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Mason Bees

Mason Bees

by Jim Conley

 – CSU Extension

    Whenever we think of pollinators of the insect world, honeybees are probably the first that come to mind.  They’re certainly the best known and most cultivated bee species in the world.  The fact that they make honey makes them even more popular than their pollination service!  But, there are more than 3,500 species of solitary bees in North America.  Also called pollen bees or native bees, these efficient pollinators often do the lion′s share of pollinating crops.  Pollen bees have a number of advantages over honeybees as pollinators.  Many are active early in the spring, before honeybee colonies reach large size.  Pollen bees tend to stay in a crop rather than fly between crops, providing more efficient pollination.  Because they fly rapidly, pollen bees can pollinate more plants.  Pollen bees are usually gentle, with a mild sting, and do not get disoriented in greenhouses.  Pollen bees make very small amounts of honey, but it’s not collectable.

    Entomologists at the USDA Ag Research Service Bee Lab in Logan, UT have been studying native bees for some number of years, looking at nesting structure, pollination habits and how to attract native bees to orchards or fields.  The blue orchard bee, also known as the blue mason bee, is gaining attention as an effective pollinator.  You may see the blue mason bees for sale in many garden catalogs, along with housing structures.  Each female makes her own nest, and lays her owns eggs, providing enough food for each individual offspring.  The female flies for about six weeks in the spring, collecting pollen from various flowering plants.  They make their next in round tunnels, dividing it up with mud partitions into individual cells for each egg.  After building the nest, the adults die and the eggs inside the nests hatch and the larvae feed on the pollen in their individual cell.  By mid-summer, the larvae spin a cocoon and enter the pupal stage of development.  In the fall, they become adults and spend the winter inside the nests and emerge the following spring.  Because they use mud to partition off the cells, the mason bees prefer sites with a constant supply of water which is used to make the mud.

    Mason bees are well adapted to Colorado.  You can build your own mason bee house and see if you have some mason bees occurring naturally in your vicinity.  Simply find a large block of untreated wood, something like a 4” x 6” timber.  It could be any length; something like 12” in length would be a workable size.  Drill holes that are ¼” to 3/8” in diameter, and about 5” deep.  You can space these holes about ¾” apart, thereby creating a lot of holes in a relatively small piece of wood.  You can drill them in neat rows, or drill them in various patterns across the face of the wood.  Once you complete the drilling, clean any sawdust or wood shavings out of the holes as much as possible.

    Inexpensive artificial nests can be created out of paper or plastic straws (roughly ¼"-3/8" in diameter) packed into a milk carton, coffee can, or PVC pipe and then glued together.  These nests can be attached to tree trunks, fence posts, or the side of a shed, between three and six feet off the ground.  The nests should be placed so that the holes are horizontal and the bees receive at least morning sun.  Shelter from rain, snow, and wind, and from pests like woodpeckers and mice, should also be provided.  

    During the winter Mason bees are dormant in the nest.  You’ll increase their survival if you bring the nest into a sheltered place during the winter, something with a temperature range of between 30 and 45 degrees, maybe a garage or inside the window of an outside shed.  In early spring, the nest should be moved outside and placed where the morning sun will shine of the front.  Mason bees can help your flowers and gardens, and you’ll be helping the environment by fostering this important pollinator.