Pollination is the transfer of pollen from a flower’s male reproductive organ to the female receptive part, enabling fertilization and the production of seeds and fruit. Bees are the most numerous and effective pollinators globally, facilitating the reproduction of countless plant species, including a significant portion of the world’s crops. Their unique anatomy and foraging behavior have established a deep co-evolutionary partnership with flowering plants.
Why Bees Visit Flowers
Bees visit flowers seeking two distinct floral rewards: nectar and pollen. Nectar is a sugary liquid produced by specialized glands called nectaries, serving as the bee’s primary source of carbohydrates and energy. Foraging bees consume some nectar for immediate flight fuel and store the rest in a honey stomach to carry back to the hive. There, it is converted into honey.
Pollen, the fine, powder-like substance produced by the anthers, provides the protein, fats, and micronutrients necessary for the colony’s growth. It is important for feeding developing larvae, which consume pollen mixed with nectar to create a brood food like “bee bread.” The high protein content of pollen is also used by queen bees to mature their ovaries and begin laying eggs. These resources reward the bee for unintentionally moving genetic material between plants.
The Mechanics of Pollen Transfer
The physical transfer of pollen begins as the bee flies, generating a positive electrostatic charge on its body due to friction with air molecules. Flowers, which are electrically grounded, typically carry a negative charge, as does the pollen itself. This difference in electrical polarity aids pollen collection. As the positively charged bee approaches the negatively charged flower, pollen grains “leap” from the anther onto the bee’s body without direct contact.
A bee’s body is covered in dense, branched hairs called setae, which are effective at trapping and holding the fine pollen grains. The pollen that sticks randomly to these body hairs is responsible for pollination, as it is likely to rub off onto the next flower visited. The majority of the collected pollen, however, is intentionally groomed by the bee into specialized structures for transport. Honeybees and bumblebees pack the pollen into a concave area called the corbicula, or pollen basket, on their hind legs to carry the load back to the nest.
When the bee enters a new flower of the same species, the pollen grains adhering to its body brush against the flower’s receptive female organ, the stigma. This sticky stigma captures the pollen, completing the transfer and enabling fertilization. The bee’s visit temporarily weakens the flower’s negative electric field by neutralizing some of its charge. A subsequent bee can detect this change, signaling that the flower has been recently depleted of nectar and pollen, allowing the bee to efficiently bypass the flower.
How Flowers Attract Specific Bees
Flowers have evolved adaptations, often called pollinator syndromes, to attract their intended bee visitors. One method involves visual cues, particularly color. Bees can see ultraviolet (UV) light, which is invisible to the human eye, and are sensitive to colors in the blue and violet range.
Many flowers display intricate UV patterns, known as nectar guides, which act like landing lights to direct the bee toward the nectar and pollen sources. The shape of the flower also manages the bee’s visit, often forcing the bee to rub against the anthers and stigma. Some flowers offer a broad, flat petal structure to serve as a landing platform for heavier bees.
Scent is another attractant, with flowers releasing volatile aromatic compounds that serve as long-distance chemical signals. Bees detect these scents from far away, using them to locate the reward. The combination of colors, scents, and physical structures ensures the bee is effectively dusted with pollen and directed to the precise location for reproductive success.