Thanks all for the suggestions, your efforts to help are greatly appreciated. Yesterday afternoon I discovered that they were in fact drawing comb under the hive so I cried uncle and moved one side of the screen up on the two problem hives. Things are sorting themselves out now, order is quickly being restored. While frustrating, I think I learned some valuable lessons that should serve me well in the future. To that end I'll explain in a bit more detail what "I think" went wrong for others to learn and/or correct me on what I think I learned. Here's a photo as it sits right now.
The two hives on the left are three full medium brood box hives, one has a capped super and a shallow, the other a shallow. These hives are not being fed and weigh in at. 130 and 110 lbs. These are the hives where things went wrong, more on that in a minute.
The other three hives (3-4-5) are roughly a medium and a half each and originated as a result of my first attempt at breeding my own queens this year, something I would encourage everyone to do, great sense of satisfaction seeing the process and saving a few hundred bucks. They are being fed (with quart jars over the Vivaldi inner cover surrounded by an empty super) as our flow is all but over and they are drawing foundationless frames.
The middle hive, the all white one is where I spotted the robbing activity earlier this week. It was without question robbing, I watch them all make orientation flights every day but this was a much larger cloud than normal and bees were rolling around all over the ground, left a pretty good pile of bees in fact. Having been robbed out last year I wasn't going to let it happen again, making robber screens for all hives was on my list this week and I had already decided on a design and gathered materials. When I saw the robbing I quickly suited up and blocked the entrance on all three small hives which were 2-3 inches wide. Within an hour or so I built the screens and waited for dark to install them. The plasticell under the screen was and remained closed on all three of the smaller hives. All three quickly learned how to get in and out easily on their first day and were virtually unaffected by the new robbing screens.
Back to the mess. Having witnessed a bit of bearding on the two larger hives in the days prior I opened the plasticell tray under the screen 2-3 inches. The entrances on these two hives were also wide open in the days prior to the screens going on and they used if all. Knowing that I would have fewer foragers with the flow coming to an end, I gave them a 7 inch opening on the robbing screens, about half what the had been using. Wednesday (day one) was wild, it looked like an all day orientation scene, bees were everywhere, in/on/around the hives but very few seemed to be finding the access point of the new screens. As darkness fell there were fewer bees around so I thought it might be OK. The next mornings light revealed where they went, under the hives. They filled the area between the plasticell and the screen and then bearded down the size if a soccer ball below that. Thursday saw no improvement, in fact most foragers were just returning to under the hive. Mid afternoon I suited up and stuck my head under the back, they were setting up shop. I unscrewed one side of the robbing screen and moved it up a bit and pulled the plasticell out for a few hours to disrupt their cozy new digs. Within an hour or so wandering bees started stumbling across the original opening and re-entering the hive. Foragers kept going under but more and more would crawl back out and find the entrance. Last night there were just a few hundred bees under the hives so I replaced the plasticell trays under the screens. Bees are still returning under the hive but now that the screen is blocked off they come crawling back out and seem to be finding the entrance. I probably have a few hundred bees trapped under each hive but I'm willing to sacrifice them to rite the ship.
What I think I learned.
- keep the screen cover in place for several days when adding robbing screens. Under the screen smells/feels too much like being in the hive, lost bees will call it home.
- when adding robbing screens, probably better to also reduce the original entrance behind the screen to slow the departing bees down and give them an extra adjustment to get out.
- be sure the flow is over, had I done this a week or two ago it could have cost me a lot of honey.
Thanks again all.