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An apple blossom must have pollen from another apple variety dropped or brushed on its stigma to produce an apple. The more foreign pollen on the stigma, the bigger and better the apple.


If your tree is small, you can do this yourself with a Q-tip. Just gently wiggle the Q-tip in the open blossom of the pollenizer and then gently wiggle the Q-tip in an open blossom on your apple tree. Only pollinate the biggest and best blossom of every cluster, one blossom per cluster. Only one apple per cluster will remain after thinning, so don't waste your time pollinating blossoms which will later be thinned. Do this when the temperatures are above 14°C (57°F) and it is sunny and dry.

If your trees are too big to hand-pollinate, rather than wait for the blue orchard bees (BOBs) to find your apple trees, try putting out nesting cells and nurture your own colony of blue orchard bees.

The Blue Orchard Bee. Osmia lignaria. (aka the Orchard Mason Bee).

Honeybees (HB) only account for 15% of the pollinating done by bees. The rest is done mostly by solitary bees and bumblebees.

Native solitary bees are found throughout North America, Europe and Asia and are important pollinators of fruit trees and vegetables. The blue orchard bee is one species of solitary bee that normally nests in beetle tunnels in trees, holes in fences, holes in lawn furniture and wooden patios, wooden window casings, anywhere they can find a ready-made hole of approximately 5/16" (7.5mm). They are solitary, but gregarious i.e. they work alone, but like to nest in groups. They will use artificial nests such as blocks of wood drilled with 5/16" holes, or cardboard straws with an inside diameter of 5/16". The blue orchard bee does not look like a honeybee or a bumblebee, it looks more like a blue bottle fly. The female blue orchard bee is the size of a honeybee and is black with a blue orchard bee metallic sheen. Male blue orchard bees are slightly smaller and have a patch of white fuzz on their foreheads. When a black fly is at rest, the wings form an inverted 'V' like a fighter jet plane; when a blue orchard bee is at rest, the wings are parallel to the body. This is one way to tell them apart, but once you know them better you will notice that the flight pattern of a bee is different from that of a fly.

For an excellent book on blue orchard bees with colour photos, see How to Manage the Blue Orchard Bee as an Orchard Pollinator by Jordi Bosch and William Kemp. 2002. This book is out-of-print but it is available online for free.

An individual blue orchard bee can set in excess of 2000 apples per day, by comparison, an individual honeybee sets only 30 per day. This difference occurs because individual orchard bees work faster than honeybees, stay within the orchard, contact stigmas consistently, and prefer orchard flowers to those of weeds or other crops.

Life Cycle of the Blue Orchard bee.

In the Spring, after a few days at 14°C (57°F), the males emerge and sit in the sun waiting for the females to emerge. After another few days of 14°C, the females emerge. They mate immediately and set off to find and provision nests for their eggs. The ideal nest is wood or cardboard, 5/16" inside diameter and six inches long with a dead end. If the holes are only 1/4" in diameter she will lay male eggs, if the hole is only 4" long she will lay mostly male eggs and it is female eggs we want her to lay because the female blue orchard bee does all the work collecting pollen and thereby pollinating the blossoms.

The female collects pollen and nectar from nearby flowers and puts it in the far end of the hole. She keeps collecting pollen and nectar until she has a pollen lump and then she backs into the straw and lays her egg on the pollen lump. Next she constructs a mud wall to seal that cell from predators and parasites. When the wall is finished, she sets off to provision another cell for another egg. According to Jordi Bosch & William Kemp (references), each female blue orchard bee visits an average of 1875 flowers to provision one cell.

Each bee will lay 20-30 eggs and each cell is about 3/4" long so each female blue orchard bee will fill two or three of the six inch straws. She must store her eggs inside her so she knows which eggs will produce female blue orchard bees (fertilized eggs) and which will produce male blue orchard bees (unfertilized eggs). She lays female eggs in the inside of the straws where they are most safe from predators, and male eggs on the outer cells of the straws, but she lays twice as many male eggs.

After about a week, the egg hatches into a larva and eats the pollen and nectar for about a month (it takes less time if the temperatures are warmer), spins a cocoon and pupates inside the cocoon for July, August and into September in my area (south coastal B.C.). By mid September, an adult blue orchard bee is inside the cocoon. It spends the winter inside the cocoon and in the following spring, once the temperature has reached 14°C for a couple of days, he/she emerges from the cocoon.

Coincidentally, apple pollen is viable at 14°C so their life cycle ideally coincides with the apple blossoms.

We call our nests 'bee condominiums' and we bundle thirty straws together and put them in a recycled plastic pop bottle.

We also have what we call a 'pull-apart'. This is a wooden condominium that can be taken apart in the winter and you can see exactly how many cocoons you have.

Our work with the blue orchard bee has shown us that

  • blue orchard bees are present in the Pacific Northwest.

  • blue orchard bees nest readily in cardboard straws.

  • there are at least three different solitary bees occupying these cardboard straws and one solitary wasp.

  • when the straws were put in a two liter pop bottle, we had 100% of cells filled by blue orchard bees in three weeks.

  • 94% of the cocoons in blocks with three inch holes were holding male BOBs.

  • blue orchard bees emerge in early March in southern Vancouver Island, early April in Aldergrove, B.C.

  • blue orchard bees fly about 100' looking for pollen.

Bee condominiums can be placed at any height, but ideally put them where you can watch the activity of the bees daily

Put the condos facing east or south in a spot protected from the wind and the rain.

Blue orchard bees do not defend their nests, so they do not sting aggressively. I was stung once when I trapped a blue orchard bee between my arm and my side. The sting was like a mosquito bite, but it was not itchy. As with other members of the bee family, male bees have no stingers.

Important note!!

I learned a hard lesson in 2008. For four of five years I have been putting my cocoons out in batches, about 20 cocoons at a time. I wanted to see what % of bees emerged from the cocoons (98-100%) and how long I could keep the cocoons in the cooler and then have the bees emerge and start collecting pollen (until June 30).

I'm getting very busy with my nursery and in March 2008, I said to myself: "Quit diddling around and put them all out!"

I put them all out at the end of March. My usual bloom time for apples is mid-April until mid-May.

On April 12 we had our first lovely warm day of the year. Many male BOBs emerged. Usually the females emerge three or four or five days later depending on the temperature.

The weather turned cool and wet and I didn't see my first female until May 1, nineteen days after the males had emerged. I had a very low return rate, maybe 10% of usual.

My hypothesis is that the males died before the females emerged and fewer females were inseminated and those inseminated females laid fewer eggs.

Now, I advise everyone: "Unless you have a real surplus of cocoons, don't put all your cocoons out at once!! Wait until the apple blossoms are at the 'loose cluster' or 'pre-pink' or 'pink' stage". The blossoms which are not opened in this diagram are at the 'pink' stage. This year I'm going to put my cocoons out at the 'loose cluster' stage for Dolgo, my earliest crabapple.

After three or four days where the daytime highs reach 14°C (21°F), the males will emerge. After another four or five days where the daytime highs reach 14°C (21°F), the females will emerge.

What doesn't work very well:

  • Open-ended straws. The bee spends at least one day making a mud back door. We want her pollinating our blossoms not working on a back door!

  • Plastic straws of 5/16" diameter. The blue orchard bee cannot get the mud to stick to the plastic

  • Wooden blocks with masses of holes and no orientation cues

  • Wooden blocks with holes only 3" deep

  • Straws or holes longer than 7"

What doesn't work at all:

  • mounting the condo on a post or pillar.

  • mounting the condo at the edge of a wall of a building or fence - try to put it in the middle of the wall of the building or the middle of the fence.

  • mounting the condo in a tree (too shady).

  • condos with no windbreak or rain protection at the entrance to the straws.

What we don't know:

  • how the blue orchard bee orients to her nest when she is 100' away? 15' away? when she has landed on her condo?

  • who else is using these cardboard straws? Some are leafcutter bees and some are berry bees, Osmia atriventris, and there is a solitary wasp.


A surprise BOB nest in a garden flat in the greenhouse.

Above on the left is the bottom side of a garden flat that was sitting right-side-up in a stack of garden flats on a shelf in the greenhouse for more than a year. The blue orchard bees used the cells formed between the shelf and the bottom of the flat as cells for their eggs. These cells measure 9 mm wide x 3 mm high (3/8" x 1/8") so you can see that the female blue orchard bees are versatile!

Another interesting thing about this flat is that some of the cells are filled with masses of pollen and no blue orchard bee or cocoon (see photo above right). These are cells that were infested by pollen mites. The pollen mites took over the pollen wad from the blue orchard bee and multiplied in the pollen mass.

The center picture is of cells with cocoons showing some extra thick walls at the back of the holes.

Why did the blue orchard bee use this plastic flat if we know she will not use plastic drinking straws? Good question! We know the plastic on the garden flat is dull and rougher than a drinking straw. Maybe it is rough enough that the blue orchard bee will use it. Maybe she thought she'd found the ideal site (in a greenhouse, in the sun, nice and dry) and she said "I guess I'll put up with the plastic walls".

Washing Blue Orchard Mason Bee Cocoons by Lenn Basaraba

Blue Orchard Mason Bees are parasitized by a very aggressive mite, Chaetodactylus krombeini, the hairy fingered mite, which competes with the larvae for the nectar and pollen deposited as food supplies for the developing larvae. In order to assist the bees to overcome the depredations of the mites, it is necessary to separate the mites from the bees, and give the bees a chance to get ahead of the mites. The BOB cocoons are waterproof, and when the adult bee is hibernating in the cocoon the cocoons can be moved and handled without serious consequence.


A favoured method of separating the BOB from the mites is to wash the cocoons in water to remove all signs of the mites, mite eggs and mite hatchlings.

Since any process such as this is likely to miss a mite egg or two which will lead to development of mites, and as re-infestation from other colonies occurs regularly, it is necessary to wash the cocoons every year.

The following process is recommended:


  • The cocoons should be washed each year between the end of October and the end of December (for the Lower Mainland where the bees emerge in March).

  • Install cleaned Nest Boxes outside by the end of February.

  • Place a thin cardboard box with cocoons near the clean nest box by the end of the first week in March. Place in a location where box will not be wet by rain.


  • A scraper to scrape clean the nest block grooves containing the cocoons. A screwdriver of suitable width, shaped to conform to the shape of the groove, works well.

  • An Exacto knife or single-edge razor blade

  • A Rubbermaid wash-basin, 16 inches diameter x 8 inches deep. (Dimensions are recommended only)

  • A wire sieve of about 1/16” to 3/32” mesh, 8 inches diameter X 5 inches deep

  • Buckets for clean and dirty water (optional, if no faucet and sink are available)

  • Paper Towels

  • Cardboard boxes are hand-made from file cards or you can use ready-made small cartons from such items as flat fillets of anchovies, Scotch tape, Certo, and Jello.


  • If using Nest Boxes made of pieces of wood with slots routed into them:

  • Dismantle the Nest Box, separating the pieces of wood.

  • Scrape all the contents of the slots into the Rubbermaid wash-basin.

  • If using cardboard straws in a ‘pop-bottle’ nest box:

  • Slit the straw at one end, and unravel it in a spiral fashion and place all the contents of all the straws into the Rubbermaid wash-basin.

  • Fill the clean water bucket with clean, cold or tepid water.


  • Pour three inches or more of clean water into the wash-basin, and stir the mud /mites/cocoons/water mixture to release any viable cocoons so they will float to the top. Note: The cocoons are waterproof and contain some air, so they will float. The adult bees in the cocoons will not be damaged by gentle handling.

  • Skim the cocoons into the sieve, and dispose of the mud/mite/water mixture into the second bucket.

  • Place three inches of clean water in the wash-basin.

  • Submerge the bottom of the sieve until the cocoons just start to float.

  • Swirl the cocoons in the sieve as though panning for gold. The cocoons rubbing against the wires of the sieve will dislodge the mites and mites eggs and any other matter adhering to the exterior of the cocoons.

  • The water will become discolored as the mites are scraped from the cocoons.

  • Lift the sieve from the water, dispose of the dirty water in the second bucket, and pour three inches of clean water into the wash-basin from the first bucket.

  • Submerge the bottom of the sieve, etc. Repeat until the water remains clear, about 7 or 8 changes of water. Some people recommend a 0.05% bleach solution (15 ml of 5% bleach to 4 liters of tepid water) for the second to last rinse.

  • Lift the sieve from the water, and allow the cocoons to drain.

Drying and Storing:

  • Turn out the cleaned cocoons onto multiple layers (4 or 5) of paper towels. Spread them out 1 cocoon deep, and lightly dry them with other paper towels.

  • Place the cocoons on a dry paper towel, spread out 1 cocoon deep, and leave them overnight to air dry.

  • At this time the cocoons can be ‘candled’ to remove any cocoons containing parasitic wasps, undeveloped bees, etc.

  • Separate the cocoons – the small ones are males, the large ones are females. If your nest box contains nest holes about 6 inches long, each hole or tube will contain about 5 - 6 males and 3 - 4 females.

  • Place enough cocoons into a small cardboard (file card) box to populate the nest box next year. Place male to female cocoons in the box in a ratio of 2 males to 1 female. Install at least 20 males and 10 females in each box.

  • Store the cocoons in a cool dry place, such as an unheated garage until early March, when the box containing the cleaned cocoons should be placed near the clean nest box, out of the rain, in preparation for hatching, and a new season of pollination. Pierce a ¼” diameter hole in the box to allow the hatched bees to emerge.

Flowers that provide food for the bees:

Sometimes the bees will emerge in a warm spell before your apple tree blooms, or they may still be looking for pollen after your apple blooms have faded. In 2004 in Aldergrove, the first female blue orchard bees emerged about April 3rd and I still had a few female bees working on May 14. My first apple blossom opened on April 10 (Manchurian crabapple) and my last apple blossom faded on about May 6 (Reinette Rouge d'Etoilee) so the female blue orchard bees emerged one week before my first apple blossom and continued for one week after my last apple blossom.

Make sure the bees have a constant supply of pollen and nectar. Solitary bees are attracted to pussy willows, early yellow Asteraceae (dandelions, leopard's bane, groundsel, hawkweed), buttercups, wallflowers, forget-me-nots, violets, plum, cherry, pear, apple, Labiatae (nettles, mints, Lamium), Leguminosae (peas, beans, vetches, clovers), Ericaceae (heath, heather, Pieris, Gaultheria, blueberries, Rhododendrons and Azaleas), black currants, raspberries, blackberries, and Umbelliferae (dill, parsely, carrots).

To purchase Blue Orchard Bee cocoons, see bottom of page labelled 'Orchard Trees'. 

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