> However, I can feel the intense heat load under the hive cover, and on the
> sides of the hives facing the sun.  Weak colonies definitely benefit from
> shade, but I don't know whether there is actual benefit to strong colonies
> by giving them top ventilation.  I've seen that it is common in Australia 
> to
> use ventilated covers.

I have insulated pillows under the lids year-round.

> This is one of those cases where it makes perfect sense to provide
> ventilation to allow the hot air to naturally thermosiphon.  However, I've
> learned not to trust *common sense* in bee management.

I think that top ventilation can be very helpful some times and some places, 
but knowing in advance exactly when and for how long is difficult in the 
north. In the south, summer temperatures are usually less changeable.

For example, we are told that we will have nights as cold as 4 degrees C 
over the next few days.  Some years, we have 35 degree weather on these same 
days, and sometimes we might have frost.

Bees cluster at 14 degrees, so we can be sure that in a drafty hive, the 
bees will cease all work in the supers, while they might be able to continue 
or at least occupy more comb in a tighter hive.

A hobbyist with a few hives in the back yard (me?) might be able to run out 
and open and close vents daily with predicted weather changes, but when I 
was commercial it took a week to visit all my yards -- assuming the creeks 
didn't rise.

I have not done controlled experiments, but I have had lids blown off, and 
that is the ultimate in top ventilation.  Needless to say, I put them back 
on, and so would most beekeepers.

My opinion, formed when producing comb honey, is that once bees are driven 
out of an area in a hive by cold, they are more reluctant to store there in 
future.  My goal has always been to keep the supers area warm and dark. 

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