Mason Bees

Without pollinators, the earth would be in serious trouble.  In fact life can't exist without pollinators.  North American honeybees are in a critical decline due to mite infestations which carry deadly viruses.  I know for a fact that some summers I never see a honeybee.  The gardener must rely more and more on other pollinators.

An excellent pollinator for the backyard gardener is the mason bee, osmia lignaria, also called the blue orchard bee.  It's a solitary bee and very gentle.  They don't sting and look rather like a large fly.  We've been providing nests for them for a number of years now.

A simple nest can be made from a block of wood with holes drilled in it.  The holes must be 5/16" inside diameter and at least 6 to 8" deep.  This last measurement is important because the eggs producing females are deepest in the hole, with eggs producing males on the outside.  Since the females are the ones who do all the pollinating, it is key that the most female eggs are provided for.

Another simple nest can be made of straws - again with an inside diameter of 5/16" - and placed in a plastic drain pipe to hold them together.  The ends of the straws must be crimped off.

The most satisfactory nests are ones which can be opened and cleaned since mites can kill off mason bee populations also.  We purchased ours from Quack Farm Nursery, who in turn got their supplies from Beediverse, the company of Dr. Margriet Dogterom who has been researching and promoting Mason Bees for over 30 years.  These days, mason bee supplies and even mason bee cocoons can be purchased from most nurseries.

Today was a lovely, sunny day and when I checked our nests, which are under the south-facing eaves of the potting shed, I could see that some of the straws have the mud plugs missing.  A careful search of the nearby flowering currant showed lots of bumblebees, but no mason bees.

Mason bee nests sheltering under the potting shed eaves

The first bees to emerge are the males.  They are distinguishable from the females by white hairs on their heads and longer antennae.  They stay near the nests waiting for the females to emerge so that they can mate with them.  The females immediately set about gathering pollen.  They take the pollen back to the nesting site and when they have a plug of pollen, they lay an egg on it and seal it in with mud.  Then off they fly to gather more pollen and lay another egg.  This all takes place in the spring at a time when fruit trees are blooming.  It's important that once mason bees start filling up the nesting tunnels that they are left strictly alone until the fall.  If the nesting site is moved, the eggs could fall off their pollen store.

Last summer's bees busily filling up tunnels

In summer, the egg hatches into a grub and starts eating the pollen plug.  When fully grown, it spins a cocoon and changes into a pupa.  Eventually it becomes an adult bee and stays that way until the following spring, when it emerges and starts the cycle all over again.

Anyone can promote the well-being of mason bees.  Now that spring is here, cocoons are readily available at nurseries.  Consider buying some and setting out some nesting blocks for them.  More information can be had at the Beediverse website.  There are books and DVDs available to help you set up your colony.  This is a win-win proposition for everyone from the bees to the planet!