Morphological constraints and nectar robbing in three Andean bumble bee species (Hymenoptera, Apidae, Bombini)

We report differences in foraging behavior of three Andean bumblebee species on flowers of Digitalis purpurea (Scrophulariaceae). Bombus atratus was a potential pollinator while B. hortulanus and B. rubicundus collected nectar by robbing through holes. We attribute behavioral differences to physical constraints. B. atratus has a longer glossa and a larger body size and is able to reach the nectaries, whereas B. hortulanus and B. rubicundus have shorter glossae and smaller bodies and probably must rob nectar through holes at the base of flowers.