Taken on 21st April 2008, Lincoln UK. There are no queens, only males and females as they parasitise B. terrestris nests, thus needing no workers. I saw two at the same time, females I imagine.
On 30th June 2008, feeding on species Dahlia flower (possible D. merckii). This could be a male.
They have no pollen baskets as they do not need to collect pollen, the workers in the nests they parasitise provide.
On Rosa 'Crazy For You'. They have larger yellow marks at the edges above the white tail than the similar B. bohemicus.
On 1st August, leaving a Dahlia flower. They seemed to prefer pink Dahlias.