Re: Top cover doesn't close
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You certainly can add some weight to the cover, with no adverse effects.
But a cover that doesn't close completely is not necessarily a problem. Some beekeepers have only top entrances, some have both top and bottom entrances.
And there isn't much you can do to keep hive beetles out, if the bees can get in the hive, then certainly so can the beetles.
--- Victor Hugo - "Common sense is in spite of, not the result of, education.”