Smitten by Mason Bees

by Rita Lynn

We hear a lot about the plight of the honey bee, its reduced numbers, and its susceptibility to diseases, Africanization, parasites and hive collapse.  We also hear about the critical need for pollinators, being reminded that a third of our food supply and a third of the feed for our meat sources depend on bees for pollination.

Surprisingly, the majority of crop pollination is performed not by honey bees, but by native bees that do not produce honey.  For example, of the 1700 bees trapped for a study in a West Virginia forest, only 34 were honeybees.  The remainder consisted of a variety of native bees.  In addition to native bees being more prevalent than we might realize, they are also much more efficient pollinators than honeybees.  It takes about 360 honeybees to pollinate an apple tree, but just 6 native orchard mason bees can do the same job!

Like many native bee species, mason bees (Osmia spp.), also called orchard mason bees because of their emergence when fruit trees are flowering, are solitary creatures.  They form their nests in proximity to other mason bees, but they do not interact with them.  Each female bee is a queen, and she inhabits and maintains her own home.  They are called by some “the gentle bee,” in that they rarely sting, and people can approach the nest without risk.  If a mason bee should somehow be threatened enough to sting, the reaction is more like a mosquito bite than the sting of a honey bee or a wasp, and the sting does not trigger an allergic reaction in sensitive people.  These factors make them the ideal “pet” pollinator for our urban gardens.

Mason bees will pollinate almost any flower within 100 to 300 feet of the nesting site.  Early in the season, dandelions might provide pollen, but mason bees usually emerge just when the fruit trees need their services.  The queen then gathers the pollen, lays an egg in her nesting tube and deposits pollen for nourishment.  She then encapsulates that egg with a wall of mud.  She continues this process of laying eggs, usually putting 6 to 10 in each tube.  (As you might have gathered, this nest construction gives rise to the mason bee name.)  The queen is able to lay eggs that will be female bees first, and then lay eggs that will develop as males closer to the opening of the tube.  This process continues for the six-week lifespan of the queen.  During the summer, the eggs develop into larvae and then small, egg-shaped pupae.  The following spring, if they are developing in the wild, the male bees will emerge first and be available to mate with the females as their emergence follows.

My interest in mason bees stems from a display at Reiman Gardens two or three years ago.  The exhibit demonstrated several simple methods for attracting these bees to yards and orchards.  Specifically, mason bees have four crucial needs: pollen, mud, safe nesting tubes, and protective quarters for the nesting tubes.  A fifth element – harvesting and storing the bee cocoons under refrigeration from fall until blossoming begins the following spring – could also be added for improving the likelihood that bees will survive over the winter.

With regard to nesting holes, mason bees use tubes with openings 5/16ths inch in diameter and a length of about 6 inches.  In the natural setting, the bee might use a hollow reed or a woodpecker hole.  To house them in our yards, we can provide holes made of paper or reeds.  The pieces of bamboo that are often provided for that use are not ideal, because they cannot be opened for harvesting the cocoons without injuring them.  Plastic drinking straws are also not recommended, because they do not allow good air circulation and promote fungal growth.

Numerous structures can serve as the protective home.  The structure needs to be deep enough, or have a protruding roof, to protect the nesting tubes from the weather.  You can buy relatively expensive wooden homes of several designs, you can construct a home from lumber using instructions provided in the sources below, or you can even use a mailbox or a large PVC pipe.  The home then needs to be mounted on a solid, east-facing surface that is protected from wind, at about head height.

  Because of the process of enclosing each egg with a wall of mud, a source of moist clay mud within 20 to 50 feet of the nest is of critical importance.  Once you have all the elements in place, you can purchase mason bees from sites listed below in groups of 10 cocoons.  Then it goes without saying that application of insecticides, if done at all, must be done very carefully to avoid killing the very bees that you have so enthusiastically invited.  Note, however, that it is too late to start mason bees this year, and at least one of the online sources is sold out of mason bee cocoons for this season.

In fall, to protect the bee cocoons from winter elements, predators and diseases, it is recommended that you harvest the cocoons.  I won’t go into this process here.  It’s all clearly explained in the sources shown below.  And do log in to the websites listed if you are interested in mason bees or any other of the bee species native to our area.  These websites offer a user-friendly wealth of background information as well as complete instructions for raising native bees.  They also provide a source for acquiring the materials needed and the actual bee cocoons.

Incidentally, Cedar Falls code allows homeowners to keep bees as long as written permission is obtained from adjacent property owners.  Waterloo City Hall informs us that there is no problem putting up a mason bee house within city limits to attract and assist local bees.  However, if you intend to import any bees, you need a special permit unless you live in an A-1 zoning district.  If you intend to import any mason bees, we would urge you to first check with your local government regarding any restrictions or permit requirements for your location.

Wouldn’t it be great if we ourselves could supply pollinators for our gardens and neighborhoods?  It’s one of those small steps we can take to add quality to our environment.  It’s also an activity that adds fun and interest to our yards for people of all ages.

SOURCES – click on the topics at the top of the page for extensive information