper entrance are not there to block cold air but to luxuriate in warm air. And now I’m thinking they might be waiting for a hall pass as well.
Happy New Year to everyone, and thanks for another good year.