It’s March. Depending on where you live, your bees might be out foraging in a full-on spring situation, or maybe you’re like me here in Minnesota, staring at bare willow branches, willing those first glimmers of yellow-green to appear. It’s the most exciting time of year for beekeepers. The whole season is ahead of us. Everything is possible. Even dead-outs.

The only thing to dampen a spring mood is peeking into a colony and finding it completely, irrevocably, dead. The end of winter is a common time to find dead-outs, and a few things could cause death, but the cold in and of itself is not typically one of them.

If bees die of cold, it’s probably in conjunction with wet (condensation gathering on an inner cover and dripping down) or in conjunction with dwindling cluster size, which in turn can be related to a failed or failing queen, or sick bees. A small cluster may dwindle into death or not maintain a stable temperature to keep the spring brood warm. A small cluster also has a hard time moving up to access honey as needed and could end up starving. 

What can you learn from your spring dead-outs? The number-one lesson is the importance of late summer management. 

While we often blame hunger and cold for winter dead-outs (what beekeeper hasn’t wished to bring her bees inside by the fire on a cold January night?), they are less-likely culprits. More often, bees die from high levels of mites and the viruses they vector. A large, healthy cluster going into winter with plenty of honey (in northern climates, we leave upwards of 80lbs per full-sized colony) should be able to withstand frigid temperatures. However, bees going into winter with high mite levels rarely make it through the following season. 

How can you confirm what killed your bees? Two main places can provide you with clues. First is your beekeeping notebook (or app). Flip back to October/ November of last year: what were your mite levels going into winter? Did you do a good job managing them by providing high-count colonies with a fall treatment? Did you note any signs of disease like deformed wings, dwindling cluster size, or brood disease? Did your bees have enough food stored at the time you wintered them? 

Next, you can look into your dead-out colony for clues. If there’s honey left in the colony, you can pretty much rule out starvation. Looking at the bees closely, you can estimate when they died: “fresh” (intact) looking bees means a recent death; decomposing, wet bees means they probably died before the new year.  

“Fresh” (intact) looking bees means a recent death; decomposing, wet bees means they probably died before the new year. 

Mite poop (frass) is a pretty good clue that your bees died of high mite levels (and associated viral health problems). Mite poop looks like sugar crystals on the sides of brood cells. If you see a ton of this white stuff on the outside cells of food frames, circle back to your notebook to determine if this is a colony you fed syrup to in the fall; crystallized sugar syrup stored in cells can be confused with mite frass! 

Once you determine why your bees died, you can decide whether to reuse equipment. Boxes and bottom boards may need a scrape and a paint job but are typically fine to reuse for many years. Frames are a trickier question, and everyone has their own standards. I usually reuse honey frames (with or without honey), and in the case of brood frames, I reuse unless they have one or more of the following: dead brood, signs of disease, a history of disease, or a high level of grossness I can’t deal with.  

What can you learn from your spring dead-outs? The number-one lesson is the importance of late summer management. For newer beekeepers, late summer can be the most intimidating time of year. Colonies are big, heavy, gluey, and sometimes increasingly defensive. You’re intimidated by robbing, mite testing, or squashing your queen when it’s too late to replace her. But dig into your colonies, you must. Late August is when the queen lays the “winter bees,” workers who take the colony through the cold months. They need to be healthy, with low mite levels. When brood production stops and that final round of bees emerge, mite counts can skyrocket. Fall is the most crucial time to get those mite counts low. 

While mite-vectored viruses aren’t always visible (if they are, it’s often too late), they are present and spread through mites. Maybe it will be possible for beekeepers to assess their virus levels in real-time or even treat them directly one day, but for now, mite loads are the best indicators of disease loads. So, if you did have dead-outs this spring, plan to be a tough-on-mites beekeeper next fall while also making sure nutrition levels are high (leaving enough honey or feeding syrup) and queens are young and healthy going into winter. 

Originally published in the February/March 2022 issue of Backyard Beekeeping and regularly vetted for accuracy.