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orchard mason bee on blue flower

AirBnBee: Welcoming Orchard Mason Bees to Your Garden

Want to be a beekeeper, but not at the expense of your day drinking time? Would you like to feel smug about supporting pollinating insects without the routine chores (and expense) of setting up honeybee colonies?

Unless your neighborhood is regularly strafed by pesticides and herbicides, we guarantee that you have a resident population of mason bees. You can boost their numbers and help out the locals by providing them with a healthy nesting environment in your home garden or orchard. In return, you'll have more productive fruit and nut trees, vegetables, and berries. Everyone wins!

An introduction to the mason bee

There are about 140 native mason bee species in North America, including the blue orchard mason bee (Osmia lignaria)—the star of this article. Mason bees earned their name because of the clay partitions they build to separate egg cells in long, thin nesting cavities. Their favorite nurseries are hollow reeds and stems, but they'll also nest in narrow rocky crevices or holes in trees made by borer beetles and woodpeckers. In developed areas, you'll find them in stacked woodpiles, between roofing shingles, and inside open-ended drip irrigation tubes.

Mason bees are solitary, meaning they don't cooperate as colonies. Females are single moms, collecting pollen to deposit in each nest cell. When the larva hatches from the egg, it devours the pollen, pupates, and finally phases into the adult stage before hibernating through the winter.

Blue orchard mason bees look like pudgy, four-winged houseflies. Their bodies are iridescent black, and the males, which are significantly smaller, have adorable tufts of white hair on their heads. Only the females gather pollen, which they carry on their bellies. Both sexes drink nectar, brushing up against and distributing pollen among various early spring flowers.

Mason bee fans swear that, on a per-bee basis, they're one hundred times more efficient pollinators than European honeybees though they're only active early in the season. They're certainly easier to manage, they only sting if they're physically manhandled, and they don't tick off bug-aphobe neighbors. 

Choose the right mason bee house for you

orchard mason bee house

Whether you're on a shoestring budget or you're all-in on a deluxe mason bee propagation system, you can support a thriving population of native pollinators without much effort or expense. If you like to mess around with basic woodworking projects or you want another side hustle, you've found the perfect hobby.

Basic specifications for mason bee nest materials

Ideal cavities are 5/16" in diameter and six to eight inches long. As a general rule, a female will lay an egg for every linear inch, often with a bonus cocoon or two in seven-inch tubes.

Because mason bees can control the sex of their offspring, they lay three or four female eggs in the back of the tube, placing the male eggs in front. If a predator attacks the nest cavity, the cocoons at the front end serve as the sacrificial lambs. (Sorry, guys).

These are popular artificial nest systems:

  • Paper straws in cardboard sleeves set out in bundles
  • Grooved and stacked wood trays with or without straws
  • Natural reeds, canes, stalks, and bamboo cut at the nodes (which are solid)
  • 6" deep holes drilled into untreated lumber, logs, or dead trees

Mason bees are vulnerable to bacteria, viruses, mites, and predatory wasps. Providing clean nesting holes will improve the health of your local pollinator population and lower mortality rates.

Our recommended mason bee system

The best housing system for mason bees allows you to remove and clean individual cocoons each fall. Washed orchard mason bee cocoons are far less likely to sustain disease and parasites in your native population and your housing system. Emerging bees won't have to crawl through mite-infested cells on their way to freedom.

Our favorite system uses routed wooden trays that, when sandwiched together into blocks, form rows of tubes. They can be secured with straps or bolts, with cardboard affixed to the back, and cleaned out after the cocoons are removed.

You can use paper sleeve tubes inside the grooves, or let the bees set up their nests on the bare wood. If you choose the latter route, separate the blocks and gently scrape the cocoons from the grooves. Slit the paper straws to remove the cocoons. Female cocoons are up to twice as large as males, and you should have about a 50/50 split. 

Protecting your mason bee nests from weather and predation

Your goal is keeping the mason bee nests dry, and preventing birds, rodents, and wasps from destroying the nests. Here are three popular housing designs for mason bee tubes, with links to do-it-yourself instructions:

  • Open-faced wooden box: You can go crazy with this groundbreaking design. Like put a sloping roof on it, or add a hinged door on the back. This will hold your tray blocks or bundled tubes.
  • Drilled blocks with overhanging roof: This excellent Instructable includes tips for rolling your own liner straws!
  • 3" or 4" PVC pipe: This design is popular with the pros, and this video nails the details. You can substitute the PVC with tall metal or plastic coffee cans. 
  • Routered trays: Scroll down to the second set of instructions for a simple grooved tray design.

Leave a one or two-inch gap between the front of your blocks or tubes and the edge of the outer container. This will help keep nests dry, but also allow you to cover the entrance with hardware cloth or a coarse tulle fabric predator barrier. Use duct tape or elastic to secure tulle to cylindrical containers. If you permanently affix wire mesh to the front of your wooden nest boxes, add a removable back for access. 

Sourcing dormant orchard mason bees

Mason bees are usually available for sale mid-November through February. Get your cocoons or filled nest tubes from a local source whenever possible. You'll have the best success with bee genetics adapted to your climate, natural forage, and insect diseases. You'll also reduce the chance of introducing new diseases to local pollinators. If you purchase your mason bees online, there is never a guarantee you'll get bees from your region, no matter what the seller says. Local garden supply retailers might claim their bees are locally-sourced, but if they, too, ordered online, they could simply be repeating what their supplier told them.

Check with your local agriculture extension office for orchard mason bee supplier referrals

Your local university agriculture extension agent probably knows how to hook you up. Depending on your state, they may have an in-house apiculturist who knows the professional pollinators in your area.

You've heard about commercial beekeepers renting honey bee hives to growers during the bloom season. Did you know there are mason beekeepers who offer similar services? They set out nests in the spring and the fall, they'll have three to seven times as many viable cocoons depending on predation, weather, and disease. If they end up with more tubes or cocoons than they can use for the next season's contracts, they'll put them up for sale — usually to local Master Gardener's programs or orchardist clubs, who, in turn, sell them each year as fundraising campaigns.

They sometimes use a variety of tube-nesting species, but that's a positive. Mason, and leafcutter bee species fill their own niche, with some remaining active later in the season than orchard mason bees, which tend to die off within six weeks of emergence. 

Cleaning and storing orchard mason bees

Once the females have begun laying eggs on the stored pollen balls, the nests shouldn't be disturbed until mid-October when pupae have transitioned to the more stable adult phase. At this time you should bring your nest boxes inside, clean the cocoons if you wish, and store them until spring.

Optimal conditions for storing cocoons is between 35°F to 40°F. Keep loose cocoons and filled straws in a perforated paper sack or cardboard box placed in a sealable bag or sealable plastic food container. Throw in a clean, damp sponge for humidity, and remoisten as needed. 

Lawn Care Academy outlines two brilliant and easy methods for cleaning mason bee cocoons

If you live where winter temperatures hover between freezing and 45°F, you can place the boxes off the ground in a sheltered garage or outbuilding. You can leave them in place year-around if you're super lazy, but you'll have a higher mortality rate. 

Setting out cocoons and tubes in spring

Male bees will break dormancy when daytime temperatures reach 50°F to 55°F, with the females waking up a few days after. It may take several days for cocoons in cells to emerge from their nests. Bees in loose cocoons tend to emerge a few days sooner. You can keep your bees dormant and stagger deployment (ha, makes them sound like little soldiers) well into early summer for best bloom coverage, but mason bees perform best in cooler spring temperatures. 

Provide two to three nest tubes for each female cocoon, or seven tubes for each filled nest tube. Throw in some extra tubes for bees already in your area. 

Place your bee houses high and dry

Affix your mason bee house to a fixed, wind-sheltered structure at least three feet off the ground. Set them to face southeast to east. Ideal spots are tree trunks, under the eaves of houses and outbuildings, and vertical posts on solid fences. Drill small drain holes in the undersides of horizontal-hanging plastic or cylindrical metal containers, or tip them forward just enough to let water or condensation drain.

We recommend putting loose cocoons in the bottom half of a cardboard jewelry-type box and sliding the open box into a gap in your bee house. Leave enough room above for the bees to crawl out.

Mason bees spend their free-flying adult stages with 200' of their chosen nesting sites, which are as close to their own birthplaces as possible. When they emerge, they'll be pretty hungry so be sure your orchard buds are at least in the "popcorn" stage, and other plants are in bloom. Dandelions are a major food source for all types of bees. To heck with your neighbors and their perfect lawns! Let your dandelions grow!

Mason bees can't build their little cell walls without a nearby source of damp mud with high clay content. If you have nothing but gorgeous, crumbly soil, you can bring in clay from elsewhere — or even buy clay packaged specifically for mason bees.

A few words on leafcutter bees

Leafcutter bees (the Megachile genus), like their mason bee cousins, are extremely efficient pollinators that also nest in long, narrow voids. According to Colorado State University Extension, leafcutter bees are attracted to plants with canelike, pith-centered stems such as roses, blackberries, and raspberries. They dig out nest cavities in the soft centers of cut stems and line them with leaf snippets. They'll use old, hollow canes as well.

As their name implies, leafcutters damage foliage. This isn't much of a problem with equalized populations, though too many leafcutters in an area can endanger the health of valuable ornamentals and cane crops. Most of the time, gardeners and commercial producers consider the leaf cuts as quid pro quo for efficient pollination. Unlike mason bees, they're active throughout the growing season. If you set up a mason bee nesting habitat, chances are a few female leafcutters will move in. That's a good thing. 

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