The Mason Bee—A Solitary Pollinator

The mason bee is a gentle beneficial insect. There are over 100 species in North America, including the orchard mason bee, which pollinates apples, cherries, and other tree fruits, and the blueberry bee.

The mason bee builds nests in woody perennial grasses with hollow slender stems and natural holes, creating single cells for their brood, which are set apart by mud dividers (hence their name).

They also create their nests in holes in wood that wood-boring insects have created.

These are solitary bees. They don't live in colonies, as honey bees do. There are no queens; every female is fertile and lays eggs.

They are not a destructive bee if found around the house or in house cavities.

They do not attack, although they may sting you if they think they're in life-threatening danger.

Most mason bees of the Osmia genus are metallic blue or green, or black in color, and slightly smaller than the honey bee. One species in Europe is red.

In each egg chamber that the female builds, the larva eats the food left for it until it makes its cocoon. Once the transformation is complete, the adult hibernates in the cocoon for the winter.

Spring repeats the cycle (some say the female gathers food, lays eggs and does the mud work until she dies from exhaustion). She lives for about a month and can produce one or two eggs each day.

Unusual Nesting Habits

The mason bee is noted for its unusual solitary nesting habits:

• Upon emerging from hibernation, the female mates with waiting males.
• The female finds a long, narrow tube (a hollow twig, bored hole, or even a mason bee nest you can purchase.
• She places a mud plug at the bottom of the hole.
• She gathers nectar or pollen and places it in the egg chamber for the larva to eat.
• She lays one egg in each chamber.
• She seals that cell with a mud plug, which forms one wall of the next chamber.
• She repeats the process, laying the female eggs at the back of the tube, males nearer the front, until the tube is filled. She may then move on to another nesting site.

The mason bee has been pollinating for millions of years on North America. Without them, some of today's tree fruit might have been lost long before the honey bee was brought to North America.

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