Mason bees may be the world’s solitary saviours

Mason bees like making their nests in naturally occurring gaps between cracks in stones or walls or in other dark cavities.

Over 300 species of Osmia or mason bees are found across the Northern Hemisphere. They are often metallic green or blue, though many are blackish and at least one species is rust-red, explains Alberton Record.

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Mason bees are solitary creatures

Unlike honey bees or bumblebees, mason bees are solitary and don’t need a hive to survive. Every female is fertile and makes her own nest. No worker bees for these species exist.

When the bees emerge from their cocoons, the males exit first. The males typically remain near the nests waiting for the females. Some are known to actively extract females from their cocoons. When the females emerge, they mate with one or several males. The males soon die, and within a few days, the females begin provisioning their nests.

Osmia females typically nest in narrow gaps and naturally occurring tubular cavities. This could mean hollow twigs or branches, but can also be in abandoned nests of wood-boring beetles or carpenter bees or in other small protected cavities. They do not excavate their own nests. The material used for the individual cells can be clay, mud, grit, or chewed plant tissue.

Provisioning the nest and laying eggs

Within a few days of mating, the female will have selected a nest site and begun visiting flowers or blossoms to gather pollen and nectar for her nests. Many trips are necessary to gather enough pollen and nectar.

Once she has collected what she needs, the bee backs into the hole and lays an egg on top of the provision mass. She then creates a partition of “mud”, which doubles as the back of the next cell. The process continues until she has filled the cavity. Female eggs are laid in the back of the nest, and male eggs towards the front. Once a bee has finished with a nest, she plugs the entrance to the tube and then may seek out another nest location.

Within weeks of hatching, the larva has probably consumed all of its provisions and begins spinning a cocoon around itself and enters the pupal stage. The adults mature in autumn or winter, hibernating inside their insulatory cocoons. Most Osmia species are found in places where the temperature drops below 0°C for long periods of time.

Mason bees improve pollination in fruit and nut production

Solitary bees produce neither honey nor beeswax. Their nesting habits make for easy cultivation and a number of Osmia are commercially propagated in different parts of the world to improve pollination in fruit and nut production.

They are used both as an alternative to and as an augmentation for European honey bees.

Mason bees used for orchard and other agricultural applications are all readily attracted to nesting holes – reeds, paper tubes, nesting trays, or drilled blocks of wood. In their dormant season, they can be transported as intact nests (tubes, blocks, etc.), or as loose cocoons.

Solitary bees are docile and rarely sting when handled. Their sting is small and not painful, and their stinger is unbarbed.

Watch: A mason bee pulls a nail out of a wall to use the resulting cavity as a nest.

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