Osmia: Powerhouse Pollinators

The blue orchard bee (Osmia lignaria) is a fast efficient native pollinator of early spring flowers. In the apple orchard 250 to 300 of these powerhouse pollinators can do the equivalent work of 90,000 (two hives) honey bees.  Part of this success is due to their ability to visit more flowers per minute and to transfer pollen more effectively.  It is also helpful that some Osmia species specialize on flowers in the rose family which include apples, almonds, plums, cherries, strawberries, black berries and raspberries.  Most species are considered generalist pollinators and will visit a wide variety of flowers including tube shaped and asymmetrical flowers such as beardtongue, mints and flowers in the pea family.   Take a few moments to observe these spring pollinators and it is easy to see how they run circles around honey bees.     

Osmia spp. pollinating a strawberry flower

The blue orchard bee belongs to the Megachilidae family, one of 7 bee families. It is certainly easier to identify these bees to their genus Osmia but increasingly more difficult to differentiate between individual species.  150 species can be found in North America with just 27 species east of the Mississippi River.  Osmia translates to mean “odor” which refers to a unique lemony scent that females use to help locate their own nest.   As a solitary bee, every female makes her own nest using preexisting holes such as hollow tubes, stems and even crevices in walls. 

Osmia spp. putting the finishing touches on a phragmites tube

Bees in the Megachilidae family all collect pollen on brush like scopa hair on their abdomen instead of on their hind legs like most other bee species.  Bees in this family are also more robust with stout bodies. Many Osmia bees in the eastern United States have a metallic blue hue and are often mistaken for flies.

With tattered wings this Osmia is probably enjoying nectar after completing her life’s work.

Osmia have earned the common name of mason bee because they utilize mud to create partitions between their brood chambers.  In each chamber the female lays one egg and provisions it with “bee bread” a mixture of pollen and nectar.  To collect enough pollen for one egg, the female takes 15 to 35 trips, visiting approximately 75 flowers on each trip.  It takes approximately 1,875 flower visits to collect enough pollen for a single egg.   Female eggs are laid in the back of the tube while males eggs are found in the front.  This methodology certainly protects the female larva from possible predation of birds looking for a meal and sacrificing a few male bees for the cause certainly makes ecological sense.  Over the course of the year, the egg hatches, the larva grows, spins a cocoon and remains in its pupal stage until it emerges as an adult bee the following spring.   

Bufflehead Mason Bee on Beardtongue

Bees in the Megachilidae family are part of the 30% of bees that make use of artificial bee houses and nest in paper tubes, phramite stems, bamboo and other hollow stemmed plants.  Holes drilled into wood are also attractive to these bees but when bees reuse nesting holes there is always a chance of disease transmission.  If the bee house is portable it can be taken down after the nesting season and kept in a protected area at the ambient temperature of the season and placed back into position in the late winter or early spring.  This practice protects the nest box from predation.  There is no need to buy bees to populate your house, there is good chance bees are already present and will quickly utilize the new home.  

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