What morphological characteristic often distinguishes cuckoo bumblebee females compared to social bees needing to forage?

Reduced or entirely absent scopae

A key morphological marker separating cuckoo females from their social counterparts relates directly to their differing roles in resource acquisition. Social bumblebee females (queens and workers) have well-developed structures called scopae on their hind legs specifically designed to carry large quantities of pollen back to the nest. Because cuckoo bumblebee females have absolutely no need to forage for their own young—relying instead on the labor of the host workers—their corresponding pollen-carrying structures are either significantly reduced or entirely absent. Observing a large, fuzzy bee without noticeable pollen loads on her legs is a strong indicator that the individual is a parasitic cuckoo female.