Red Mason Bee - Osmia rufa L. (syn. O. bicornis) - Biology and Breeding

The red mason bee collects pollen on the underside of its body. It scrapes pollen off of anthers to a dense brush of hair under its abdomen. This species is one of the most efficient pollinators due to gathering great amounts of pollen in their nests and their high activity on flowers.

Red mason bees start flying already in the first half of April and usually stop at the beginning of June, that is during blooming period of most plant species in moderate climate. Males are the first to emerge. Females hatch few days later and they are immediately fertilized by the males. During next days females look for suitable nesting sites. They especially like hollow plant stems and different kinds of holes fret by other insects and wood pests. The female starts the nest with a thick clay plug then she starts collecting pollen. It takes 30 to 40 flights to fill up one cell. After gathering a sufficient amount of food supply (about 200 mg), the female lays a small, about 1.5 mm, oval and shiny egg and seals the cell with a clay wall separating it from another cell. The female builds from a few to even 20 cells (on average 7). After sealing the last cell she secures the entrance with an additional thicker plug.

Larva hatches about 7 days from sealing a cell and it intensely feeds on the stored pollen. Now the tube cannot be subjected to shaking because once the larva falls off the pollen it is not able to find its way back to the food.

After about a month, when the pollen is eaten, the larva spins a multi-layered and quite hard cocoon. During next few weeks it undergoes metamorphosis inside the cocoon and in the second half of summer the cocoon already contains an adult insect (an imago). The imago does not come out but hibernates throughout winter until spring of the next year (one generation per year).

Females usually make 30-40% of population. Fertilized eggs from which females hatch are laid first and then male, unfertilized eggs are laid.

The red mason bee is a very calm bee. It has a sting but is completely unaggressive and in addition its breeding is very easy. This bee is the most common solitary bee in Poland, thus, natural colonies of this insect can be found almost everywhere and in such sites it is usually enough to put out some nesting material. It is very likely that females will inhabit such material. When no natural colonies are present it is necessary to purchase some cocoons.

Preparing the Nesting Material

The best and the easiest way of preparing the nesting material for the red mason bee is cutting reed stems into 10-15-cm pieces. Location of nodes in the tube is not important because females enter the tubes from both sides using spaces between the nodes. Internal diameter of reed should be 6-8 mm. Required number of tubes depends on the number of cocoons you have. Assuming that 35-40% of population are females and every female should have two nests, then for 1000 cocoons we need 700-800 reed tubes.

So prepared nesting material needs to be tied into bunches of about 70-80 tubes and placed in wooden boxes. Tying the tubes prevents spilling out of the material from boxes. The boxes should be roofed. This will secure the tubes from getting wet. Reed needs to be packed as tight as possible so that it would not fall out of the box.

Cardboard boxes with cocoons can be placed under the roof or hang under the wooden box so they would not get wet. The cocoons should be put out on a warm and sunny day at the beginning of April, after first spring plant species blooming but no later than 2 weeks before anticipated cultivated plants blooming.

Now, the only thing left to do is securing the tubes from birds. The most sufficient way is to cover the front of the box with steel or plastic mesh with 3-4-cm holes. Such mesh does not bother working females and protects nests from unwanted visitors very efficiently.

2-3 weeks later, after bees hatching, cardboard boxes with empty cocoons need to be removed and burned as the remnants may contain parasites. In autumn, the inhabited reed tubes should be transferred to a cool and dry place. They can also be left in place but they need to be dump-proofed very carefully.

In order to keep the cocoons in good hygienic condition and obtain maximum increase in the red mason bee population it is necessary to take the cocoons out of the tubes and to overwinter only properly established, healthy cocoons. For more information see the 'Overwintering' section.

Dariusz Teper