Corbiculum or not?

The corbiculum is a flattened area of the tibia on the rearmost leg.  The structure enables a female bumble bee (queen or worker) to collect and transport pollen back to the nest.  If you can see a ball of pollen on the rear leg, you know the individual is a female.

All males and cuckoo bumble bee queens lack a corbiculum.

Hunt bumble bee showing leg segment identification
This Obscure bumble bee worker shows just how much pollen an individual can gather and bring back attached to her corbiculum.
A male bumble rearmost leg shows no evidence of pollen carrying, and the leg itself is not very flattened, with lots of hairs.

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