The honeybee is a highly effective pollinator, but the collection of pollen is a deliberate and complex biological process, not an accidental byproduct of foraging. Pollen serves as the hive’s main protein source, providing the essential amino acids, fats, and vitamins necessary for colony growth and survival. Worker bees, which are exclusively female, collect this nutrient-rich material primarily to feed the developing larvae. A successful foraging trip requires the bee to use specialized tools and a precise, multi-step mechanical action to gather and secure the microscopic grains for transport back to the colony.
Specialized Anatomy for Collection
The body of a honeybee worker is covered in thousands of branched, feather-like structures known as plumose hairs. These hairs are crucial for the initial adhesion of pollen grains, trapping them much like a dense brush as the bee moves across the flower anthers. This dense layer of hair effectively turns the bee’s entire body into a collection surface.
The bee’s six legs are segmented and adapted for different roles. The forelegs are used primarily for cleaning the antennae and the head, while the middle legs sweep pollen from the thorax and transfer it down the body. The hind legs, however, are the most specialized, featuring two structures instrumental in both processing and carrying the load.
One key feature is the corbicula, or pollen basket, a polished, concave area located on the outer surface of the hind leg’s tibia. This basket is bordered by a fringe of long, stiff hairs that hold the collected mass in place during the flight home. Located at the joint between the tibia and the basitarsus of the hind leg is the pollen press, which performs the mechanical work of compression.
Initial Pollen Removal
The collection process begins as the worker bee lands on a flower. Its body is already positively charged due to friction from flying. This electrostatic charge helps the negatively charged pollen grains leap from the flower’s anthers and stick to the bee’s plumose hairs. As the bee works to gather nectar and contacts the flower’s reproductive parts, its body becomes heavily dusted with pollen.
The bee then performs a grooming ritual to move the scattered grains toward its packing apparatus. It uses its forelegs to brush pollen from its head and eyes, transferring the material to its middle legs. The middle legs then sweep the pollen from the thorax and abdomen, passing the accumulated mass down to the hind legs.
Before the pollen is compressed, the bee mixes the dry, powdery grains with regurgitated nectar or honey. This moistening creates a sticky substance, sometimes called pollenkitt, which helps the individual grains adhere to one another, forming a cohesive mass. This clump is now ready for the final mechanical step of being secured for transport.
Packing and Securing the Load
The moistened pollen mass is transferred to the inner surface of the hind leg, specifically onto the basitarsus. The joint that connects the basitarsus to the tibia functions as the pollen press, a mechanism for compaction. This press consists of two adjacent plates that articulate with each other.
The bee uses stiff, comb-like hairs, known as the pollen rake, located on the inner edge of the tibia, to scrape the pollen off the basitarsus of the opposite hind leg. The loose pollen is combed into the open cavity of the pollen press. The bee then brings its leg segments together, closing the press like a hinge.
This closing action compresses the loose pollen mass into a dense, solid pellet. The pressure forces the newly formed pellet through the joint and up onto the outer surface of the tibia, where the corbicula is located. Each time the bee repeats the scraping and pressing action, a new layer of pollen is added to the mass in the corbicula, pushing the existing pellet further up.
The growing pollen pellet is held securely within the concave depression of the corbicula by the stiff, inward-curving hairs. The bee continuously works both hind legs, creating two distinct, brightly colored pellets, often referred to as “pollen pantaloons,” one on each leg. Once the corbiculae are full, the bee can carry a load of pollen that may weigh up to half of its own body weight before returning to the hive.