Mason bees, belonging to the genus Osmia, are solitary insects that play a remarkably effective role as early-spring pollinators. Unlike social bees, each female works alone, constructing her nest and provisioning for her offspring without the aid of a colony. Their name derives from their habit of using mud and sometimes other materials to seal the individual cells within their nesting tunnels. Understanding the diet of these beneficial insects is centered on recognizing the distinct nutritional needs between the active adult and the developing larva.
Adult Nutritional Needs
The active, flying adult mason bee primarily consumes nectar to meet its immediate energy demands for flight and survival. Nectar is a sugary fluid produced by flowers, serving as the essential carbohydrate source that powers the bee’s intense foraging activity. Both males and females require this energy for their brief, busy lives. Adult mason bees, especially the nest-building females, also require water, which they can obtain from the nectar itself or from nearby sources. While adults do ingest some pollen during foraging, they do not consume it in the large quantities that honey bees do for their own protein needs.
Provisions for the Next Generation
The primary purpose of the female mason bee’s foraging is not for her own sustenance but to create a provision for the next generation. Within a prepared nest cell, she meticulously collects and stores a specialized food mass known as a pollen loaf. This loaf is a dense, nutritious mixture of collected pollen and nectar, often mixed with the female’s saliva. Pollen provides the protein, lipids, and micronutrients necessary for larval development, while the mixed nectar introduces moisture and carbohydrates. The female deposits a single egg directly onto this loaf, which must sustain the larva entirely through its growth, pupation, and hibernation until the following spring.
Once the food provision is complete and the egg is laid, the female seals the chamber before moving on to provision the next cell. This careful provisioning ensures the larva has a balanced and complete diet throughout its development. The quality of the pollen, in terms of its protein-to-lipid ratio and mineral content, directly affects the survival and body mass of the emerging adult bee.
Preferred Pollen and Nectar Sources
Mason bees are generalist pollinators, meaning they collect pollen and nectar from a wide array of early-blooming plants. Their emergence in early spring perfectly aligns with the bloom period of many commercially important fruit trees. Common foraging targets include apple, cherry, pear, and almond trees, making them invaluable for orchard pollination. They also utilize other early-flowering plants like dandelions, maples, willows, and certain berry shrubs. Mason bees are particularly effective at cross-pollination because they carry pollen dry, on stiff hairs located on the underside of their abdomen, called the scopa.
Their foraging range is quite short, typically limited to a radius of 100 to 300 feet from their nest site. This requires nearby and continuous floral resources to successfully complete their provisioning cycle.