Re: Lowest observed foraging temperature
As others noted, bees will forage down to about 35F and I have seen them doing so a few times. It is always in bright sunshine with little or no wind.
This behavior is well documented with some bees spending the night usually near flowers on which they are foraging. Regarding bees foraging by moonlight, this has been observed a few times and appears to be a genetic trait. Even though Russell advertised bees as "moonbeams", I too suspect it was just snake oil. His description stated that they foraged earlier and later than most bees though still during daylight.
I concluded from all of that that bees do not always go home every night.
NW Alabama, 50 years, 20 colonies and growing, sideliner, treatment free since 2005, 14 frame square Dadant broodnest