Mason bees are early pollinators.
Ron Spendal

science environment

Here's Why The Magical, Mysterious Mason Bee Is A Gardener's Best Friend

By Ian McCluskey (OPB)
April 1, 2019 11:30 p.m.

Native Oregon bees with incredible pollinating powers are becoming popular with backyard gardeners and orchardists.

Every spring, when the first flowers bloom, mason bees appear.

You’ve probably seen a mason bee, but chances are you didn’t know it.


Mason bees do not have the classic yellow and black stripes of the honeybee, or the plump fuzziness of the bumblebee. Rather, they are a metallic blue-green — like a house fly. (In fact, they are often mistaken for flies.) But these little bees are native to Oregon and, because of their incredible pollinating powers, are becoming popular with backyard gardeners and orchardists.

They are one of the very first pollinators to emerge in spring. Good news for Oregonians, because this means they pollinate our delicious apples, pears, cherries, blueberries and raspberries.

Mason bees are also non-aggressive and almost never sting. Unlike honey bees, they have no hive with a queen and honey to protect.

Gardeners have discovered mason bees, realizing that with some basic knowledge, they can become bona fide beekeepers.

The Master Gardener And His Bee Boxes

Ron Spendal was one of those gardeners.

When he retired about 15 years ago, he went through the Oregon State University Master Gardener program.

During that time, he attended a lecture on mason bees. Inspired, he bought some cardboard tubes and set out to raise some mason bees himself.

Spendal is the type that when he does something, he goes deep; as soon as he heard about about mason bees, he studied everything he could.

He realized that there actually wasn’t that much published in the scientific literature and what he did find was limited. Of the few studies he found, he noticed some of the information wasn’t lining up with what he was observing where he lived in Washington County, Oregon. He realized those data must have come from other parts of the country with much different climates.

So, he set out to find some answers that would help him locally.

While most folks set up a single box to raise their mason bees, Spendal didn't stop there. He went out across Washington county to local commercial orchards, schools and natural areas, like the Jackson Bottom Wetlands Preserve.

He built and now monitors around 40 nesting sites and a total of about 550 nesting trays out across the county.

Ron Spendal has set up dozens of bee boxes, such as these at Jackson Bottom Wetlands Preserve.

Ron Spendal has set up dozens of bee boxes, such as these at Jackson Bottom Wetlands Preserve.

Todd Sonflieth / OPB

Mason bees, like other native bee species, usually live in holes and cavities. So Spendal turned to his woodworking skills.

One of the first experiments Spendal conducted helped him determine exactly how big a hole mason bees prefer. After making dozens of wooden trays with various sizes of channels, he discovered that while mason bees can generally adapt to nearly all sizes, that they clearly prefer 5/16th of an inch.

He didn’t stop there.

One of the challenges of cardboard tubes was that he couldn’t look inside them to see what was happening. So Spendal designed a wooden tray with a plexiglass side, so he could see exactly what the bees did each spring.

Ron Spendal designed and built his own nesting trays so he could study mason bees.

Ron Spendal designed and built his own nesting trays so he could study mason bees.

Todd Sonflieth / OPB

The Short, Happy Life Of The Mason Bee

When the spring days warm, mason bees begin to emerge.

The males appear first. They crawl from the tunnels and fly to nearby flowers to fuel up on nectar.


Then they hang out and wait for the females. As soon as the females stumble out from their cocoons, the males quickly mate with them.

“Their active life is short,” Spendal says. After only one to two weeks of freedom outside, they die.

The female has the hard work to do. Every day she visits flowers for pollen and nectar. Then flies back to her tunnel. Deep inside the tunnel, she brushes the pollen off her furry belly into a small ball of yellow powder. It’s barely the size of a pea, but it’s just enough food to feed one of her offspring for a year. “This little pollen pile represents roughly 1,875 flower visits,” explains Spendal.

She’ll gather pollen every day, lay an egg and build a wall. Day after day for about 30 days. She lays female eggs to the back of the tunnel, and males in the front. She can lay up to 30 eggs in her brief 6-8 weeks outdoors. Then she dies.

A female mason bee collects pollen, then seals up the nest chamber with mud.

A female mason bee collects pollen, then seals up the nest chamber with mud.

Todd Sonflieth / OPB

Spring turns to summer. Other bees are buzzing, but the mason bees are out of sight.

Deep inside their sealed tunnels, the eggs become larvae, eating the pollen pile left by their mothers. Then the larvae spin cocoons, where they will pupate into fully-formed adults and sleep through the rainy fall and frigid winter.

Once the average temperatures hit and stay at 55 degrees, the mason bees begin to stir. The males begin to chew through their cocoons.

“It’s been living off of its body fat, so when the temperature starts to rise that means its metabolic rate rises, and if it’s exhausted its body fat, it’s starving to death, so it needs to get out of the cocoon to get some nourishment,” Spendal explains.

Once free from the cocoon, the males stretch out their wings, fly off to find nectar, and wait for the females.

And the cycle begins again.

A male mason bee emerges from his cocoon.

A male mason bee emerges from his cocoon.

Todd Sonflieth / OPB

Secret Super Pollinator Power

Mason bees are also called  “blue orchard bees” for their color and their ability to pollinate orchards.

To put their ability in perspective: it takes between 30,000 and 40,000 honey bees to pollinate an acre of apple trees; it takes only about 250 mason bees to do the same work.

The reason they are so good at pollinating fruits, berries and flowers is actually because they aren’t as good as honey bees in collecting pollen.

Honey bees are rather proficient at collecting pollen: they go systematically from flower to flower and tuck the powdery pollen into pouches on their back legs, mixing it with nectar to make it a more solid and easy to transport paste.

Mason bees, on the other hand, are a little less efficient and elegant. In comparison, they “belly flop” into a flower, covering their furry abdomens with pollen. They seem to zigzag randomly flower to flower, spilling as much pollen as they are collecting. In this way, they’re not as effective as gathering pollen for themselves, but really great at scattering pollen.

They don’t fly far, either. In fact, their range is usually only as far as they need to fly to find two things: pollen and mud. This usually makes their range less than 300 feet. Or, in other words, your backyard and your neighbors’ backyards.

Backyard Bees For All

Spendal has taken it upon himself to share his passion for mason bees. He teaches a dozen or more workshops a year and makes regular visits to elementary schools.

If he had his way, everyone would raise these little native bees in their backyards.

“I think anybody that can raise mason bees should raise mason bees,” Spendal says. “If you do raise mason bees in your backyard, you’re probably going to improve the pollination that’s occurring in your yard and your surrounding neighbors’ yards.”

Raising mason bees is fun, perfect for backyard gardeners, school gardens and hobbyists. But in the larger picture, they are vital. 33 percent of our diet is dependent on bee pollination, according to Spendal. And of our critical agricultural crops, 75 percent are dependent upon bee pollination.

So this spring, if you see a solitary blue-green insect hovering around the first blooms or frequenting a small patch of mud, it’s probably not a fly, but rather a native mason bee. And it’s doing a lot more work for us than is apparent at first glance.

Listen to a conversation on mason bees with "Oregon Field Guide" producer Ian McCluskey in the audio player below.

Ron Spendal applied his woodworking skills to design nesting trays for mason bees.

Ron Spendal applied his woodworking skills to design nesting trays for mason bees.

Todd Sonflieth / OPB


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