What specialized reproductive strategy defines B. flavidus within the Bombus genus?

Obligate social parasite (inquiline)

The defining characteristic of *Bombus flavidus* within the diverse *Bombus* genus is its role as an obligate social parasite, often referred to as an inquiline. This means that unlike most bumblebees that establish their own colonies, the female *B. flavidus* relies entirely on the nest-building and provisioning capabilities of other *Bombus* species. Her survival and reproductive success are contingent upon successfully infiltrating a host nest—known or suspected hosts include *Bombus terricola* and *Bombus impatiens*—at the precise time the host colony has begun raising its first true workers. This specialization represents a major evolutionary divergence within the genus, despite sharing the genus's characteristic fuzzy appearance.