What specialized structure, used by social bumble bees for transport, is absent on Bombus flavidus hind tibiae?
Pollen basket (corbicula)
A defining morphological characteristic that clearly separates parasitic cuckoo bumble bees like *Bombus flavidus* from their social relatives is the complete absence of the pollen basket, also known scientifically as the corbicula, located on the hind tibia. In social bumble bees, the corbicula is a highly specialized structure designed for packing and transporting large quantities of pollen, which serves as the essential protein source necessary for larval development. Since *B. flavidus* females never produce a worker caste and rely entirely on usurping a host colony where the host workers manage all brood provisioning, the logistical requirement for collecting and transporting protein-rich pollen is eliminated, resulting in this physical adaptation being absent on the cuckoo queen.
