Double screens are suggested to use in breader colonies as to make the hive queenless and yet allow the warmth to travel upward. for both a starter and a finisher. The only difference I see between the two is the easy of sliding in and out of the door....... just wondering if the warmth/ airflow is a help, or if the other queens phermones travel up enough to create a problem or if it is just kind of a personal preferance?
I have also seen a double screen with entrances used as a 2 queen colony seperator so that one queen can't reach the other like they may be able to do with a excluder...