Bombus terrestris vs. lucorum

[laetoli]

I understand that it's often not possible to distinguish B. terrestris workers from B. lucorum ones without getting the beasts under a microscope. Nevertheless, I've noticed quite a few of whichever in my garden have a thin yellow edging just above the white tail (see image). Is this distinctive for either of them?
Thanks,
Paul

[eucera]

indeed... this would be B. terrestris. The "coffee stain" is typical, but not an invariable character of B. terrestris workers

I am sure you know that B. lucorum is in fact a complex of at least 3 species within the UK, so the taxonomic situation is somewhat fluid withing B. lucorum sensu lato