Baby Bumbees

[plowter]

Can any ABers help me identify some bumblebees I've seen recently?
They're small - half the size of normal bumbees.
Body is all black, no bands. Tail is vaguely reddish-orange.
They seem to like potholes in road.
This is in Edinburgh.

Had a quick scan through BumBee Conservation Society leaflet.

What's that bumbee?
http://bumblebeeconservation.org/images/uploads/Resources/BBCT_Whats_that_bumblebee.pdf

The bees I've seen are much smaller than normal bumbees. Any suggestions? - apart from baby bumbees?

[SlackAlice]

Masonry Bee?

http://www.bpca.org.uk/pages/?page_id=145

[wildwood]

How about this one?

http://www.bumblebee.org/lap.htm