There was a piece of metal on top to prevent bird from entering, but bees are of course way smaller.
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This is a close up of the top of the chimney, to put things in perspective: there is a bee hovering on the left side.
I grabbed inside the chimney, there were maybe 8 bees in there on top of this piece of comb:
After careful inspection at home I found there were eggs inside the comb:
But there weren't enough bees to keep them warm, and there suddenly was no queen!
Next time when I'm in the neighborhood, i will put some fine bee-resistant hardware cloth underneath the big one, to keep the bees out.
My first chimney bees