a Przemek Skoskiewicz snip (and a similar question from Mr Dunbar)... 

Would you mind elaborating what you mean by "robber guards" in this  
context? Do you mean something like this:  
http://www.brushymountainbeefarm.com/10-Frame-Moving-and-Robbing-Screen/productinfo/517/?

my comments...
Sometimes called robber guards and sometimes referred to as florida moving screens (although I certainly never saw them used in that manner when I did keep bees in Florida).  Mine are nether as pretty nor as expensive as those in Mr Skoskiewicz link < basically mine are three thin strips of wood a bit of 1/8 inch hardware wire and are attached with small number of framing nails and some staples.

Some years ago I began making up late season nucs.  When my queen rearing neighbor from down in Navasota sat down large well populated hives which had just come out of North Dakota there was always a serious bout of robbing... so my use of these was originally about limiting robbing in small populated hives.  While investigating these I ran into a very old article in the ABJ and it casually mentioned that they also could play a part in making hives less defensive.  So when I had an event similar to the one mentioned in the article (already described by myself) I install these on those hives and I don't think you would call the change miraculous but it did make a huge difference and fairly quickly < ps knocking down the tall weeds ahead of the girls getting all pissey I still think is what set off this event for me.  I also begin mounting these on hives here at my house since my neighbors mowing could get the girls wound up on occasions.

How does it work?  Speculating for certain and taking certain ideas from the article with the robber guards 1) the threat of robbing is much reduced and 2) with the ladder/wall in place the guard bees at the front door don't get quite so nervous when any movement passes by the front entry (and they have to climb over the ladder if they do recognize some threat).

Since then I have had a number of folks (new beekeepers) that complained in a fashion similar to the article quite typically with 2 year old hives that had grown quite populated.  Evidently the circumstance sometimes had become bad enough that 'their significant other' had said quite flatly.... 'either the bees go, or you go'.  A good number of these have emailed me after the fact that said that the robber guards did make the difference between them keeping bees or not.

Finally I do not want to give the idea/impression that robber guards are a total cure since bees can and will become angry for any number of reasons but NO ONE should think that angry bees automatically point towards africanization.  At least here hungry starving bees (and the high correlation with this and robbing) will turn perfectly good european bees into monsters.  Even your everyday european bee can hurt you badly (or in my own experience even worse) if circumstance turns in a bad way.      

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