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Mason Bees

The Orchard Mason Bee ( Osmia Lignaria ) is a gentle, beneficial insect that has great potential as a pollinatator of fruit trees and a large variety of food crops. It is found throughout most of North America, particularly in wooded areas but often around homes in towns and cities.

The Orchard Mason bee is usually slightly smaller than a honey bee and a shiny dark blue like a fly. Males are smaller than females, have longer antennae and a tuft of light colored hairs on the face. Females have hairs on the underside of the abdomen, called the"scopa", adapted for carrying pollen.

Homeowners sometimes become concerned when they see the bee entering cavities under shake siding, around windows or other small holes in their house. These are not destructive insects as they do not excavate holes in wood, though they will clean out loose debris. No controls are recommended as no damage is done.

Nesting Habits

The female's natural nesting site are existing holes in wood. She chooses holes slightly larger than her boby, usually 1/4 to 5/8 inches in diameter. The bee first places a mud plug at back of the hole, then brings 15 to 20 loads of pollen and nectar to build a wad the size of a small pea. She collects pollen from spring flowers, including fruit tree and berry blossoms. If you watch the bee closely as she enters the nest you can see the pollen she has gathered on the underside of her abdomen.

When the female has provided a sufficent supply of food for the larvae, she lays an egg and then seals the cell with a thin mud wall. She then collects provisions for another cell and continues in this fashion until the hole is nearly full. A 6 inch tube can contain 6 to 8 bees. Finally the bee plasters a thick mud plug at the entrance. Protecting the developing bees from some predators. Some Wasps and Leaf cutter bees also build nests in such holes but their nests can be distinguished from the Orchard mason bee nests by the characteristics of the plug. The plug of the Mason bee is always rough while the Wasp prepares a smooth plug and the Leaf cutters seal the holes with chewed up leaves.

During the 6 to 8 weeks the female Mason bee is active she can produce one or 2 eggs each day. The larvae hatches from the egg after a few days and begins to eat its provisions. When the pollen-nectar mass is completely eaten in about 10 days, the larvae spins a cocoon and pupates within in the cell.

Near the end of summer the bee transforms to the adult stage but hibernates in the cocoon throughout winter. In the spring when the weather has warmed up sufficiently, the males begin to emerge by chewing their way out of the cocoons and through the mud plugs. The females, which are almost always in the inner cells of the tunnel, emerge several days later. During cool weather one or two weeks may be required for all bees to emerge.

Females mate soon after emerging, then begin nesting in 3 to 4 days.

This Bee is Gentle

The Orchard Mason bee is non-aggressive and will only sting if handled roughly or if it should get trapped under clothing. You can get very close to the nests for viewing and they will just fly around you. They will not attack to protect their nesting site. This is an excellent bee to have around children.

Collecting Orchard Mason Bees

If you wish to enhance local populations you can set out nests to collect the bees.  Attach the nests to a house or other structure near where you want pollination. Some protection from rain is desirable. You may also place nests on dead trees or posts in wooded areas near streams where there is a good supply of mud for nest construction and wild flowers on which to forage.

Position nests where they will receive morning sunlight. I like to have them at eye level which makes them easy to watch. Put the nests up just before the first spring blossoms and remove them in early to mid-summer when nesting is completed. Store them in an unheated structure that does not heat up beyond ambient temperatures. Great care must be taken not to bump the nest and disturb the developing larvae.

Using Mason bees in Orchards

If you wish to develop large populations you should store the nests under humid refrigeration at 35 to 40° F. This will permit control of emergence time and reduce predation and parasitism by the insect enemies of the bees. Do not place the nests in cool storage until late fall to assure complete development of the adults. The following spring, place the tubes in the orchards in shelters facing east to catch the morning sun. To hasten emergence, incubate the nests at room temperature for 24 hours before placing the bees in the orchard. The occupied tubes and some new nesting tubes should be in place a few days before apples begin to bloom, or earlier if other fruit bloom such as cherries, is available. Females do the majority of the work, males also visit flowers, but they do not live as long and are not as effective as pollinators.

If no natural mud source is available near the nesting shelters, dig a shallow hole, line it with plastic, and fill it with moist soil. A simple drip irrigator can be made from a plastic bucket and a piece of drip irrigation tubing to keep the soil moist.  

The orchard mason bee also has a tendency to fly away rather than reusing nests that have been previously been occupied. Supplying clean nesting will ensure they stay where you want them. Relatively large populations have been developed in 2 or 3 years in urban situations.

Cleaning the cocoons

Cleaning the cocoons will help control the Pollen mites (Chaetodactylus krombeini) that the Mason bees pickup during their visits to blossoms they have pollinated. The mites then take up residence in the bees nesting hole. The mite will then consume the pollen the Mason bee larvae needs for its full development. If the mite population is excessive they will eat so much pollen the larvae will starve. They may also attack the egg and developing larvae. Providing clean nesting holes every year helps greatly in controlling these pests.

Leave the cocoons in their tubes until November when the bee is fully developed. Remove the paperliners from the cardboard tubes, place the liners in a bucket of water until the glue dissolves making the removal of the cocoons.easy. There will be a lot of debris to clean. You will find on the internet mention of washing them in a weak bleach solution. This is helpful but not totally effective, some mites and eggs will remain.

Place the loose cocoons in a cool bucket of water and swirl them around for several minutes, this will separate most of the mud and many mites. Remove the cocoons, dump the water and repeat with clean water. Do this until the water stays fairly clean.  Now prepare a 5% unscented bleach solution and  swirl the cocoons around in itfor 5 minutes. Rinse with fresh cool water, let them dry on a paper towel at room temperature and you are finished.

The cocoons should then be stored for the winter. You can store them in the crisper section of your fridge. Most fridges are frost free which will dehydrate the bees and kill them so being in the crisper section will provide them with humidity. My wife does not allow me to do this. She has a strange aversion to having bugs in the fridge. Fortunately there is another option. Place the cocoons in a mouse proof container that allows some air movement. I use a cardboard shoe box place inside a rubbermaid tote. Do not layer the cocoons more than 3 high. Store outside in a shed, carport or some such structure where they will stay dry and not heat up above outside ambient temperatures. Check on them occasionally. Protect from long periods of extreme cold

 Spring time release

Early spring is the time to put out the Mason bee's home and cocoon. The face of the home should be facing east or south-east. This gives them morning sun which warms them and gets them out pollinating for you that much earlier in the day.

blue orchard mason bee cocoon

To release your bees you can insert cocoons into the back end of the tubes.  Care must be taken that the nipple end of the cocoon is towards the front of the hole. The nipple is clearly evident in the above photo. This is the head end. If put  in facing the rear they will hatch out facing the rear and can not turn around to get out. It's a death sentence. You can fill the tubes with several cocoons, but the small cocoons should be towards the front of the tube as these are the males and they will hatch prior to the females. Place the tubes in the Mason bee home along with fresh empty tubes for the bees to fill up.

You can also temporarily attach a mouse proof container, with the cocoons inside, to the side of the home and let them hatch out of that. Of course there must be a small hole, 5/16 or a bit larger will do it, on the side near the bottom made for them to exit. 

If your bees are already in tubes simply place them with fresh empty tubes into the Mason bee home.