Most of us know by now that bee populations are in dangerous decline. Concerned gardeners have responded with increased interest in pollinator gardens, native plants, and organics, and in the chemical “friendliness” of purchased plants—wanting to be sure they’re safe for their busy little guests. It takes a bit of research, but it’s simple enough and something we all can do.
Mason Bees: Valuable Early Spring Pollinators
Leaving dried stems of perennials and grasses is another way to assist, providing nesting sites for pollinators including mason bees, active in early spring. Stems should be cut in winter to 12-15 inches for a tidier look and to allow bees to enter, and then left alone, as the bees don't hatch until the following spring. New growth will soon cover the old stems. Mason bees will also use "bee motels," small structures containing nesting tubes one can place in their yard that offer additional egg-laying habitat for these valuable creatures.
To the uninitiated, it may seem dangerous to invite bees to nest near your home. Won't they damage your house by boring into the wood, and possibly sting you if you get too close? Some can, like carpenter bees and wasps. But mason bees are different.
Why Mason Bees are Safe to Have in Your Yard:
Second, mason bees are non-aggressive, fairly docile, and at times may even accept gentle handling without complaint. Males don't even have a stinger. And in the unlikely event a female does sting, their venom is quite mild, akin to a mosquito bite.
Still, perhaps all the old cartoons where swarms of bees form into various shapes and mercilessly chase those that pester them have planted concerning images in your head. Well, don't worry--that type of protective behavior doesn't apply to mason bees. Not all bees are social--living, working, and chasing humans and animated bears around in a cooperative mass. In fact, most native bees are solitary, though females are often happy to nest near each other. The male mason bee is designed to live just long enough to perform his one useful task—mating--so he’s got other things on his mind. Mason bees don’t have the social structure necessary, let alone the inclination, to chase you into the frog pond.
Female Mason Bees: Industrious Single Moms
Mason Bees: Highly Efficient Pollinators
Due to their particular feeding method and habits, they are much more efficient pollinators than honeybees, and pollinate up to 95% of the flowers they visit. They are less discouraged by cool temperatures and rainy weather than honeybees.
How to Set Up Mason Bee Houses in Your Yard
- Nesting holes should be 5/16” in diameter and no less than 6 inches deep, not drilled all the way through--the back must remain closed. The depth is important, as the female will lay fertilized eggs (which will become females) in the back of the nest, and unfertilized (male) eggs toward the front. This leaves the female eggs well-protected, ensuring the higher number of female bees necessary to maintain the species.
- You can use drilled blocks of wood, bamboo tubes, or pre-made kits with cardboard nesting tubes. If your nests cannot be cleaned at least every 2 years, they should be replaced. This prevents the spread of insects and disease.
- Mason bees key on patterns, especially in blue and black colors, to navigate back to the proper tube. Painting the shelter, and painting the ends of the individual tubes and arranging colors randomly will greatly assist them in finding their way.
- Place your nests 4 to 7 feet off the ground, facing east or southeast, as bees need warmth to be ready to fly. Keep from hot sun in summer--south or southwest are exposures not recommended as developing bees may literally fry. Be sure nests are protected from wind and rain--place under eaves or in a shelter.
- Mason bees use mud to seal off the egg chambers, so be sure there's a handy supply near the nest. If your soil is sandy, set out a dish of wet clayey soil for them to gather.
Caring for Mason Bee Nests:
Mason bees will pupate in summer, and winter over as dormant adult bees, to hatch as temperatures warm to about 50 degrees in the spring. To keep your sleeping beauties safe from predators and disease, it is recommended to harvest and clean the cocoons in the fall. It's simple, and takes about 10 to 15 minutes.
- Gently open the tubes and separate the cocoons from the nesting material, destroying any C-shaped cocoons (this may indicate the presence of chalkbrood, a devastating disease).
- Wash the cocoons in a water/bleach mixture (1/4 cup bleach to 1 gallon water) and remove any that sink or have holes.
- Gently dry and store in a breathable wrap (like a nylon stocking), and store at 30-40 degrees and 50-60% humidity. Generally an attached unheated garage is suitable. See links at bottom for more info.
- Alternatively, tubes may be stored intact once nesting activity has completed, but handle delicately and be sure to set upright with mud-sealed ends at top. This will ensure that the eggs stay in contact with the food supply.
- Release bees in spring when temperatures have warmed appropriately, near their nesting site.
More Information:
Harvesting Cocoons: https://davidsuzuki.org/queen-of-green/how-to-harvest-and-clean-mason-bee-cocoons/
From the Xerces Society for Invertebrate Conservation: https://www.xerces.org/publications/books/managing-alternative-pollinators
Garden Cleanup for Pollinators, a study by North Carolina State Extension Service: https://content.ces.ncsu.edu/garden-cleanup-for-pollinators-trim-perennial-stems-in-their-first-winter
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