Mason bee at an insect hotel in spring.

Mason Bees, Osmia spp.

  Mason bees are named for their habit of using mud or other "masonry" products in constructing their nests, which are made in naturally occurring gaps such as between cracks in stones or other small dark cavities.
Mason Bee, Osmia spp.

Mason bees are common in the United States, especially in forested regions, but they are also found in many other parts of the northern hemisphere.

About 140 species of mason bees are found in North America out of about 200 species worldwide. Mason bees are named for their habit of using mud or other "masonry" products in constructing their nests, which are made in naturally occurring gaps such as between cracks in stones or other small dark cavities

The Blue Orchard Bee, Osmia lignaria, is the Mason Bee species that is native to Wisconsin and the species you are most likely to see in your garden.

Read more: Natve Bee Parasites: Wasps


Mason Bee nest.

It’s much easier to identify a mason bee by its behavior than its appearance. There are various types of mason bees and their characteristics will differ. Listing each one’s identifying traits would be quite a task!

Some mason bees look a lot like honey bees, others can easily be confused with the common house fly. In general, they are smaller than the average honeybee and grow to about 0.3 inches. They are most commonly identified by the metallic tint on their skin.

Mason bees have faint lines that appear as stripes across their skin. Unlike in some other bees, these stripes are never yellow or red. They will follow the color of the bee’s skin—shiny, metallic, and black, blue, or even green.


Mason Bee, Osmia spp.
Habitat: Woodland, gardens and orchards
Development: Complete metamorphosis
Food: Herbivore
Flight Period: Early-late spring, a few active in summer.
Description: Small to medium sized bee, with a blue/green metallic body which is moderately hairy.
Length: 0.5 inches
Wingspan: 1 inch

Mason bees emerge from their cocoons in the spring. Males emerge first and remain near the female nest and try to extract females from their cocoons. When the females emerge, they mate with one or more males. Males soon die and females begin to provision new nests.

The females soon begin to collect pollen and lay eggs. Larval bees feed for several weeks inside their closed cells. They pupate in late summer and spend the autumn and winter as adults inside their pupal cocoons in the nest. They emerge from the cocoons in the spring, coinciding with flowering of many orchard crops. The new generation of bees then begins the cycle over again.

Mason bees are solitary.


Mason bees are very effective pollinators. Two or three females can pollinate the equivalent of a mature apple tree in one season. Their range of plant pollination is several hundred feet so they are useful for gardens and small orchards. They fly in cool or rainy weather and can supplement or replace honey bees as commercial pollinators in some situations.

  Help Homeless Mason Bees

Homeless Mason Bee, Osmia spp. Since Mason bees do not use hives like honey bees. In nature, mason bees place their eggs in holes drilled by beetles or woodpeckers. The bees will also use spaces between roof shingles or other narrow openings around the garden. There are a number of commercial products that you can purchase to house mason bees or you can make your own!

Once you have your mason bee house, the first step will be deciding where to hang it. The optimal location to hang your mason bee house is 6 to 7 feet off the ground, preferably under an eave of your house, garage, shed or some other shelter. If this is not an option, choose a house design that provides adequate shelter from the elements on its own

After bees mate, the female places eggs in the holes. Each egg is separated by nectar and pollen—it is at this time that the bees’ pollen-gathering also pollinates plants.

After the pollen and nectar is placed, the female places a mud plug in the tube (hence the term “mason”), then repeats the process with more eggs, pollen, nectar and plugs. When the tube is full, she finishes with a heavy mud plug and her work is done.

In the spring, the mature bees emerge from the holes. Males exit first. Females emerge after males because the eggs are placed deeper in the tubes. This is a protective measure, assuring a good female population to help keep the species going.

  Should You Purchase Mason Bee Cocoons?

The answer is No!

Mason Bee Larvae.

Why? Because most native bees live their lives in a very small area, one they are adapted to. Once you begin shipping them around, you also ship whatever diseases and parasites they might have. In addition, you are putting them into an environment they are not accustomed to and they may die.

When you look at honey bees, you can see the damage done by shipping. Honey bees all over the continent have shared their diseases and parasites. They have shipped infected bumble bees around to the point where an entire group of species is in rapid decline and faces possible extinction.

Why do we want to repeat this folly with mason bees? Why can’t we learn from our mistakes? Distribution of native bees should be strongly discouraged along with sell-back programs. If they are not native to your own backyard, they are not really native.

If you want to raise mason bees, put up mason bee housing and be patient. You will get a few the first years, more the second year, and after a while you will have many. They will be locally adapted, strong, and free from imported ailments.

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