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beehive collapse over winter

Why My Bees Died Over the Winter - Conducting A Hive Autopsy

Mar 18, 2023

The hardest part of beekeeping is handling the death of a hive, but when a hive perishes, the beekeeper has to put aside their emotions and figure out the cause of death before the evidence is lost.

Why would you want to examine a bunch of dead bees? 

The two main reasons for wanting to determine the cause of your hive's death is that you want to learn from your mistakes so you can increase your hive's survival rate next year and to make sure it is safe to reuse the honeycomb in other hives. 


Watch my YouTube video about determing the cause of the your hive's collapse over winter.

Post a question or read other people's stories in the comments below the video.


The top culprits to causing a honeybee hive to die during winter are:

  1. varroa mite infestation
  2. starvation
  3. not enough ventilation/condensation
  4. nosema
  5. tracheal mites
  6. animal attack
  7. failing queen

Let's take a look at each one of them, so you know the signs of a hive loss due to this culprit and what you can do next year to prevent this from happening again.

Notice that I didn't include cold weather!


Cold weather does not kill honey bees. Honey bees can withstand very cold temperatures. In order for bees to survive cold weather, they need three things:

  1. Good health

  2. Lots of food

  3. Insulation


The bees make their insulation. As a beekeeper, you can provide them extra insulation in the form of bee cozies or wrapping the hive with roofing paper, but these things are not necessary. Did you know that Russia and Ukraine are some of the biggest honey-producing countries in the world? My great grandfathers had bees on their farms in rural Poland and Ukraine and they did not have bee cozies to keep their hives warm. The bees vibrated their flight muscles and produced their own heat as they have been doing for many years.

As a beekeeper, your job isn't to make the hive as warm as possible, it's your job to make sure they are healthy and have lots of food! 

So let's get to the list of culprits for your hive loss.


#1 Varroa Mite Infestation

The #1 killer of honey bee hives in the winter! Many beekeepers think that this isn't the problem because they treated their hives once or twice over the spring and fall. Maybe they treated before they closed the hive up for winter, but did they do a mite test? Did they know how many mites were in their hive? Most importantly, did they test their hives for mites in the late summer/early fall? 

A little bit of background on what a honeybee hive does in order to survive winter

In mid/late summer, the queen bee will lay eggs for the winter bees. These bees have different fat deposits, different hormone profiles and are the only ones designed to live for months. When these bees are pupating in the hive, it is also late summer/early fall when varroa mite levels can be high. Robbing happens during this time of year, bringing in many varroa mites on the backs of the robber bees. You won't see all of these mites because over 90% of them are hiding in the cells with the pupating winter bees, weakening the bees and giving them viruses.


If winter bees have viruses, they won't be able to form a strong cluster and insulate the hive.


Signs Your Hive Died from a Varroa Mite Infestation over Winter

  1. Your hive died in the fall or early winter.
    Hives weak from varroa usually perish not long after the temperatures go below 40F. Since the winter bees are weak, they cannot form a strong cluster to stay warm and they die fairly early in the season.
  2. Varroa on the bottom board. 
    A lot of dead mites on the bottom board can be a sign of an infestation. Usually you want to do a count and see how many mites per 100 bees you see, but since that isn't possible, look to see if you see a lot of mites on the bottom board.
  3. Unhealthy, capped pupae present
    In a healthy hive, the remaining pupae emerge in the fall. If you are seeing capped cells where pupae never emerged, cells with a hole in the capping or cells with bees' heads facing you and their tongues sticking out, that is a sign your hive had a varroa infestation. In a healthy hive, the pupae emerge on their own. 
  4. Your hive was large in the summer and appearing healthy
    Big hives with a high population in the summer often have a high varroa mite population come late summer. Lots of bees means lots of mites and once the bee population goes down, the mite population stays high, leaving your hive overun with viruses and mites. Hives that swarmed in the summer or requeened had a break in their brood cycle and so have a considerable lower level of mites in the hive.
  5. Lots of honey in the hive
    With lots of honey in the hive, it is safe to assume that the hive did not starve. 
  6. Mite feces seen in the hive
    Mite feces, known as guano, can be seen on the edges of the hive cell walls and is white. Do not confuse this with crystallized honey. You'll see this strictly on brood frames, not honey frames.
  7. A tiny cluster of dead bees
    Tiny clusters of bees is a sign that the winter bees were weak and could not survive. A tiny cluster is a cluster that is the size of a softball or smaller.
  8. Spotty brood
    Along with sick-looking brood, if you seeing spots of capped brood, that is a sign of weak winter bees.
  9. No Varroa Mite Management in the summer or fall
    Whether you treat your hives for mites or not, it is still important to know what your hive's mite levels are. Without conducting a mite test, the beekeeper will not know if a hive is infested with mites. You cannot look for mites on your bees or put a sticky board under your hive to get an accurate reading. You have to take a sample of bees in order to get an accurate reading.

Watch my video on how to do a mite test. It's easy to make and only takes 5 minutes.


How to Prevent a Varroa Mite Infestation

Test one hive in your apiary every month with an alcohol wash.

If your hive has a high mite count (3 of higher), it is recommended that you treat your hives to lower the mite levels. Usually, the beekeeper will treat in the spring (before the bees start bringing in a lot of honey), late summer (after you harvest your honey for the year) and once more in the fall before the hive is closed up for the winter. 

See my video about when to treat your hives and treatment options for you to use.


#2 Starvation

Lack of food is another common cause of a honey bee hive to die over winter. The best food for your bees is the honey that they gathered, but the beekeeper can also add dry, white sugar or make candy (also known as fondant) and put that at the top of the hive. 



You do not want to feed your bees a liquid sugar syrup during the winter!


Signs your hive died from starvation are:

  1. No food in the hive
  2. Bees died with their heads in the cells (see photo below)
  3. Cluster is surrounded by empty frames and although there is food in the hive, it is far from the cluster.
    This is common with top bar hives when the cluster starts in the center and moves to one side of the hive. They starve, not able to break the cluster and access the honey on the opposite end of the hive. 

How to Prevent Your Bees from Starving over Winter

Make sure your hive has ample food. If you have a langstroth hive, you want your honey to form a bell shape in the hive with the largest amount of honey at the bottom, and gradually decreasing the amount of honey in the upper boxes. 

You also want to make sure there is a super full of dry, white sugar or fondant above the upper most box in the hive.

After a couple of months, start checking on the hive to make sure they have enough food. On warmer, sunny, low wind days, add more food under the lid if needed.

An easy way to see if your hive needs food is by lifting one end of the hive to see how heavy it is. As the weeks go by, you'll notice the weight of the hive decrease.

For most of the U.S., 50lb of honey in the hive is sufficient. In the colder, northerm states, 60-70lb is needed.

Make sure to keep track of how much honey you put in your hive each fall and how much is left in the spring to see how much food your bees ate over winter.


#3 Nosema

Nosema is a parasite caused by a fungus. Nosema affects the bees' diggestive tract and will kill a hive over winter. 

Signs of nosema:

  • Brown/yellow streaks on the outside walls of the hive
  • Send a sample of dead bees for testing to a bee lab
  • Population was strong in spring but got smaller in summer


You cannot prevent a hive from getting nosema. It is an unfortunate thing when it happens and one reason why beekeepers should have more than 1 or 2 hives in their apiary.

If you think your hive had nosema, it's important to send the bees to a lab for testing or examine bees under a microscope. 


If your hive had nosema, do not resuse the comb! You have to dispose of the comb or you can infect your other hives.


#4 Tracheal Mites

Another cause of honey bee hive loss that is out of the beekeeper's hands is tracheal mites. The only way to know for sure you have tracheal mites is by sending a sample of bees to a lab for testing,

Signs Your Hive Has Tracheal Mites:

  1. Hive was healthy in spring and then smaller in the summer
  2. Dead bees spread all over the hive, not in a cluster
  3. Bees trembling outside, in front of the hive


Unfortunately, there is no way to prevent this from happening. The good news is that this isn't a common cause of hive loss that you should be seeing across all your hives or see year after year. It is a problem the beekeeper will come across occasionally.


#5 Animal Attack Killed Your Bees

An obvious one, but signs an animal killed your hive are:

  1. Hive was knocked over
  2. Animal feces inside hive
  3. Comb was eaten

It's important to check on your hives (not open the hive, just stand near the hives to observe them, coming and going or listen to the buzzing by putting your ear on the wall of the hive). Sometimes the beekeeper will blame a rodent or animal for destroying a hive, but the hive was already dead. The animal is just taking advantage of a free meal. The sooner you realize a hive has collapsed and can examine it, the greater the chancec you'll figure out the correct cause of death.


  1. Use mouse guards over the lower entrances
  2. Put up an electric fence to keep bears and larger animals away

I've occasionally had a hive tipped over by a cow or wild boar. I do not put fences around my hives because it is a rare occurance.


#6 Poor Ventilation/Too Much Moisture

People often think they need to keep their bees warm, but if the bees are healthy, they produce their own warmth. What the beekeeprs needs to do is make sure there's ventilation.

When warm air is produced by the bees, this air needs somewhere to go, or condensation will form and drip on the cluster, killing it. 

The bees also need ways to leave the hive to go on a cleansing flight.

Signs your hive died from poor ventilation/moisture:

  1. Wet inside the hive
  2. Mold in the hive (not on the cluster)
  3. Entrances blocked

How to Prevent Your Beehive from Getting Attacked by Animals

Make sure the hive has an upper entrance, a lower entrance and a moisture board to collect any moisture that may be accumluating.

Check on the hive weekly and scrape away dead bees accumulating on the bottom board. You do this by scraping the board with your hive tool. Do not open the hive! You can put the hive tool in through the lower entrance. Make sure the lower entrance is clear for the bees to come and go.


#7 Failed Queen

A failed queen is not as common as the other causes of a colony to collapse, but still can happen. 

Signs Your Hive Died Over winter Because of a Failed Queen

  1. Queen cells on the brood frames
  2. Colony was alive by late January but no brood when it collapsed
  3. Brood may have been spotty in the summer
  4. Queen is over 2 years old

Ways to Prevent a Failed Queen Over Winter

You can requeen hives with a queen that is 3 years or older to prevent the possibility of her not laying come late winter. Personally, I do not pinch my queens based on age. I only requeen if the hive is struggling and a new queen is the only way to get the hive to be healthy and heavily populated again. However, it is up to each beekeeper to make this decision. Don't let anyone else tell you what is wrong or what is right!

In Conclusion

It's never easy to figure out a hive's cause of death. If it was obvious, we would have done something sooner to prevent it! Most likely, you'll never know without a doubt the cause of death. All you can do is take detailed notes as best you can, talk with other beekeepers about methods they use to successfully overwinter their bees, and try to use better techniques next year.

As always, you can ask me! 

Sign up for my online beekeeping class. It includes mentorship so you can email me directly questions you have. Include photos and/or videos and we can troubleshoot together!

Click here to enroll today!


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