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Mason bees in a honey bee hive

Mason bees, leafcutting bees, and other cavity nesters are incredibly easy to please. The hype you hear about their tubes needing to be a specific diameter, or a special length, or placed in a particular location is mostly nonsense. Left alone in the wild (as they were for millennia) the bees find all types of cavities that please them, from beetle borings to woodpecker holes to hollow reeds. In the wild no one measures the diameter, cuts them to length, or holds them parallel to the ground. We humans can be terribly self-important.

But just like everyone else I have neat rows of little tubes—paper straws in empty vegetable tins—and the bees certainly use them. A tin full of straws takes about three days to fill at the height of orchard bee season. These early bees are followed by other types of masons and leafcutting bees, all angling for a spot in a green bean can. Luckily for them, my dog eats a can of green beans each and every day, so when a can fills up I simply pull it off the bee shelf and add another.

But the bees in the straws are the tip of the iceberg. These are the gregarious masons that like to live (it seems) on the same block as everyone else. Other individuals nest to a different drummer.

A couple weeks ago I was checking my honey bees when I noticed mason bees flying in and out of an empty hive that was sitting between two very active colonies on the edge of the woods. You wouldn’t think mason bees would go there, with the air teaming with pheromones and threatening sounds. Curious, I opened the hive and found masons actively building away. What cavities were they using? Brood comb, of course. If you think straws in a can are tightly packed, you ought to take a good look at an empty brood comb. Claustrophobia big time.

Seeing these nests reminded me that I had a section box from the previous year that held some mud nests. I went to check on the section box, which I had put outside a month ago, and sure enough two of the bees, Osmia aglaia, had already emerged. These bees, sometimes called berry bees, are active later in the season and reach their peak after the orchard masons are done for the year.

Many species of bee in the family Megachilidae nest in empty tubes and tunnels, so it is not too late to put out your cans and paper straws. Get a dog with a green bean fetish and you can keep filling cans all summer long.

Honey Bee Suite

This brood frame was inside an empty bee hive. © Rusty Burlew.
This brood frame was inside an empty bee hive. © Rusty Burlew.
Mason bees at work in a brood frame. © Rusty Burlew.
Two Osmia lignaria at work in a brood frame. © Rusty Burlew.
Mason bees living in a section frame. © Rusty Burlew.
Osmia aglaia nests in a section honey frame. I have no idea why they all like the upper left-hand corner. © Rusty Burlew.
Plenty of paper straws. A can fill up in about three days. © Rusty Burlew.
Plenty of paper straw nests. A can fills up in about three days and then I replace it with a new one. © Rusty Burlew.

Mason bees actually sting, kind of

Yesterday I got my first sting of the season. That would not be remarkable except for one detail: the culprit was a mason bee. A mason bee! I have never before been stung by such a creature.

I’ve been keeping mason bees for about seven years, and during early spring the area around my patio is black with them. With all the carrying on they do, you wouldn’t even notice I have honey bees. Honey bees are always on a distant mission and they fly up and out. I only ever see them at the hive entrance. Mason bees, on the other hand, have an abbreviated foraging distance and do most of their work within several yards of their birthplace.

Overly-friendly bees

Not only are there lots of them in a small area, but they are quite chummy. By that, I mean they have no issues about being close to humans, very close, and they will often investigate your nose and ears as potential nesting sites. Talk about irritating.

Several species of mason bee live in my area and appear at different times of the year. The ones active now are the so-called orchard masons, Osmia lignaria. They appear about the same time as the orchard tree blossoms in the northern states and are quite content to pollinate them. But they are generalists and can also be seen on all types of flowers, including dandelions and flowering shrubs.

The sting of a mason bee

Yesterday I was on the patio cutting more paper straws to fill more cans. It seems I’ve been doing this every few days because as fast as I put up new ones, they get filled. I was measuring straws and cutting when I felt something on my wrist. I looked down to see a mason caught between my wristwatch and my sleeve. I pulled back my sleeve and she flew away.

For a while I wondered if she stung me. What I felt wasn’t really a sting but more like a little pinch. I couldn’t see anything, so I shrugged it off, thinking maybe I felt her feet while she was struggling to free herself.

But about five minutes later I noticed a typical sting mark: a raised white welt about a quarter-inch in diameter surrounded by a red patch about two inches across. So she had stung me! But seriously, it was something that would never pass for a sting in a honey bee’s bag of tricks.

I’ve been stung by alkali bees and alfalfa leafcutters, and they are less than 10% of a honey bee’s sting. But this sting was less than 10% of leafcutter sting. If I hadn’t actually seen the mark, I wouldn’t have believed it.

Attracting mason bees with paper straws

Over the years I’ve changed my nesting box set up. Now I use paper straws cut to fit the length of a metal can. I spray-paint the cans, although it’s not necessary, and simply fill them with straws of various diameters. When I started doing this seven years ago, about ten bees nested in my straws. Now it’s ridiculous how many live here, many hundreds.

In the autumn I put the cans of straws in my garden shed to keep them out of the rain. And then, in the spring, I put the straws in a hatching box. A hatching box is just a box with a tiny hole at the bottom. If you put the hatching box near a new set of straws, the bees will leave the hatching box and use the straws for their nests. By using new straws every year, you can reduce the number of parasites the bees have to contend with.

When the straws are full, your home will do

Even though I keep installing more straws, I have mason bees living in the drain holes of all our windows, nesting in the edges of the sliding patio door, tucked under the eaves and behind the fascia, squeezed in the siding, and folded into the outdoor chairs.

The orchard masons are just beginning to wind down for the year, but soon the green berry bees, Osmia aglaia, will start making their appearance. For now, they are still in the hatching boxes and waiting for warmer weather.

If you want to know where to find paper straws, everything I know about them is on a separate page called “Paper straws for native bee nests.”

Honey Bee Suite

Preparing mason bee housing
Preparing pollinator housing with empty cans and paper straws. © Rusty Burlew.
The straws get filled in just a few days. © Rusty Burlew.
hatching box
Hatching boxes. Just lay the straws inside. © Rusty Burlew.

A lewd and lascivious swim in the soup

You’d think my backyard was some kind of bee bordello. Behind my house, a large group of male mason bees is hovering, darting, circling and bumbling along the roof line. Occasionally one lands on the pollinator housing to rest, while another suns himself on the windowsill. But a newly-hatched female Osmia peeking out of her tube is enough to stir them all up, and the frenetic careening begins anew.

One mating pair was on the side of my house. When I tried to get a photo, the pair dropped off the siding and landed in a foil-lined flower pot that contained three inches of malevolent-looking rainwater.

Much to my surprise, the water bothered them not a bit. The male must have found the girl of his dreams because, without separating, they circled round and round in the disgusting water, tracing little ripples on the surface. After I clicked a few shots, I reached in and rescued them, placing them on the edge of the foil. Believe it or not, liberation at the hands of an impossibly large human (at least in bees terms) deterred them not in the least.

About a minute later, the attached pair dropped from the foil and landed in the sun. The male, looking bedraggled and damp, was destined for a bad-hair day. The female seemed infinitely patient.

Finally, after another two or three minutes, the male flew away. The female groomed her antennae, fluttered her wet wings, then flashed away. I wonder if they would have drowned if I hadn’t fished them out. I wonder if they are always so oblivious while they’re rolling in the hay. . . . Wow, the things we do for love.


A mating pair of mason bees drops in a pot of water.
A mating pair of mason bees drops in a pot of water. © Rusty Burlew.
The  bee couple sitting on a piece of foil, dripping wet.
The bee couple sitting on a piece of foil, dripping wet. © Rusty Burlew.
Undeterred, the bees dry off in the sun.
Undeterred, the bees dry off in the sun. © Rusty Burlew.

Mason bee “menage a trois”

Caught in the act! This mason bee threesome was photographed by UK beekeeper Philippa Burgess. She got the shot a couple of years ago as the little tower of bees perched in her back garden for thirty minutes or more.

Although we don’t have this species in the states, these bees appear to be Osmia rufa, also known as the red mason bee, a very common in species in Europe. The female is both larger and hairier than the males; the males are more slender with unmistakably white faces.

As with other bees in the family Megachilidae, the male red mason emerges first and hangs around the nest area waiting for females to emerge. Males compete for females and may mate many times during their short lives.

As soon as the female mates, she begins to search for suitable nest locations, such as abandoned insect holes, cracks in wood, or hollow reeds. Once she chooses a home, she begins the process of collecting provisions—both nectar and pollen—and laying eggs. The female red mason uses mud to build partitions between the egg chambers and to seal the entrance to her nest.

These bees are active six to eight weeks in late spring. Once the eggs are laid, it takes about 15 weeks for the baby bee to become an adult. This adult bee, still in a cocoon, spends the remainder of the winter in a resting stage, and will not emerge until the following spring.

In this unusual photo, it appears that both males found the female at the same time. Soon, the males will move on looking for other mates, and the female will begin her life’s work.

Great catch, Philippa. Thanks so much for sharing!

Osmia rufu mating threesome
A mating threesome, Osmia rufa. © Philippa Burgess.


Putting the squeeze on mason bees


Talk about claustrophobia. Just looking at this bee gives me the heebie-jeebies. Conventional wisdom says a blue orchard mason bee (Osmia lignaria) likes a 5/16th-inch nesting hole. This hole is smaller, only 1/4 inch, drilled specifically for leafcutters. Apparently, no one in the bee world is reading my mind because the masons are eschewing the larger holes in favor of a tight fit. They remind me of women struggling into small garments—just hold your breath and sque-e-e-e-eze.

Even though they give me confined-space anxiety, I love to watch these workaholic bees. Returning from a foraging trip, the females look like big black flies with one exception: the undersides of their abdomens are painted with colorful pollen. The bees crawl into their holes head first, back legs flailing for purchase against the sides of the tunnel. After a few moments, they back out, do a quick 180, then re-enter tail-end first.

Mason bees make odd little noises while they work. Sounding a lot like bugs in glass jar, they make vibrate-y, echo-y noises that sound like distress . . . and maybe it is. Panic attacks?

When they’re not carrying pollen, the bees haul in the mud they will use to seal up each compartment until the nest is complete.

My worst mason bee problem occurs each year right here at my desk, which is near a double-paned window in a white vinyl frame. On the outside of the house the frame has two little drain holes. Every year the mason bees go into those holes and build nests. From the inside of the house I can’t see any opening at all, but somehow the bees hatch to the inside. Sometimes I find them on the windowsill or sometimes they get caught between the window and the screen. I’ve rescued five so far this year, and a sixth I found dead on the carpet.

The other odd thing has to do with pollen mites. One year I purchased mason bees from a place in Oregon and for the next two years had serious pollen mites. I never purchased bees after that. Instead, I just built housing and let the wild masons move in. Since then, I’ve seen no mites. Each afternoon I net as many bees as I can and check for mites, but for three years now, I’ve come up clean. I’m wondering if local populations have local resistance. Perhaps shipping them around the countryside is the wrong thing to do—it certainly didn’t help the honey bees or the bumble bees. Serious food for thought.