Why do bees often use only a single nectar source but often use many sources of pollen at a time?
Beekeepers often observe their bees flying past nectar sources, sometimes the very flowers that those beekeepers have planted as pollinator forage!, to a single source the bees prefer. As beekeepers we can understand that the foraging population of a colony will collect nectar in the most efficient way, utilizing division of foraging duties, waggle dances, pheromones and all forms of communication to concentrate its efforts on a major, rewarding nectar flow. So, bees often pass by sources that the colony deems less desirable.
However, as beekeepers know, a colony forages for pollen foraging differently. We can see by the pollen colors on the corbiculae (pollen baskets) of returning foragers that the colony collects different kinds of pollen simultaneously. At least 4 different pollens are visible in the pollen baskets of the workers in the photo below. Why the difference? There are a number of reasons given by bee researchers such as varying nutritional quality of different pollens and the needs of the colony but the simplest and possibly the most important reason is simple:
Bees can't taste test pollen! When foragers collect pollen, they can not tell the quality of the pollens they collect at the time of collection. Nectar can be tasted and even shared as part of waggle dance recruiting other foragers to a better or best source of nectar. Pollen is not easily digested by bees; each pollen grain has a protective "shell" called the exine that the digestive system of the individual bee is not designed to break down. Honey bees ferment pollen with nectar and enzymes (bee bread) to make it digestible, and even best utilize it via the creation of jelly by worker bees using their hypopharyngeal and mandibular glands.
How many pollens can you count in this photo?