Mason Bees

Wikipedia > Mason Bees:

Mason bee is a common name for species of bees in the genus Osmia, of the family Megachilidae. They are named from their habit of making compartments of mud in their nests, which are made in hollow reeds or holes in wood made by wood-boring insects.

Species of the genus include the orchard mason bee, Osmia lignaria, the blueberry bee, O. ribifloris, and the hornfaced bee, O. cornifrons. The former two are native to the Americas and the latter to Japan, although O. lignaria and O. cornifrons have been moved from their native ranges for commercial purposes. The red mason bee, Osmia rufa, is found across the European continent. There are over 300 species across the Northern Hemisphere, and more than 130 species of mason bees in North America; most occur in the temperate regions, and are active from spring through late summer.

Osmia species are usually metallic green or blue, though many are blackish. Most have black ventral scopae which are difficult to notice unless laden with pollen. They have arolia between their claws, unlike Megachile or Anthidium species.”


Orchard Mason Bees On Vancouver Island

by Gord Hutchings


Orchard Mason Bees, Osmia lignaria, are a proven, effective pollinator, perfectly suited for the urban gardener and commercial grower alike in improving their crop production.

Multi-layered condo design that can be taken apart and cleaned. This shows females at the entrance of their condo where each bee takes ownership of a channel and lays her eggs.

To give a bit of background to this fascinating native species, OMBs are distributed throughout Southwestern Canada and Western United States and along with many other native species play an integral role in the pollination of plants in North America. A pollination crisis is looming in North America and many other parts of the globe due to loss of natural habitat, altering the plant-pollinator interactions that are critical for crop production. OMBs emerge only once a year as adults, usually around early March and live until early June. After mating, the female locates suitable egg-laying chambers that will be secure for her offspring.

Female depositing pollen and nectar from her scopa and crop respectfully, providing food source for the larva. The small white grain of “rice”, is the egg.

In the wild, suitable nesting chambers consist of fissures in bark, other insect holes or hollow reeds. Around urban developments, egg-laying chambers can be found in house siding and roofing, holes where bolts have been removed, even gaps in lawn chairs and any other place that provides a blind channel. To encourage OMB females to lay their eggs in a human-designed home, OMB keepers create residences with a variety of channelled orifices called ‘condos’. Condo is a perfect description for these chambers as the OMB females come together to lay eggs but prefer to remain completely independent of one another, similar to the behavioural pattern of the Purple Martin (which some birders may be familiar with!).

The female creates mud divisions within each channel creating a ‘cell-like’ structure where she can provide nectar and pollen for her offspring. Females are laid first so that they are deeper in the channel with the males laid at the entrance, providing the first line of defence should a predator attack the channel entrance.

Individual female scraping pollen off the venter of her abdomen, (with her hind legs) called the scopa.

The overall length and shape of the channels is an important factor in determining the ratio of females to males, as well as how efficient it is for the female to lay down her mud partitions. With the help of my father (who kick started my interest in OMBs!) combined with my research at university, I determined that the optimum length of the channels needed to be 30cm (12”) and square in shape for easier production with a table saw. The clear inspection cover on each tray of the condo allowed me to observe the progress of each female in her channel.

Developing larvae spinning their cocoons before they metamorphose into full adults and diapause over the winter. Winged adults emerge the following Spring.

The more females produced in these channels means a greater volume of pollination since it is the females who do the majority of flower visitations. Important discoveries and structures like the Orchard Mason Bee condo can hopefully be used as a template for other pollinating bees as critical natural habitat continues to be reduced in many important food producing areas of the world.

The end of their flight and egg-laying season is normally around late May or early June in our region. The eggs hatch and the larvae develop within each cell, feeding on the pollen and nectar provided by the mother. When the larvae are ready for metamorphosis, they spin their cocoons and begin to transform within, to become a fully developed adult throughout the winter, diapausing until ready to emerge next Spring, beginning the cycle all over again.

Cocoon extraction and cleaning and close inspection for parasitoids.

In the depths of winter, the bee-keeper can help out their population of bees by extracting all the cocoons and cleaning off all of their associated mites, and riding the channels of any dead bees. The use of sand is the best and safest method for this important procedure. This leaves a clean, ready-to-go brood for next year that hopefully will choose your cleaned condos ready for occupation next Spring.

The best method for cleaning parasitic mites, is the sand method as seen in my video, “How To Clean Orchard Mason Bees Using Sand”.

Emerging boxes and transportation containers full of cocoons.

Sand cleaning method prevents the cocoons from getting wet in the bleach cleaning method, and it removes all the mites.

Some of my condos set up pointing both east and west, along the south side of my house deck. Each tray has a clear film covering the channels to view the bees and their developments within.

Our open-channel design of condo tray which has proven very successful. Can you spot the twin eggs on the one cell? It’s in the left box, on the top right corner. Also note the active female in the right chamber. The cover has been removed and flipped over for better photography.

Bee backing into channel

Bee laying egg.

Orchard Mason Bee Cocoon Cleaning

Cleaning orchard mason bee cocoons.

That pink fuzz you may occasionally see on the body of our little bees,a very annoying parasitic mite, is Chaetodactylus krombeini Baker. This mite is also most likely thriving within the condo throughout the life cycle of the bee. To help out your bees for next season, it is highly recommended to properly remove all the mites from your bees which are contained within the brood chamber cells of the condo. Trying to wipe off the mites from individual adult bees is not only difficult, but may result in a mild sting from the bee (females only).

Brood cells with pollen pillow and attached egg and mud walls.

In early winter from November to January, all cocoons can be cleaned and assurances of other species of beneficial bees and wasps can be extracted and cleaned. Please consult our Youtube demonstration video titled: “How To Clean Orchard Mason Bees Using Sand”Part 1 and Part 2. Remember to keep bees cold or at the outside temperature so as not to fool the bees into “spring” emergence!

Parasitic Chalcid wasps developing larvae within bee, within its cocoon.

Store dried cocoons in a cardboard or wooden box and keep outside in a secure, dry place. A garden shed or vehicle works well, as long as the cocoons are not subject to moisture too much or predation. Mould is hard to avoid if any dampness occurs.

Commercial Leaf-cutter bees set-up in alfalfa field in Saskatchewan.

When close to the end of February have cocoons in a container with a hole in it to allow bees to emerge and escape to start the cycle all over again.

Hutchings open-tray system showing multiple, conglomerate of cells. An active female is on the right even though clear cover has been flipped open!

Orchard mason bee condos set-up in backyard garden.



by Nick Guthrie


Honeybee populations on Vancouver Island are rapidly being destroyed by mites. Blue Orchard Bees (Orchard Mason Bees Osmia lignaria) are native to our area and are 17 times as efficient at pollination of fruit trees as honeybees. These bees are not available to fertilize later food crops as the parent bees die in early summer.

Mason bees may well be able to take over the fruit tree pollination if we give a little help.

The bees are about 7/16 inches long and look like blue bottle flies except for having 4 wings rather than two. The male is a little smaller and has two longer antennae. The female has long belly hairs to hold pollen.


The bees emerge from their over-wintering nests in the spring after about three days of 14°C (57° F) maximum day time temperature. In nature, they generally have been in beetle-made holes or other similar narrow spaces. The males are the first to appear as they come from the outer portion of the “tube”. They feed briefly and await the females which come from the deeper part of the tube.

The natural emergence of these bees is generally around March locally, but this can vary artificially if the nests are man-made and are kept in cooler temperatures until the plum or early apple trees just begin to break into bloom. The nests are then moved to a warm location.

The females emerge 3-4 days later than the males, and fertilization occurs almost immediately. The males die soon afterward without doing any pollination. The female gathers a little nectar and about 20 loads of pollen and builds a little pyramid inside a suitable nest site. Then a single egg is laid on its end in that mass of food. She then gathers about 10 loads of clayish soil and builds a wall which seals off the egg with its food supply. Hence the name, Mason Bee. This sequence is repeated until she has provisioned, laid, and walled-off about 30 eggs. The one female will fill two or three 6” holes with eggs.

It is useful to know that she will lay eggs into holes only to a maximum of about 6” deep. She will continue to lay eggs for only 5-6 weeks. Also, as the egg-laying process brings her to the last inch or two near the surface, she withholds sperm from the eggs she lays, thus the last eggs of one hole will develop into males. So males will begin to grow only in the area near the surface, while all the deeper laid eggs will produce females. For our purposes, it is important to understand that if we want a large majority of females to be born, shallow holes such as 3-4 inches deep, are almost useless – they will predominantly yield males which do not pollinate and are not needed in large quantities for population expansion. Thus, in our efforts to optimize the production of bees, it seems that 6 inches depth is ideal.

The newly laid eggs hatch into larvae in about three days and they devour their food for the next 25 days. Then they spin a cocoon inside of which they become adults before winter time. It is important that the nest not be moved or even vibrated much between March and the end of September (as the eggs and larvae will suffocate), at which time it can be moved to a garage or other unheated space until next spring.



CVGSS has hundreds of 5/16 inch diameter milkshake straws; clusters of these straws are free to you. After being cut off to a length of 6 inches, they can be inserted snugly into ¼ inch holes drilled in a Styrofoam piece. The Styrofoam is preferably 2 inches thick, though thinner will do. Also the red or blue variety is preferable to the white Corolite kind because the latter collapses easier. Of course, recycled is better than new. The holes should be grouped on a ¾ inch grid pattern so as to satisfy the bees’ need for social distance. The holes ideally are made on a drill press so as to keep the angles and positions tidy. As the diagram shows, the styrofoam block can be shaped to fit into the mouth of a 750 ml. yogurt tub. If, instead, you have an old apple juice tin – the kind which holds about 1 1/2 liters – that would be just as good. Or how about a 2 liter pop bottle cut off as in the diagram below? Any weather-proof odour-free container which can house these straws with the spacing suggested is usable. Have fun and make extras for presents!


  • Drilled holes – As with any of these nests, we can use any unpreserved wood except red or yellow cedar. 6 inch deep holes can be drilled in a large piece of wood which has at least one dimension of 6 inches, on a pattern where the distances between adjacent hole centres is no less than 3/4″. Old pieces of bridge timbers or barn posts do very well if they have no preservative in them. I use a piece of pegboard with its 1 inch hole spacing and a paint bomb to spray-paint the holes’ locations. A drill press and a brad point 5/16 inch drill bit can be used to cleanly and accurately position the first 2-3 inches of each of the holes. Then remove the wood block from the drill press and use a standard 5/16 inch auger bit in a portable electric drill to take the holes to the 6 inch depth. It is important with any of these nests to make the holes clean, as the bees are unable to move obstructions from the holes. See the diagrams.

  • 5/16 inch core box router bit – This cutting tool is used in a router which is mounted in a table to cut to a depth of 5/16 inches. The bit costs over $40 and can be ordered from the House of Tools. As the diagram shows, a piece of dressed 1×6 of about 3 feet plank can be grooved repeatedly with this tool, being sure to keep the grooves no less than 3/4 inches between adjacent hole centres The 3 foot plank can then be cut into 6 inch sections which can be drilled vertically in their exact centres, stacked to any reasonable height and then bolted together with º” ready rod. This technique is slightly faster than drilling, but is much more expensive if you have to buy the router . The advantages are that the ready rod can be unscrewed for cleaning of the sections and that many layers of grooved 1×6 can be stacked.


  • Dado – This method has recently been shown to be effective in attracting and housing the bees. It is probably cheaper than the router method for most DIY people, as table saws are more common than routers. We need to mount a very sharp dado cutter in a table saw to cut 5/16 inches deep and 5/16 inches wide grooves, which are 3/4 inches minimum between hole centres As with the router method, we can use dressed 1×6 planks to cut multiple grooves, then cut the plank into 6 inch sections and bore them to accept ready rod. In my limited experience this is quicker than the router or drilled method and is the method I favor now.
  • Straws – Plastic milkshake straws are the right internal diameter (5/16 inch) and price, but unfortunately, the plastic material encourages moulds to grow because of the trapped humidity. Various businesses on the Internet sell cardboard dispose-after-one-use straws for about 25 cents each. I find the price excessive and am looking for a better deal. Also, I don’t like to throw things away, so haven’t worked with this method. I understand that local suppliers are selling cardboard straws more cheaply recently so we’d better keep this option open.


  • Presuming you have such straws available, get a 2 litre pop bottle and cut the top third of it off at an angle. Get a handful of fiberglass insulation or similar non-rotting material and, after cutting the straws to the 6 inch length, wrap them in enough material to get the requisite æ inch elbow-room distances, and stuff them in the bottle. The centre of the bottle’s bottom can be drilled to receive a screw which can be used to hold the assembly to the south side of your house. Rotate the bottle so as to provide an umbrella effect. This method is clearly the fastest; it should take about 15 minutes to make and mount a nest.

The other methods take about an hour to make a nest with 30 or so holes. This size of nest would easily be enough to care for the pollination of the fruit trees in 3 city lots.

For the first three methods, a back and roof with an overhang need to be made of any available thin material, such as linoleum, thin plywood or aluminum sheeting. A builder’s stapler or short nails can be used for their attachment. Also, a piece of perforated strapping metal needs to be fixed to the centre of the upper back so that you can screw the nest to your house or shed.


The nest can be at any height off the ground; the bees are interesting to watch and sting only very feebly and only when tightly confined. The nest must “see” the early morning spring sunshine but must be sheltered from rainfall and wind. So it seems ideal to screw it to the south side of a building under the overhang of the roof. If the nest is attached to a tree or post it will have reduced bee traffic because of the wind. The bees are helped by any sort of color pattern near the holes so they can distinguish their holes from all the others. Just use colored crayons to do the decoration. To reiterate, the nest must not move at all until the end of September because we don’t want to disturb the growing bees; this may be a factor in the nest’s placement.


  • Be inventive and watchful in creating variations on these bee nests/condos
  • Place a shallow dish of wet clayish soil close by so the bee won’t have to travel far for masonry supplies.
  • I have used Styrofoam with the router method. I made sure to allow the routed pieces several months to out-gas. Carpenter ants may take over; they may not. I think the trial may be interesting.
  • Talk to the local gardening clubs. There may be places where there are large populations of the bee and you can load a nest or two this year and bring them over to your place to begin a population increase next year.
  • Contrary to the information above, many people have good results by just drilling 5/16 inch x 6 inch holes in fence posts.
  • Whatever you do, you are helping to boost the population of a native animal.


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