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Sorry, but I never heard that lenght of glossa (tongue) or of malar space is a distinction character within the Bombus terrestris/lucorum group. As far as I know, queens (ony) can be recognized by some details in color pattern and by puncture of head and last tergum. Workers are not distinghuishable, and males are nearly impossible to distinghuish. B. terrestris is a more or less dark species, whereas the others are lighter. But I am not able (or never tried it seriouly) to identify the four species in this group. My knowledge comes from a scientific presentation last year, and there are some recent examinations and publications about the terrestris/lucorum group.

Separation to former Psithyrus species works by less dense hairiness, lack of collecting facilities on hindlegs and other characters in (former) Psithyrus.

Regards, Christian

Regards, Christian