I drilled holes in a few hive bodies last year. This serves as winter ventilation in the upper boxes — moisture is a killer for a hive during the winter. I do a few other things to prevent moisture from building up, but was reminded of the ventilation holes yesterday when I saw the photo above. The bees filled in the hole with material that looks like what they would use to cap a brood cell.
They probably did this because the hole is not above their clustering area, like a normal configuration. Instead, the hole is right next to the cluster. You can see how close it is the main entrance (you can see bees coming in and out to the right of the beige stick below the hole). When I first saw the hole, I thought it looked I didn’t drill completely through the box, even though I knew I had. Looking inside the box at the hole is a smooth wall. It is opaque.
Honeybees instinctively know how to survive. They are very clever.