Found at Mistley this afternoon sunning itself on a tree trunk. It was watched turning itself to get the best advantage.
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Are you sure it didn't have a white tail? There's a hint in the photo, but it's not clear enough to be sure. Seems a bit early for pascuorum, which usually follows on after the other common bumbles, whereas tree bumblebee B hypnorum was out today here in Tunbridge Wells.
There did not appear to be a white tail,I think the sunlight reflected of the smooth bark appears to give it a light rear. I am familliar with hypnorum I recorded two sightings last year here in North Colchester so ruled this out. You have set me thinking what else it could be and Spring Flower Bee had crossed my mind but this bee seems too gingery for that. Perhaps its the one that will eventually get away.
It's definitely not the (male) flower bee Anthophora plumipes, which I see a lot and has quite a different overall look (and behaviour). So it's a choice between hypnorum (which seems to have got a number of votes since my original comment!) and pascuorum.
Lat/Lng: 51.944832, 1.069616
OS grid ref: TM110318