bee biology

Happiness is a mid-winter cleansing flight

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


Warm air rises from the cluster (center) and keeps the candy board warm. Some heat escapes through the upper entrance, where the bees leave for cleansing flights. The heat near the ground escaped from my pump house. © Rusty Burlew

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.



  • Rusty, a very happy New Year to you and your loved ones, bot human and bee!

    I am in total agreement with your top entrance in winter and your theory behind it, especially when endorsed with the thermal image.

    If bottom entrances are reduced for winter and the upper entrance is small in size, it is more likely an advantage rather than a disadvantage, allowing CO2 to escape and the atmosphere within the hive to circulate and remain fresh. If the entries are too large, then the circulation will be too great and the bees will not be able to compete with the amount of cold air rushing through the hive.

    There will be variables, local winter conditions and wind strengths, dry cold with little wind flow, or horrid wet windy winter conditions, direction of prevailing winter winds and the locations of the entries relevant to it will all have a bearing on how well the temperature is maintained within any hive, but I for one would be happy to over winter down here in the deep south Pacific with a system similar to the one you run.

    Great to see your colonies have shown you they are surviving the cold and can find cleansing flight windows.

    In regard to the housekeeping, perhaps they have matron bees that suggest if you are going to leave the house, why not take some trash with you. Like when you tell your teenager that informs you they are going to their room to take their folded laundry with them.

  • Hi Rusty,
    Enjoy your web page.
    Re: winter flight… I have 2 colonies where I have been seeing a few workers fly out at temperatures as low as 28 deg. F. Of course, they never return. The “fliers” I netted from one of those colonies are 100% infected with Nosema as are most of the bodies on the landing board. Just an interesting (to me) observation. None of my colonies were treated with Fumigilin-B in the fall (I’m tying to get away from using antibiotics). It will be interesting to see if they survive our interesting PNW winter.

    • Dave,

      Interesting observation. In many places Nosema ceranae seems to be displacing N. apis, but N. ceranae is mostly a summer problem while N. apis is a winter problem. I thought I had a N. apis hive last winter, but it turned out to be ordinary dysentery. I suppose I should pull out the microscope and do some random checks.

  • Happy New Year 2017 to you Rusty, Family and Bee’s. May Good Health, Much Happiness, Prosperity in the Home and Hives, and Many Blessings from our God.

    Thank you for all your Beekeeping Wisdom and experiences you have shared with your readers.
    Your efforts and insights are deeply appreciated.

    May God Bless All Beekeeper’s worldwide and may God continue to Bless the United States of America!

    Jim Harper
    OFGC, Chief Beekeeper
    IL Master Gardener
    O’Fallon, IL

  • Lovely post Rusty made me feel close to my bees. You do that a lot. Thank You and a wish for you and yours for a Bee-Right 2017.

  • Hi Lady Rusty,

    Happy New Year. Thank you for taking your time to put together this amazing blog.
    Best wishes from London, UK


  • This is my second year trying to be a successful beekeeper. I am unable to attend any meetings of the local beekeepers association for a number of reasons that include finances, all meetings are scheduled to take place at a time that I normally am trying to take care of my girls, and I simply do not like driving long distances at night in an old truck that gets 9 or 10 MPG at best. So your posts are very important to this poor old country boy who was forced to retire early.

  • Had a warmer day yesterday and checked on my two hives. One had no activity and appears dead. Dead bees were all over the hive, even on the winter patties. They look like they are in suspended animation. The other hive was bubbling with bees. The hive that is alive produced more honey and was more defensive. Basically a hardier hive. Hope they make it.

    Have a healthy and safe 2017.

  • Hello Rusty,

    Happy New Year! Last Tuesday, December 27th, the temp. hit 52 deg. here in Pa. for a few hours in the afternoon. Both hives became very active. There must have been 500 plus bees crawling up the front of each hive box and flying about the back yard. My son was in from college and helped me do a winter inspection for food stores, good thing we did, both hives had eaten almost all of their 7 lbs blocks of sugar I placed on around mid November. I had two 5 lbs blocks made up for emergency feeding so we placed them in. The clusters are not very big, both around the size of a small cantaloupe, one just a bit bigger than the other. Is that a good size for the last week in December? They were only single 8 frame deep going into winter. We only had them open long enough to get the food in and see their size; it wasn’t warm enough to check any frames. I now feel I have to make up two 10 lbs sugar blocks with a protein patty sandwiched in the middle for each to get through winter. I’ll try to slip them into the hives toward the end of January, or the first week of February. Sooner if the long term weather outlook is bad. I’m just happy to see them still alive at this point. The only part that scares me now is that our coldest months are mid Jan to the end of Feb. If they can hold on till then our temps should level out and stay above single digits at night. Can you think of anything else I should be doing for them, or is it more or less up to fate now? Thanks for your help.

    • Jeffrey,

      Those clusters sound small. Still, if they have plenty of food, they may be able to make it. Just be careful they don’t run out. After the winter solstice, which we recently passed, they queens should begin laying again, so it would be helpful to get some protein in the hives as well. If you have dry substitute you can just mix some into their sugar or give them a small patty of it. They will have to work hard to stay warm, so a good food supply is the most important thing.

  • Rusty,

    Being a first year beekeeper, I have had some wins and losses when it comes to my bees. I find reading your blog, with all of your successes, keeps me hopeful that my bees will survive their first winter. My bees came out for their first cleansing flight on December 27th, where it was 53° here in CT. I was pleasantly surprised when I went out to greet them and record the happy event.

    Thanks for proving such valued information! I greatly appreciate it!

    Happy New Year!


  • Rusty,

    I love your site and visit it frequently, but not enough to learn this. Should I decrease the size of my lower front entrance ? I have a metal reducer on it now that has holes for entering/exiting etc. My upper entrance is merely a round bee-sized hole in the back of the box. FYI I have a brood box only, no supers. I live in zone 6-b northern central Ky with normally wet winters and short cold 15-25 degree spells, then 40ish temps. The photo of your hive entrance shows 4 bees squeezing together to get out. Mine could allow 10 -15 at a time. The reducer drops it down to 6 or so. Advice for a newbie?

    • Fran,

      I have both upper and lower entrances on my winter hives. The lower one is about three times larger than the upper one. As long as you’re keeping the mice out, you can use two larger entrances. There are no exact rules and all colonies are different.

  • First, a happy new year to you and many thanks for this informative and interesting blog.

    I lost my first hive last year due to excess moisture, so I added a Vivaldi board with an upper entrance this year. I noticed the other day that they’d almost covered the entire entrance with propolis but left just enough room to squeeze by. I figure they know what they’re doing so I’ll just leave them to it.

    You’re so right about the 50° mark! As soon as it gets that warm, even for an hour or less, I start seeing activity. After last year and removing dead bees from the landing board all winter, this certainly is encouraging!

  • Greetings. Another viewpoint may be that the bees are not luxuriating at the upper entrance, but that they are there doing a job. Perhaps they are trying to stop the outflow of warm air leaving the hive so that cold air can’t come in. Thanks for a great site.

  • Hello,

    In order to lose less heat through the upper entrance should one close the lower entrance during the cold period?

    • Francisco,

      You can, but make sure you have ventilation from somewhere. Cold isn’t really an issue with honey bees as long as they are dry, but excess moisture along with cold will kill them.

      • Hi Rusty,

        Thanks heaps for sharing all your info, I cannot suck up enough bee info and you are very helpful. I live in a zone 8 climate, the least we get is -5 C (23 F), but we do get a lot of strong wind (as my hedge plants are growing) and we basically get a lot of fog (low cloud) which can persist often all day long. Fog so you cannot see 20m ahead on the road. I still wonder if it is better to have ventilation, or not, in winter and spring. I am fascinated by many accounts of long hives, that they often are touted as super healthy, and interestingly not very well ventilated. My bees in a Langstroth have a blue board base and 2 entrances (big fan of multiple entrances, they have 4 of Filipe’s ‘intrances’). I am thinking, in early winter, that they are too ventilated- it’s not the cold, it’s the moisture the air holds. They are about a foot off the ground on a metal stand that blocks no wind. I left them 8 frames of honey in two 8-frame deeps. Went in to winter extremely strong. Local advice seems to swing from one extreme to the other. Any insights? thanks Rusty and all. And I am very very sorry to hear about your bear. : (

        • The reason the advice swings so much is that every hive is different. The best you can do is open your hives and have a look. Do you often see moisture accumulating? Then maybe they need more ventilation. If they are warm and dry, leave them alone. There is no magic formula, so you need to suss out the situation and go from there.

  • Happy New Year to all! Wanted to let you know that after sending a donation, my email no longer came up ready to use at the end of the comments. Like I’d been wiped off the subscriber list. No idea if I did something wrong or PayPal. It’s alway something, lol. LISA

  • Thomas D. Seeley claims that honey bees “Go out to defecate and gather water when it’s 42 and sunny.” Anyone see differently? How does a colony keep the hive warm enough to raise a brood in mid-Jan. to mid-Feb.? It sure seems like it would be difficult to keep the larvae fed and warm.


      • So the queen only lays eggs under the cluster and the workers (winter bees), always feed them under the cluster? So when it’s very cold, they always are in a cluster–when getting honey–during trophallaxis–etc.? I’m told winter bees have never been well-studied, so it’s hard to get details concerning how they raise brood when it’s below zero.

        • Mike,

          There is plenty of room inside the cluster to raise bees. The cluster has a “shell” which is much denser than the inside of the cluster where bees can move around. It’s not below zero in the nursery area, it’s more like 94 F, so brood rearing proceeds pretty much like normal. The winter bees have protein reserves in their fat bodies which allow them to secrete the proper brood food even in the absence of fresh pollen.

          • Excellent information. So can winter bees continually feed larvae without having to “replenish” their supply of food? Don’t they have to keep feeding each other (the winter bees), through trophallaxis? And doesn’t that require that they often get honey and water (mostly from condensation in the hive), to mix to feed each other? I only was asking about how they keep the larvae warm when it’s below zero “outside.” When it warms up enough for them to go outside, they must take turns.

            • Mike,

              You need to read today’s post. But yes, certain bees are assigned to go get food and bring it back to the cluster. Then it is distributed via trophallaxis. Those bees have a name but I can’t remember what they’re called. Retrievers, or something. They don’t raise too many bees in the dead of winter. The number gradually increases after the solstice.

          • How many larvae does the average winter colony have to feed at once? Do some of the colonies there have larvae now?
            Your climate must be very similar to New York State and Michigan, where Thomas D.Seeley (NYS-Cornell) and Zachary Huang (Michigan State U.), claim queens start laying eggs between mid-Jan. to mid-Feb. Both claim winter bees haven’t been well-studied. How many winter bees are in an average colony now?

            • Mike,

              We are actually a little warmer here: further north (47°N) but warmer because of the Pacific influence. I would say mid-January for the beginning of brood rearing, just guessing. The size of the colony is dependent on the subspecies. I run carniolans which tend to have smaller winter colonies than, say, Italians. But I don’t know how many are in a winter colony.

  • Happy New Year Rusty. As first year beekeepers, my husband and I love your blog. I have a question about the upper entrance. My husband says there is a small entrance in the lid, specifically the inner cover. I noticed a small cut out on the side of the inner lid. Is this a sufficient opening for the girls? I’m thinking we need to drill a hole in the top box. Your thoughts? It was also a warm day in upstate NY, and the girls were out in force! I was very happy to see them doing their flights. Although we had 2 full boxes of honey, we put pollen patties in the hive last week. we did see a couple of bees near the top of the hive which prompted us to do this. It seems they prefer the patties or there is no honey left. We will keep our eye on them and add more as needed. Thanks Rusty!

    • Robyn,

      I think the little entrance in an inner cover is fine for winter. That’s the kind I use and the bees hang out behind it and look out. I use a drilled hole in the supers for summer, but not for winter. That’s not to say it wouldn’t work just fine, but I never did it that way.

  • Today was very warm in’ Michigan, 60 degrees. I figured the bees would be flying so I paid them a visit. They were, but there was the strangest sound. It sounded like rain, but it was sunny. I was trying to figure out where this was coming from when I looked up into the oak tree and saw a whole lot of bees flying around up there. Then I looked at my coat. Ochre splatters galore. That ain’t rain, that’s a whole lot of bees pooping up there. Anyway. I checked on them a lot during the day and found something odd. Toward sunset there were a lot of bees out of the hive, just hanging around near the bottom entrance or on the ground. They were alive, but sluggish. I tried to scoot them back into the hive, not a lot of good that did I will bet. My question is why didn’t they take a cleansing flight and then go back into the hive? Why would they stay out, get chilled and die? Especially when they were right there at the entrance. ?? sk

    • Sharon,

      I don’t know. Some bees close to their end may leave the hive rather than die inside, but that wouldn’t be a large percentage. How many bees are remaining? Did you check the next day to see if any went back in? Or did they all die?

      • I did go back yesterday and take a look. Cleaned the bottom board while I was at it. Those bees that came out for the cleansing flight did not go back in, all dead at the hive’s entrance. Also, lots of dead bees on the bottom of the hive. I would say maybe 2 cups worth as a way of envisioning this. We’ll see. The dink swarm seems to be doing fine. We did talk about my bad timing with varroa treatment in an earlier conversation. I knew I was off by a lot (my mom died right about the time I should have started treatment for varroa in August and it all just got away from me), so maybe I am seeing more consequence of that too. The temperatures are normalizing again, getting cold, so they are back inside. I did open the screened bottom board on both of these hives to increase their ventilation and they do have a top entrance (actually two) for stale air to escape. Hope this helps. They looked pretty healthy tho. I do have a question about nosema. Do I understand correctly you can diagnose at home if you have a microscope? Thanks for your help.

        • Sharon,

          Many bees die every day just from attrition, so you have to take that into consideration. And yes, it is easy to check for Nosema with a microscope of at least 400x.

        • My bees did this on a warm day as well. They weren’t swarming but got out en masse for a cleansing flight and as the air cooled about 3 pm (it’s winter here now) they were still returning home, and a few dozen were lying all around on the ground. I warmed them up in the sunshine, gave them some sugar syrup, and put them at the hive entrance. Many went back in, and some did not and seemed to get rejected. I don’t understand why they couldn’t muster up the energy to go into the hive. They were all young bees. I have found no nosema in poop or chalkbrood under the hive.

  • Hi, I really enjoy reading all of your articles! Unfortunately we lost both of our hives early this winter. We didn’t harvest any honey, so we also hadn’t added any supplemental feed. We had 2 heavy & early snowstorms and they both died after the 2nd one. We hadn’t put up the insulation around the hives yet.

    Inspection showed lots of honey and a few bees head first in cells but mostly just dead in between the frames. We have a traditional langstroth and a long langstroth hive. We’re starting again this spring and are exploring options to improve their situation during unpredictable weather changes in fall & winter.

    Definitely going to add the insulation earlier. Thinking about adding some sort of overhead cover (4 posts with a roof) or even surrounding the hive with a portable greenhouse or tent. How far do they fly for cleansing flights? We’ll have an opening for them to get all the way outside, but would it be feasible to have the enclosure big enough so they don’t always have to leave when it’s super cold?

    Thanks again for all the advice you share!!

    • Cara,

      I can’t answer since I don’t know where you live, but one caution. Just because your colonies died after the second snowstorm doesn’t mean they died of the cold. More likely, it was mites or mite-vectored viruses, or perhaps Nosema. A healthy colony rarely dies of cold, and snow often provides an insulating layer, sort of like an igloo. Be super careful of tents or greenhouses. If the bees get false impressions of outside temperature, they may fly out, become disoriented, and die. Far northern beekeepers who keep bees inside all winter keep their spaces dark so they don’t fly out.

  • Here in Northern Idaho we finally had a nice calm sunny 50 degree day….my hive was so active with cleansing and foraging flights from the upper entrance that I was flabbergasted. I added some fondant to carry them into March and will add some protein patties after that when the weather warms. Even noticed many workers foraging on the green grass and plants within about 20 yards…looking for signs of a first flower or two. Everyone looked to be very happy for the signs of winters end…we hope!

  • Wednesday we had our first day of temps in the upper 40s in one hundred years. (Well, the first day all year at the very least.) There were dead bees in the snow around EastHive, my only remaining Not Dead Yet colony. As usual, I didn’t know if I should be happy that the undertaker bees were working, or sad that bees were coming out and dying of cold. There were a few yellow/brown drops of bee poop, but nothing I’d worry about.

    Thursday, when I checked the bee yard again, EastHive and everything around her including the three deadouts, was absolutely covered in splatters of bee poop. I have had bees since 2014 and all the bee poop I’ve seen in all that time wouldn’t add up to that one day’s production of bee poop. It looked like there had been a yellow/brown rainstorm.

    It was so yucky that, as the warm spell continued, Friday I went out with a bucket and a rag to clean it off, and believe me I’ve never bothered washing off my hives, or even our cars before, though as we all know, our cars are the usual target of “cleansing flights.” I’m not all that concerned about outdoor tidiness, but this was just appalling. Of course, warm water and vigorous scrubbing were totally useless against the mess. Oh well. At least bee poop doesn’t smell bad.

    I don’t think there’s a question here. I just wanted to share.

    • Roberta,

      I’ve got one hive like that, too. The inside is clean, so I think everyone took a cleansing flight at once. I tried to clean it with handfuls of snow, but it’s gross.

  • A long time ago when I could actually carry hives through the winter, we had a warm sunny late winter day, and I went out to check the hives. I could actually hear the bees, but could not see them. In addition to their buzz there was another little tick sound. My attention was on trying to locate the bees when it occurred to me to look up. There they were flying around in the branches of the oak tree. The tick sound was me getting rained on by bee poop. By the results on my white coat they must have felt immensely better when they returned home.

  • Rusty, how often do bees defecate in summer/flying weather?

    I’m guessing foragers eat mostly nectar and don’t have lot of solids build up…

    And even the nurses hold it in until their first orientation, despite eating all that pollen to feed the brood…

    So my guess is that they don’t go very many times in their short life. Maybe less than 5?

    Just wondering how late I could get away with feeding pollen patty, because some colonies don’t have enough winter bees.

    • Sean,

      Interesting because I would say the opposite, like every day. Nectar is full of solids, including ash and pollen. And it’s also full of water, which increases bulk.

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