Overlooked Pollinators

You’ve all had enough schooling to know that much of our food requires pollination, and so honey bees are the heroes, making sure we all get to eat.  And they are, don’t get me wrong.  But there are some unsung pollinating heroes that are overlooked, and one of them is our native Orchard Mason Bee (Osmia Ligaria).  I didn’t know they existed until my friend Joe McNew told me about them.


The Orchard Mason Bee is the undisputed champion at pollinating some of our most desired fruit trees: apples, pears, cherries, plums, and peaches.  They are better pollinators that honey bees because they visit more flowers, up to 1600 per day.   Another plus is that the mason has more body hair that pollen sticks to, which ups the likelihood it falling off onto a receptive flower when the bee is grocery shopping for pollen and nectar.


You’ve likely seen an orchard mason bee, but may have mistaken it for a large fly.  They are 2/3 the size of a honey bee and have a metallic blue/black color.  There are some major differences between the two bees.  The mason bees work alone, and don’t form the complex social hive of the honey bee.  Each female makes her own nest and lays her own eggs.  But they are gregarious and like to build nests close to each other. They are not aggressive in the least, and won’t gang up to defend their nests. They are capable of a mild sting that I’m told is not very painful.


The mason bee’s signature characteristic is their nest building.  They make nests in holes in wood or the hollow stems of weeds and such.  They do not bore holes, and so must seek them out.  They use mud in the nest building process, hence the name mason.  The ideal nest site is a hole around 5/16 inches in diameter and maybe 4-6 inches deep.  The female will enter the hole and build a  chamber in the bottom out of mud, fill it with pollen and nectar, then lay a single egg on it.  She then seals that chamber with mud, and builds another in front of it.  This process continues until she reaches the outside of the hole, which is then sealed with a thicker mud wall.  She works hard at this from March until June, when she dies probably of exhaustion.  The eggs hatch in a few days and the larvae live on the food stored in their chamber until early summer.  Each larva then spins a cocoon and goes into the pupal stage of their development.  In the fall the pupae have fully developed into adult bees, but still have to wait until spring when flower blooms are available.  So they enter a state called diapause, a sort of suspended animation where they sleep through the winter.  In the spring they chew their way out of their chamber, mate, feed on flowers, and start the nest building process over again.


Orchard mason bees are so beneficial that it’s worth helping them out by providing nesting holes, which are not that easy to find in nature.  You can take 6×6 or 4×4 inch blocks of scrap lumber (untreated) and bore a series of holes 5/16 inches in diameter and spaced  ¾ inches apart.  Don’t bore all the way through the lumber.  Hang the nest boxes on the east or south side of a building so it receives direct sunlight in early spring.  Make the boxes as plain or ornate as you wish.  I glue 2×6 pieces of scrap lumber together to make my blocks, so you can really do it on the cheap.  There are plenty of web sites on line that show you how to build nest boxes. My thanks to Joe McNew for help with this article.

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