Did your bees die of cold or starvation?

Many people argue that wintering honey bees seldom die of cold. Instead they die of starvation, either because they could not reach the food or because their food supply ran dry. In truth, the reason a colony dies in winter is usually much more complex than simply cold or starvation.

Thousands of bees but no food

When a colony dies of starvation, the results are often striking. I’ve seen huge populations of dead bees in a hive—dead bees piled deep on the top bars, crammed between the frames, covering the bottom board. Bees, bees everywhere and not a scrap of food anywhere. It is one of the saddest sights ever. But even so, did the bees die of cold or starvation? Once they ran out of food, they could no longer keep themselves warm. So which is it?

Similar questions arise every day. If a plane runs out of fuel and crashes, did the passengers die because of the crash or because the plane ran out of fuel? You can make many arguments. If the plane didn’t run out of fuel, it would not have crashed. On the other hand, the simple act of running out of fuel didn’t kill anyone, but the impact did.

Remember, honey bees are wizards at keeping themselves warm. When you see a dead colony, it helps to ask, “Could feeding the colony have saved it?” To me, that answers the question. If it’s obvious that lack of food was the ultimate cause of death, then yes, they starved. The bees ran out of fuel, just like the plane. When the fuel runs out, the wizards are toast.

A critical mass of bees

Bees die of the cold when the colony isn’t large enough or healthy enough to keep itself warm. To keep itself warm, the colony needs a certain number of healthy, well-fed bee bodies to generate the heat. How many bees is that? Well, assuming the bees are perfectly healthy, that will depend on factors such as the climate, weather, hive type, genetics, the distribution of the food supply, moisture accumulation, and protection from predators. I’ve seen baseball-size colonies make it when conditions are right.

On the other hand, if the colony lacks a sufficient number of healthy, well-fed bee bodies, all bets are off. If the colony is sick due to disease or parasites, if the colony is malnourished, queenless, or if the colony genetics is poorly suited to the environment, it may succumb to the cold. When the colony is not healthy to begin with, no amount of feeding, wrapping, supplementing, or general mollycoddling will make any difference.

The last straw

It is easy to look at dead colonies and say, “My bees died of the cold. They were fine before the cold snap, but that finished them.” This is like saying the passengers died from a plane crash when, in fact, they were doomed the second the plane ran out of fuel. To prevent catastrophes in the future, it helps to understand the ultimate cause.

Assuming a colony is healthy and has easy-to-reach food, it should be able to keep itself warm if it is large enough. The question to ask first is, “Why is the colony so small?” Maybe it resulted from a late swarm or a late split and is, in fact, perfectly healthy. If that is the case, your overwintering strategy should include ways to keep that small colony warm. Perhaps a little mollycoddling is warranted.

Sifting through the reasons

On the other hand, if the colony is small for an unknown reason—especially if it dwindled recently—it may not be healthy enough to overwinter. Many colonies, whose deaths were attributed to cold weather, were goners for other reasons. They couldn’t keep themselves warm because they were already sick or weak or being decimated by pests. A colony of sick bees won’t make it, no matter how much food you give them because food isn’t the limiting factor. As more die, fewer remain to keep the colony warm.

I don’t have answers here. My point is simply that the perennial argument about whether bees died of cold or starvation is often pointless. Instead of just blaming the cold, try to understand why your bees were vulnerable to cold in the first place. Once you have some ideas, you can tweak your practice and become a better beekeeper.

See the conclusion: “Bees head-down in cells.”

Honey Bee Suite

A beehive in the snow. Do bees die of cold or starvation?

In beekeeping it is easy to blame the wrong thing. Do bees die of cold or starvation? Sometimes it’s neither. © Rusty Burlew.

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  • Our best strong hive had 100 lbs of honey, plus fondant. Yet when we inspected all were dead everywhere, estimate 15000 bees. Found 11 mites, two hive beetles. We search all through the dead, no queen found. Very sad.

  • Its easy to tell if they died of severe cold or starvation. If there is no honey left available in the cold weather, its starvation.

    I have only a few hives, so I have the time to manage a plastic covering, known as a stand up green house. I have a opening on top to exhaust air. This blocks the biting cold wind that will make the bees use more honey to stay warm and possibly starve.

    I also use a 12 volt heating pad at the bottom that helps when the temps go below 15 degrees F. Its not high heat, but keeps the inside at about freezing temps.

    I realize that this would be impractical for big operations. With a few hives I can easily manage their overwintering. Every morning I check the hive and on warm days open up the front flap so the bees are not trapped. At night I close them to protect from the cold and wind.

  • Hi Rusty, I would just add, to the pointless part, that a large colony without stores will die in warm weather also. The outside temperature has little to do with survival for all the reasons you stated. In many studies, bees were kept alive and healthy down to -20f and when warmed were fine. Most anecdotal accounts say you need at least three seams of bees for successful thermoregulation but many small nucs with healthy bees have less and winter great. Healthy bees, meaning low levels of varroa predation during the summer months will help with survival. Most of the time the unexplained winter deaths are neither cold or starvation but rather a high viral load that impedes metabolic functions.

  • I had hives die this year with frames of honey just two inches away, their butts were sticking out of sucked dry comb.

    • I had bee die with fondant 1 cm away. They need it right on top of them, like literally on top of them.

      • Isn’t it likely your bee died of something besides hunger? Lots of things refuse to eat right before they die of something else.

  • Great article as always. Thank you Rusty, very good points. Ask the right questions and dig a little deeper, don’t assume you know.

  • I have often wondered about the cold. I’m getting my first set of bees this April but I have been reading and worried about the overwintering process.

    I also have chickens and when it gets really cold out we we put a little warming mat in the coop in addition to a water heating mat. I’m curious why, if cold is a problem, there is no use of heaters for hives. Obviously you wouldn’t want a warm hive with bees eating lots of their stores, but why not use a heater like the one for the chicken water. It only turns on if the temperature goes below 35 degrees. It would seem like a great idea, yet I don’t read of beekeepers using them.

    • Petey,

      The problem with adding heat is it fools the bees into believing the outside temperature is warmer than it actually is. Then they fly out and die.

      • I wonder if that’s what my bees are doing. It gets below zero a lot here in MN so I wrap the hives in black tar paper. Many times this winter I’ve found hundreds of bees out in front of the hive. Now I have a cpl boards blocking the midday sun off the hive. Some bees are are 100 feet away. Yesterday we had 4 new inches of snow and I bet over a hundred bees dead out in front and some a long distance await. I wonder if that wrap is fooling them.

        Does anyone else up here in the cold see the same thing happening. Thanks.

  • Always enjoy your posts. If you insulate the hive and the bees are warmer do they eat more than if it’s cooler? Or do you think they eat more in a colder hive?

    • Randy,

      Increased activity causes them to eat more. They seem to eat less in cold hives. But insulation doesn’t add heat, it only keeps their body heat from escaping as fast.

  • Perhaps more than just being cold, the bees died because of condensation dropping on them. Bees can usually keep themselves cool in summer and warm in winter, but they can’t keep themselves dry. Bee quilts are one answer, good ventilation is another.

  • Hi Rusty,

    Speaking of cold and it definitely is right now here in Olympia WA. Just curios have you reduced the entrances to your hives or are they wide open in this cold?

  • Rusty, I lost all three of my large hives this winter. The two Italians went first, they perished in December, not during the sub 0 temps but during the temperature rollercoaster that followed them. Below zero temps to mid 40s back to single digits, Fahrenheit, in 24 hours. I looked like they broke cluster to get food and were never able to re-cluster before torpor set in. I found them scattered all over the hive upper and lower boxes some face in cells some just sitting on comb. Then in the 3rd week of February I lost my strongest hive after the same type of event only I found them 3 solid inches deep on my bottom board completely covering the slatted rack slats. It was very of disheartening.

    I thought for sure that when I checked the nuc that I had more or less done bare bones winter prep too would have befallen the same fate. Amazingly it was booming. I tried not to disturb it accept to top off its emergency food supply. I am going to examine that little hive very well this spring to see how come it did so well when the others that had extensive winter prep failed.

    Now my question. I want to move that nuc into one of the vacant hives this spring. All 4 of them sit alongside one another no more than 28 inches apart in spacing. Should I remove the hive closest to the nuc and place the nuc on that spot now while it’s cold and they are clustered, then in spring when they get rolling swap out the nuc for the full hive and exchange brood comb? Or should I just do it all in the spring at one time? I guess what I’m asking is, will they get disoriented being so close together while exchanging domiciles? I guess as long as the queen is in the new hive and the old nuc is no longer present they will move in? Your thoughts would be welcome. Thanks.

    • Jeffrey,

      Once the bees start flying in the spring, the foragers will always go back to the original location. I think it will be easiest to put the nuc in its final position now, as you suggested. Then in spring, when you change the frames around, they won’t have any trouble finding their new home.

  • Rusty,

    A very eloquent article. I just had a weak colony die that had lots of candy in the hive but not close enough, perhaps? It seems to me that your analogy is perfect and the common link between starvation and the plane crash is actually – enough bees to do all the jobs that are needed. Without enough bees to do the housework, and also heat the hive there are no spare bees to go and get lunch. Could that be the vicious circle with the bees making a decision to heat and feed eggs first, before going to eat. So food runs out (even if there is a cake of food just above them) and they die doing their priority jobs and sacrificing the individual self.

    • Michael,

      Possibly. But it doesn’t take much of a drop in temperature before the bees become unable to move. So it may be impossible to travel to the food, even if it is only inches away.

  • For three years I thought I was doing great as a beekeeper. Lost one out of two hives the first year, one out of three hives the second year, and one out of four hives the third year.
    Then this last year I lost three of five hives in the spring and two of the remaining two hives in the winter.

    The spring losses were all my overwinter hives that swarmed and then failed to requeen in the coldest, wettest spring on record in my area. Not really enough resources to save them from the two new package hives I had, but a better beekeeper would have gotten them each a new queen from somewhere. A worse beekeeper would have blamed it on wax worms, but a better beekeeper would have combined before the wax worms took over. I did do some practice combines with them, and learned a tremendous disgusting amount about wax worms, so at least it was a learning experience, though a very sad one.

    As for the winter losses, both “died of starvation” during a cold snap in a hive full of honey stores. One had a huge cluster; the other had a tiny cluster. I just took a really close look at the tiny cluster one (because I needed to disassemble it to repair the screened bottom board) and what I found was a ton of mites. I was surprised at how closely you have to look to find mites between bee segments. I had treated (MAQS) but I hadn’t retested. I am mostly writing this because I admire Rusty so much for writing about things that go wrong, rather than (my normal impulse) denying my own mistakes.

    I also had converted to horizontal hives because just how many times do I want to drop a full deep, and catch it on my knee with the invariable concomitant stings, before I look for a work-around. But I have not yet gotten a horizontal hive through the winter. Now that I’ve read posts here on the physics of bee hives, I’m thinking maybe I can run horizontal hives spring, summer, and fall, then stack them up for the winter.

    Anyway, new packages pre-ordered. Bad beekeeper here, getting ready for spring.

    • Roberta,

      You bring up such an interesting topic: searching for mites. I think most people sift through the bees, find a few mites, and say, “Nope. Not mites.” But as you noticed, if you start pulling the dead bees apart, you can often find the mites between the abdominal segments. I still believe mites are the reason for colony death about 80% of the time, but it’s hard to convince people of that.

  • Hi Rusty,

    Your article on “Did my bees die of cold or starvation?” was pretty comprehensive but I find it misses the influence of hive insulations and effects of top venting.

    1. “A critical mass of bees” is most likely a function of the thermal resistance of the hive as the cluster tries to maintain an outer cluster surface temperature. I am running a crude experiment on seven hives. Condensation does not appear to be an issue. Admittedly, there is not much data out there.

    2. “healthy and has easy-to-reach food” – I would think both issues are related to hive thermal resistance, especially “easy to reach food”, meaning warm enough to move and eat. “healthy”, I am biased on this being older, I just think it feels good to be warm with lower metabolic rates versus “shivering”.

    I have been through some of the worse possible natural temperature-humidity test. Days and days of coastal rain, 99-100% RH and fooooogy, no sun with rising temperatures approaching internal hive temperatures.

    Still learning,

  • Timely advice Rusty, thank you. We are on high alert here in the UK because we all felt the worst of winter was over and had started to pat ourselves on the back only to be told that a massive ‘high’ over Scandinavia is going to give us two or 3 weeks of easterlies, sub zero daytime temps and several degrees of wind-chill. Oh Boy. Terrific. Maybe time for some mollycoddling?

    • Ray,

      We are experiencing unusually cold temperatures, too, after a week when the bees were flying. Crazy weather.

  • Thanks Rusty,

    That’s what I was thinking but I wanted to confer with someone with more experience before I kill anything else. Sorry, that was in bad taste, I’m joking of course in an attempt to shake off the losses with humor. I do take this seriously and I’m striving to learn more and raise survivors, after all they are living creatures and if it were my dog that froze to death I would be mortified.

    If this NUC makes it, and I mean to see that it does. Even If I have to bring them into the garage for the rest of the winter, of which surprisingly enough my wife suggested. If that was my idea I would be in divorce court right now. Hahahahaha! I will attempt to figure out why, “Little meant more”. Best of luck to all and thanks again Rusty.

    • Phil,

      In the past few years I’ve been using a rotation of OA dribble, Apilife Var (thymol), and HopGuard. So far, so good.

  • Hi Rusty,

    Starvation is made evident by bee butts showing from the cells. They die trying to get the last iota of honey from the bottoms of the cells. The only time I had this happen was years ago with a swarm in a nuc. They had syrup both at the top and at the bottom entrance. But when the temp dropped, the cluster was too small to reach the top or bottom. It was heartbreaking to see all those bee butts!!! Of course I know better and always place honey frames in nucs, but there’s nothing like a teaching experience 🙁 🙁

    Best to you,

  • Rusty I agree about the mites being the main cause of losing a hive. The virus weakens the hive so much they can’t function properly. This was our fourth year trying to keep bees and we finally made it through this crazy weather in the north Georgia mountains with my only two hives alive. They seem fine now but I know we aren’t out of the woods yet. Our hives on the edge of the woods by some bottom land pasture. It’s very windy so when we had extreme cold we put up wind breaks. Do you think that helped the hives or just made us feel better? ?

  • As always, the most rational, reasoned article around. I used to say that, if you lined up all the bee experts, they would point in every direction. While there is some support for that, I have gone full circle. This year, I am using front entrance feeders. Why? If I open the hive body to pull a frame or two, replace them with an inside feeder, fill the feeder, and close up. I have disturbed the hive more than I would like in the winter. Then, the feeder, being on the top of the colony, requires the bees to migrate well above the cluster. Then, they have to climb down into the internal feeder and many of them die. Drowned. Not healthy. So, I have pulled all the supers, froze the frames, and on March one, I will place a super on the top with the frames containing the most honey and pollen atop the upper deep. Hit 45 today and a gazillion bees were everywhere. My most shameful act (as a bee keeper) was when we took too much honey from our two colonies and they both starved that winter. No stores, dead bees butt up in the frames. Heart breaking. Truly. Our best to you.

  • It is March 2nd 2018 in Michigan, winter has been cold with heavy snow. My hive has been active the past week and more so as of two days ago because of our strange weather high 50s foraging for maple pollen I suppose since so many maple trees in this area. Everyday prior to the cold snap I noticed them doing orientation flights. Lots of buzzing lots of bees erratic flight around the hive but gentle bees landing on me unlike if they were being robbed. This hive overwintered with all its food stores and will need to be split as soon they show signs of swarming. I know this hive has potential for creating new hives they pulled comb in 3 brood boxes, 2 supers and toughed it out in horrible Michigan unpredictable weather and are still kicking. I was hoping to make a few nucs by end of April with some Carniolan queens any advice on using Carniolan queens for making nucs or splits from existing Italian hives?

    • Craig,

      Some people say it’s harder to get them to accept the Carniolans, but I’ve never had a problem. Just watch how the bees react to her while she’s in the cage.

  • I appreciate your advice on this Rusty. I would think acceptance may rely also if I leave the newly separated brood boxes queenless long enough so they are desperate enough to accept a queen they do not know. But not sure how long few hours or day to leave them without a queen. I would think it shouldn’t take them that long to figure out they don’t have a queen.

    • Craig,

      I’ve read that it takes a colony about 15 minutes to know they are queenless.

  • Also I wanted to ask if planting any type of herbs around the hives whether it will help with common hive pests, beetles, ants etc? I was thinking of planting lemon grass, thyme, lavender around them but in your experience would you think this will help at all with minor pests?

  • Hi from Western Maryland Rusty! 1st year beekeeper going into 2nd spring and I appreciate your great site and the valuable information! Moisture quilts made and used on my 2 Carni nucs and my bees and I thank you for the help! Started in late May…long story-bad timing for grafted queens in our area this cool,wet spring and my supplier moved up in altitude by 400ft to a new apiary and was supposed to have nucs by mid May at latest!…they were surprised by their new micro climate to say the least…needless to say I fed them like crazy the whole season to get about 1 1/2 mediums of “honey” for them. I was astounded at my sugar tab by seasons end!! My weaker hive suffered the loss of most foragers around mid June. Thousands of bees dead on ground in front of hive. Most with tongues sticking out. Suspected pesticide kill. After driving the area saw a lot of brush along side of roads burned back from chemical treatment apparently- a lot was honeysuckle. I pulled capped brood from my unaffected booming hive at a rate of a frame or two every 2 weeks until I saw foraging pick back up and the queen began to lay again. Then again later in the season around mid August both hives had sick bees all over ground but not dead. Abundant feces on the grass where they were hanging. No feces in hives. Most couldn’t fly but would make it back into hive somehow every night. I worried and wrung my hands talking to club members and suppliers trying to decide what I had and what should be done or what medication I may need. Diagnosis and recommended treatments were all over the place and I decided to wait and see… (I picked up the Api Life Thymol , but ended up not using due to an early cool period) Will use this spring. Sickness persisted for about 1 week and then almost overnight was gone and things returned to normal. Treated with oxalic vapor(sorry I know you don’t care for the vaporizers much and I respect that-thankfully no horror stories to report and I tried to keep my Tim the Toolman AHH-AHHs in check while I treated 😉 ) late IMO- around Thanksgiving. Hundreds of mites dropped almost immediately. After a second treatment a week later, I saw none in 48hrs. The bees stayed clustered low in hive as I could see them from bottom entrance until the real cold moved in. Left dry sugar on plastic foundation and they have been all over it every time I peek in there. We still have some cold unpredictable weather to go but I am growing more optimistic by the day. Saw a fair amount of pollen coming in around Valentines Day with lots of orienting and hives stuffed with bees. Easily 8-10 frames packed full in both hives! Found a couple medium brood frames with eggs, larva and capped brood in both hives and saw the dark queen in one as well. Sorry for the long winded post, but wanted to relay my first year experience thus far and will be staying vigilant during the starvation month at hand. Weighed hives in November and strong was 145lb with 4 mediums high and weak was 120lb with 3 mediums high. Both still feel about 50-70lb and saw lots of capped honey frames in each. Will be starting deeps this year to compare growth rates and overwintering differences. 1 of my suppliers told me I would kill my bees keeping them in all mediums. Opinions definitely abound…I appreciate the work you have put into this site again- I look forward to your and others opinions here. Thanks and happy beekeeping! Nate