Yellow and brown colour, large,round and full body, very fluffy or hairy
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What makes you think that this is a male rather than female white-tailed bumblebee?
This will probably not sound very helpful, but for the same reason as I think George Clooney is male - it just looks male! I don't think there is anything objective to point to, like counting antennal segments or a yellow face or the structure of the hind leg, but the rather fuzzy yellow belt, the pale fringes to the tergites, and the broad and long collar all shout male lucorum group once you know them well.
recording wildlife with The Recorder's Year on www.hbrg.org.uk/TRY.html.
Lat/Lng: 52.9731, -1.1485
OS grid ref: SK572420
My garden, on sunflower and Sedum plants.