Foraging on resources that fluctuate over time, such as floral nectar and pollen, presents animals with the problem of finding currently available foods as quickly as possible. Several insects, as well as many vertebrates, are known to solve this problem by following other foragers on novel food sources. However, information obtained from other foragers may not always be valuable. For example, one species may prefer a food item that is difficult to exploit for other species with different morphology. Therefore, animals may adjust their responses to other foragers while searching novel foods, depending on whether they are similar in their food preference. Here, we conducted field experiments to test whether nectar-collecting bumble bees make such adjustments. Proboscis length in bumble bees significantly varies among species. Because proboscis length of bumble bees influence the handling efficiency and choice of flowers, following heterospecifics would be less beneficial than following conspecifics, or even costly for individuals. Using the ``interview bouquet'' technique, we allowed free-foraging bees to choose between two inflorescences of novel flower species, one of which was occupied either by a conspecific bee or a heterospecific bee with shorter proboscis.

Results/Conclusions

The test bees chose the two inflorescences at similar frequencies when a conspecific was presented with unfamiliar flowers. In contrast, they tended to choose unoccupied inflorescences when a heterospecific was presented with unfamiliar flowers, and when a conspecific was presented with familiar flowers. These results suggest that bumble bees can alter their tendency to follow other foragers on novel food sources depending on whether the resident is conspecific or heterospecific. This ability would reduce the costs of sampling unsuitable flowers and then enhance their fast and accurate assessment of variable food resources in bumbe bees.