What specialized structure found on social female hind legs is vestigial or lost in cuckoo females?
Corbiculae (pollen baskets)
The parasitic lifestyle results in predictable morphological trade-offs directly reflecting the functions the bee must perform and those it no longer requires. A critical anatomical difference separating the Yellowish Cuckoo Bumblebee from its social counterparts is the near or total loss of the corbiculae, commonly known as pollen baskets. These specialized structures on the hind legs of social female bumblebees are essential for collecting and transporting large loads of pollen needed to provision developing larvae. Since the parasitic female does not engage in gathering food for her young—as the host workers perform this task—the adaptation for collecting pollen has been genetically removed because it no longer provides a fitness advantage.
