The usual reason given is to lure bees up to the top super to finish it 
off, which also makes the lower available and noticed. Another reason is 
to reduce capping travel stain by bees not wiping their feet before 
entering, so capping's are whiter.

You will find beekeepers in both the upper super and lower super camps. 
I have had no trouble with bees filling upper supers. I uncap to extract 
so no need for whiter cappings. I tend to put two or three on at once 
and not one at a time.

Best advice I got on supering is to look for burr comb on the deep's top 
bars before supering. Then you know they are ready.

Bill Truesdell
Bath, Maine

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