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Why did my bees die?

This is a question often asked and sometimes difficult to answer. The beekeeper looking at a dead colony is left with clues that can sometimes indicate the cause of death. More often though the beekeeper looks at the “crime scene” and makes an incorrect assumption. We’ve all heard it, “Wax moths killed my bees.” or “They got robbed.” or Small hive beetles killed them.” Most often though these are the results of problems that were missed or not addressed earlier.

I like murder mysteries. And, like in murder mysteries, what kills the bees isn’t always the most obvious suspects. It’s not the one the mystery writer wants you to initially think it is. After all what fun would that be? Instead the beekeeper must use some logic in backtracking the history of the colony to solve the mystery. Many times the downward spiral started some time back and we missed it before it lead up to wax moths, robbing, small hive beetles, or other maladies.

This past winter I had a 9% overwinter loss coming into the spring buildup. All in all, in today’s world of beekeeping that’s pretty good. Early in this season’s buildup, in February, I rotated boxes as a swarm prevention technique. I noted that a particular row of hives were not building up as fast as my other hives. As I rotated the hive bodies I inspected and found that they were all queen-right though so I just chalked the slow buildup up to “one of those unexplained things.”

That row of thirteen colonies coming into spring lost six colonies AFTER that first box rotation of spring. All of my other colonies continued to grow and expand.  Granted the ones lost were not the strongest but they had queens (I saw them). How were these different than the ones that were thriving? Time to put on my detective hat. They were unique in that they are all on same row, were not taken down in size last fall (I just ran out of energy), and had older queens. So what killed them? I don’t know but I suspect the stress of the box rotation on an already stressed colony. How were they already stressed? Why did they not build up like the other areas in my bee yard? Thinking about the differences: this group  had older queens, larger hives usually have/maintain higher mite counts,  and were in  an isolated  row in the bee yard.  I don’t know exactly which stressor was the largest but I suspect some or all of the above come into play.

Now my overall losses were at 27% instead of the 9% prior to this event and most likely because I failed to reduce size, monitor this row for Varroa better, and not re-queen in the fall. Which exactly? Beekeepers always want to know which one is the culprit. I don’t know. Maybe it was multiple stressors and not just one. But I do have some excellent suspects! Regardless of which stressor killed these colonies I failed to do that which a good steward should have done for these bees. Ultimately it’s on me.

So, after writing the above I was further pondering the possibilities while making up some sugar syrup, and I was thinking about the stressors and it came to me what killed those colonies. Distilling it down to a single element – laziness. I should have taken those hives down to 2 boxes post nectar flow last summer. I should have monitored Varroa better in that row instead of assuming it would be the same as the newer hives in other areas. And I should have re-queened as would have happened easily if I had made splits last year when I should have taken them down in size. My laziness killed those colonies. So there, I came up with a single cause, identified the culprit, and solved the mystery!

It won’t happen again. Maybe something else but not this.