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Autopsy of a Dead-Out

Why Did My Bees Die?

It's an all-too-common question every spring. Many beekeepers, both novice and experienced walk out to the bee yard to see how many of their colonies made it through the rough winter. There are a litany of reasons why a hive doesn't survive. We could talk about colony collapse disorder and other zebras that fly down from the center of the universe to destroy all of our hard work; but a better use of time and brain power should be spent on a more common culprit: Us.

Winter losses are common. Too common. The Bee Informed Partnership reports on annual losses each year. This data is, of course, only worth anything if we as beekeepers submit our numbers to them annually. That being said; 2017-2018 was a hard season for many beekeepers. Across the country, BIP reports an average 40% annual loss of our colonies. This includes the backyard hobbyist and the commercial beekeeper alike. In my home state of Virginia, the data showed a 65% loss, with numbers probably higher at the hobbyist level due to suspected low reporters. The heavy majority of these losses were reported in the winter.

When I get calls about dead-outs. I start by asking "why do you think the hive is dead?" The more common answers I get are:

"I opened my hive and all my bees are in a pile on the bottom board"

-Yup, that colony is dead

"There are a ton of dead bees on the landing board and ground in front of the hive"

- That one may actually be a good sign. How would the bees get out to the landing board? They were probably carried out by other bees. Housecleaning is a common chore to be done during winter when the cold weather breaks. If you have bees on your landing board, especially ones without pollen on their hind legs, this is probably just hygienic behavior of the colony trying to clean out the ones that didn't make it.

"I don't hear anything inside"

-Again, not a guarantee. hearing bees through the walls of the hive gives us comfort that the girls are still alive in there, however it is also a sign of high metabolism. Quiet bees are actually a good thing. Russian bees are known to be quiet during winter. This combined with the fact that the Russian bees go through winter with a smaller cluster can sometimes trick the beekeeper in thinking there is no bees inside, when in fact they are very efficient and doing just fine.


So once we are sure the colony is died, it is time to start the autopsy. Before even visiting the yard, I usually ask three questions that may lend themselves to finding out what may have lead to the colony's demise:

1. What were your mite counts going into winter?

2. How were your fall food stores and what have you done for winter feeding?

3. What ventilation strategies have you done during your winter preparations?

The reason I ask these three questions is because the three major reasons why colonies die over winter: Mites/ diseases, starvation, moisture. There are other reasons that have less of a culpability from the beekeeper. Bears, mice, small clusters (which could be normal depending on the species) can all attribute to winter losses.

The name of the game is simple:

Go into winter with healthy bees, free of diseases and pests, with plenty of food and a well-ventilated hive.


But that didn't happen, so Now what? Let's look at a few clues that could help us find out why the hive died and what we can do next year to prevent the same mistake.

Butts Out, No Food

This one is pretty easy to figure out. Bees that die with their butts out are scrounging for

food. When you get entire frames of adult bees that are dead inside their comb with their butts out, that is a common sign of starvation. The damning evidence that confirms our suspicions is the lack of food stores. Even if there are stores in the hive, we have to look at the location of the food compared to the location of the cluster. If winter is too harsh, or the cluster is very small, the bees can have a hard time migrating around the hive to find food. This is also true with emergency feed. Some beekeepers will say "how can they starve, I had dry sugar on my inner cover." While the attempt at feeding overwinter was valiant, the harsh temperatures can sometimes impede the bees from making the short trip out of the brood box and up to the inner cover (or Vivaldi boards) to get the sugar. Dry sugar is also not stored like syrup or honey is, so it is quickly metabolized and passed around the colony for a quick snack. There are also a lot of bees commonly found on the bottom board. because the bees died of starvation, the ones that didn't die in the comb were too weak to take off and leave, so their final resting place is on the floor of the hive.

Lots of Food, Lack of Bees

As a general rule, when a colony is dead with a plentiful food source we then begin to look in the frames for signs of pests and diseases. The signs and symptoms of things like CCD, foulbrood, etc will be talked about on a different blog, but the first suspicion of a high disease load is a lack of treatment prior to winter. As has been talked about all over the internet, the winter bees need to be healthy for them to be effective. Treating for mites in the fall is the first and one of the most important ways to get your bees through winter.

The one phrase that gets any seasoned beekeeper to cringe is "I didn't see any signs of

varroa." We know that varroa breed and live inside the brood cells with the larva. If you see varroa on adult bees (known as phoretic mites) then you already are behind the eight ball. But how can you tell if there was mites in a colony with no bees or brood? Take a look at the cells. If you clear away the carcass away from where the cluster was, you may see white granules inside the comb. This is guanine acid and is a sign of varroa defecation.

Unlike starvation, many bees with diseases will try and leave the hive to die if they are able to. This is another key finding when deciding on starvation vs. disease.

Sometimes we see an overabundance of food in the colony. In a dead colony, this is often protein patties. Protein patties are a breeding ground for small hive beetles. SHB overwinter with the cluster, so if you crack you hive open and find tons of SMB larvae in your protein patties, start to look at that as a potential cause. Only put enough protein patty in your hive that the colony will consume quickly. Placing an entire pad on your top box is a huge invitation for SHB larvae.

Water, Water Everywhere

Moisture kills bees over winter. As is said time and time again: Cold bees are fine. Cold wet bees are dead bees. Moisture in the hive leads to mold growth, and the bees will actually freeze once they are wet and cold. Preventing moisture build-up is all about ventilation. New beekeepers often focus their efforts on sealing up the hive for winter, but the placement of proper ventilation channels is more important than covering your hives with styrofoam and trash bags.

Ventilation basics starts with keeping lower entrances free from debris such as snow or dead bees. Upper entrances are also a great way to improve airflow and give the bees a backup exit if the lower entrance is covered. The use of quit boxes is also a very helpful way to absorb moisture. Weather you use something commercially available like a Vilvaldi board or a simple quilt box, the goal is to get the moisture out of the hive and off your bees (more on this during our winter preparations post).

Small Cluster

Small clusters are usually a secondary cause of colony death over winter. That is to say: Why is the cluster so small. Often times this can be due to diseases as discussed above, while other causes of smaller clusters are simply due to the species of bee. If the population of bees were small going into winter, then you will certainly have a small cluster coming out of winter. Additionally, engaging in aggressive hive manipulation during cold winter days will also kill off much of the brood and adult bees, leading to lower winter populations. Prevent pathogenic small cluster sizes by keeping your bees healthy in the fall and limiting brood nest disturbances during winter.

MYTH: Wax moths Killed the hive

Every now and again you hear a beekeeper talk about how they lost a hive due to a wax moth infestation. This is not the case. Like small cluster-related deaths. Wax moths are secondary causes of colony destruction. Wax Moths are opportunistic feeders. They exist in your hive because your hive was unable to defend against them. They do not come in to a previously healthy hive and cause havoc. This is why the most common place we find wax moths is on empty frames being stored for later use. If you see wax moths or their cocoons, realize that the hive has been weakened by another cause.


So now what do I do?

The next step after you discover why the hive has died is to decide what you are going to do with your equipment. The big decision that needs to be made without failure is did the hive die from a bee-specific problem (moisture, DWV, Varroa/PMS, starvation) vs. a severe communicable and reportable condition such as American or European foul brood. What we know about varroa-originated diseases and parasitic mite syndromes is that they effect the brood in many different stages of development. If you see dead brood at various stages of development, especially emergence, then it is probably not AFB/EFB.

Lacking any diseases that could be passed to other colonies, the frames can be reused for the next year's hives. As a general rule, I brush off and vacuum as much of the dead bees and junk as I can, throw the frames in the freezer for a few days, and store them in a tight space away from those wax moths. If you have chickens, they will be more than happy to help clean the frames out. If you fed syrup prior to winter, you can feed those frames back to the bees, but you should not harvest them for human consumption. If you have mild mold growth, the freezer and bees will clean all that out and remove the bee carcasses stuck in the cells. If you frames are covered in mold it may be best to pitch it.

The most important thing you can do is NOT GET DISCOURAGED! We are all life-long learners when we make the conscious decision to get into beekeeping. Learn all you can, understand your mistakes, and start the planning and preparation to improve your practices for the following year.


If you'd like to learn more about the Bee Informed Partnership, visit


Milbrath, M. (2016, March 8). Why did my honey bees die? Retrieved February 20, 2019, from

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