Originally Posted by Mattinho
I forgot to add that I am in central Scotland (West Lothian to be precise!)
Your Bumblebees appear to be, (and given your location) are almost certainly Bombus pascuorum
and are most probably Queens and Males
Given that you saw two different sizes of Bumblebee it is likely it was a nest you disturbed.
Technically the Bumblebees do not hibernate, the name used for this part of their life cycle is is diapause. Some newly emerged and fertilised queen Bumblebee species can enter the overwintering stage as early as June or July.
Once the bee has entered diapause and has unfortunately been unearthed it is not likely to survive, even if an artificial hole is made for them. Sad but true.
Several Bumblebee species nest underground, others in walls or holes in old stone buildings, yet others may occupy an old birdbox.
After last years Monsoon period the Queens produced by all the Bumblebees in my area, were very small in comparrison to their usual size. This has resulted in smaller Workers and Males being produced this year. Overall the numbers of Bumblebees seen this year, are appreciably less than usual. It may just be happening in my part of the world, but I suspect not.
I cannot recollect a year out of the last fifty when Bumblebees have been so small in size or so few in number.