Rare Bumblebees in Newark?

I shared a couple of pictures on social media, taken with my mobile phone at Sconce Park, in the wallflower bed at Rumbles cafe. It's a habit I've developed, there are always things to photograph and these bee pictures always seem to come out very vividly. They are among the best nature pictures I've taken on the smartphone.

I've seen these black bumblebees before, and had always identified them as male field cuckoo bumblebees, not having found any other black bumbles to identify them as. But when I published these pictures, Roger @chardbirder kindly pointed out that cuckoo bumblebees do not have pollen sacs, which these bees clearly do.

He proposed that in stead of Bombus Campestris - the field cuckoo bumblebee these may actually be Bombus Ruderatus, the ruderal bumblebee, a far rarer species. These are actually the only TWO black bumblebees to be found.

This is not conclusive, as Roger said, ruderatus is a large species, and these guys didn't seem tht big to me. But the presence of a pollen sac is indisuputable.

I hope they are ruderal bumblebees, I just love the thought that our town park harbours something that is really quite special!

A black bumble, with a pollen sac

Another view