Last year I had a hive that for some reason a huge number of bees preferred to live clustered under the screened bottom board. Try as I might I could not get them to move into a box. Both of last year's hives died over the winter.
One week ago I got four nucs and installed them. These nucs came from a completely different source than last year's bees. And, just like last year, I am having a tremendous robbing problem. I installed robber screens on all four hives in the evening after the bees stopped flying. The next day I noticed a number of bees who could not figure out how to get back inside their hives due to the screens. On a couple of these hives a lot of the bees had clustered under the screened bottom boards. I assume they chose to gather there because they can smell and see "home". So I slid in the debris board under each hive to close off the screened bottom boards. (I was also hoping to reduce the odor of honey and sugar syrup coming from the hive through the SBB and attracting robbers.)
Today when I inspected the hives I noticed that one hive - curiously the one in the same location as last year's hive with the bottom dwellers - had a large number of bees between the bottom board screen and the debris board. The entire space was full of bees. Hundreds and hundreds of bees. I don't doubt that I trapped a few bees when I slid in the debris board several days ago but those bees should be dead by now. Somehow these bees found their way into this small space. I slid the debris board out and smoked them but the bees did not want to leave the screened bottom board. So I got another bottom board (screened but with the debris board in place) and another brood box and moved all the frames to the new box. I temporarily left the robber screen off the new box so the stragglers could find their way back into the hive. When I left them a clump of bees was hanging from a front corner of the old bottom board.
Now it is dark and several hours after I moved the frames to the new box. A small cluster of bees (fist size) are between the screen and 4X4 support post and a small number of bees are on top of the screen to top off that clump of bees. I guess they prefer being under the screen to being inside their hive.
No, I don't think a queen is in that clump of bees. I found no evidence that my hive had swarmed plus I found the queen during the inspection and she was safely placed in the new box.
Why do my bees have a propensity to cluster under the bottom board screen? Is this a common problem with SBBs? Is robbing made worse due to using SBBs? Should I leave the debris boards in place all the time to try to prevent the bees from clustering under the bottom board and to control odors to reduce robbing? Are screened bottom boards just a bad idea? Should I replace all my bottom boards with solid bottom boards?