Each year beekeepers brace themselves for the reality that their bees may not survive the winter. Even the most experienced beekeepers lose colonies. But why do our bees die? If they were doing so well in the summer, why would they lose strength and die off (or disappear) in the fall? They were alive in December but dead in January, what happened? In my opinion, not all bees have what it takes to survive from one year to the next. Genetics can play an important role in their survival. But is there more to it than that? Are there things that we can learn from examining the remains of a colony? Will these clues help us to refine our beekeeping skills? YES!
Honey Bees are supported by scaffolding that is made up of nutrition, a well functioning queen, mite and disease resistance, and appropriate housing. A beekeeper has the opportunity to provide additional support when the scaffolding becomes weak and the bees begin to show signs of stress.
Let’s first talk about the cyclical nature of the life of a honeybee colony (keep in mind I am in the Pacific Northwest and so this timeline will not apply to all regions).
In January and February the colony is at its smallest, made up of the queen and the “fat winter bees” that were raised in the fall. By now the summer bees have perished, and after a small winter break the queen will begin laying eggs again. The amount of eggs that will go onto hatch and grow into adult bees will be determined by the amount of worker bees that can care for them, and the amount of food that’s available. Weather can make or break this initial phase of brood rearing. In Oregon, we typically have false starts to spring, meaning we will have a stretch of warm weather that stimulates plants to begin blooming and then there may be a freeze or a return to cold rainy weather, which slows foraging and decreases the quality of pollen available. The result is a colony that has begun brooding up suddenly has too many mouths to feed and not enough food. The brood may be cannibalized by the adult bees, or in some cases the entire colony will starve to death (see photo of starved bees & a varroa mite to the right).
During spring, the surviving colony or newly installed package/nuc will continue expanding their population. When the first nectar flow begins, the bees will begin building fresh white comb and quickly putting it to good use. The rapid expansion, coupled with a nectar flow will stimulate swarm preparations. If the colony swarms, it will allow for an important interruption in the brood cycle that will inhibit the reproduction of varroa mites. As the beekeeper, you can also take advantage of swarm preparations and make a split (only when the colony is showing signs of being ready and the weather is holding steady). Some colonies have the population and resources to support being split more than once. Again this provides an opportunity for natural mite reduction in the colony receiving a brood break. Swarming and splitting may continue into June, however I don’t recommend making splits beyond that time unless you are purchasing mated queens to install and have fully drawn combs available to give your new colonies.
In Oregon the main nectar flow is over in July and when it stops, comb building slows down significantly and the dearth begins. The bees will become more protective of their hive and may be more challenging to work with. Another interesting thing that happens at this time is a shift in the varroa mite to bee ratio. When resources are tighter, the bees will produce less brood. This is a subtle transition and it takes several months for the colony to appear smaller. But during this time, the varroa mites may have established themselves in the colony and will continue to quickly reproduce, meaning varroa levels peak after honey bees reach their peak for the season. Monitoring varroa levels and applying interventions (including supplemental nutrition) is more critical now than at any other time in the season! Here is a great resource for varroa management produced by the Honey Bee Health Coalition.
As the summer transitions into fall, the nurse bees are raising the generation of bees that will raise the “fat winter bees.” If these nurse bees have a compromised immune system from mites (see mite lodged under a bees abdominal plate to the left), viruses, poor nutrition or pesticide exposure, it will have a direct impact on the health of larvae that they are tasked with nourishing. If those undernourished larvae have those same pressures as they emerge as adult bees who will raise the “fat winter bees” then your colony will not only have unhealthy winter bees, it will also not have enough winter bees to keep the cluster warm during the winter season. Keep in mind, winter bees are also the ones that will raise the first generation of spring bees, and so the health and population of your winter bees is critical!
Fall is a delicate time for bees. They are focused on protecting their food stores, they may reduce the size of their entrances with propolis to protect against intruders like yellow jackets and robbers, and to reduce drafts as the weather becomes cooler. If you have a high mite load and viruses you will begin to see signs of trouble, if you haven't already. When I am consulting with beekeepers, fall is a heartbreaking time to take on new clients because so often they are calling for help because their once healthy hive is crashing. When it is so late in the year, recovery is unlikely (see to the right a brood comb from a colony that died from mite load and related viruses).
If the colony has survived thus far without significant pressure from mites or viruses, and has adequate stores it may seem that winter success is a sure win! NOT SO FAST. There is still work to be done! Late fall mite testing and hive weatherization are important. A colony can become reinfested with mites after receiving a fall treatment, or become infested by robbing out a weak colony that is on the verge of collapse.
November and December are typically brood-less periods, or times when the hive has the least amount of brood. A treatment of oxalic acid can be very effective to remove the majority of phoretic mites that remain from the active season. Additionally this is a time to add a moisture absorbing quilt box and insulation (please research the pros and cons of hive wraps and what is recommended for your region). Also adding emergency food (dry sugar or fondant) can be a life saver for colonies that eat through their food stores too quickly.
Now that I’ve given a simplified overview of a colony's year long cycle, let’s talk about the nitty gritty of inspecting your dead colony for clues!
Chose a nice day when your other colonies are flying so you know for sure that the one you are opening is dead. Ideally, you will have the chance to inspect your hive shortly after it has died and before too much mold will have taken over. I always start by removing the lid and smelling the hive. It should have a sweet, slightly fermented scent. If it smells sour or foul like rotting meat or sulfur please be extremely cautions, this could be a sign that your colony was infected with AFB, a highly contagious bacterial infection.
If the hive smells "safe" as described above, remove the frames one by one. Note the amount and the arrangement of honey stores and if the remaining cluster of bees is close by. In some cases, the cluster of bees has become so small that they cannot stay warm enough to move through the hive to reach the honey. We can say that the colony died of starvation, but we also need to consider what led to such a small cluster in the first place. Viruses can cause bees to fly or crawl away from the colony and also shorten their lifespans. Was the colony able to raise enough winter bees?
If you see mold on the cluster of bees, it is less an indication of too much moisture in the hive and more a result of decay. Their bodies hold moisture and when they die they may appear wet or moldy if you do not discover them right away. Be sure to look for the queen in the cluster. If she isn't there, search the rest of the hive and bottom board. If you cannot locate your queen then there is a chance that she died or was killed in the fall and the colony was unable to replace her.
Next look for signs of recent brood rearing. If brood rearing was recent, the cluster of bees should be close by. Do the brood cappings have pinholes, or appear to have been torn open while the bee inside was still pupating? If you turn the frame slightly, do you see white flecks of debris inside of empty brood cells? This is evidence of mites. Examine the bodies of the bees for mites and deformed wings. You can even open up brood cells and examine the pupae for mites.
Now move through the rest of the frames and set aside ones that should be cleaned up before your next colony moves in. This is a personal preference, use your discretion. I prefer to discard of frames that have significant amounts of dead brood or mold, or if the comb is so old that the hexagons are round and the comb has become nearly black.
Was there a pile of dead bees blocking the entrance? Bees can become trapped inside of a hive if there are too many dead bees blocking their way out. This is easily preventable by providing an upper entrance.
Do you see evidence of robbing? Honey comb that has its cappings ripped off will have a jagged appearance. Also check the bottom board for evidence that there was fighting, such as wings and legs scattered around and a pile of wax debris below where the honey frames were located. Robbing would indicate that your colony was weak in the fall and unable to defend itself.
If your colony appears to have run out of food (few frames of capped honey, bees found dead head first into cells), think back to the spring and summer nectar flows. Was the colony a late nuc, package, or swarm that didn't have enough time to build up a robust workforce? Did you provide supplemental feeding? Did you harvest too much honey?
Do you see brown streaky blotches on the frames and combs? This could be dysentery or nosema.
Is your hive almost completely void of bees? When a colony is under stress in the fall, they may abscond. This is an effort to relieve themselves of what ever was causing them ongoing discomfort (robbing or high mite load for example). This is different from swarming because it is not a reproductive event. In fact, myself and many beekeepers I know call it "Bee Suicide" because there is no way that a colony can start from scratch so late in the year.
Another observation I like to make is how much propolis the hive is coated with (see well propolised frame in picture). While it can be sticky and messy to work with a heavily propolised hive, I consider it an important element of colony health. If you aren't seeing very much propolis, you can take this opportunity to encourage propolis application in the hive boxes by scratching up the insides. Bees have an instinct to smooth out rough surfaces with propolis so you will be helping to foster that!
Whatever the cause of death, think of it as an opportunity to better anticipate the needs of your next colony. Additionally, you now have (hopefully) some nice drawn combs and honey to give the next bees that you care for.
I will be visiting more of the topics discussed here in future posts. In the meantime, thanks for reading and happy beekeeping!