Mason Bees (Osmia lignaria) are an early spring pollinator, they are a small blue black solitary bee that we see in our gardens when the fruit trees are in bloom.
With the crash of Honey Bee populations in North America their role has become more important since with better pollination we will get larger more abundant fruit tree yields and our other plants and trees will be happier.
Mason Bees are very efficient pollinators, better than Honey Bees for a couple of reasons, one is they fly in colder weather so their better for early spring pollination, also they gather the pollen differently, instead of pollen baskets the pollen gathers on the stiff hairs of their abdomens, since its packed looser than on a pollen basket it tends to rub off when visiting flowers allowing for better pollination.
We can increase the population of Mason Bees in our yard by providing them housing, they like a clean hole 5" to 7" long in wood, 5/16" in diameter, one female be will use one or more holes, she will keep laying eggs till she dies.
Depth of the holes are important since the female eggs are layed first then the male eggs, if the hole isn't deep enough there won't be the correct ration of male to female.
Holes drilled in wood will eventually fill with parasites like the mites in the top picture and the bee survival rates will decline.
I like to use stacked routered boards for bee houses, they are easy to clean and to remove the cocoons for cleaning, I can see the difference on the bees when I take the pictures a lot less mites!
The male bees chew their way out of the cocoons when the temperatures are warm enough to wake them up in the late winter early spring, the males then wait for the females to emerge and mate with them as soon as they are out.
Once mated the females find a mud supply and a hole, they first seal off the back of the hole with mud then proceed to collect pollen and build a pollen ball that they lay there egg on, once the egg is laid she will seal off that chamber and start collecting pollen for another pollen ball, she will continue this for as long as she can, once the hole is filled she will seal the end with mud then start another hole.
The eggs will hatch and the larva will consume the pollen, then spins a cocoon out of silk, by fall the fully formed bee will be in the cocoon waiting for spring and warmer weather.
I like to make my bee houses out of cedar, I rout the slots with 5/16" half round milling bit, its hard to find 5/16" round router bits. I just rout a long board then cut the boards to length after, then slide them in the box, its all dark inside just like the bees like it, you can wrap your boards in black tape if there is any light shinning into the holes.
Where I live a south facing wall under the eaves works best, keeps it out of the rain, and they need the heat from the sun to get active.
Its also good to put a predator guard in front, it can be some hardware cloth with 1/2" holes or a cover with a hole for the bees to get through. A woodpecker can do a lot of damage.
You also can build in a compartment for the cocoons so they will be safe when you put them out.
Cleaning and Storing the Cocoons.
First I take apart the bee houses and remove the cocoons with a plastic scraper made for the job, I separate anything that doesn't look like Mason Bee cocoon. then separate the cocoons from the mud.
Cocoons after first wash, still lots of mites and pollen attached.
Next I dump out the dirty water and fill the tub with a weak bleach solution ( four liters of tepid water and a cap full of bleach), I place the cocoons back in and agitate them around, I use a small sieve and scoop some up and swirl them in the sieve this loosens the attached material, then I rinse under tap tap and place on some paper towel for inspection.
I check for mites and other contaminants, dump out the old solution and fill the tub up with some clean weak bleach solution and repeat till there nice and clean, look for small dots on the paper towel, you want less than 10 per square inch, these are the small mites.
Looking a lot cleaner.
This years cocoons drying getting ready for storage, I would have had more but the woodpeckers consumed some fo them.
I place them in the fridge in a sealed container, with some paper towel, once in while I will take them out and give them some air, to much moisture and they will go moldy but you don't want them to dry or the bees will die, if they do go moldy rinse them in week bleach solution again and they will be fine.
Almost all my cocoons had healthy bees this year so this worked well, so I did the same thing this year and took pictures to document the procedure, please feel free to ask questions or contribute more information, or share what you do.
I recommend the book Pollination With Mason Bees by Dr. Margriet Dogterom, I use it as a reference.