bee biology plant-pollinator mutualisms

Nectar collection by honey bees

While folks envision industrious honey bees bringing home loads of silken nectar, they often don’t account for the other payloads that arrive on the landing board. Honey bees actually collect three other substances: pollen, water, and propolis. Today’s post is a brief overview of nectar collection. Later I’ll write about the other three.

Nectar is usually secreted from glands called floral nectaries that are found in various places in a flower depending on the species. They are usually found at the base, but may also be on the sepals, petals, or stamens. While foraging bees climb deep inside the flower looking for the sweet liquid, pollen sticks to the bee’s body. On any given foraging trip, honey bees tend to visit only one species of flower. As she travels from flower to flower she inadvertently picks up more pollen grains while some of the previous ones rub off on the anthers of the next flower. Quite accidentally—at least from the bee’s perspective—cross pollination has occurred.

It is believed that flowering plants co-evolved with bees. The plants that survived where the ones that produced the sweetest, most attractive nectar. Since the bees were more attracted to these plants, they were the plants most likely to get pollinated and produce the next generation. This phenomenon is what biologists call a plant-pollinator mutualism: the plant benefits from the bee and the bee benefits from the plant and they both evolve to work ever-more-closely together. Some mutualisms are so specific that one and only one particular species can pollinate a particular type of flower. These mutualisms have garnered much attention recently because the extinction of one of the partners means the automatic extinction of the other.

Over the course of about 80 million years, flowers have developed other specialized ways to attract bees including colorful petals, distinctive patterns called “honey guides,” and landing platforms—widened or fused lower petals that make a visit easier for the bee. Many of the patterns are ultraviolet—unseen by humans but extremely attractive to the pollinators. The bees, in turn, developed tube-like mouthparts that can reach deep into a flower like a straw, brushy bodies that collect pollen, and bristly legs that can be used like combs to remove pollen from their abdomens.

The nectar is swallowed into an organ known as the “honey stomach,” a part of the esophagus that expands as it fills. Once the honey stomach is full the bee returns to the hive where the payload is transferred to a waiting worker in a process called trophallaxis. Once in the hands—okay, the honey stomach—of an in-hive worker, the long process of converting nectar into honey begins.


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