Size‐related foraging differences of bumble bee workers

. 1. Large Bombus vagans workers concentrated their foraging upon deeper florets of cow vetch ( Vicia cracca ) more than did smaller workers. Large and small workers did not differ significantly in their foraging rates, which were measured in several ways. 2. The average depth of vetch florets varied between sites on the study area, but significant differences did not occur on a single inflorescence. The foraging differences of large and small bees probably result from a fine partitioning of the microhabitat. 3. When the nectar‐robbing B.terricola was present, many B.vagans workers became secondary robbers at holes made in vetch corollas. Small B.vagans workers robbed significantly more frequently than did large workers.