Michael Bush wrote: Sometimes that solar gain allows them to rearrange stores so they don't "cold starve" or it gives them a quick cleansing flight on a warm day that they might not have gotten, so it could save them. On the other hand, as has been pointed out, if there is too much solar gain too often it makes them more active than they should be for the actual climate..
I thought about it and concluded - why bother.
A typical successful bee tree (or a cave) is well insulated and does not react much to "solar gain" due to both (1)insulation and (2)significant thermal mass that surrounds the colony. A typical bee tree will react to average and consistent external temperature changes, but not much to daily (or even hourly) temperature swings. These are the conditions that the bees evolved about for the last X millions of years.
With that, a good hive (for the bees) should replicate those conditions as well.
There are arguments that bees need no insulation.
Not so sure.
I feel bees can survive despite
The question is - for how long?
Successful bee trees continued being occupied and re-occupied for many, many years in a row.
Indeed, a colony may get by one season on an open branch.
Here is a video of bees that wintered successfully totally exposed (Ukraine, zone 5 of USA, video taken on April 10, 2014). But that was a very well sheltered place in some dense woods and a very strong colony, as you can see. Also, they were hanging under a very heavy log meaning they do have a well insulated and air/vapor proof top while having totally ventilated sides and bottomhttps://www.youtube.com/watch?v=UUJtFgweNDw
Still, I have much doubt a colony can survived on an open branch 5 years in a row in most temperate climates.