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What's Buzzing: Mason Bees

 

Mason bee carrying mud to nest.  Photo from crownbees.com


What’s Buzzing:  Mason Bees
by Lydia McCracken, Propagation Intern, Gardens on Spring Creek

To gardeners, the first welcome signs of spring might come from the blooms of crocus or grape hyacinth.  But for these plants, one the most welcome signs come from the unsung heroes of spring – mason bees.  Tucked away over winter in their mud and clay nests they were eating, growing, resting for the early work that must be done. As daily temperatures reach 55 degrees, this hero is springing into action and has already been spotted at the Gardens on Spring Creek! 

Mason bee entering cavity nest to unload pollen. Sealed cavities are complete nests with multiple brood cells.

Mason bees are a non-aggressive solitary bee belonging to the genus Osmia. They get their name from the masonry work they use building their unique nests. Although their appearance varies from species to species, they are often a metallic green, blue or blackish color and smaller in size than the average honeybee.  You may have even mistaken one for a common housefly!

Colorado is home to 946 native bee species! We rank as the fifth most bee diverse state according to the University of Colorado Museum of Natural History. Of these native bees, 76 species are mason bees, with 40 of these species occurring right here in Larimer County. With so many mason bees in our own gardens, it is crucial to know who this pollination hero is and why they are so helpful to early spring gardens.

Honeybees, bumble bees and butterflies often get credited for the necessary work of pollination, but they are just a part of the story. Native pollinators play a crucial role, especially of early spring flowers.  The Gardens on Spring Creek, and many gardeners, plant native plants in the hopes of supporting these local heroes. But who are these early pollinators and why are they so important?

Mason bees have been hidden away in their nests since last summer. They were laid as eggs in cells of mud and clay with enough food to fully mature as larvae. By fall, they developed enough to spin their cocoon to pupate.  By October, they became fully formed adults but remained in their nest hibernating over winter, waiting for spring weather to arrive.

Now mason bees are buzzing into action! The males are the first to emerge in order to mate with the female mason bees who emerge shortly after. Once the female mason bee has mated with several males, the true work of her short life begins.  Adult mason bees only live for four to six weeks. So you need to get outside now to catch them in action!  Females use already existing holes to make their nests. You can find them building their cavity nests inside hollow plant stems or wood, cracks in walls or rocks or even empty snail shells!  At The Gardens, we provide crevices made from reed that can be found in our Sustainable Backyard Garden.

The female mason bee will take up to 10 trips carrying mud to the cavity to create one cell. Once the walls of the cell are constructed, she needs to gather enough food for her young to mature to adulthood. Depending on her species, trips collecting nectar and pollen can vary. On average, each single cell requires around 25 foraging trips. In some species like the Blue Orchid bee, this can be as many as 75 trips!  Once the pollen loaf is big enough, the female mason bee lays a single egg in the cell before sealing it up with another wall and starting the next cell. When the nest cavity is filled with brood cells, the female may seek out another cavity for the start of another nest.

Their constant work foraging for pollen and nectar is the reason they are so vital to early spring plants. Mason bees have superhero abilities when it comes to pollination.  In just one day, the work of a single mason bee is comparable to the work done by over 100 honeybees! According to a supplier of solitary bees, Crown Bees, a honeybee can visit 700 flowers a day and pollinate about 5 percent of the flowers visited.  Mason bees are able to visit 2,000 flowers a day with a 99 percent pollination rate. 

The anatomy and behavior of mason bees allow them to be great pollinators as depicted by this Osmia georgia covered in pollen.  Image from the Missouri Department of Conservation.

This is due to a variety of reasons. Honeybees often “cheat the system” when it comes to pollination. They will visit a flower from the side and, on some plants, even chew through the petal just to reach the nectar source, completely ignoring the plant's reproductive organs. Mason bees tend to “belly flop” on flowers trying to reach pollen and nectar sources. This means they come in contact with the plant’s reproductive organs each time they visit a flower. Many bees collect pollen in pollen sacs located on the hind legs of the bee. This sac is designed to hold pollen and results in less pollen being used to pollinate the plants. Mason bees have special hairs lining the underside of their entire abdomen. The pollen is held loosely by these hairs and easily falls off as the bee moves from flower to flower.

Mason bees are efficient pollinators and they are not afraid of Colorado’s erratic spring weather patterns. Honeybees and other bees are less active on cooler drearier days but our heroes, the mason bees, are hard at work, rain, clouds or shine.

Native bee home in the Sustainable Backyard at the Gardens on Spring Creek.

Spring is a busy time for gardeners and bees. Let it BEE known, we will BEE planting some beautiful spring annuals, in addition to our spring bulb offerings, for you and the mason bees to enjoy. Join us to meet the heroes of the Gardens on Spring Creek. We’re open rain or shine!

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