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Mason Bees: Fun and Friendly

You don't have to be a beekeeper to keep mason bees.

Pennsylvania is home to about 300 different species of bees. Some of my favorites are the mason bees. They will not drill holes in your deck, shed, bark or sting. Best of all, they are easy to “keep” and do a fantastic job of pollinating our flowers.

When most people think of bees, they imagine venomous insects that sting a lot. Bees have a much worse reputation than they deserve. If you were stung by a shiny insect with bright yellow and black stripes, it was probably a yellow jacket or a hornet, not a bee. The vast majority of our native bees are simply not interested in stinging humans. Even our imported honey bees will generally not bother us unless we flap around, wear fruity perfume or venture too close to their hive. 

My dad kept honey bees when I was growing up in Seattle. Even though his year-round efforts yielded about 200 pounds of honey, he always told us four boys to go easy on it. “It’s not your main source of carbohydrate,” he would grump.  He knew it took an estimated 55,000 bee miles and two million flower visits for every pound of honey. These and other honey statistics  surely came to his mind as he saw us slathering it on chunks of my mother’s homemade bread.  Eventually, my dad gave up beekeeping when his allergies kicked in. A single sting would make his face swell up like a purple New Zealand rugby football. 

Some years ago, my mother introduced me to mason bees. Like other solitary bees, mason bees do not need to defend the resources of a hive filled with sweet and irresistible honey.  Mason bees are not in the slightest bit aggressive. I currently have two coffee-can sized containers sitting right above my back patio door.  Each is filled with about 700 developing bee larvae. Mother mason bees have provided me with hours of companionship while they dote on their offspring.  I will never get a single ounce of honey from them.  They just don’t make it.  Fortunately, I can buy top grade honey from several local beekeepers.

Two peacefully coexisting species of mason bees provide my springtime entertainment. Orchard Mason Bees (Osmia ligneria) are native to North America and are common in the Lehigh Valley. Hornfaced Bees (Osmia corniforns) were introduced from Japan in the 1970’s to help pollinate apple orchards. They are now also very common in this region. They are both in the same bee family (Megachilidae), which is a different family from honey and bumble bees (Apidae).  Both species of mason bees are about the same size as honey bees. 

Mason bees enjoy a lifestyle that is similar to carpenter bees, but they do not drill their own holes. Unlike honey bees and bumble bees, where a queen establishes a colony consisting mainly of sister worker bees, individual mason bee mothers gather pollen to feed their own babies. They typically build nests in tubes that they find, such as hollow sticks or holes in wood that other insects have already drilled.  To keep mason bees, all you need to do is put a bunch of tubes outside in the early spring, and nature takes care of the rest. The first year, you might only have a few bees show up. Don’t get discouraged! Over a few years, most mason bee “keepers” are able to generate as many bees as they care to provide tubes for.

Mason bee season typically starts around mid-April and winds down by late-May. This coincides with the flowering times of most fruit trees. The females spend their days gathering pollen, and fashioning it along with nectar into pea-sized loaves of home made “bee bread” which she carefully assembles in a protective tube.  After she lays an egg on the bee bread, she builds a mud barrier and repeats the process. This how they got the name “mason” bee. In the tubes that I use, each female will repeat this process about 10-13 times.  As she lays each egg, she gets to choose whether she wants it to grow up as a girl or boy. She typically decides to save the males for the front end of the tube. If a bird pecks out a few boys from the end of the tube, oh well… there are plenty more to go around! Since the males are at the front of the tube, they come out first in the spring, waiting for younger females to emerge a few days later. After a few weeks of competing with other males for amorous encounters with females, the males will die. However, to fuel their escapades, they do need to sip nectar, so also deserve a bit of credit for their pollination services. 

Backyard gardeners or fruit growers in the Lehigh Valley take note. Mason bees are actually more effective pollinators than honey bees.  Studies cited in a free USDA publication on Orchard Mason Bees estimate that in some settings, about two hives of honey bees (each with around 25,000 bees) are required to do the same work as just 250 female Orchard Mason Bees. These studies were met with "one-handed applause" from the beekeeping industry, but the point of these experiments was not to suggest that mason bees should replace honey bees in all settings. 

Mason bees will work better in colder weather than honey bees. They will not gum up the pollen they collect with “glue” into little blobs that hang on their legs, like honey bees do. Farmers that have incorporated Orchard Mason Bees into their pollination plans have seen significant growth in crop yields. In Japan, Hornfaced Bees take care of about 75 percent of the pollination work for their sizable apple crop. The first year my mother released them in her garden in Seattle, the resulting apple crop on the neighbor's tree broke down several of its branches. The neighbor’s apple tree had not been properly pruned for several years, so this will not happen to any of your apple trees.

There are two ways to “keep” mason bees. One is by setting out wooden “bee blocks” with holes drilled in them. The other way is to use commercially available cardboard tubes.

You can make your own bee blocks drilling 5/16” holes in a block of untreated wood.  Alternatively, a quick search of the Internet will reveal several suppliers of bee blocks. Some blocks come with a variety of different sized holes. These have the advantage of providing homes for different species of native bees. If you want to establish a strong mason bee population using bee blocks, it’s best to alternate between two sets of blocks: one block for the bees from the previous year and a different empty block for bees to start nesting in. In early spring, put the block out in a dry, somewhat shady and protected spot. I put mine below an eve of the house. After Memorial Day, when all of the holes are filled up, it’s a good idea to take the block out of the garden and store it in a cool indoor location. Early next spring, when you put last year’s bee block back out in the garden, put it in a cardboard box with some bee-sized holes in it. You want the bees to be able to get out of the cardboard box. Since they can’t see the wood block holes from the outside of the cardboard box, they won’t go back in. This way, this year’s bees will not be able to return to last year’s block. This “two block” system allows some bees to start setting up shop before others have woken up from their winter sleep. Wooden blocks need to be properly scoured out and sterilized with a small amount of bleach between uses, or the mites they harbor will kill the bees that use them. Having only one block makes this step more complicated than it needs to be.

Knox Cellars in Washington State sells parasite-resistant and reusable cardboard tubes with disposable paper liners that come in a convenient can. In May, when all of the tubes are filled with bee larvae, I put lids on the cans and store them in my garage for the rest of the summer. This keeps the tubes dry and away from hungry birds while the larvae develop into adults. In the Fall, I put the cans of tubes in the refrigerator for the winter months. It isn’t absolutely necessary to keep them in the fridge, but it protects them from wild fluctuations in temperature and improves survival rates. Please, don’t put them in the refrigerator until Fall! The mason bee tubes from Knox Cellars are not cheap, but they work better and are easier than anything else I have tried.

It is not yet known whether some problems that have vexed honey bees, like colony collapse disorder, will affect mason bees. Like other native bees, mason bees are susceptible to insecticides, mites and parasitic insects. Maintaining the health of our native bee populations will definitely have an important impact on agriculture.

Pollination services provided by bees are vitally important to many of the most delicious parts of the produce section. Kids need to understand how bees are part of our food supply, and we need to encourage them to appreciate the work that bees do for us. Keeping mason bees is a fun and easy way to see the work that bees do, while providing the neighborhood with a source of gentle and efficient pollinators. 

Many thanks to Rachel Hamelers and Ola Edwards for their helpful comments in preparing this blog!

This post is contributed by a community member. The views expressed in this blog are those of the author and do not necessarily reflect those of Patch Media Corporation. Everyone is welcome to submit a post to Patch. If you'd like to post a blog, go here to get started.

Valerie McCracken June 06, 2012 at 10:20 PM
Thanks so much for writing another very intereesting piece! I wonder if you have knowledge of "cicada-killing" wasps? If so, would you share it? Our yard has been home to them for the past several summers. Although they look intimidating, they do not seem at all aggressive with humans.
Michael Powell June 08, 2012 at 05:14 PM
Marten, Thanks for a great article. With regard to making our own bee blocks, would drilling holes in cedar wood be ok? Cedar wood is untreated, but that of course is only because it has its own protective properties. Would those same properties also deter/hinder mason bees?
Marten Edwards June 08, 2012 at 05:55 PM
Great question, Michael. I could not find a definitive answer based on research. Some sources suggest avoiding cedar. If you use paper liners in your block and remove the bees from the block at the end of the summer, it might not matter what kind of wood you use. Here is a link to some valuable information about keeping Mason bees, including a way to clean the cocoons at the end of the summer to reduce mite and parasite problems. http://clackamascountymastergardeners.org/10-Minute%20University/10-Minute%20University%20pdf%27s/Orchard%20Mason%20Bee.pdf
Michael Powell June 11, 2012 at 05:03 PM
Thanks Marten for the article. Is it correct to figure from their article that, following removal of the cocoons and storage in a container in a refrigerator, the cocoons need only be placed outside in the container, lid off, before early Spring? The adult bees in the cocoons can handle that exposure? How long before Spring may they be put outside? Figuring not to lose their Spring hatch timing by waiting too long to put them outside.
Marten Edwards June 11, 2012 at 05:37 PM
I typically wait until I don't see any hard frosts in the forecast before putting them out. They have adapted to our climate, so they should not be harmed if they are put out too early. One thing you can try is to see when the bees are naturally starting to become active. Pieris (http://en.wikipedia.org/wiki/Pieris_japonica) is an early bloomer and very attractive to bees. By the time it is flowering, the bees should be released.

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