Found it in a suburban area close to the coast and the dunes 3 weeks ago.
http://images.google.be/imgres?imgurl=http://www.bumblebee.org/images/muscorum.jpg&imgrefurl=http://www.bumblebee.org/uncommonSp.htm&h=160&w=211&sz=10&hl=nl&start=9&sig2=PpzX4p_C8pYfN9-fvVG-ag&tbnid=eI0JAJThP3fZGM:&tbnh=80&tbnw=106&ei=8Dz8RsrAFI6QwAGas5zWDw&prev=/images%3Fq%3DBombus%2Bmuscorum%2B%2B%26gbv%3D2%26svnum%3D10%26hl%3Dnl%26sa%3DG
http://www.judywoods.dial.pipex.com/insects/northmosscarderbeethum.jpg
another pic.;
The habitat fits, but it states that Bombus muscorum has no black hairs on the abdomen.
http://www.bumblebee.org/uncommonSp.htm
Bombus pascuorum is very variable, it may be that but it may be something else! I had a bee which I wasn't even certain it was a bumblebee until I studied the shape of it's tail, it looked very silvery white and I had thought at first it was a solitary bee, it was also extremely small. I sent the pic for ID, and yes, it was B. pascuorum!
Look at the rich colour on this one,
http://www.bumblebee.org/pasc.htm
Yes, it does look similar, but I remember this bee was quite large (around 2 cm) and looks more round and 'fat' than a Bombus pascuorum unless also the body shape and size is variable like you suggest, then it is really a family to get desperate about!!!
I am very surprised at the huge variation of B. pascuorum, the size suggests that could have been a Queen.
This is the small, silver one which is B. pascuorum.
I have also seen these silvery ones!
Just today I found one that looks very similar to the one of the coastal area, only a little smaller in size. I went back to the place where I found the weird bug or nymph (shield bug or cricket or whatever..)I posted in a previous thread in the hope I would find an older specimen and the plant it was found on, but had no success. Instead I found a lot of other interesting critters..
This bumble bee was also very slow and drowsy feeding like with its last efforts on a dead-nettle.
and a pic.of its head;
