Bumblebees play a significant role in natural ecosystems and agriculture. Pollen, a fine, powdery substance produced by flowering plants, is central to their activity. It contains the male reproductive cells of plants, essential for their reproduction. This article details what these insects do with this vital plant material.
Why Pollen is Essential
Pollen is a primary food source for bumblebees, supplying protein, fats, vitamins, and minerals. This nutritional composition differs from nectar, which provides carbohydrates and serves as the bee’s main energy source for flight and activity. The protein and fat in pollen are important for the growth and development of bumblebee larvae, ensuring they mature into healthy adult bees. A consistent supply of pollen supports the queen’s egg-laying capacity and contributes to colony health and expansion.
How Pollen is Collected and Stored
Bumblebees possess specialized adaptations for collecting pollen. Their bodies are covered in dense, branched hairs, which effectively trap pollen grains as they move across flowers. For many flowers, bumblebees employ “buzz pollination” or sonication. This involves the bee grasping the flower and rapidly vibrating its flight muscles, which dislodges pollen from the anthers, coating the bee’s furry body.
Once covered in pollen, the female bumblebee uses specialized brushes and combs on her legs to gather the grains from her body hairs. She then transfers this pollen to structures on her hind legs called corbiculae, also known as pollen baskets. These are bare, concave areas surrounded by stiff hairs, into which the pollen is pressed and compacted, often moistened with nectar or saliva to form a sticky pellet. These visible pellets are then transported back to the nest.
Pollen’s Role in the Colony
Upon returning to the nest, collected pollen is unloaded and sustains the bumblebee colony. The pollen is processed by mixing it with nectar and saliva, creating “bee bread.” This bee bread is stored within the nest, either in wax pots or directly in brood cells, depending on the bumblebee species.
The stored pollen mixture serves as a food source for developing larvae. Young larvae consume pollen directly, which provides nutrients for their rapid growth. The queen bee also consumes pollen, particularly after hibernation, to stimulate her ovaries for egg-laying and maintain her health. Adult worker bees consume pollen to meet their nutritional needs, supporting their foraging activities and other colony duties.
Bumblebees as Pollinators
While bumblebees primarily collect pollen for their colony’s needs, their foraging activities naturally lead to incidental pollen transfer, making them important pollinators. As they move from flower to flower, pollen adheres to their fuzzy bodies. Some of this pollen is then inadvertently deposited onto the stigmas of other flowers, facilitating plant reproduction.
This incidental transfer is ecologically and agriculturally important. Bumblebees are effective pollinators due to their ability to fly in cooler temperatures and lower light conditions than many other insects, extending the pollination window. Their large size and buzzing behavior also make them effective for pollinating certain crops, such as tomatoes, blueberries, and strawberries, which benefit from the pollen release their vibrations provide. This pollination service contributes to crop yields and plant ecosystem health.