Celebrating our Native Mason Bees

Early morning strolls through the summer garden at our little McKay Alto homestead can only be described as an angelic wakeup call. The capacious songbird melody wafts on a gentle breeze as the golden rays of sun push through the cool air that has settled in our little draw. The dahlias, peonies, sunflowers, yarrow and lupine bloom rich burgundy, cotton candy pink, canary yellow, snow white, and intense purple. The flowers are abuzz with bees busy at their morning routine. As the steam rises from my coffee mug, tickling my nose hairs, a small, dark, peculiar bee avoids the others, settling in on an unoccupied sunflower bloom. I lean in for closer inspection.

What's your first thought when someone mentions pollination or pollinators? Is it flowers? Bees? Honey? Allergies? A gambling man would put money on it being honey and honey bees (why wouldn't it bee, right?). While none of us could fathom a life without honey, the pollination is what's critical to the success of native plant reproduction and diversity, and crop and fruit production.

Honey bees are a vital part of our ecosystem, and because of the succulent honey they produce, they are most commonly recognized for pollination and conservation efforts. But when it comes to effectiveness, honey bees will forever live in the shadow of our solitary natives.

Washington State is home to approximately 600 native bee species, ranging in size and shape from bumble bees to sweat bees, none of which build hives. But the lesser known and easily confused with other less desirable flies are the mason bees.

A few common species like the blue orchard bee (Osmia lignaria) frequent our gardens and orchards, as well as our landscaped city blocks and urban homes. While some native species, like the emerald green sweat bee Agapostemon femoratus are obvious, mason bees are nondescript, dark colored or lightly striped, and smaller than honey bees. These are the bees that we see frequently but pay little mind or mistake for something else.

Mason bees are aptly named for their reproductive habits. The female mason bee often occupies holes in wood with larvae secured behind mud plugs for safe development. Mason bees don't excavate holes, rather they clean debris from suitable spaces, pack them with pollen that they carry in on their belly, and seal in an egg. The female repeats this process until the space is full with the female eggs deposited at the back of the space for protection from predators. Eggs are laid in May, and larvae hatch and feed on the pollen until the following spring, when they emerge to complete their lifecycle.

Mason bees are quite docile and lead solitary lives. Since they only reproduce once each year, they don't need extensive hives or honey production, but also forfeit the glamour of their extraordinary pollination abilities. A single mason bee can visit up to 2,000 flowers per day and just a few orchard mason bees can pollinate the same number of fruit trees as thousands of honey bees. For this reason, the blue orchard mason bee is prized as one of the few native pollinators managed in agriculture.

Similarly, mason bees have become rather popular on the pollinator market with bee houses readily available. Many houses use small, hollow bamboo shoots that can be replaced over time. Some scientists caution against the bamboo shoots in store-bought houses because the porous material holds moisture, promoting disease, mold and parasites. Other experts with the Xerces Society support the bamboo shoots, which seem to be a suitable material when kept sheltered from the elements. Storing occupied houses in an unheated shed or greenhouse over winter is a good practice. Materials like paper straws and breathable woods need to be replaced after the larvae vacate each spring.

Houses can also be hand-made by drilling holes in wood blocks 19/64th to 3/8th inch in diameter and six inches deep. Be sure not to pack them in too tightly, maintaining a minimum of ¾-inch spacing between holes.

Hang houses about six feet high and secured on an east-facing surface where they will receive morning sun to stimulate activity. Ensure the house is secured tightly and doesn't swing in the wind. You may also want to enclose it in chicken wire to keep flickers and woodpeckers from discovering the tasty larvae. Finally, once the larvae have hatched in the spring, replace the disposable parts and sanitize the rest with a 1-part water to 3-parts bleach solution before rehanging.

Native mason bees are a treasure of the Pacific Northwest, encouraging biodiversity and enhancing flower gardens and fruit crops. If you really want to see native bees at the height of their glory, take a hike in the Blues around mid-July. The wildflowers are at peak bloom and thick with native bees of all kinds.

If you are a gardener, have an orchard, or have an interest in conserving our native pollinators, you can reap their pollination benefits with a fraction of the time and space required of honey bees. Hanging a bee house sounds a bit silly, as does being excited to see the little holes plugged with mud. But it's another way to interact with nature at home, and that is something worth celebrating.

Now is the time to hang that house given spring has sprung and the mason bees will emerge very soon. If you give it a shot, drop a Letter to the Editor this summer with your observations. Let us know if you can identify the other native bee making home alongside the masons (they use leaves rather than mud to secure their larvae).

For more information, the U.S. Geological Survey and the Xerces Society provide excellent online resources.